AgroMet Handout for Horticulture St. 2014.docx

JINKA UNIVERSITY
COLLEGE OF AGRICULTURE AND NATURAL RESOURCE
DEPARTMENT OF HORTICULTURE
Course Tittle: Agro meteorology
Course Code: HORT211
ECTS Credits (CP): 2
Year/Semester: Year II, Semester I
Lecture Note
Compiled by Abebe A. (M.sc)
January, 2022
Jinka, Ethiopia

1.Introductory Concepts in Meteorology and Climatology
1.1.Definitions of terms: weather, climate, meteorology and climatology
Weather: is the atmospheric condition of a place or a given location at a particular time or for a
short time
Climate: of a place is therefore the average weather conditions obtained through the synthesis of
weather elements prevailing there for over a period of 30-35 years.
Meteorology is the study of weather or all atmospheric processes including temperature, air
pressure, and chemical composition. Meteorology is considered a branch of atmospheric science
which deals with weather phenomena and weather changes over a short timescale.
Climatology is the study of the behavior of the atmosphere and changes in temperature,
pressure, and other atmospheric factors over a period of time. Climatology is a science that deals
with the study of the climates of different parts of the world. It is a branch of atmospheric
science, but the study of climate can be related to every other aspect of the earth system
including the geosphere (solid earth) and hydrosphere (terrestrial water reserves) because climate
affects Earth’s entire surface.
Weather and Climate Compared
Weather and climate are explained by the same element in combination but weather and climate
are not one and the same.
Atmosphere: is a thick gaseous envelope which surrounds earth from all sides and is attached to
earth’s surface by gravitational force The lower region called the hemisphere, extends from the

surface to 80 –100km above the earth and has a more or less, chemical composition. Beyond this
level, the chemical composition of the atmosphere changes in the upper region known as
heterosphere. The hemisphere is the more important of the two atmospheric regions for human
beings because we live in it. It contains three major groups of components; they are constant
gases, variable gases and impurities.
It plays important role in
Existence of life on earth
Providing all necessary gases for biosphere
Filtering incoming solar electromagnetic radiation
Providing energy to earth’s biospheric ecosystem
Distribution and redistribution of energy on earth’s surface
Definitions of Agro meteorology:
A branch of applied meteorology which investigates the physical conditions of the
environment of growing plants or animal organisms
An applied science which deals with the relationship between weather/climatic conditions
and agricultural production.
A science concerned with the application of meteorology to the measurement and
analysis of the physical environment in agricultural systems. The word ‘Agro
meteorology’ is the abbreviated form of agricultural meteorology.
To study the interaction between meteorological and hydrological factors on the one hand
and agriculture in the widest sense, including horticulture, animal husbandry and forestry
on the other (WMO).
Agro meteorology is a science investigating the meteorological, climatological and
hydrological conditions which are significant for agriculture owing to their interactions
with the objects and processes of agricultural production.
It is the study of those aspects of meteorology which have direct relevance of agriculture.
Agro meteorology puts the science of meteorology to the service of agriculture to help
the sensible use of land, accelerate production of food and to avoid the irreversible abuse
of land resources.
Agro meteorology is defined as a branch of meteorology which investigates the
relationship of plants and animals to the physical environment.

Agro meteorology is defined as the study of responses of living organisms to the physical
environment (water, air, soil). The living organisms are cultivated plants, livestock,
insects and microorganisms.
Agrometeorology : transforming knowledge of weather & climate to useful information
for agriculture .
Difference between Meteorology and Agro meteorology
The objective of Agro meteorology
To discover and define the meteorological, climatological and hydrological
problems which are relevant to agricultural production.
Apply this knowledge of the atmosphere and soil to practical agricultural use.
It attempts to enhance agricultural production by controlling physical
environment.
To forecast weather and crop yield accurately.
1.2.The scope of meteorology and climatology
The scope of Agro Meteorology can be illustrated through the following few applications.
1. Characterization of agricultural climate:
For determining crop growing season, solar radiation, air temperature, precipitation, wind,
humidity etc. are important climatic factors on which the growth, development and yield of a
crop depends Agro-meteorology considers and assess the suitability of these parameters in a
given region for maximum crop production and economical benefits.
2. Crop planning for stability in production:
To reduce risk of crop failure on climatic part, so as to get stabilized yields even under weather
adversity, suitable crops/cropping patterns/contingent cropping planning can be selected by
considering water requirements of crop, effective, rainfall and available soil moisture.

3. Crop management:
Management of crop involves various farm operations such as, sowing, fertilizer application.
Plant protection, irrigation scheduling, harvesting etc. can be carried out on the basis of specially
tailored weather support. For this the use of operational forecasts, available from agro met
advisories, is made
e.g. 1) Weeding, harrowing, mulching etc are undertaken during dry spells forecasted.
2) Fertilizer application is advisable when rainfall is not heavy, wind speed is<30
km/hr and soil moisture is between 30 to 80%
3) Spraying/dusting is undertaken when there is no rainfall, soil moisture is 90% and
wind speed is<25km/hr.
4. Crop Monitoring: To check crop health and growth performance of a crop, suitable
meteorological tools such as crop growth models. Water balance technique or remote sensing
can be used.
5. Crop modeling and yield –climate relationship:
Suitable crop models, devised for the purpose can provide information or predict te results about
the growth and yield when the current and past weather data is used.
6. Research in crop –climate relationship:
Agro-meteorology can help to understand crop-climate relationship so as to resolve complexities
of plant process in relation to its micro climate.
7. Climate extremities:
Climatic extremities such a frost floods, droughts, hail storms, high winds can be forecasted and
crop can be protected.
8. Climate as a tool to diagnose soil moisture stress:
Soil moisture can be exactly determined from climatic water balance method, which is used to
diagnose the soil moisture stress, drought and necessary protective measures such as irrigation,
mulching application of antitranspirant, defoliation, thinning etc. can be undertaken.
9. Livestock production:
Livestock production is a part of agriculture. The set of favorable and unfavorable weather
conditions for growth, development and production of livestock is livestock is studied in
Agrometeorology. Thus to optimize milk production poultry production, the climatic normal are
worked out and on the suitable breeds can be evolved or otherwise can provide the congenial
conditions for the existing breeds.
10. Soil formation:

Soil formation process depend on climatic factors like temperature, precipitation, humidity, wind
etc, thus climate is a major factor in soil formation and development.
1.3.Elements and controls of weather and climate
Elements of Climate and Weather
1.Solar radiation:
Solar radiation is the radiation, or energy we get from the sun. It is also known as short-
wave radiation. Solar radiation is probably the most important element of climate. Solar
radiation first and foremost heats the Earth's surface which in turn determines the
temperature of the air above. Unequal heating of the Earth's surface creates pressure
gradients that result in wind. The amount of solar radiation that reaches any one spot on
the Earth's surface varies according to: Geographic location, Time of day, Season, Local
landscape, Local weather. Measurements for solar radiation are higher on clear, sunny
day and usually low on cloudy days.
2.Temperature :
Temperature is a very important factor in determining the weather, because it influences
or controls other elements of the weather, such as precipitation, humidity, clouds and
atmospheric pressure.
3.Air masses-
An air mass is a large body of air with generally uniform temperature and humidity. Air
masses control the characteristics of temperature, humidity, and stability.
4. Winds:-
The horizontal movement of the atmosphere is called wind.
Wind can be felt only when it is in motion.
Wind is the result of the horizontal differences in the air pressure.
Wind is simply the movement of air from high pressure to low pressure.
The speed of the wind is determined by the difference between the high and low
pressure.
The greater the difference the faster the wind speed.
Closer the isobars stronger the winds.
5. Pressure systems:
Air pressure is the weight of air resting on the earth's surface.
Air has specific weight.
This weight exerted by the air is atmospheric pressure.
It is defined as the force per unit area exerted against a surface by the weight of air above
that surface in the Earth's atmosphere.
Pressure systems have a direct impact on the precipitation. In general, places dominated
by low pressure tend to be moist, while those dominated by high pressure are dry. The
seasonality of precipitation is affected by the seasonal movement of global and regional
pressure systems.

6.Ocean Currents:
Ocean currents greatly affect the temperature and precipitation of a climate. Those
climates bordering cold currents tend to be drier as the cold ocean water helps stabilize
the air and inhibit cloud formation and precipitation. Air traveling over cold ocean
currents lose energy to the water and thus moderate the temperature of nearby coastal
locations. Air masses traveling over warm ocean currents promote instability and
precipitation. Additionally, the warm ocean water keeps air temperatures somewhat
warmer than locations just inland from the coast during the winter.
7.Topography:
Topography affects climate in a variety of ways. The orientation of mountains to the
prevailing wind affects precipitation. Windward slopes, those facing into the wind,
experience more precipitation due to orographic uplift of the air. Leeward sides of
mountains are in the rain shadow and thus receive less precipitation. Air temperatures are
affected by slope and orientation as slopes facing into the Sun will be warmer than those
facing away. Temperature also decreases as one move toward higher elevations.
8.Humidity:
Atmospheric moisture is the most important element of the atmosphere which modifies
the air temperature.
Humidity is the measurable amount of moisture in the air of the lower atmosphere.
There are three types of humidity:-
a) Absolute humidity: - The total amount of water vapor present in per volume of air at a
definite temperature.
b) Relative humidity: - Is the ratio of the water vapors present in air having a definite
volume at a specific temperature compared to the maximum water vapors that the air is
able to hold without condensing at that given temperature.
c) Specific humidity: - Is defined as the mass of water vapor in grams contained in a
kilogram of air and it represents the actual quantity of moisture present in a definite air.
The humidity element of weather makes the day feels hotter and can be used to predict
coming storms.
The humidity element of climate is the prolonged moisture level of an area that can affect
entire ecosystems.
9.Precipitation:
Precipitation is the term given to moisture that falls from the air to the ground.
Precipitation includes snow, hail, sleet, drizzle, fog, mist and rain.
Precipitation is simply any water form that falls to the Earth from overhead cloud
formations.
As an element of weather, precipitation determines whether outdoor activities are suitable
or if the water levels of lakes and rivers will rise.
As an element of climate, precipitation is a longterm, predictable factor of a region's
makeup.

For instance, a desert may experience a storm (weather) though it remains a typically dry
area (climate).
10.Cloudiness:
Clouds are suspended water in the atmosphere.
Clouds are usually the most obvious feature of the sky.
Clouds give us a clue about what is going on in our atmosphere and how the weather
might change in the hours or even days to come.
Each type of cloud forms in a different way, and each brings its own kind of weather.
Clouds play multiple critical roles in the climate system.
In particular, being bright objects in the visible part of the solar spectrum, they efficiently
reflect light to space and thus contribute to the cooling of the planet.
A small increase in cloud cover could, in principle, balance the heating resulting from
greenhouse gases.
Clouds are the base for precipitation.
In summer cloudy days provide protection from the rays of the sun.
In winter cloudy skies at night diminish nocturnal radiation and check the fall of
temperature.
Clear calm winter nights are usually the coldest and help in condensation.
Factors Controlling Climate and Weather
(1) Latitude (2) Altitude (3) Land and sea surfaces (4) Mountain barriers (5) Local topography,
ocean currents and (6) Vegetation or forest
(1) Latitude:
It is defined as the angular distance of a place from the equator and is expressed in degrees,
minutes and seconds. It is a principal control of climate and determines the solar energy received
and temperature of a place. Different types of climates according to latitude are equatorial,
tropical, sub-tropical temperate and polar climates.
(2) Altitude:
It is defined as the height from mean sea level (MSL) and is expressed in meter. Temperature
decreases with height. According to altitude there are two type of climate viz mountain climate
and plateau climate.
(3) Land and sea surfaces:
As the distance from sea of a place increases the difference between maximum and minimum
temperature during a day and year increases. Depending on land and water bodies there are two
types of climate such as maritime and continental climates. In maritime climate humidity is more
and moderate temperature prevails. In continental climate the difference between maximum and
minimum temperature is highest.
(4) Mountain barriers:
Mountains or hills interfere with wind flow controlling the temperature, rainfall and wind. Wind
ward side receives more rainfall while leeward side receives less rainfall and remains dry.
(5) Local Topography:

Undulation or unevenness of the surface changes the wind velocity which may change the
temperature. Hence weather changes and fluctuations are more.
(6) Vegetation and Forest:
In forest climate due to evapotranspiration water vapour increases, humidity increases and
temperature decreases. It also reduces incoming radiation and wind velocity.

2. Basic Concepts of the Atmosphere
2.1. Nature and origin of Atmospher
There is general agreement on that earth had no atmosphere initially. It is believed that the
existing atmosphere was formed from the gases emitted from the interior of earth. In particular,
water vapour and carbon dioxide (CO2) were released and subsequently formed the oceans and
large quantities of lime stone; i.e calcium carbonate. Some oxygen was formed both by
decomposition of water vapour and from photosynthesis of the limited plant life existing then.
Eventually, enough oxygen was accumulated for the formation of ozone layer in the upper
atmosphere. Since this layer acts as an ultraviolet filter, absorbing much of the harmful
ultraviolet part of the solar radiation before it reaches the earth’s surface, life could expand
rapidly both on land and ocean surface. Photosynthesis, then, could increase the production of
oxygen. Nitrogen in the atmosphere is evolved from the earth’s interior and has accumulated to
its present level. The important point to appreciate is that the evolution of atmosphere which may
seem quite simple, took 3 to 5 billion years. Only in the last tens of millions of years have the
world’s oxygen and nitrogen levels been about what these are today.
When the Earth was formed 4.6 billion years ago, Earth’s atmosphere was probably mostly
hydrogen (H) and helium (He) plus hydrogen compounds, such as methane (CH4) and ammonia
(NH3).
Those gases eventually escaped to the space.
The release of gases from rock through volcanic eruption (so-called outgassing) was the
principal source of atmospheric gases.
The primeval atmosphere produced by the outgassing was mostly carbon dioxide (CO2)
with some Nitrogen (N2) and water vapor (H2O), and trace amounts of other gases.
2.2 Present composition of the atmosphere
The atmosphere may be broadly divided into two vertical regions. The lower region called the
hemisphere, extends from the surface to 80 –100km above the earth and has a more or less,
chemical composition. Beyond this level, the chemical composition of the atmosphere changes in
the upper region known as heterosphere. The hemisphere is the more important of the two
atmospheric regions for human beings because we live in it. It contains three major groups of
components; they are constant gases, variable gases and impurities
The average composition of the atmosphere is presented in Table 2 below. Although some of the
gases like water vapour and ozone are highly variable, the atmosphere is well mixed and is constant
in composition in the lower layer referred to as the homosphere. At the higher levels, the
heterosphere, there is little mixing and so diffusive separation tends to take place up to about 100km.
Generally the composition of the atmosphere changes with the height above the sea level. Water

vapour is limited to10-12km while at higher levels oxygen and minor constituents such as carbon
dioxide are dissociated by solar ultraviolet radiation.
Constant Gases: Two major constant gases make up 99% of the air by volume, and both are
critical to sustaining human and other forms of terrestrial life. They are nitrogen (n) which
constitutes 78% of the air and oxygen (O2) which accounts for another 21%. Survival depends
on oxygen and nitrogen. The oxygen and nitrogen is relatively inactive but bacteria convert it
into other nitrogen (n) compounds essential for plant growth.
Variable Gases: They collectively constitute only a tiny proportion of the air. They contain
certain atmospheric grades in varying quantities essential to human well-being. Examples
include; carbon-dioxide (Co2) 0.04% of dry air and is a significant constituent of the atmosphere
in terms of its climatic influence and vital function in photosynthesis. Water vapour is an
invisible gaseous form of water (H2O), more sufficient in capturing radiant energy because of its
storage capacity. Ozone (O3) is a rare type of oxygen molecule, composed of three oxygen
atoms instead of two, laying between 15km and 50km above the earth. It has the ability to absorb
radiant energy, in particular the ultraviolet radiation associated with incoming solar energy.
Other variable gases present in the atmosphere include; hydrogen, helium, sulphur dioxide,
oxides of nitrogen, ammonia, methane and carbon monoxide. Some of these are air pollutants.
They can produce harmful effects even when concentrations are one part per million (ppm) or
less.
Impurities: The atmosphere contains great number of impurities in form of aerosols (tiny
floating particles suspended in the atmosphere). Impurities play an active role in the atmosphere.
Many of them help in the development of clouds and rain drops. Examples of aerosols include;
dust, smoke, salt crystals, bacteria and plants spores.
Table 2 The Composition of the Atmosphere.
ppmv and ppbv are parts per million and parts per billion by volume respectively

2.3 Vertical thermal structure of the atmosphere
Atmospheric division based on temperature distribution/ variation with respect height in the
atmosphere.
The atmosphere is divided vertically in to four layers.
1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere

(1)Troposphere
The word “Tropo” means mixing or turbulence and “sphere” means region or layer. This is the
lower layer of the atmosphere. The average height of this layer is about 14 km above mean sea
level. At the equator it is 16km and at the poles it is 7-8 km height. Under normal conditions the
height of the troposphere changes from place to place and season to season. This is layer is called
the “ seat of all weather phenomena” because various types of clouds, cyclones, storms and
anti-cyclones occur in this sphere due to the concentration of almost all the form of water
vapour, dust particles etc, in it. Generally there is decrease of temperature with increasing height
at a normal lapse rate of about 6.5°C per kilometer. The wind velocity increases with height and
attain the maximum at the top of this layer. The troposphere is heated from the below because
most of the radiation from the sun is absorbed by the earth’s surface. In this layer about 75% of
total gases and most of the moisture and dust particles are present. At the top of the troposphere,
there is a narrow layer separating it from the stratosphere, which is known as the “Tropopause”.
It is a transitional zone and it is a characterized by no major movement of air.
(2) Stratosphere
This is a layer exists above the tropopause and extends to altitudes of about 50-55 km from the
surface. This layer is called as a “seat of photochemical reactions”. In this layer temperature
remains practically constant at normal 20 km and is characterized as isothermal because the air is
thin, clear, cold and dry. In the upper part of the stratosphere the temperature are almost high as
those near the earth’ surface, which is due to the fact that the ultraviolet radiation from the sun is
absorbed by ozone gas in this layer. Less convection (upland transport or vertical movement)
takes place in the stratosphere because it is warm place at top and the dry and cold at the bottom.
Wind speed is higher and air circulation pattern exists. The upper boundary of the sphere is
called the stratopause is the transition zone between troposphere and stratosphere. Above this
layer there is a steep decrease in temperature. There is a maximum concentration of ozone
between 30 and 50 km above the surface of the earth and this layer is known as the ozonosphere.
The ozone has a property of absorbing ultraviolet rays. If there is no ozone in the atmosphere life
would not have existed on the earth.
(3) Mesosphere
The layer between 50 and 80 km is called as mesosphere. In this layer the temperature decreases
with height. The upper bounding of this layer is called the mesospause. It is the transition zone
between stratosphere and mesosphere.
(4) Thermosphere
The thermosphere also called Ionosphere lies beyond the mesosphere at a height about 80 km
above earth’s surface and extends up to 400 km. The atmosphere in the thermosphere is partly
ionized. Enriched ion zones exist in the form of distinct ionized layers. So, this layer is called as
the ionosphere. According to some climatologists the layer between 80 and 140 km is known as
the thermosphere and beyond that Ionosphere exists. The ionosphere reflects the radio waves
because of multiple reflections of radio wave beams from the ionized shells. So, long distance
radio communication is possible due to this layer. The outer most layer of the earth’s atmosphere

is names as the exosphere and this layer has beyond 400 and 1000 km. Hydrogen and Helium
gases predominate in this outer most region. The density of atoms in this layer is extremely low.
So, there is no collision between the neutral practices.
Isotherms: The lines joining places having equal atmospheric temperature on a geographical
map.
2.4 Heat transfer in the atmosphere
The earth does more than absorb or reflect shortwave insulation; it constantly gives off long
wave radiation on its own. When the earth’s land masses and oceans absorb shortwave radiation.
It triggered rise in temperature, and the heated surface now emits long wave radiation. One or
two things can happen to this radiation leaving the planetary surface; either it is absorbed by the
atmosphere or it escapes into space.
The major atmospheric constituent that absorbs the earth’s long wave radiation are carbon
dioxide, water vapour, and ozone. Each of these variable gases absorbs radiation at certain
wavelengths but allows other wavelengths to escape through an atmospheric “window.” Up to 9
percent of all terrestrial radiation is thereby lost to space, except when the window is shut by
clouds. Clouds absorb or reflect back to earth almost all the outgoing long wave radiation.
Therefore, a cloudy winter night is likely to be warmer than a clear one. The atmosphere is
heated by the long wave radiation it absorbs. Most of this radiation is absorbed at the lower,
dense levels of the atmosphere, a fact that helps account for air’s higher temperatures near the
earth’s surface. Thus, our atmosphere is actually heated from below, not directly by the sun
above. The atmosphere itself, being warm, can also emit long wave radiation. Some goes off into
space, but some known as counter-radiation, is reradiated back to the earth. Without this counter
radiation from the atmosphere, the earth’s mean surface temperature would be about -20
O
C,
35
O
C colder than its current average of approximately 15
O
C. The atmosphere, therefore, acts as a
blanket.
The blanket effect of the atmosphere is similar to the action of radiation and heat in a garden
greenhouse. Shortwave radiation from the sun is absorbed and transmitted through the
greenhouse glass windows, strikes the interior surface, and is converted to heat energy. The long
wave radiation generated by the surface heats the inside of the greenhouse. But the same glass
that let the short wave radiation now acts as a trap to prevent that heat from being transmitted to
the outside environment, thereby raising the temperature of the air inside the greenhouse. A
similar process takes place on the earth, with the atmosphere replacing the glass. Not
surprisingly, this is called the basic natural process of atmospheric heating greenhouse effect.
Human being may be influencing the atmosphere’s delicate natural processes through series of
activities which may trigger sequence of events that could heighten a global warming trend with
possibly dire consequences for near-future environmental change.

Heat moves in the atmosphere the same way it moves through the solid Earth or another
medium. What follows is a review of the way heat flows and is transferred, but applied to the
atmosphere. Radiation is the transfer of energy between two objects by electromagnetic waves.
Heat radiates from the ground into the lower atmosphere.
In conduction, heat moves from areas of more heat to areas of less heat by direct contact.
Warmer molecules vibrate rapidly and collide with other nearby molecules, transferring their
energy. In the atmosphere, conduction is more effective at lower altitudes where air density is
higher; transfers heat upward to where the molecules are spread further apart or transfers heat
laterally from a warmer to a cooler spot, where the molecules are moving less vigorously.
Heat transfer by movement of heated materials is called convection. Heat that radiates from the
ground initiates convection cells in the atmosphere.

3: Atmospheric moisture (air humidity, hydrologic cycle, precipitation, cloud,
fog, mist, dew, wind, air masses and fronts, El Nino and La Nino)
3.1 Air Humidity
Humidity – an expression of the amount of water vapor in the air.
• There are several ways to measure humidity:
Vapor Pressure (Pressure)
Absolute Humidity (Density)
Specific Humidity (Mass Ratio)
Mixing Ratio (Mass Ratio)
Relative Humidity (Percentage)
Dew Point Temperature (Temperature)
Vapor Pressure – The part of the total atmospheric pressure due to water vapor.
Absolute Humidity: - Absolute Humidity – The density of water vapor (mass of
water vapor in a volume of air).
Specific Humidity: - The mass of water vapor per unit mass of air.
Mixing Ratio: The mass of water vapor relative to the mass of the other gases.
Relative Humidity: The amount of water vapor in the air relative to the maximum amount
possible.
3.2 Hydrological Cycle (Atmospheric Water Balance)
Concept of Hydrologic Cycle
Water gets transformed from liquid to solid, solid to liquid, liquid to vapour, vapour to liquid
and vapour to solid states. The sun’s radiation, acceleration due to gravity, ability of the water to
flow and several other properties of water, make this transformation more effective and regular.
The basic input to the world’s water masses comes from precipitation.
Precipitated rain (or) snow falls overland. Processes like infiltration and peroration moves the
water down to the groundwater systems. Some amount of water flows towards the sea as runoff.
The surface water collected in lakes, ponds, swamps, seas and oceans get evaporated into the
atmosphere. The vegetation transpires the water collected from the soil moisture. Evaporated and
transported water enters into the atmosphere as vapour.
Collected water vapour gets condensed to form the clouds. Clouds more towards the land and
starts precipitating again. These processes continue. This endless circulation of water is known
as the hydrologic cycle.
It is of two kinds as terrestrial hydrologic cycle and global hydrologic cycle. The terrestrial
hydrological cycle is of a special interest as the mechanism of formation of water resources on a
given area of the land, like a river basin or a watershed. The global hydrological cycle deals with

its role on the global climate and other geological and physical processes. It is obvious that the
role of different processes involved in the hydrological cycle and their description have to
depend on the chosen spatial- temporal scales.
Components of the Hydrologic Cycle
The circulation of water masses seen in all spheres of the earth involves several causative factors
and components. The major components (or) elements of the hydrologic cycle are: Precipitation
Evaporation Transpiration Evapotranspiration Surface Runoff Condensation Infiltration
Groundwater base flow Sublimation Interception.
3.2.1 Evaporation, transpiration and evapo-transpiration (ETP)
Evaporation is the process of converting a liquid (or) solid into a gas, through the transfer of heat
energy. In hydrologic cycle this conversion is towards water vapour. Heat energy can convert
water mass (or) ice into a vapour. Evaporation occurs more rapidly when there is increase in
temperature and also flow of wind. It also depends on the boiling point and vapour pressure. The
greater a substances vapour pressure, the more rapid the substance gets evaporated and escape
into the air. Open water evaporation is the theoretical evaporation flux from a smooth shallow
water surface (with no storage of energy) when subjected to the ambient meteorological
conditions. Pan evaporation is the evaporation flux from an evaporation pan. Soil evaporation is
the evaporation flux from the soil. Under the conditions of constant temperature, humidity and
wind, evaporation from the large water surfaces of the earth must remain constant. A temporary
increase in temperature results in increased evaporation and also increased precipitation. Water
gets evaporated more rapidly in dry air. This is due to the fact that dry air has only a fraction of
the maximum vapour pressure of water. It is also essential to note that the evaporating molecules
absorb heat from the surroundings. Huge volume of water evaporates from the ocean surfaces.
The amount varies from place to place. It is called as evaporation discharge. The greatest amount
is around the equator, where the intensity of solar radiation is more.
The factors affecting evaporation are
a) Air Temperature
b) Relative Humidity
c) Incoming radiation
d) Wind speed
e) Duration of bright Sun shine
f) Geomorphic conditions of the region.
The amount of water getting evaporated from a free water surface is measured using
evaporimeters or pans.
Evaporation from soil surface
The water molecules present in the soil matrix also get evaporated with great difficulty, unlike
those which are released from the free water surfaces. The amount of water vapor present in the
atmosphere varies greatly from time to time, but the dry gases do not change materially in
quantity from season to season. It may be remarked at this point, however, that about half of the

total moisture present in the atmosphere is found below an elevation of about 6000 feet, and less
than one tenth of it occurs above an elevation of 20,000 feet
Transpiration
Transpiration is the process of releasing the water absorbed by the plants through their root
system after utilizing the nutrients for building their tissues, in a specified time. Vegetation
including numerous growing plants, play a significant role in the hydrologic cycle. The water
which is drawn into the plants rootlets from the soil moisture, owing to osmotic pressure moves
up through the plants stems and leaves. Through the stomatal openings, the water is released out
as water vapour. The amount of transpiration depends on the density and size of the vegetation
existing in place. The amount of water used for irrigating the crops get transpired into the air.
Transpiration is dominant during the growing season of crops in agricultural lands. Most of this
happens during day time, when photosynthesis is active in plants. Transpiration is limited due to
the shortage of soil moisture is some places. The controlling factors of transpiration are:
a) Temperature
b) Solar radiation
c) Wind and
d) Soil moisture.
Evapotranspiration (ETP)
Evaporation is the evaporation flux from intercepted water and from the soil. Transpiration is
molecular diffusion of water vapour through the stomatal aperture of leaves. Evapotranspiration
is the combined effect of both evaporation of water from the soil, surface water bodies, snow, ice
and transpiration from vegetation. In a well-irrigated land, it is difficult to separate evaporation
from transpiration. The total water loss due to both evaporation and transpiration is called as
evapotranspiration. Majority of the water loss due to evapotranspiration happens during summer
months and growing seasons. There will be no (or) little loss expected during winter months /
period. Two terms as potential evapotranspiration and actual evapotranspiration are used to
denote these conditions. Actual evapotranspiration is the total evaporation flux of a cropped
surface. The actual evapotranspiration depends mainly on
a) Atmospheric factors
b) Soil water characteristics and
c) Physiological factors of the crops and other vegetation.
The rate of evapotranspiration is controlled by several climatic, hydrologic, soil and
geomorphological conditions of a region. Soil texture and permeability play the major roles in
this process. Potential soil evapotranspiration is the theoretical evaporation flux from the soil, if
the soil would sufficiently be supplied with water. Potential evapotranspiration is the sum of the
potential soil evaporation and transpiration. The major use of potential evapo(transpi)ration data
is generally for:
1. Water resources planning,
2. Agricultural and irrigation management, and
3. Research.

3.2.2. Condensation
The sun’s radiant energy evaporates water from surface water resources, including seas and
oceans. This water rises upwards as water vapour and reaches the atmosphere. The process of
evaporation continues until the air becomes fully saturated with maximum amount of moisture. It
is called as Saturation Humidity. It is directly proportional to the temperature of the air. It is
expressed in grams/ cubic metre of air. At 0 degree C, humidity of air is 4.874 gm/ cu.m and at
30 degree C it is 30.38 gm/cu.m. Relative humidity is a term used to denote the ratio of the water
vapor content of the air to the water vapor capacity of the air. The term absolute humidity is used
to denote the number of grams of water per cu.m of air. If the air mass reaches the dew point,
then the condensation process begins. Humidity is measured using hygrometers. Through the
process of condensation clouds are formed and moved towards the land frontiers.
Condensation in the atmosphere takes place around small particles of substances present in the
air, which have the affinity for water. These form the hygroscopic nuclei surrounding the
condensation nuclei. These condensed water vapour masses get precipitated the form of water
molecules. Precipitation is the process by which this transformation happens in the atmosphere,
under certain specific conditions.
Condensation depends on several factors. The notable areas are:
a) Adiabatic cooling.
b) Mixture of two air masses of different temperatures
c) Contact cooling.
d) Radiational cooling.
Among these, the most important condensation process is the adiabatic cooling which leads to all
kinds of precipitation.
Condensation leads to cloud formation. Condensed clouds of smaller sizes may quickly
disappear on a hot day. Cloud condensation nuclei, which vary in size from 10-5 to 10-1 mm, are
required to condense water vapour at dew point. Typical cloud condensation nuclei are meteoric
dust, windblown clay and silt, volcanic material, sea salt and combustion products. Natural
concentrations of cloud condensation nuclei vary from 100 to 300 cm
-3
, but may locally become
10 to 100 times larger due to human activities. When a vapour condenses, heat is released.
Condensation also leads to the formation of fog. Before precipitation to happen, the cloud
droplets sized from 0.001 to 0.2 mm have to grow to 0.4 to 4 mm in diameter to reach a fall
velocity that exceeds the rate of uplift.
Cloud droplets may grow at temperatures above 0 degree Centigrade. The droplet collision
occurs due to differences in fall and lift velocities caused by the differences in droplet size. The
world’s water vapour is equal to about 2.5 cm thickness, on an average, if it is distributed all
over the surface of the globe.

3.2.3 Clouds
Clouds are suspended water in the atmosphere. Clouds are usually the most obvious feature of
the sky. Clouds give us a clue about what is going on in our atmosphere and how the weather
might change in the hours or even days to come. Each type of cloud forms in a different way,
and each brings its own kind of weather.
Clouds play multiple critical roles in the climate system. In particular, being bright objects in the
visible part of the solar spectrum, they efficiently reflect light to space and thus contribute to the
cooling of the planet. A small increase in cloud cover could, in principle, balance the heating
resulting from greenhouse gases. Clouds are the base for precipitation. In summer cloudy days
provide protection from the rays of the sun. In winter cloudy skies at night diminish nocturnal. A
clear calm winter night are usually the coldest and helps in condensation.
3.2.4. Precipitation
Precipitation is the process of transforming the water vapour into a liquid or solid form,
depending upon the temperature of air near the clouds. The term precipitation is a common term.
It includes a variety of forms of precipitation. It includes mist, rain, hail, sleet and snow. The
term precipitation and rainfall are always used synonymously. Precipitation mainly depends on
the water vapour present in the atmosphere. When the air temperature is well below the freezing
point, clouds may form tiny ice crystals.
For precipitation to form, a sequence of four processes must occur:
1) Atmosphere must have sufficient water vapour present, which is cooled to dewpoint,
2) Condensation of water vapour on cloud condensation nuclei
3) Growth of water droplets, and
4) Importation of water vapour.
Precipitation includes rain, snow, sleet, hail, dew, hoar frost, fog and rime. Among these only
rain and snow provide significant totals in the hydrological cycle. Precipitation reaches the
earth’s surface in several forms.Large liquid water droplets form rain. If the ice crystals in the
ice-crystal process do not have time to melt before reaching the earth’s surface, the result is
snow. Sleet refers to pellets of ice produced by the freezing rain before it hits the surface. If the
rain freezes after reaching the ground, it is called freezing rain (or glaze). Soft hails pellets
(sometimes called snow pellets) can form in a cloud that has more ice crystals than water
droplets and eventually fall to the surface. True hailstones result when falling ice crystals are
blown upward from the lower, warmer part of a cloud, where they gain a water surface to the
higher, freezing part where the outer water turns to ice. This process, which often occurs in the
vertical air circulation of the thunder forms, may be repeated over and over to form larger
hailstones.
3.3 Clouds
Clouds have been defined as a visible aggregation of minute water droplets and/or ice particles in
the air, usually above the general ground level.

3.3.1 Dew, fog and cloud
Dew
Dew is moisture that condenses at the ground level. The layer of air within about a metre above
the ground experiences rapid changes in temperature from day to night. Therefore the
temperature may be cooler on the ground than the air above. Consequently, the air temperature
close to the ground may cool to below the level needed for condensation. Moisture therefore is
observed on grass and on the surface of some objects such as those with metal surfaces. If the air
above also cools below the condensation level, fog will form.
Surfaces cool strongly at night by radiative cooling
–Strongest on clear, calm nights
The dew point is the temperature at which the air is saturated with water vapor
If a surface cools below the dew point, water condenses on the surface and dew drops are
formed
Fogs
Fog can be described as a cloud forming very close to or at ground level. It requires air
with sufficient moisture to cool or to be cooled to a temperature to achieve condensation.
Once condensation occurs, visibility decreases dramatically. It therefore becomes very
hazardous.
Fog does not necessarily have to be uniform, or widespread. Some areas may have thick
fog whilst others may miss out completely. Fog is more common in valleys and near
creeks or streams. It also most commonly occurs overnight and during the morning.
However, in colder climates where fog is more common, it may last all day.
Several types of fogs commonly form
– Radiation fog
– Advection fog
– Upslope fog
– Evaporation (mixing) fog
Clouds
Clouds result when air becomes saturated away from the ground
They can be thick or thin, large or small
contain water drops and/or ice crystals
form high or low in the troposphere
Even form in the stratosphere (important for the ozone hole!)
3.3.2. Development and formation of clouds
Clouds are forms of condensation, formed when air is moved away from the land water surface.
In particular, most clouds are condensation forms which have resulted from a lifting process
away from the surface. Those associated with strong rising air currents have vertical
development and a puffy appearance. Those resulting from a gentle lifting or other methods of

cooling tend to spread into layers. Thus the method of their formation is largely accountable for
their appearance.
Cloud Formation
Air contains moisture and this is extremely important to the formation of clouds. Cloud is formed
around microscopic particles such as dust, smoke, salt crystals and other materials that are
present in the atmosphere. These materials are called “Cloud Condensation Nucleus” (CCN).
Without these, no cloud formation will take place. Generally, clouds are made up of billions of
these tiny water droplets or ice crystals or combination of both.
3.3.3. Classification of clouds
Clouds are categorized by their height, appearance and vertical development
1.High clouds
– Generally above 16,000 ft at middle latitudes
– White in day; red/orange/ yellow at sunrise and sunset
– Made of ice crystals
• Main types - Cirrus, Cirrostratus, Cirrocumulus
oCirrus
• Thin and wispy
• Move west to east
• Indicate fair weather
oCirrocumulus
• Less common than cirrus
• Small, rounded white puffs individually or in long rows (fish scales; mackerel
sky)
oCirrostratus
• Thin and sheetlike
• Sun and moon clearly visible through them
• Halo common
• Often precede precipitation
2.Middle Clouds – 7,000-23,000 feet • Main types – Altostratus, Altocumulus
Altocumulus
– <1 km thick
– Mostly water drops
– Gray, puffy
– Differences from cirrocumulus
• Larger puffs
• More dark/light contrast
Altostratus
– Gray, blue-gray

– Often covers entire sky
– Sun or moon may show through dimly
• Usually no shadows
3.Low Clouds - below 7,000 ft
• Main types – Stratus, stratocumulus, nimbostratus
Stratus
– Uniform, gray
– Resembles fog that does not reach the ground
– Usually no precipitation, but light mist/drizzle possible
Stratocumulus
– Low lumpy clouds
– Breaks (usually) between cloud elements
– Lower base and larger elements than altostratus
Nimbostratus
– Dark gray
– Continuous light to moderate rain or snow
– Evaporating rain below can form stratus fractus
4.Vertically developed clouds (via convection)
• Main types – Cumulus, Cumulonimbus
oCumulus
– Puffy “cotton”
– Flat base, rounded top
– More space between cloud elements than stratocumulus
oCumulonimbus
– Thunderstorm cloud
– Very tall, often reaching tropopause
– Individual or grouped
– Large energy release from water vapor condensation
3.4 Precipitation
It is the total supply of all forms of moisture emanating (coming) from the clouds and falling to
the ground. OR Precipitation is deposition of atmospheric moisture.
It is the most important phase in the hydrological cycle.
Precipitation (Ppt) is the immediate source of stream run-off, hence its occurrence, distribution
and intensity determine the hydrologic behavior of streams, namely total discharge, discharge
regime, and quality of the discharge.
The mechanism of how ppt is formed in the high atmosphere is a subject matter of
‘meteorology’.
3.4.1. Origin, forms and types
Origin of precipitation:
Origin or formation of precipitation may be.

1.In the high atmosphere irrespective of soil surface or vegetation cover (rain, snow).
2.Near the ground (mist, fog)
3.At the ground surface (Dew, rime)
FORMATION OF PRECIPITATION:
Formation of precipitation needs following conditions and processes:
Presence of moisture:
Water vapors’ presence in the atmosphere only conditions for precipitation. Water vapors
are always present in cloudy and even in the dry atmosphere.
Condensation process:
Condensation nuclei present in sufficient quantity condense to form droplets due to a
decrease in atmospheric temperature. These droplets are further condensed to form clouds
and in the form of fog near the ground.
Cooling process:
Cooling takes place by:
Mixing of air masses of different temperature by radiation or by the dynamic
ascent of air. Such cooling leads only to fog formation.
The lifting of air produces more cooling which produces:
Convective precipitation (horizontal and vertical mixing of rising air). It is
a light shower to cloudbursts.
Cyclonic precipitation (Convergence of air currents in low-pressure
zones). It is the major source of precipitation in plains, in low lands in
monsoon season.
Forms of precipitation
Ppt can occur in one of the several forms
It may change from one form into another
Basically, we distinguish b/w liquid (rain) and solid precipitation (snow)
Different forms of precipitation can be divided into
A. Liquid form
B. Solid form
Liquid form of precipitation includes:
Dew: water droplets which are deposited by direct condensation from the surrounding are
layers on horizontal surfaces.
Fog: cloud-like mass or aggregate or layer of minute globules of water ice crystals
suspended in the atmosphere or near the earth surface.
Mist: thin fog in which horizontal visibility is greater than 1 mm where water vapors are
smaller than fog
Solid form of ppt includes:
Snow: – ppt in the form of ice crystals results from sublimation i.e. from water vapors
directly to ice.
Snow flank: – is made up of a number of ice crystals fused together.

Hail; – is ppt in form of balls or bumps of ice crystals over 5mm diameter formed by
alternate freezing and melting as they are carried up and down in highly turbulent air
currents.
Sleet: – is frozen raindrops cooled to the ice state, while falling through the air at
subfreezing temperatures.
Glaze: – is the ice formed when drizzle or rain freezes as it comes in contact with the
cold object at the earth.
Rime & Frost – is light feathery sidle like ice crystals which are deposited to when the
dew point temperature is below freezing point.
Grapple: – It is a form of snow in soft pellets having Non –uniform surface.
Types of precipitation
Precipitation is often typed according to the factor responsible for lifting and cooling of
the moist air.
A.Convective precipitation:-
Energy form the source ‘sun’ reaches the earth by passing through different zones in the
form of rays.
On reaching the atmosphere, these reduce the bulk of air and increases its temperature
With less bulk, light air tends to rise in a cooler, denser, surrounding.
For every 200 ft, 1
O
C temp is reduced.
By vertical convection, the ascending air expands and in consequence cooling
dynamically
This leads to convective precipitation.
The difference in temp b/w air masses may be caused by unequal storms (or, it can be
caused by differential cooling of the upper air layers.)
Convective ppt is spotty, and its intensity may range from light showers to cloudbursts.
B.Cyclonic precipitation:-
This is the main type of ppt occurring in the plains and in fact, much of the monsoon ppt
in the lowlands of Pakistan is of this type. (80 to 90% )
As solids heat and cool more quickly than liquids:
A land mass is, therefore, heated more quickly in summer and cooled more easily
in winter than the oceans which surround it and so does the air above the land
mass.
In summer over the hot land mass, the air heats and rises and a low-pressure zone or
cyclone is created.
High pressure, anticyclones, persists over the neighboring cooler oceans, and air currents
begin to converge from the high-pressure zones to low-pressure cyclones.
As these currents meet, they ascend.
The summer monsoon in Pakistan originates from this unequal heating b/w the oceans
(the Indian Ocean and the Arabian Sea)
In winters, the mechanism is reversed, and winters blow off-shores (NW monsoon).

C.Frontal precipitation:-
In conjugation with the convergence of air masses of different temp in low-pressure cyclones,
fronts (a line along which one mass of air meets another that is different in temperature or
density) may be formed and air can be forced to ascend mechanically in that warmer, lighter air
glides over denser, cooler air.
Occasionally, also, cold air gets wedged under warm air
In this way, frontal storms, originate out of the conflict of warm and cold air masses.
Frontal storms are caused by the force of a layer of warm air over a layer of colder as a longer
period. In cold front, warm moist air produces intense rains over a small area. In a warm front,
cold air produces rain falls over a large area.
D.Orographic precipitation:-
Results from the mechanical lifting of warm moist air over mountain barriers.
It is causal by lifting of air when traversing mountain range laying across their paths.
Much of the rain in the outer Himalaya hills both during the summer monsoon and in winter.
3.4.2. Seasonal and spatial distribution
Rainfall is a crucial determinant in agricultural economy as crop yield is vulnerable to spatially
and temporally uneven distribution of rainfall. There are a lot of factors contributing to rainfall
distribution patterns. The economy of Ethiopia is largely driven by rain-fed agriculture.

However, Ethiopia is located in the tropics and varies significantly in regional altitude , ranging
from 210 m below sea level to over 4500 m above sea level in the Simien Mountains in the
north. There are three rainfall seasons in Ethiopia, which are known as the Kiremt, Belga and
Bega. The Kiremt season is the main rainy season and usually lasts from June to September,
covering all of Ethiopia except some parts. The Belga season is the light rainy season and usually
lasts from March to May and is the main source of rainfall for the water-scarce southern and
southeastern parts of Ethiopia. The Bega season is the dry season and usually lasts from October
to February, during which the entire country is dry, with the exception of occasional rainfall that
is received in the central sections. Short cycle crops that are cultivated during the Belga and
Kiremt seasons constitute 5-10% and 40-45% of national crop production, respectively. Long
cycle crops, such as maize and sorghum, are grown during the entire Belga and Kiremt seasons
and are responsible for 50% of national production.
Global Seasonal Variation of precipitation
The temporal variation in global precipitation is directly linked to the seasonal changes in the
heating of the Earth. This affects the movement of global pressure systems and air masses.
Areas of high precipitation are usually moving north and south during the year following the
migration of global pressure and wind systems. The migration of the ITCZ across the Equator
keeps this region very moist.
The north - to - south shifting of ITCZ creates: summer dry climates pole ward of the
subtropical high but summer wet - to the equator ward side. However, into the mid-latitudes,
frontal uplifts keep most of the seasons humid and moist.
As one moves poleward, the precipitation becomes more variable and seasonal as the drying
effect of the subtropical is experienced.
In the cold Arctic or Antarctic very little moisture is available in the air for the formation of
precipitation.
Spatial Variation of precipitation
As we go far from the equator, the rainfall becomes more variable and seasonal. In the tropics
(10
o
- 23.5
o
) the maximum amount of precipitation falls during summer. As the ITCZ shifts
pole-ward it brings precipitation with it. Later as it moves out of the subtropical region and shifts
back to equator-ward, a dry season follows (sets in). The length and intensity of the dry season
tends to increase toward the poleward limits of the tropics.
The subtropics (23.5
o
- 35
o
) can be very dry or wet, depending on the location of ITCZ. The
equator-ward side of the subtropics tends to be quite dry. As one moves poleward of the
subtropics, the amount of precipitation increases though it has a seasonal character. In Africa it is

at about 23.5
o
N that the great Sahara Desert is found where the average annual rainfall is
estimated to be only about 43.8 mm (1.74 in). The extremely dry conditions are a result of the
combustion effect of the subsiding from the subtropical high. But annual precipitation increases
as we move to the poleward limits of the subtropics, especially on the east coast of continents
This is mainly due to the moist air masses that blow onshore.
Generally:-
Precipitation decreases as one moves from the equator toward the subtropical regions and
the poles.
The largest annual precipitation totals straddle the equator while the driest regions on
Earth lie near the Tropic of Cancer.
In addition, precipitation becomes more seasonal as one moves away from the equator
primarily due to the shifting locations of global wind and pressure systems.
The ITCZ is the region where tradewinds originating in the semi-permanent subtropical
highs converge causing air to rise.
The combinations of convergence and convection lifts, the air become cool and
ultimately condense its moisture into clouds and precipitation.
3.5 Air Masses and Fronts
3.5.1. Air masses
An air mass is a body of air with fairly homogenous characteristics extending over a large area,
spreading over more than 1000 kilometers across the surface of the Earth. The depth may extend
to few kilometers and can reach from ground level to the height of the troposphere. When a large
body of air remains over a specific area for a long period, the temperature and humidity
characteristics of the air is influenced by the underlying surface and an air mass forms. The air
mass is characterized by the properties of temperature, moisture (humidity), and lapse rate which
remain fairly homogeneous throughout the air mass. Horizontal changes of these properties are
usually very gradual. Air masses form an integral part of the global planetary wind system.
Therefore, they are associated with one or other wind belt. When two air masses of different
density and temperature meet each other, the transition region is characterized by discernible
gradient of different atmospheric properties. These transition zones are called as fronts which are
the harbinger of major weather changes on the surface of the earth.

3.5.2. Fronts
Front is a zone of transition between two air masses of different density and temperature and is
associated with major weather changes. In reality, the point at which two air masses touch is not
a well defined, abrupt separation. It rather extends in both horizontal and vertical direction. As a
transition region between two adjacent air masses of different densities, a frontal zone is
characterized by significant density gradient. A frontal zone is bounded by a frontal surface. The
frontal surface is the surface that separates two air masses. It is the surface next to the warmer air

(less dense air). Since the temperature distribution is the most important regulator of atmospheric
density, a front almost invariably separates air masses of different temperatures.
3.5.3. Weather forecasting
Weather is the most important factor, which influences agricultural operations and crop
production. A substantial portion of crop is lost due to aberrant weather. The pre-harvest loss
may range between 10 and 100% in various crops. The post-harvest loss is mainly due to rains
and excessive humidity.
Weather forecast is the prediction of weather for the next few days to follow.
Forecasting is the process of estimation in unknown situations from the historical data. Weather
forecasting is one of the most scientifically and technologically challenging problems around the
world in the last century. Weather forecasts are often made by collecting quantitative data about
the current state of the atmosphere and using scientific understanding of atmospheric processes
to project how the atmosphere will evolve in future. Present weather conditions are obtained by
ground observations, observations from ships, observation from aircraft, radio sounds, doppler
radar and satellites. Modern high-speed computers transfer the many thousands of observations
onto surface and upper-air maps. There are various techniques involved in weather forecasting,
from relatively simple observation of the sky to highly complex computerized mathematical
Fronts
1.Warm and cold
2.Stationary
3.Occluded
4.Drylines

models. Weather prediction could be one day/one week or a few months ahead. The accuracy of
weather forecasts however, falls significantly beyond a week. Weather forecasting remains a
complex business, due to its unpredictable nature. It remains a process that is neither wholly
science nor wholly art. It is known that persons with little or no formal training can develop
considerable forecasting skill. For example, farmers often are quite capable of making their own
short term forecasts of those meteorological factors that directly influence their livelihood. The
notable improvement in forecast accuracy that has been achieved since 1950 is a direct
outgrowth of technological developments, basic and applied research, and the application of new
knowledge and methods by weather forecasters.
Types of weather forecasting
Generally, there are two methods used in weather forecasting namely the empirical and
dynamical. The empirical approach is based upon the occurrence of analogues and is often
referred to by meteorologists as analogue scale weather if recorded cases are plentiful.
Dynamical approach is based upon equation and forwards of the atmosphere and is often referred
to as computer modeling. Modern computers make forecasts more accurate than the earth take
photographs of clouds from space. Forecasters use the observations from ground and space,
along with formulas and rules based on experience of what has happened in the past, and then
make their forecast. Meteorologists actually use a combination of several different methods to
come up with their daily weather forecasts. They are
a) Persistence Forecasting; The simplest method of forecasting the weather is persistence
forecasting. It relies upon today's conditions to forecast the conditions tomorrow. It can be useful
in both short range forecasts and long range forecasts.
b) Synoptic Forecasting; This method uses the basic rules for forecasting. Meteorologists take
their observations, and apply those rules to make a short-term forecast.
c) Statistical Forecasting; Meteorologists ask themselves, what does it usually do this time of
the year? Records of average temperatures, average rainfall and average snowfall over the years
give forecasters an idea of what the weather is "supposed to be like" at a certain time of the year.
d) Computer forecasting; Forecasters take their observations and plug the numbers into
complicated equations. Several ultra-high-speed computers run these various equations to make
computer "models" which give a forecast for the next several days. Using all the above methods,
few days.

A. Importance
Weather has many social and economic impacts in a place. Among different factors that
influence crop production, weather plays a decisive role as aberrations in it (up to 50% variations
in crop production). The rainfall is the most important among the required forecast, which
decides the crop production in a region and ultimately the country’s economy. The planning for
moisture conservation under weak monsoon condition and for flood relief under strong monsoon
condition is important in a region. A reliable weather forecasting when disseminated
appropriately will pave way for the effective sustainability. One can minimize the damage,
which may be caused directly or indirectly by unfavourable weather. The recurring crop losses
can be minimized if reliable forecast on incidence of pest and diseases is given timely based on
weather variables. It helps in holding the food grain prices in check through buffer stock
operations. In good monsoon years when prices fall, the government may step in and buy, and in
bad years when price tend to rise, the government may unload a part of what it had purchased.
Judicious use of water can be planned in a region depending up on the forecast.
B. Type of Weather Forecast
There are three types of weather forecasting for agriculture.
1. Short range forecast - It is valid for 24–48 hours with 70–80% accuracy. Short range forecast
gives emphasis on temperature, wind velocity and directions, duration of sunshine, time and
amount of precipitation and relative humidity. It helps in scheduling irrigation, adjusting time of
agricultural operations and protecting plants from frost.
2. Extended forecast - It is valid within 5 days with 60–70% accuracy. It gives emphasis on
type of weather, sequence of rainy days, normal weather, sequence of rainy days, normal weather
hazards in farming such as strong winds, extended dry or wet spells. This type of forecast helps
to determine sowing time and depth of sowing; in planning of irrigation; in making decisions on
harvesting and time of spraying to get higher efficiency and in managing labourers and
equipments.
3. Long range forecast - It is valid up to 4 weeks to the season. It has emphasis in abnormality
of temperature and precipitation. This forecast will be helpful in deciding soil moisture
management, irrigation scheduling, selection of crops, managing irrigation with limited water
supply and deciding cropping pattern and crop yield.

C. Advantage of Weather Forecasting
Though the losses due to weather factors cannot be avoided completely, the losses could be
minimized by making adjustment with weather through timely and accurate weather forecasting.
The weather forecasts also provide guidelines for long range seasonal planning and selection of
crops suited to the anticipated climatic condition. By forecasting anticipated heavy rains,
• Irrigation from wells can be avoided by which we can save electricity.
• The harvesting could be advanced if the crop is in maturity stage.
• Threshing of harvested produce could be done before rains by which crop losses can be
avoided.
Loss of seed, diesel, labourer and time can be avoided by not sowing in unsuitable weather.
Fertilizer losses can be avoided by not applying during unsuitable weather condition for fertilizer
application. Similarly pesticide wastage can also be minimized.
D. Weather Forecasting Organization
Suitable organizations have been set up in most parts of the World for weather forecasting.
Accepted international norms for measuring weather elements and representing them in
international code are being adopted by all the participating countries.
E. Tools
Synoptic charts and crop weather calendar are the tools for making weather forecasts.
1. Synoptic charts - An enormous volume of meteorological data is being collected from all
over the world continuously round the clock through various telecommunication channels. To
assess, assimilate and analyze the vast data, they have to be suitably presented. For this purpose,
the observations are plotted on maps in standard weather codes. These maps are called ‘Synoptic
maps or charts’. Synoptic charts display the weather conditions at a specified time over a large
geographical area. The surface synoptic charts plotted for different synoptic hours (00, 03, 06,
09, 12, 15, 18, 21 UTC) depict the distribution of pressure, temperature, dew point, clouds,
winds, present and past weather. In place of GMT, UTC (Universal Time Co-ordinate) is used.
The upper air charts are also prepared at the standard pressure levels of the atmosphere (different
heights) of the atmosphere wherein the pressure, wind and temperature are plotted. The surface
charts together with the upper air charts provide a composite three-dimensional weather picture
pertaining to a given time. Thus, it gives a birds eye view of the state of atmosphere at a time
over a large area and is a important tool used by operational meteorologists and scientists. The
surface synoptic charts are the most used charts. It contains the maximum number of

observations with the largest number of parameters plotted and often forms the base on which
the pressure level charts are built up. The pattern of the pressure distribution is brought out by
drawing isobars, troughs, ridges, lows, highs, depressions, cyclones, fronts and discontinuities.
These systems are clearly marked and labelled using appropriate symbols and colours.
2. Weather calendar - In order to provide the farmers with an efficient weather service, it is
essential that the weather forecaster should be familiar with the crops that are grown in a
particular agroclimatic zone. The type of forecast warnings to be given depends on the stages of
the crop. The farmers should become familiar with weather bulletins and learn how to interpret.
To meet the above requirement, the detailed information collected from the agricultural
departments has been condensed by the IMD and presented in a pictorial form known as crop
weather calendar. This calendar has three parts viz., (a) Bottom part, (b) Middle part, and (c) Top
part.
(a) Bottom part provides the activities related to crop or information related to phenological
stages of the crop and the months.
(b) Middle part gives information regarding normal weather condition required for active crop
growth. It is divided into different sections according to rainfall, rainy days, minimum and
maximum temperature, pan evaporation and sunshine hours.
(c) Top part gives information related to the weather abnormalities or to take precautionary
measures. Top part is divided into different sections according to dry spell length, high wind,
heavy rainfall and cloudy weather.
3.6. El Nino and La Nino
El Nino and La Nina represent opposite extremes in the El Nino/Southern Oscillation (ENSO).
The ENSO cycle refers to the coherent and sometimes very strong year-to-year variations in sea-
surface temperatures, rainfall, surface air pressure, and atmospheric circulation that occur across
the equatorial Pacific Ocean. El Nino refers to the above-average sea-surface temperatures that
periodically develop across the east-central equatorial Pacific. It represents the warm phase of
the ENSO cycle. La Nina refers to the periodic cooling of sea-surface temperatures across the
east-central equatorial Pacific. It represents the cold phase of the ENSO cycle.
El Nin o and La Nin a are naturally occurring phenomena that result from interactions between
the ocean surface and the atmosphere over the tropical Pacific. Changes in the ocean surface

temperatures affect tropical rainfall patterns and atmospheric winds over the Pacific ocean,
which in turn impact the ocean temperatures and currents. The El Nin o and La Nin a related
patterns of tropical rainfall causes changes in the weather patterns around the globe as seen on
the diagram to the right.
El Nin o typically lasts 9-12 months while La Nin a typically lasts 1-3 years. They both tend to
develop during MarchJune, reaching peak intensity during December-April, and then weakening
during May-July. However, prolonged El Nin o episodes have lasted 2 years and even as long as
3-4 years. Due to the peak intensity during the winter months, impacts to the weather patterns are
also most noticeable in the winter.
A historically strong El Nino that began in the spring of 2015 and peaked during winter 2015 has
since begun to weaken. There are strong indications that the ENSO phase will shift to La Nina by
this fall and a 75% chance this will persist through the Northern Hemisphere winter. What does
this mean for Southeast Alaska? Below is the latest January-February-March 2017 outlook from
the Climate Prediction Center (CPC). It should be noted that the effects of ENSO can be
influenced by other atmospheric parameters, which are hard to determine several months out.

4. Agro-ecology and Agro-climatic classification of Ethiopia
4.1. Climate zones and seasons
Agro-ecological zonation is done in different ways in different countries. In Ethiopia two
classification systems are known that include the traditional agro- ecological zones and the
elaborated agro-ecological zones developed by MOA and EIAR. The traditional zones include
Bereha, Kolla, Woina Dega, Dega, Wurch and Kur where many kinds of crops are grown in each
of these ecological zones. A major attempt to carry out an agro-ecological zonation for the
country. Principal information for characterizing the major agroecological zones (MAZs) and
sub-zones was the moisture regime, the thermal regime, and physio-pedomorphic regions of the
country. All studies confirm the importance of altitudes above sea level as the primary
denominator of agro-ecological zonation.
As the climate is rather complex, it has been the topic of many studies and several classification
systems have been applied to the Ethiopian situation. The Ethiopian traditional system uses
altitude and mean daily temperature to divide the country into 5 climate zones. Both the Köppen
and the Thornthwaite classification systems have also been applied. Another broad classification
can be made using the rainfall distribution though the year – giving the distinction between the
monomodal and the bi-modal and a diffuse rainfall region. However, the most useful for
agricultural purposes is the agroclimatic zones which used the water balance concept, the length
of the growing season (including onset dates) at certain probability levels. In this way three
distinct zones can be identified namely the area without a significant growing period (N), areas
with a single growing period (S) and area with a double growing period (D) (Fig. 1). This
information should be able to form the basis on which to build the seasonal forecasts with
particular emphasis on the specific crop choices in each region.

Ethiopian Seasons
Kiremt or Meher (Summer) - June, July and August are the summer season. Heavy
rain falls in these three months.
Belg (Autumn) - September, October and November are the spring season sometime
known as the harvest season.
Bega (Winter) - December, January and February are the dry season with frost in
morning specially in January.
Tseday (Spring) - March, April and May are the autumn season with occasional
showers. May is the hottest month in Ethiopia.
4.2. Agro-climatic classification of Ethiopia
Climate classifications, the formalization of systems that recognize, clarify, and simplify climatic
similarities and differences between geographic areas in order to enhance the scientific
understanding of climates. Such classification schemes rely on efforts that sort and group vast
amounts of environmental data to uncover patterns between interacting climatic processes. The
earliest known climatic classifications were those of Classical Greek times. Such schemes
generally divided Earth into latitudinal zones based on the latitudes, i.e. the Equator, the Tropics
of Cancer and Capricorn, and the Arctic and Antarctic circles, respectively and on the length of
day. Modern climate classification has its origins in the mid-19
th
century, with the first published
maps of temperature and precipitation over Earth’s surface, which permitted the development of
methods of climate grouping that, used both variables simultaneously.
Methods of Climate Classification
Different schemes of climatic classification are broadly differentiated as either empiric or genetic
methods. Empirical methods make use of observed environmental data, such as temperature,
humidity, and precipitation, or simple quantities derived from them (such as evaporation). In
contrast, genetic methods classify climate on the basis of its causal elements, the activity and
characteristics of all factors (circulation systems, fronts, jet streams, solar radiation, topography
etc.) that give rise to the spatial and temporal patterns of climatic data. Hence, while empirical

classifications are largely descriptive of climate, genetic methods are explanatory. However, for
all practical applications empirical classifications are widely adopted. In this section two classic
and most widely accepted climatic classification schemes of Koppen and Thornthwaite have
been discussed.
Climate Types of Ethiopia
Currently, major agro-ecological zones of Ethiopia include
1)Kolla, lowland (500-1500 masl)
2)Woina-Dega, mid-highland and 1500-2300 masl
3)Dega, highland, with respective elevations above 2300 masl
4)Wurch very cold above 3700 masl
Kolla (Tropical zone) - is lowland (500-1500 masl) in elevation and has an average annual
temperatureof about 27 degree Celsius with annual rainfall about 510 millimetres. The Danakil
Depression (Danakil Desert) is about 125 metres below sea level and the hottest region in
Ethiopia where the temperature climbs up to 50 degree Celsius. Below the Weyna Dega belt
there is the Kolla belt, where there are moisture limitations for crops such as potatoes, wheat and
pulses. However, sorghum is a dominant crop in the Kolla belt, and teff and maize will also be
grown if rainfall permits. It is a belt where temperature conditions are much warmer than in the
highlands, and where there is also higher rainfall variability and recurring drought conditions.
Below the Kolla is the Berha Belt, where no rain fed cultivation is normally possible. Hot
temperatures and persistent drought render the area unsuitable for rain fed agriculture, currently
large-scale irrigation systems along major rivers have been developed in some parts of Ethiopia,
particularly along the Awash River.
Woina dega (Subtropical zone) - includes the highlands areas of 1500-2300 metres in
elevation has an average annual temperature of about 22 degree Celsius with annual rainfall
between 510 and 1530 millimetres. The most dominant Ethiopian agricultural belt is called
Weyna Dega. All major rain-fed crops can be grown in most parts of this belt, particularly teff
and maize. This is a belt where both agro-climatic as well as ecological conditions are highly
suitable for rain-fed farming. The lower part of the Weyna Dega is also suitable for cash
crops such as coffee and tea, or for Inset another major staple crop of southern Ethiopia.

Dega (Cool zone) - is above 2300 metres in elevation with an average annual temperature of
about 16 degree Celsius with annual rainfall between 1270 and 1280 millimetres. The Dega
zone usually is a zone where crops such as barley would be expected to grow in this belt.
Within the Dega, a differentiation can be made between the High Dega belt, where only
barley and sometimes potatoes are grown, but no wheat and pulses, and a Lower Dega or
"Dega proper" belt, which would additionally allow for wheat and pulses, but still be an area
with relatively cold climatic conditions and no teff or maize grown.

4.4. Relationship between climate and crops
A large number of crops are grow in Ethiopia that include cereals (teff, wheat, barley, corn,
sorghum and millet); pulses (faba bean, chickpea, haricot bean, field pea, lentil, soybean, and
vetch); oilseeds (linseed, noug, gomenzer, sesame, and groundnuts), vegetables (pepper, onion,
tomato, carrot, cabbage, and kale), root and tubers (potato, enset, sweet-potatoes, beets, yams);
fruits (apple, peach, plum, grape, banana, citrus, papaya, pineapple, mango and avocado); fibers
(cotton and sisal); stimulants (coffee, tea, chat and tobacco) and sugarcane (EIAR, 2007; 2011).
About 16.5 million hectares of land is devoted to the cultivation of these crops in different
agroecologies of the country. Among all crops, grains are the most important field
crops occupying about 86% percent of the area planted.
1. Bereha (hot lowlands, <500 meters, In the arid east, crop production is very limited , in the
humid west root crops and maize are largely grown)
2. Kolla (lowlands, 500 - 1,500, sorghum, finger millet, sesame, cowpeas, groundnuts)
3. Woina Dega (midlands, 1,500 - 2,300, wheat, teff, barley, maize, sorghum, chickpeas , haricot
beans)
4. Dega (highlands, 2,300 - 3,200, barley, wheat, highland oilseeds, highland pulses)
5. Wurch (highlands, 3,200 - 3,700, barley is common)
6. Kur (highland, >3,700, primarily for grazing).
4.5. Effect of climatic elements on crop production
Crops are influenced by the environment in which they are grown. Nearly 50 % of yield is
attributed to the influence of climatic factors. The following are the atmospheric weather
variables which influences the crop production.
1. Precipitation
2. Temperature
3. Atmospheric humidity
4. Solar radiation
5. Wind velocity
6. Atmospheric gases

1. Precipitation
oPrecipitation includes all water which falls from atmosphere such as rainfall, snow,
hail, fog and dew.
oRainfall one of the most important factor influences the vegetation of a place.
oTotal precipitation in amount and distribution greatly affects the choice of a cultivated
species in a place.
oIn heavy and evenly distributed rainfall areas, crops like rice in plains and tea, coffee
and rubber in Western Ghats are grown.
oLow and uneven distribution of rainfall is common in dryland farming where drought
resistance crops like pearl millet, sorghum and minor millets are grown.
oIn desert areas grasses and shrubs are common where hot desert climate exists
oThough the rainfall has major influence on yield of crops, yields are not always
directly proportional to the amount of Precipitation as excess above optimum reduces
the yields
oDistribution of rainfall is more important than total rainfall to have longer growing
period especially in drylands
2. Temperature
Temperature is a measure of intensity of heat energy. The range of temperature for
maximum growth of most of the agricultural plants is between 15 and 40ºC.
The temperature of a place is largely determined by its distance from the equator
(latitude) and altitude.
It influences distribution of crop plants and vegetation.
Germination, growth and development of crops are highly influenced by temperature.
Affects leaf production, expansion and flowering.
Physical and chemical processes within the plants are governed by air temperature.
Diffusion rates of gases and liquids changes with temperature.
Solubility of different substances in plant is dependent on temperature.

The minimum, maximum (above which crop growth ceases) and optimum temperature of
individual’s plant is called as cardinal temperature.
3. Atmospheric Humidity (Relative Humidity - RH)
Water is present in the atmosphere in the form of invisible water vapour, normally known
as humidity.
Relative humidity is ratio between the amount of moisture present in the air to the
saturation capacity of the air at a particular temperature.
If relative humidity is 100% it means that the entire space is filled with water and there is
no soil evaporation and plant transpiration.
Relative humidity influences the water requirement of crops
Relative humidity of 40-60% is suitable for most of the crop plants.
Very few crops can perform well when relative humidity is 80% and above.
When relative humidity is high there is chance for the outbreak of pest and disease.
4. Solar radiation (without which life will not exist)
From germination to harvest and even post harvest crops are affected by solar radiation.
Biomass production by photosynthetic processes requires light.
All physical process taking place in the soil, plant and environment are dependent on
light
Solar radiation controls distribution of temperature and there by distribution of crops in a
region.
Visible radiation is very important in photosynthetic mechanism of plants.
Photosynthetically Active Radiation (PAR - 0.4 – 0.7µ) is essential for production of
carbohydrates and ultimately biomass.
0.4 to 0.5 µ - Blue – violet – Active
0.5 to 0.6 µ - Orange – red - Active
0.5 to 0.6 µ - Green –yellow – low active

Photoperiodism is a response of plant to day length
Short day – Day length is <12 hours (Rice, Sunflower and cotton), long day – Day
length is > 12 hours (Barley, oat, carrot and cabbage), day neutral – There is no or less
Influence on day length (Tomato and maize).
Phototropism –– Response of plants to light direction. Eg. Sunflower
Photosensitive – Season bound varieties depends on quantity of light received
5. Wind velocity
The basic function of wind is to carry moisture (precipitation) and heat.
The moving wind not only supplies moisture and heat, also supplies fresh CO2 for the
photosynthesis.
Wind movement for 4 – 6 km/hour is suitable for more crops.
When wind speed is enormous then there is mechanical damage of the crops (i.e.) it
removes leaves and twigs and damages crops like banana, sugarcane
Wind dispersal of pollen and seeds is natural and necessary for certain crops. Causes
soil erosion.
Helps in cleaning produce to farmers.
Increases evaporation.
Spread of pest and diseases.
6. Atmospheric gases on plant growth
CO2 – 0.03%, O2 - 20.95%, N2 - 78.09%, Argon - 0.93%, Others - 0.02%.
CO2 is important for Photosynthesis, CO2 taken by the plants by diffusion process from
leaves through stomata
CO2 is returned to atmosphere during decomposition of organic materials, all farm
wastes and by respiration
O2 is important for respiration of both plants and animals while it is released by plants
during Photosynthesis
Nitrogen is one of the important major plant nutrient, Atmospheric N is fixed in the soil
by lightning, rainfall and N fixing microbes in pulses crops and available to plants
Certain gases like SO2, CO, CH4, HF released to atmosphere are toxic to plants

4.6. Climate related hazards in Ethiopia
Ethiopia is vulnerable to climate change induced disasters such as drought, epidemics, flood,
conflict, earthquake, pests, wildfire and landslide, amongst others. These different hazards occur
with varying frequency and severity. Some result in nationwide disasters, while the impacts of
others are more localized.
4.6.1. Drought
It is a climatic abnomaly characterized by deficient supply of moisture. The drought can be
defined in terms of moisture deficiency, which is a balance between the water availability and
water demand.
How water supply becomes deficient? Such deficiency results from, 1) Sub-normal rainfall 2)
Erratic rainfall distribution 3) Excessive water need 4) Combination of all the above three
factors.
Classification of drought: Drought on different basis is generally classified into three
categories.
A.Time of occurrence
B.Based on source of Water availability
C.on the basis of medium:
A.Time of occurrence: According to Thornthwaite (1947) there are four types of droughts,
(a) Permanent (b) Seasonal (c) Contingent and (d) Invisible drought
(a)Permanent drought: It is found in the desert areas where, in no season the
precipitation equals to the water need. Plants therefore are adapted to dry conditions.
Agriculture is impossible without irrigation facilities in this region.
(b)Seasonal drought: This drought can be expected in each year. These droughts are
resulted from large seasonal air circulation changes. Agriculture is possible during the
rainy season or with the use of irrigation in the dry season. Regions of seasonal
drought have well defined rainy and dry seasons.
(c)Contingent drought: This drought results from the irregular and variable rainfall.
They occur in any season and are usually more severe during greatest water need
periods. This drought is unpredictable.
(d)Invisible drought: This can occur at any time, even during period with rainfall, when
the daily rainfall fails to meet the daily water need of plants. As a result, there is a
slow drying of the soil and plants fail to grow at their optimum rate.
B.Based on source of Water availability
There are three types of droughts
1.Meteorological drought
2.Hydrological drought
3.Agricultural drought
(1) Meteorological drought: It is a situation where there is significant decrease from normal
precipitation over an area. The meteorological drought over an area for a year has been defined

as a situation when the seasonal rainfall over the area or place is less than 75 per cent of its long
term average or the normal. It is further classified, as moderate drought if the rainfall deficit is
between 25 to 50 per cent and severe drought when it is less than 25% of the normal.
Meteorological drought can be local or regional or sub divisional. In temporal scale it can last for
a few weeks longer in the season.
(2) Hydrological drought: Meteorological drought if prolonged, results in hydrological drought
with marked depletion of surface water and subsequent drying up of reservoirs, lakes, streams
and river and fall in ground water level.
(3) Agricultural drought: It occurs when soil moisture and rainfall are inadequate during the
growing season to support a healthy crop growth till maturity, causing extreme crop stress and
wilt.
C. on the basis of medium:
On the basis of medium in which drought occurs. Mexico (1929) has divided the drought into
two types.
1. Soil drought:
It is the condition when soil moisture depletes and falls short to meet potential
Evapotranspiration of the crop.
2. Atmospheric drought:
This results from low humidity, dry and hot winds and causes desiccation of plants. This may
occur even when the rainfall and moisture supply is adequate.
Strategy to mitigate drought OR How to overcome the drought:
1. Preventing and recycling of excess runoff
2. Deep tillage to absorb and hold maximum moisture.
3. Timely weed management to control water loss by ET.
4. Planning for suitable cropping system.
5. Selection of short duration and drought tolerant crops.
6. Contingency crop planning for abnormal weather situation.
7. Management of various inputs to suit the climate.
8. Conserving the soil moisture by agronomic practices like mulching use of antitranspirant on
the crops to reduce ET.
9. To apply irrigation.
10. Reduction of plant population to reduce ET.
11. Timing of foliage to reduce ET.
Drought year: The year is considered “drought year “when less than 75% of the normal rainfall is
received. Drought prone area: It is defined as one in which the profanity of a “drought year “is
20 to 40.
Chronic drought prone area: Is defined as one in which the probability of “drought year” is
greater than 40%.
There are seven kinds of agricultural drought:
1. Permanent drought: This type of drought is common in arid regions. Under such condition
rainfall is not sufficient to grow crop in any seasons during year.

2. Early season drought: It is due to delayed monsoon which alters optimum time of sowing,
growing season of crop, incidence of insect and pest deceases crop productivity
3. Mid-Season drought: It is caused by the breaks in the monsoon during crop growing seasons.
Drought during vegetative phase results in stunted growth low leaf area development and
reduced plant populations.
4. Late-Season drought: It is caused due to early withdrawal of rainy season It has impact at
reproductive stage leading to force maturity.
5. Apparent drought: It is caused due to mismatching of the cropping pattern with rainfall
distribution and moisture availability.
6. Contingent drought: It is caused due to irregularity of rain fall in any season.
7. Invisible drought: This type of drought occurs in humid region when daily rain water is not
enough to meet daily water requirement of the crop.
Socio economic drought It combines the impact of meteorological, hydrological and the
agricultural droughts on society in terms of economy in the region.
Agricultural practices to be taken under drought conditions:
1. Drought resistance cultivars of plants / seeds should be preferred for sowing.
2. The use of keeping fallow land as a management technique.
3. Erosion of drought affected soils and adoption of water harvesting technology.
4. Pasture land management or grasses may be grown in drought prone area.
5. Effect of drought on the lives of various insects and pests and on diseases is brought
about by reducing moisture content of their natural environment.
6. In general drought is adverse to agriculture, but it brings a measure of compensation in
greatly reducing economic loss from some pests and diseases. Powdery mildew often
flourishes in dry weather and aphids and birds, which migrate early from drying, grass
to alternative sites such as crops and orchard trees, causing greater damage.
7. Some agricultural practices can influence meteorological condition in the plant /soil
environment and these may be used to advantage under drought conditions e.g. wind
barriers can reduce evapotranspiration in their lee ward side, thus reducing the demand
on the store of soil moisture.
8. Elimination of weed and conserve soil moisture for crop use in later stage.
4.6.2. Flooding
Another climate variability induced shock in Ethiopia is also flood. Flooding caused by rivers
overflowing their banks has regularly affected people and their properties, especially in the
lowland areas of Somali, Afar, Gambella, Oromia and Amhara regional states. Flash floods
affect all regions. Some floods, such as those in 1996 and 2006, triggered disasters which
claimed the lives of hundreds of people, displaced hundreds of thousands and destroyed physical,
natural and economic assets. Ethiopia is mountainous with rugged topography and steep slopes:
the highlands are extensively deforested; rains are sometimes heavy and torrential; water
converges in river basins and causes swelling of rivers. The watersheds of the major rivers are
highly degraded with negligible vegetation cover, reducing infiltration into the ground and

increasing runoff. For instance, in the year 2006, unprecedented flash and river flood disaster
occurred between August and November with a devastating impact, particularly in Dire Dawa,
South Omo, Amahara and Somali regions. In Dire Dawa alone the livelihood and homes of
10,000 people were completely damaged and more than 250 lives were lost and productive asset
worth of birr 70 million was damaged. Moreover, during the same year, in South Omo, the
flooding due to river bank overflow has claimed the lives of 360 people and damaged the
productive assess and livelihood of more than 20,000 people in Dasanach and Ngangatom
districts. Like drought, flood and epidemics, conflict in Ethiopia has also strong relation with
climatic shocks that create scarcity of productive resources among rural community.
Epidemics, both human and livestock, are also another climate change induced shocks which lead greater
famine like that of the Great Famine of Ethiopia. Like drought, flood and epidemics, conflict in Ethiopia
has also strong relation with climatic shocks that create scarcity of productive resources among rural
community. The climate change induced shock arising from conflict goes back to its ancient history. Civil
strife has been happening between different communities in Ethiopia on boarders of land, grazing areas,
freshwater and borders of districts, village and clans. The struggle for resource control has been the major
cause of conflict and tension among the peoples of Ethiopia and many people have lost their livelihoods,
assets, and lives. Other hazards like landslides, volcanic eruption and earth quake are categorized as non-
climate change induced ones. They usually occur in some parts of Ethiopia causing damage to
infrastructure, lives, and livelihoods. However, the literature coverage on such hazards is very minimal.
Within the year 2017-2019, about 3 million are now internally displace due to conflict and climate change
induced challenges. The property of large percentage of this internally displaced is already damaged. The
Eli Nano incidence of the 2015/16 has made about 18 million people to be affected.

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