reference11BRE 109_Climatology_Mutai.ppt

Climatology

1. BRE 109: ENVIRONMENTAL SCIENCE
[Climatology Section]
BRE 3109: Environmental Science [Climatology]

2. What is the Rationale?
•What does a real estate professional do? Does climatology influence the
success or failure of the real estate industry and a real estate’s career?
•Does climatology play any role in the surveys and management of
•Commercial/residential
•Construction
•Estates
•Land/geomatics Planning and development
•Quantity
•Rural practice
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[Climatology]
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3. Course Outline
•Weather, Climate and Climatic Controls
•Solar and Terrestrial Radiation
•Elements of Climate
•Air Pollution Climatology
•Effects of Climate on Forms of Construction
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4. Weather, Climate and Climatic
Controls
Lecture 1
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5. Introduction: Definitions
•Weather- refers to the prevailing state of atmospheric
conditions in a give place and at a given time; the
instantaneous state of the atmosphere, or the sequence
of the states of the atmosphere as time passes
•Climate- long-term average state of the atmosphere
observed as weather over a finite period of time for a
number of years (at least 30 years)
•Difference- popular phrase “????? is what you expect,
????? is what you get”
•Weather and climate are related but not used
interchangeably
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6. Elements of Weather
•Although weather and climate are not identical both
are described by combinations of the same
atmospheric variables
•Primarily these elements are; temperature, pressure,
wind speed and direction, humidity, visibility, cloud
cover, precipitation
•Precipitation comprises all forms of water in liquid
and solid state such as rain, drizzle, snow, haze etc,
that reaches the surface of the earth
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7. Weather Evolution and Description
Atmospheric pressure determines the characteristics of the other
variables
It determines the direction and speed of wind , and it is the wind
that in turn moves air masses of contrasting temperature and
moisture from one locality to another
While air movement is predominantly in a horizontal direction,
there is also some upward or downward movement
Where the motion is ↑, cloud and precipitation are likely, while ↓
air movement (subsistence) favors clear skies
Example: The weather of a given place and at a given time may
be described as; overcast [radiation/cloudcover], cold
[temperature], breezy [wind], humid [moisture] and wet
[precipitation]
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8. Climatic factors/Controls of Climate
•Climatic factors are agencies that produce, or control the nature of
climate of a place
•The most fundamental control is the unequal heating and
cooling of the of the atmosphere in different parts of the earth
•While the earth as a whole loses as much heat to space as it gains
from the sun, some parts experience a net gain and others a net
lose
•The unequal heating occurs on a wide variety of geographic
scales including;
•low and high latitudes (largest and most important), continents
and oceans, snow-covered and snow-free areas, forested and
cultivated land, and even between cities and their surrounding
country sides
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9. Specific controls
•These heating and cooling differences, and the air movements
(winds) they induce, represent the overall general background
control of weather and climate
•The more specific controls are derived from various
geographic factors and include;
–Latitudinal variation in solar radiation
–Altitude
–Distribution of continents (land) and oceans (sea)
–Topography/ local effects
•Orography [mountains]
• forest cover
–Ocean currents, etc
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10. Latitudinal variation in solar radiation
•Latitudinal differences in the amounts of solar energy
received is the most basic climatic control
•In low latitudes the solar radiation is intense and the climate
is warm and tropical
•In high latitudes the solar radiation is weak and the climate is
colder
•The zone of max solar radiation shifts northward and
southward during the year(in tandem with apparent movement
of the overhead sun), thereby producing seasons
•Effectiveness of solar radiation also varies with the nature of
the surface on which the sunshine falls
•High albedo implies less heating- low solar radiation
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11. Altitude
•Temperature decreases with increasing altitude within the
troposphere
•For this reason places at higher elevation are likely to have
lower temperatures and often more precipitation than
adjacent lowlands
•High mountains on the path of prevailing winds, act to block
movement of air and hence the transfer of warm or cold air
masses
•In addition the upward thrust of air on mountains' windward
side and the downward movement on its leeside tend to make
for increased precipitation in the former and a decrease in
the latter
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12. Distribution of continents (land) and
oceans (sea)
•Continents heat and cool more rapidly than do oceans
(why?)
•Consequently non-coastal continental areas
experience more intense summer heat and winter cold
than do oceanic and coastal areas
•Large-scale monsoons- NE/SE monsoons- one of the
major weather systems influencing Kenya (how?)
•Small scale…land/sea breezes- influences coastal
weather- Mombasa morning rains (why?)
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13. Topography/ local effects
•Examples of local features are; exposure, the slope of the land,
and the characteristics of surface cover (vegetation and soil)
•In the NH, south-facing slopes receive more direct sunlight
and have a warmer climate than those with a northern
exposure, which not only face away from the sun, but are also
more open to colder northerly winds
•Areas with sandy, loosely packed soil, because of their low
heat conductivity, are inclined to experience more frosts than
do areas with hard packed soils
•Valleys normally have more frequent and severe frosts that the
adjacent slopes
•Cities are usually warmer than the adjacent country sides
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14. Ocean Currents
•Ocean currents, both warm and cold, which are largely induced
by the major wind systems (how?), are also an important
climatic control
•They are highly important in transporting warmth and chill in
a north-south direction, and so doing give some coastal regions
distinctive climates
A.Equatorial to SH transport result in warming/cooling? why
B.Equatorial to NH transport result in warming/cooling? why
C.NH to Equatorial transport result in warming/cooling? why
D.SH to Equatorial transport result in warming/cooling? why
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15. The End
Thank You for Playing Audience
The next lecture will be on:
“Solar and Terrestrial
Radiation”
Same Venue! Same Timing!
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16. Solar and Terrestrial Radiation
Lecture 2
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17. Earth-Sun Relationship
•Solar radiation is the most important sources of energy, that drive environmental processes
acting at the earth surface
•The amt and intensity reaching the earth surface is affected by the geometric relationship of
the earth wrt the sun (i.e. latitude and earth rotation and revolution around the sun)
•This geometric relationship explains why we have seasons (varying in latitudes)
•In the Midlatitudes- “autumn”, “winter”, “spring” and “summer”
•In the Tropics- “summer” and “winter” not so significant, seasons are usually in terms of
–rainfall amount as “rainy” and “dry” season OR
–temperature as “hot” or “cold” OR
–wind direction into “SW monsoon” and “NW monsoon” as in India
•In the Polar regions- the transition from “summer” to “winter” and vice versa is so sudden
that “spring” and “autumn” largely disappear
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18. Earth Rotation and Revolution
•Rotation refers to the eastward spinning of the earth on its Npole-Spole axis at a
uniform rate once every 24 hours approximately (mean solar day)
•Revolution is the orbiting of the earth around the sun; the earth’s orbit around the
sun is not circular, but elliptical with the sun at its focus
•This (eccentricity) causes the earth’s distance from the sun to vary annually
(average distance is about 150x10^6 kms)
•This annual variations in distance influence a slight change in the receipt of solar
radiation; and is therefore not the cause of different seasons
•Instead seasons are caused by the tilt of the earth’s axis of rotation
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19. The motion of the earth around the sun showing the average
distances during various months
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20. The orbital motion of the earth around the sun
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21. Tilt of The Earth’s Axis
•The earth’s axis is tilted at 23.5
0
from the perpendicular to the plane of the elliptic
•The axis of rotation remains pointing in the same direction as it revolves around
the sun; thus the earth's axis of rotation remains parallel to its position at any time
as it orbits the sun (parallelism of axes)
•The constant tilt and parallelism causes changes in the angle that a solar rays makes
with respect to a point on earth during the year called the “sun angle”
•The most intense radiation occurs where the sun’s rays strike the earth at the
highest angle;
•As the sun angle decreases, the beam of light is spread over a larger area and
decreases in intensity due to the thickness of the atmosphere, increase in
reflection and scattering of light
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22. Seasons, Solstices and Equinoxes
•Since the axis is tilted, different parts of the globe are oriented towards the sun at different times
of the year
•Summer is warmer than winter because the Sun's rays hit the Earth at a more direct angle and
also because the days are much longer than the nights; During the winter, the Sun's rays hit the
Earth at an extreme angle, and the days are very short
•Solstices are days when the
 sun reaches its farthest N & S declinations;
–Winter solstice occurs on Dec 21
st
/22
nd
and marks the beginning of winter in the NH (this is
the shortest day of the year);
–Summer solstice occurs on June 21
st
and marks the beginning of summer in the NH (this is
the longest day of the year)
•Equinoxes are days in which day and night are equal in duration. The two yearly equinoxes occur
when the
 sun crosses the celestial equator.
–Vernal equinox occurs on March 21
st
/22
nd
(beginning of spring in the NH and fall in the
SH);
–Autumnal equinox occurs on Sept 22
nd
/23
rd
(beginning of fall in the NH and spring in the
SH)
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23. The Annual March of Seasons and Solstices and Equinoxes
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24. Consider Idealized Cases
What would occur if, with all other attributes constant;
A.The earth’s orbit was circular?
B.The earth’s rotation/spin was westward?
C.The earth orientation was upright (i.e. not tilted)?
D.The earth orientation was tilted westward?
E.The earth was stationary (i.e. no rotation)?
F.The earth’s rotation was (a) faster? and (b) slower?
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25. What would happen if the orbit of the Earth around the sun
was circular?
•Since Earth's orbit is not very eccentric, we wouldn't notice much
of a difference at all. On Earth, climatological changes over the
course of the year are due mainly to the changing of the seasons as
governed by our axial tilt, and are not significantly influenced by
the marginal changes in the distance of the Sun. Note that the
Earth is actually closest to the Sun when the northern hemisphere
experiences winter.
•Mars, on the other hand, has a much more elliptical orbit than Earth,
and changes in weather due to Mars approaching and receding from
the Sun are actually nearly as significant as those caused by the
changing of the seasons. If the orbit of Mars became circular, it
would have a very pronounced impact on the climate because
annual weather variation would be governed completely by the
seasons.
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26. Planet Mars
•After the Earth, Mars is the most habitable planet in our solar system, after the Earth-
reasons??
•Of all the features of Mars, its 25 degrees axial tilt is most similar to Earth
•And because of this tilt, Mars has seasons; but since it takes twice as long as Earth to
orbit the Sun, the seasons are twice as long; The Martian year is nearly twice as long as
an Earth year(1.88 years)
•Mars also has a very elliptical orbit. Because of this, the difference between its closest
and most distant point along its orbit vary by 19%. This extreme difference makes the
planet’s southern winters long and extreme. The northern winters aren’t as long or cold.
•Evidence point out that unlike Earth, the Mars’ tilt has changed dramatically over long
periods of time
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27. What would happen if the earth’s rotation/spin was westward
•The Sun, the Moon, the planets, and the stars all rise in the E and set in the W.
And that's because Earth spins -- toward the east
•Suppose you are facing east - the Earth carries you eastward as it turns, so
whatever lies beyond that eastern horizon eventually comes up over the horizon
and you see it!
•People at Earth's equator are moving at a speed of about 1,600 km/hr – due to the
Earth's rotation; That speed decreases as you go in either direction toward Earth's
poles
•Now think about what would happen if you stood exactly at the N Pole; You'd
still be moving, but you'd be turning in a circle as Earth spins on its axis
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28. What would happen if the earth’s rotation was westward
•You may wonder why you don't feel this speed: It's because human beings have
no 'speed organs' which can sense absolute speed
•You can only tell how fast you are going relative to something else; …and you
can sense changes in velocity as you either speed up or slow down
•But we cannot really tell whether or not we are just moving at a constant speed
unless something else tips us off!
•Therefore
•“The Sun, the Moon, the planets, and the stars would all rise in the west and
set in the east”
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29. What would happen if the earth’s orientation was not tilted
or tilted differently
•At present Earth is tilted 23.5 degrees on its axis; and this is the primary reason for the
seasons
•When the Earth is tilted toward the sun the NH is in the warm season and when the Earth
is tilted away from the sun the NH is in the cool season
•Since the Earth revolves at a predictable and relatively steady rate around the sun the
cycle repeats itself every year
•In the warm season the sun is higher in the sky and it is warmer and in the cool season the
sun is lower in the sky and it is cooler
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30. What would happen if the earth’s orientation was not tilted
or tilted differently
•If the Earth was not tilted, the plane of the Earth's poles would always be perpendicular to the
sun
•The sun would always be just on the horizon 24 hours a day on every day at the poles
•Every day would be like what it currently is on the equinox since every location on Earth would
have about a 12 hour sunlight days and the noon sun angle would be about the same every day
•There would no longer be seasons- i.e. temperature and precipitation patterns would not vary
much
•It would still be warm at the equator and cold at the poles; the polar areas would have much
more uniform temperatures year round
•Across the Earth, the day to day weather would be pretty much the same
•The sun would rise and set at the same time each day
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31. What would happen if the earth’s orientation was not tilted
or tilted differently
•With no tilt, this change in Earth-Sun distance during the year would
produce a slight impact on the weather pattern
•It must be emphasized the impact would be small since the Earth-Sun
distance is not significantly different during the year
•Earth having tilt has a far greater impact on the weather pattern but without
any tilt the Earth-Sun distance would have the dominant impact on season.
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32. What would happen if the earth’s orientation was tilted
differently
•If Earth's axis was tilted significantly more than it is, the seasonal changes in
weather and length of daylight would be far greater than they currently are
•Summer and winter weather would be more extreme
•Summer days would be even longer than they are and winter days would be even
shorter.
•Even a change of just a few degrees in Earth's tilt would dramatically impact such
things as;
– the size of the polar ice caps (and therefore ocean levels around the world);
–the length of growing seasons and
–the ability of many types of plants and animals to survive
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33. What would happen if the earth stopped spinning suddenly
•The probability for such an event (earth stop spinning) is
practically zero in the next few billion years
•If the Earth stopped spinning suddenly, the atmosphere would
still be in motion with the Earth's original 1600 km/hr rotation
speed at the equator
•All of the land masses would be scoured clean of anything not
attached to bedrock e.g. rocks, topsoil, trees, buildings etc.
(swept away into the atmosphere)
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34. What would happen if the earth stopped spinning gradually
•If the process happened gradually over billions of years, the
situation would be very different
•It is this possibility which is the most likely as the constant torquing
of the Sun and Moon upon the Earth finally reaches it's conclusion
•If the rotation period slowed to 1 rotation every 365 days a
condition called 'sun synchronous', every spot in the Earth would
have permanent daytime or nighttime all year long
•This is similar to the situation on the Moon where for 2 weeks the
front-side is illuminated by the Sun, and for 2 weeks the back side is
illuminated
•This situation for the Earth is not the condition of 'stopped' rotation,
but it is as close as the laws of physics will let the Earth get
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35. What would happen if the earth stopped spinning completely
• If it stopped spinning completely...not even once every 365 days, you would
get 1/2 year daylight and 1/2 year nightime
• During daytime for 6 months, the surface temperature would depend on your
latitude, being far hotter that it is now at the equator than at the poles where
the light rays are more slanted and heating efficiency is lower
•This long-term temperature gradient would alter the atmospheric wind
circulation pattern so that the air would move from the equator to the poles
rather than in wind systems parallel to the equator like they are now
•The yearly change in the Sun's position in the sky would now be just its
seasonal motion up and down the sky towards the south due to the orbit of the
Earth and its axial tilt
•As you moved along constant lines of Earth latitude, you would see the
elevation of the Sun increase or decrease in the sky just as we now see the
elevation of the Sun change from a single point on the Earth due to the Earth's
daily rotation
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36. What would happen if the earth stopped spinning completely
•If the Earth stopped rotating, it's magnetic field would no longer be
regenerated and it would decay away to some low, residual value due
to the very small component which is 'fossilized' in its iron-rich rocks
•There would be no more 'northern lights' and the Van Allen radiation
belts would probably vanish
•Our protection from cosmic rays and other high-energy particles
would also varnish
•This is a significant biohazard
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37. (Electromagnetic) Radiation
•(3) mechanisms of heat transfer- Conduction, Convection and Radiation
•Radiation is the process by which the transfer of heat energy takes place without the necessity
of an intervening medium; Radiant energy is in form of EMR
•EMR is the dynamic form of radiated energy that propagates as wave motion equal to the
velocity of light
•It consists of electrical field (E) which varies in magnitude in a direction perpendicular to the
direction in which the radiation is travelling; and a magnetic field (M) oriented at right angles
to the electrical field
•Both these fields travel at the speed of light (c), which is the highest signal velocity that can be
attained
•This high signal velocity of EMR coupled with its low atmospheric attenuation confers a
unique positive advantage to the EM waves to be used as signals in remote sensing in general
and satellite remote sensing in particular
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38. Electromagnetic Wave
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39. Characteristics of EM Waves
•EM waves (oscillating perturbation in electric and magnetic fields) are defined in
terms of properties like:-
–Amplitude (the height of each crest/peak)
–Wavelength (the length of one wave cycle, which can be measured as the distance
between successive wave crests or troughs; usually denoted by the Greek letter
lambda (λ) and is measured in metres (m) or some factor of metres such as
nanometers (nm, 10-9 metres), micrometers (μm, 10-6 metres) or centimeters (cm,
10-2 metres)
–The frequency (and hence, the wavelength) depends on its source; refers to the
number of cycles of a wave passing a fixed point per unit of time; it is normally
measured in hertz (Hz), equivalent to one cycle per second, and various multiples of
hertz
–Speed (the speed of an electromagnetic wave is the speed of light)
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40. A depiction of properties of a wave
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41. Characteristics of EM Waves
•Wavelength and frequency are related by the following formula:
c=λν
•Where;
–λ is the wavelength (m),
–ν is the frequency (cycles per second, Hz) and
–c is the speed of light (3 x 108 ms-1
•Therefore, the two are inversely related to each other
•The shorter the wavelength, the higher the frequency and vice versa
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42. Monday, September 30, 2024
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43. Wave or Particle Model
•EMR can be represented both as a wave or particle model
•According to quantum physics, the energy of an electromagnetic wave is quantized,
i.e. it can only exist in discrete amount
•The basic unit of energy for an electromagnetic wave is called a photon
•The energy E of a photon is proportional to the wave frequency v,

??????
= v = /
ℎ ℎ?????? ??????
•Where the constant h is the Planck's constant, h = 6.626 x 10-34 J s.
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44. Generation of EM waves
•1The EM waves are generated by the oscillation of the electric charges or fields
and therefore have various frequencies
•When the charges or fields are oscillated with higher and higher frequencies a
whole spectrum of EM waves is generated. For example;
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Frequency of
oscillation
Device Frequency of
generated waves
Wavelength Name of spectral
region
Rough behavior
10
5
-10
6
Radio Transmitter Antenna 10
5
-10
6
3 – 0.3km Radio Waves
10
7
-10
8
TV Transmitter Antenna 10
7
-10
8
30m – 3m FM-TV Waves
10
9
-10
11
Electronic tube( e.g. klystrons and
magnetrons)
10
9
-10
11
0.3m – 3mm Microwave Waves
10
12
-10
14
  10
12
-10
14
0.3mm – 3µm IR Waves
10
14
Atomic or molecular electrons 10
14
0.7µm – 0.4µm Visible Waves
10
15
Electronic processes 10
15
0.3µm UV Waves

45. Electromagnetic Spectrum
•There is a wide range of frequency encountered in our physical world, ranging from the
low frequency of the electric waves generated by the power transmission lines to the very
high frequency of the gamma rays originating from the atomic nuclei
•These wide frequency ranges of EM waves constitute the EM spectrum
•It can be divided into several wavelength (frequency) regions, among which only a
narrow band from about 400 to 700 nm is visible to the human eyes
•Note: The EM spectrum is a continuous range of EMR and that there is no sharp boundary
between these regions
•The boundaries shown in the figures are approximate and there are overlaps between two
adjacent regions
•Wavelength units: 1mm = 1000 μm; 1μm=1000 nm
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46. Electromagnetic Spectrum
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47. Electromagnetic Spectrum
•Refers to the classification of radiation using wavelengths
•Each one of the wavelength category is called a spectral region
•In climatology, the important spectral regions are
Type of radiation Wavelength , λ (µ )
Cosmic rays, Gamma rays, X-rays < 0.001µ
Ultraviolet 0.001 – 0.4µ
Visible 0.4 – 0.74µ
Near infrared 0.74 – 4.0µ
Infrared 4.0 – 100µ
Microwaves 100 – 107µ
Radio 107 – 1010µ
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48. Spectral Regions
•Gamma Rays [<0.30nm] and X-Rays [0.03—30.0nm] is completely absorbed by the atmosphere
•Ultraviolet [0.03—0.40μm]: Hard UV [0.03—0.3μm] is completely absorbed by the atmosphere;
Photographic UV [0.30—0.40μm] is available and detectable with film and photo detectors but with severe
atmospheric scattering
•Visible Light [0.4 to 0.7μm] is a narrow band of EMR is available for R/S and can be imaged with
photographic film. The light which our eyes - our "remote sensors" - can detect is part of the VIS spectrum;
small relative to the rest of the spectrum. There is a lot of radiation around us which is "invisible" to our eyes,
but can be detected by other remote sensing instruments and used to our advantage.
•Infrared [0.7-300μm] is more than 100 times as wide as the visible portion; sensitive to plant and soil water
content, which is a useful measure in studies of vegetation health; used for distinguishing clouds, snow, and
ice, mapping geologic formations and soil boundaries
•Microwaves (Radar) [1mm-1m] is of more recent interest to R/S; covers the longest λs used for remote
sensing. MWs can penetrate clouds, fog, and rain. Images can be acquired in the active or passive mode.
Radar is the active form of MW remote sensing.
•Radio and TV Waves [10cm-10km] is the longest λs portion of the EM spectrum
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49. Solar Radiation
•Radiant electromagnetic energy emitted by the sun
•The sun at a temp of about 6000
0
K is the source of nearly all of
our energy
•Max emission of solar rad occurs at relatively shorter
wavelengths in the visible spectrum 0.4 – 0.7 (SWR)
•Hence solar radiation is also referred to as short wave radiation
•
•Energy of the sun is produced when hydrogen is converted to
helium
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50. Terrestrial Radiation
•The earth absorbs the solar radiation and then emits it back to
space at longer wavelengths
•The earth approaches an average temperature of 294
0
K, and
gives out long-wave radiation in the range of 4.0µ to 80µ with a
maximum at 10µ
•Terrestrial radiation is therefore termed as long wave radiation
•Water vapor in the atmosphere is a strong absorber of long
waves, particularly between 5.5µ and 7µ and above 27µ
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51. Short and Long Wave Radiations
•Radiation of wavelength less than 4µ is called shortwave radiation
•Radiation of wavelength greater than 4µ is called long wave
radiation
•Solar radiation is received only during daylight hours
•Terrestrial radiation is lost continuously during both day and night
Monday, September 30, 2024
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51

52. Greenhouse Effect
•The earth-atmosphere system is in a radiative equilibrium
•Net incoming solar radiation is balanced by a net amount
outgoing long wave radiation
•Outgoing infrared radiation is absorbed by greenhouse gases
and by clouds
•These in turn radiate infrared radiation some of which falls
back on the earth’s surface and warms further
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53. Monday, September 30, 2024
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54. Greenhouse Effect/…
•The effect of this long-wave radiation from the atmosphere is that
the earth’s surface does not lose as much heat as it would if the
atmosphere was absent
•This keeps the earth’s atmosphere warmer by about 33˚C
•This phenomenon is the green house effect
•Green house gases act as insulators (blankets) of the earth
Monday, September 30, 2024
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54

55. Factors Determining Radiation at the Earth’s Surface
•Since the sun is the ultimate source of energy in the earth-
atmosphere system, its variability determines the variability of
climate in both time (when) and space (where)
•Intensity of radiation reaching a horizontal surface of the
earth depends on:-
* solar output * actual earth-sun distance
* altitude of the sun* length of the day
* atmospheric composition * clouds
* latitude * elevation
* aspect * land and sea
distribution
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56. Solar Output
•Quantity of the sun’s radiation reaching the outer limit of the
earth’s atmosphere is called the solar constant
•The solar constant is the amount of incoming EMR per unit area
that is incident on a plane perpendicular to the rays at the outer-
limit of the earth’s atmosphere
•It is a physical constant denoted by S
o and has a value of 1370
Wm
-2
•It fluctuates by about 1 to 2% per year
– This corresponds to temperature changes of about 1°C
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56

57. Earth-Sun Distance
•Intensity of the radiation at a locality is inversely proportional to the square of
the distance from the source
•The orbit of the earth is elliptical, hence d varies as the earth revolves around the
sun once per year (365¼ days)
•The earth is nearest the sun in January (perihelion)- highest intensity of radiation
(January 3)
•The earth is furthest from the sun in July (aphelion)- lowest intensity of
radiation (July 4)
•The average earth-sun distance is 150 million km
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2
1
d
E

58. motion of the earth around the sun showing the average
distances in various months
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59. Altitude of the Sun
•The altitude of the sun is the angle at which the sun’s rays reach the earth
•Distribution of energy on an intercepting surface depends on the angle of the incoming rays
•There is more energy on a perpendicular surface than on a slanting surface
Where,
•I
s is the radiation intensity on a flat surface
•I
o
is the Incident solar beam
•Θ is the angle e between I
o and the zenith
•The sun’s altitude depends on the;
•Latitude
•time of day
•season
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cos
osII

60. The sun’s altitude depends on the
latitude
time of day
season
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61. Altitude of the Sun/…
•During the day (diurnal) cycle
– maximum intensity occurs when the sun is directly overhead (cos0˚=1) at noon
–minimum intensity occurs at sunrise or sunset (cos90˚=0)
•Seasonally, the sun is overhead at the Equator
– on March 21 and September 22 during the two equinoxes, or equal day length
•Latitudinally, the sun is overhead (during the solstices) at the;
–Tropic of Cancer on June 22 and
–Tropic of Capricorn on December 22
•Radiation intensity ranges from 92% in June and December (solstices) to 100% of the
maximum in March 21 and September 22 (during the equinoxes)
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62. Length of the Day
•The length of day depends on the tilt of the axis of rotation of the earth to
an imaginary plane of rotation of 23½°
•This determines the number of hours of sunshine
–When the earth is nearest the sun in January (perihelion)- longer
daytime hours; more radiation
–When the earth is furthest from the sun in July (aphelion)- shorter
daytime hours; less radiation
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62

63. Atmospheric Composition
•The atmosphere is composed of gases (N2, O2, CO2), liquids (water vapour) and
solids or aerosols(dust, smoke, sea salt)
•These atmospheric constituents weaken the solar radiation through selective
scattering, diffuse reflection and absorption processes
•The atmosphere;
–absorbs about 20% of solar radiation
–reflects/scatters 27% of solar radiation
•However, it is;
–largely transparent to shortwave radiation
–absorbs nearly all of the terrestrial radiation
–heated from below by long wave radiation
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64. Clouds
•Cloud cover prevents solar radiation from reaching
the earth’s surface
• Clouds reflect (23.2%) of the incoming solar
radiation
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64

65. Latitude
•The highest intensity of radiation occurs at the tropics (Tropic of Cancer and
Capricorn)
–The subtropical belt has little amount of cloud cover
•more radiation reaches the surface
–The sun’s rays are nearly vertically overhead in the tropical belt almost
throughout the year compared to 3 months
•Lowest intensity of radiation occurs at the the equatorial belt (6°N-6°S)
–sun’s rays are nearly vertically overhead in the equatorial belt for only 1
month
–equatorial belt is cloud covered most of the time
•Less radiation reaches the surface
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65

66. Elevation
•Elevation (Altitude) is the height of a point on the earth’s
surface above the sea level
•In clear sky conditions high elevations areas generally receive
more direct radiation
•But high elevation areas are observed to be cooler than low
elevation areas
–the density of air decreases with altitude
–more terrestrial radiation is lost to space
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67. Aspect
•Aspect is the angle at which solar radiation impacts a surface
–I
s is the radiation intensity on a sloping surface
–I
o
is the incident solar beam
– is the angle between I
o
and a line normal to the sloping surface
•Radiation intensity received by the surface decreases with 
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67
cos
os
II

68. Land and Sea Distribution
•Water tends to store the incident radiation it receives; Land quickly loses
the radiation it receives to the atmosphere
•The differences in their thermal properties is due to such factors as;
–specific heat capacity [1 vs 0.3-0.5 cal/g/oC)- land heats up (and cools) 2 to 3
times faster than water]
–molecular structure (transparency and fluidity)
–reflectivity [unlike snow, water reflects less radiant energy than land, except
in the morning and evening]
–phase changes of water [latent heat capacity]
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69. Global Energy Balance
•Balance between the net ISWR and the net OLWR- the amount of energy received
by the earth and its atmosphere equals the energy given out
• Even though the average temperature at any one place varies from one year to
another, the earth’s overall average equilibrium temperature does not vary much
from one year to the next.
•If the net OLWR was not equal to net ISWR, the physical environment of earth-
atmosphere system would either:
– warm up OR cool down [as a consequence of radiative imbalance]
•The earth-atmosphere system maintains its temperature nearly constant by losing an
amount of energy equal to the energy received
•This radiative equilibrium is the global energy balance
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70. Monday, September 30, 2024
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71. The Global Energy Balance cont.
•When absorbed into the earth-atmosphere system, the solar energy:
–Warms the various surfaces of the earth in accordance with their specific
heat capacity
–Drives the air and water movements in the atmosphere and oceans
•The atmosphere of the earth is heated from below by terrestrial radiation
•Therefore air temperature decreases with height
Monday, September 30, 2024
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72. The End
Thank You for Playing Audience
The next lecture will be on:
“Elements of Climate”
Same Venue! Same Timing!
Monday, September 30, 2024
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73. Spatio-Temporal Evolution of
Elements of Climate
Lecture 3
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74. Introduction
Primary elements of climate include;
1)Temperature
2)Pressure
3)Wind speed and direction
4)Humidity
5)Visibility
6)Cloud cover
7)Precipitation
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75. Temperature
•The radiant energy from the sun does not heat the air directly
•The earth is heated by the sun’s radiation, and thereafter it heats the underlying air by
conduction [from below]
•The heat is transported upwards by convection
•The variation of climatic elements with time and space are termed as temporal and
spatial variation, respectively
•The temporal and spatial variation of temperature depend directly on the temporal and
spatial variation of the net radiation
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76. Diurnal Variation of Temperature
•The diurnal temperature change is produced by the daily variation of the incoming
shortwave radiation and outgoing terrestrial radiation
•Maximum insolation is received at noon
•It takes 2-4 hours for the earth to earth up in response to the sun’s radiation
•The time delay is called is called the lag of the maximum
•The minimum temp occurs just before sunrise
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77. Diurnal Variation of Temperature
•Unlike for solar radiation, the diurnal temp curve is not symmetrical
•The duration from the min to max temp is shorter than the fall from the max to the
min temp
•The cycle of temperature during a 24-hour period is called the daily march of
temperature
•The difference between the highest and the lowest temperature is called the daily
range of temperature
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78. Diurnal Variation of Temperature and Radiation
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79. Diurnal Variation of Temperature
•The factors influencing the daily range of temperature
include;
–the material of the surface (land/sea, soil type, etc.);
–speed of wind;
–the nature of neighbouring surface and
–overhead cover (e.g., clouds, trees etc.)
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80. Diurnal variation of temperature-Material of the Surface
•Changes in temperature in a 24-hour cycle are much more gradual over the sea
than land
•The heating and cooling of water and land differs because of three factors;
–specific heat capacity [1 vs 0.3-0.5 cal/g/oC)- land heats up 9and cools) 2 to 3
times faster than water]
–molecular structure (transparency and fluidity)
–reflectivity [unlike snow, water reflects less radiant energy than land, except
in the morning and evening]
–phase changes of water [latent heat capacity]
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81. Diurnal variation of temperature-Material of the Surface
•The diurnal range of sea surface temperature, SST does not usually exceed
1
o
C
•In desert regions, surface air temperature may vary by as much as 20
o
C
between day and night
•How would the lag in daily temperature experienced over land compare to
the daily temperature lag over water? Draw diagrams for each!!
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81

82. Diurnal variation of temperature-Speed of Wind
•The diurnal variation of surface temperature is greatest in calm
conditions
•Windy conditions cause air in the lowest layers to mix with the air above
•This tends to reduce the diurnal range of temperature
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83. Diurnal variation of temperature-Neighbouring Surface
•The flow of warm air or cold air from adjacent areas can influence the temperature at a particular
place e.g.;
–Coastal effects [temp variations at the coast are large if the wind is offshore and small if
onshore- the moderating effect results in warmer nights and cooler days]
–slope effects [anabatic (upslope) winds have a cooling effect on the higher grounds during the
day & [Katabatic (down slope) winds have a cooling effect on the valley during the
night]..which one is stronger?
–urban effects [temp in large urban areas may exceed those in nearby rural fields by 1
o
C to 5
o
C
on calm clear (cloudless) nights. On windy nights temp in the city and surrounding area are
nearly equal
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84. Diurnal variation of temperature-Overhead Cover
•Cloud cover– during the day clouds reflect most of the sun’s radiation back to space,
thus reducing the temperature maximum
•Clouds also act as a greenhouse by preventing the loss of the earth’s radiation,
thereby increasing the daily minimum temperature
•Hence cloudiness reduces the diurnal range of temperature
•Forest cover (vegetation)- during the day forests intercept the incoming radiation,
and only a fraction reaches the ground surface- this lowers maximum temperature
•During the night forests have a blanketing effect; this increases minimum
temperature
•Hence, forests have a moderating effect on surface temperature
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84

85. Seasonal Distribution of Temperature
•The cycle of temp during a 12-month period is called the annual march of temp
•It takes 1-1/2 months for the sun’s heat to be released by the earth and the
atmosphere
•The annual temp range is the difference between the average temp of the warmest
and coldest months
•The annual range of temp depends on;
–latitude
–continentality (nature of the surface)
–Winds
•The annual temp range is smallest at the equator and increases with latitude- The
highest temperature range in the year occurs at the tropics of Cancer and Capricorn
(poles)
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86. Seasonal Distribution of Temperature
•The temperature range is larger over continents compared to oceans
and coastal areas because ocean surfaces delay in responding to insolation
•The lag of maximum may reach 2 months over oceans and coastal areas
•Winds can either increase or decrease temp e.g.
–air moving from the equator to the pole increases polar temp whereas
–air moving from cold oceans to warm continents has a cooling effect
(monsoons)
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87. Seasonal variation of temperature and radiation
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88. Spatial Variation of Temperature
•Spatial variation of temp depends on
–latitude
–continentality
–altitude
•Generally temp are higher in the tropics and decrease poleward because of surface
insolation; they may however be modified by wind flow
•Land surface tend to have higher temp than oceans during summer and lower temp
during winter
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89. Spatial Variation of Temperature
•Are summers and winters in the NH warmer and colder, respectively,
compared to the SH? Why?
•Does the NH have higher annual mean temp than the SH? Why?
•The warmest latitude circle on the yearly average is 10 degrees N/S?
•Temp generally decrease with height within the troposphere due to the effect of
density and adiabatic cooling
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90. Vertical thermal structure of the atmosphere
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91. Vertical structure of pressure in the atmosphere
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92. Global latitudinal variation of surface pressure/flow patterns
over uniform earth’s surface
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93. Spatial variation of surface pressure/flow patterns
•Pressure variations occur due to spatial variations in temp produced by
differential heating of the earth’s surface and atmosphere
•The pressure belts shift northward in the NH summer and southward in the
SH summer
•The mean sea level pressure patterns are not regular due to the uneven
distribution of land and seas surfaces
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94. Spatial variation of surface pressure/flow patterns
•Areas of low or high pressure occur in preferred positions with low or high
pressure at the centre of the pressure cell
•Cyclones (equatorial trough and sub-polar low) and anticyclones
(subtropical ridgeline) distort the general flow pattern
•Although wind is caused by several forces in the atmosphere, the most
important are the PGF, Coriolis and gravity force
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95. Wind
•The speed of wind generally increases with height within the troposphere because the effect of
friction decreases upwards
•The diurnal cycle of the speed of wind is determined by the daily variation of heat energy/temperature
•Wind speed reaches a max from about midday until late in the afternoon- This is due to the vertical
transfer of momentum from higher levels down to the surface by convection currents
•Late in the afternoon temp falls, convection is reduced and wind speed decreases and reaches a
minimum at about dawn
•Variation of wind direction (veering and backing)
•Monsoons and local winds (breezes, slope winds, rural-urban winds -UHI)
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96. Vertical variation of wind speed
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97. Diurnal variation of wind, temp and humidity
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98. Latitudinal variation of cloudiness/precipitation
•Max convective cloudiness occurs in the tropics, especially near the equator
•These clouds are deep and the rainfall is heavy
•Maximum frontal cloudiness occur in the mid-latitudes; these clouds are shallow and rainfall is
light
•Minimum cloudiness occurs in the subtropics since high pressure zones are associated with
subsidence and hence fine weather (dry)
•Polar latitudes receive very little precipitation, which is mostly in form of snow
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99. Latitudinal variation of cloudiness/precipitation
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100. The End
Thank You for Playing Audience
The next lecture will be on:
“Air Pollution
Climatology”
Same Venue! Same Timing!
Monday, September 30, 2024
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100

101. Air Pollution Climatology
Lecture Four
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102. Air Quality Status- Nairobi, Kenya
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103. Definition
•The earth’s atmosphere contains gases such as oxygen (21%),
carbon dioxide (0.3%), nitrogen (78%), argon (0.03%), etc in
fixed ratio
•But, due to some or other reasons, the ratio of all other gases
except oxygen increases in the atmosphere resulting in its
pollution
•Therefore, pollution of air is the increase in the concentrations of
the constituents or due to the presence of extraneous materials as
a consequence of natural or man-made activities
•Air pollution is the release or occurrence of any foreign materials
or gases into the atmosphere, which may be harmful to man,
animals and vegetation etc.
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104. Definition
•Any condition of the atmosphere in which contaminants (pollution
effluents) are present in such quantities and for such duration that
they can produce undesirable (harmful) effects on man and the
environment
•The presence in the outdoor atmosphere of one or more
contaminants (pollutants) or combination thereof in quantities and
duration as may tend to be injurious to human, plant, or animal life
or property or which unreasonably interferes with comfortable
enjoyment of life or property or the conduct of business
•Contaminants versus pollutants???
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105. Definition
•There has always been a balance between natural sources and sinks to
air pollution, but human and industrial activities have created pollution
problems that overburden the natural removal systems for pollutants
•Receptors are inanimate as well as animate bodies that receive and are
seriously affected by pollutants
•Therefore:- the addition of any substance to the atmosphere at a rate
faster than at which the atmosphere can accommodate it by absorbing,
dispersing or breaking down, and that would harm man and the
environment
•If the pollutant is soluble in water, it can enter the food chain directly
through or via aquatic organisms
•If the pollutant is not soluble in water, it may settle on plant leaves and
fruits and thus may enter the food chain
•Contrasted with environment, water, indoor and noise pollution
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106. Classification of Pollutants
•Air pollutants may be divided into two broad categories:
primary and secondary
•Primary pollutants are those which exist as initially emitted
from their source e.g.,
–sulphur dioxide (SO
2)
•Secondary pollutants are those formed in the atmosphere by
chemical interactions and photochemical reactions among
primary pollutants and other gases e.g.,
–sulphuric acid mist (H
2
SO
4
)
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107. Types of Pollutants
•Two types of pollutants: gaseous and particulate pollutants
•Gaseous pollutants include: (sulphur dioxide, oxides of nitrogen
[especially nitric oxide (NO) and nitrogen dioxide (NO
2)], carbon
monoxide (CO), hydrogen sulphide (H
2S), ozone (O
3), etc.
•Particulates are substances in the atmosphere that are not gaseous
(i.e., liquids and solids).
•Examples include: dust (may contain elements like calcium,
aluminum and silicon), smoke and soot (mainly contain organic
compounds), plastics, asbestos, acid mist (e.g., H
2SO
4), metallic
particles (e.g., cadmium, lead, nickel, mercury, arsenic and
vanadium)
•Solid and liquid airborne suspensions are called aerosols
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108. Sources of Pollutants- Natural
•Pollutants are emitted into the atmosphere through natural
processes and anthropogenic sources (i.e., man’s activities)
•Examples of natural sources of pollutants include:
–pollen from flowers
–dust blown by the wind (dust storms)
–decomposition (decay) of organic matter
–volcanic eruptions (which emit ash and gases) e.g., Krakatoa,
Indonesia (1883) & Pinatubo, Philippines (2000)
–Sea sprays (yielding sea salt nuclei)
–Forest fires ignited by lightning (yielding smoke an trace gases)
–Terpenes (substances containing hydrogen and carbon) from trees
(especially conifers)
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109. Sources of Pollutants- Anthropogenic
•There are four main anthropogenic sources
–Combustion processes
–Mineral industries
–Chemical process industries
–Food and agricultural process industries
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110. Anthropogenic- Combustion Processes
•These comprise combustion of:
– fossil fuels (i.e. coal and petroleum products) and
–incineration (i.e. burning to form ash) of refuse and combustible
waste
•Fossil fuels yield:
–SO
2, SO
3, NO
x and CO
•Incineration produces:
– CO, NO
x
, S0
2
, hydrocarbons and ammonia
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111. Anthropogenic- Mineral Industries
•These include:
–metallurgic industries (which process minerals like coal, iron and non-ferrous
sulphide) and
–non-metallurgic industries (involved in the processing of glass, ceramics (clay) and
production of cement)
•Metallurgic industries mainly emit;
–dust, SO
2, trace metals and metallic oxides
•Non-metallurgic industries emit:
–hazardous dust
•Mining emits:
–gases like methane
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112. Anthropogenic- Chemical Process Industries
•Chemical processes are mainly of four types:
•Pulp and paper industries- emit particulates and compounds
of sulphur
•Petroleum refining- emits SO
2, SO
3, NO
2, NO, NH
3 and
particulates
•Organic chemical industries (such as in the production of
plastics, rubber, paint, insecticides, soaps and detergents)-
emit CO and SO
2
•Inorganic chemical industries (such as in the manufacture of
manure and acids- emit SO
2
, H
2
S, NO
x
, hydrogen fluorides
and particulates
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113. Anthropogenic- Food and Agricultural Processes
•Examples of agricultural processes include:
•Crop spraying (for pest control)-
–emits phosphates, arsenic, lead and hydrocarbons
•Biomass burning-
–mainly emits methane (CH
4) and nitrous oxide (N
2O)
•Drying, preserving and packaging food-
–mainly emit dust
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114. Air Pollution Emission Sources
•Point source: single, identifiable source- without geometric
dimensions- either elevated or at ground-level
–instantaneous point source e.g., bomb blast
–continuous point source e.g., industrial chimneys
•Line sources: 1-D source of air pollutant emissions
–instantaneous line source …rare e.g., for military purposes
–continuous line source e.g., vehicular traffic on a roadway
•Area source: 2-D source (e.g., the emissions from a forest fire or
a landfill
•Volume source: 3-D source- essentially an area source with a
third (height) dimension e.g.,
–fugitive gaseous emissions from piping flanges or valves at various
heights within industrial facilities such as oil refineries and
petrochemical plants
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115. Effects of Weather Conditions on Air Pollution
•The concentration of air pollutants (air quality) in any region
depends greatly upon the characteristics of the weather conditions
(and is therefore sensitive to climate change)
•Weather elements influencing air quality include:
–Wind speed and direction
–The vertical temperature distribution
–Moisture
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116. Wind
•It determines the rate at which pollutants are carried away from
their sources.
•Concentration of contaminants are diluted and dispersed both
vertically and horizontally into increasingly larger volumes of air
by the turbulence of wind.
•Turbulence of a moving air mass increases with average speed.
•High winds most rapidly reduce the concentration of pollutants
while moving them far from their origin while low wind speeds,
contaminants tend to remain near their source.
•Surface features of the land can influence the local wind speed
and direction e.g. winds across mountain valley are often
channeled in the direction of the valley
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117. Temperature
•Seasons of low temperature bring increased fuel consumption for the heating
of homes and business.
•Temperature increases in the vertical and vertical turbulence due to unstable
air carries pollutants high into the cooler air above.
•In conditions of unstable air above giving rise to temperature inversion, the
movement of pollutants produced at ground level increases.
•This is due to the warm air forming above the cooler air mass making an
envelope.
•Thus during the day, warm surface air and vapors produced by industries is
steadily cooled while rising.
•When this air reaches the upper limits of the cold air mass, it becomes
heavier than the warmer air mass above.
•It is unstable to rise and the contaminants are trapped between the upper and
lower air masses.
•Gradual cooling of the stagnant air mass deposits the pollutants to the
surface below
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118. Moisture
•Water in the form of rain, snow or sleet, does not affect
pollutant concentrations as directly as wind or
atmospheric stability.
•Rain or precipitation is generally regarded as an air-
cleansing agent, although it is very inefficient.
•The moisture content of the air is an important factor in
the deterioration of materials caused by various
pollutants.
•In addition, fog usually, limits the amount of solar heat
energy reaching ground level.
•This, in turn affects the vertical dispersion of air bone
contaminants.
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119. Methods of Estimation of Air Pollution
Concentration Levels
•Personal monitoring to measure actual harm exposure
•Mathematical models that considers pollutants
concentrations and human activities as a function of
space and time in order to estimate exposure.
•Exposure is defined as a measure of pollutant
concentration available at the exchange boundaries of a
receptor at a specific time
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120. Transformation and Removal of Air Pollutants from
the Atmosphere
•Aerosol particles typically stay one week or less in the troposphere.
•Before particles return naturally to the Earth's surface, their size,
concentration, and chemical composition may change.
•The mechanisms whereby pollutants are removed from the
atmosphere are called scavenging processes
•Oxidation is a prime removal mechanism for inorganic as well as
organic gases
•There are two pathways for the atmospheric deposition:
–wet deposition and
–dry deposition
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121. Wet Deposition
•It is the process where gaseous and particulate components are
scavenged (taken up) by the means of cloud, fog and rain droplets
or snowflakes and subsequently transferred to the ground.
•Four different processes can be distinguished
–Precipitation scavenging, i.e. the removal of species by a
raining cloud.
–Cloud interception, i.e. the impaction of cloud droplets on the
terrain usually at the top of tall mountains.
–Fog deposition, i.e. the removal of material by settling fog
droplets.
–Snow deposition, i.e. the removal of material during a
snowstorm.
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122. Precipitation scavenging
•Three steps are necessary for wet deposition to take place.
–The pollutants need to come into contact with condensed water
in the atmosphere
–The pollutants must be scavenged by the droplets
–It has to start raining before the condensed water evaporates back
into water vapor, thereby releasing the pollutants back into the
air.
•Below-cloud scavenging refers to the process where pollutants are
taken up in falling raindrops i.e. rainout.
•In-cloud scavenging refers to the process where pollutants are taken
up in droplets inside the cloud. These pollutants will only wet
deposit if it starts raining from the cloud i.e. washout
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123. Dry Deposition
•This is the process of transferring gaseous and particulate
components to the ground in the absence of precipitation.
•Turbulence in the air is responsible for this process together with
a number of other factors e.g.,
–The roughness of the surface.
–The vegetation on the surface.
–The time of day and year (due to seasonal and diurnal
differences in vegetation cover, turbulent conditions,
atmospheric stability and planetary boundary height).
–The physical and chemical properties of the component being
deposited.
–The moisture content on the surface
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124. Sedimentation
•This is the simplest dry deposition mechanism
•Particles fall under the influence of gravity
•The heaviest particles are removed from the atmosphere by
sedimentation and, because they are heavy, they are found close
to their source
•In a dry still atmosphere, sedimentation processes control how
big the largest particles in the atmosphere are
•Dry deposition is, however, strongly related to atmospheric
movements, like wind
•Wind can keep large particles in the air and can carry them long
distances away from their source
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125. Effects of Air Pollutants
•Air pollution problem has local, regional, continental and
global ramifications
•Local level pollution affects the local, municipal, town and
city levels
•Regional and continental level pollution affects the
troposphere and the stratosphere levels, respectively
•Global level pollution affects the entire atmosphere
•Effects of air pollutants may be classified into two categories:
–community problems: effects on human and animal health, vegetation
and materials
–global effects: may result in climate change
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125

126. Effects of Pollutants on Human Health
•Human health can be affected adversely by gaseous and toxic
metals
•Gaseous pollutants : SO
2
, CO, NO
x
, and O
3

–SO
2
causes eye irritation, coughing and respiratory diseases
–CO causes oxygen-deficiency in body organs, headache,
breathing difficulties and coma
–Oxides of nitrogen (especially NO
2) cause respiratory diseases
(especially a lung damage illness called bronchitis)
–O
3 causes extreme fatigue, respiratory diseases and swollen
blood vessels
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127. Effects of Pollutants on Human Health
•Toxic metals: Lead, Cadmium, Nickel, Mercury, Asbestos
and Beryllium
–Lead damages blood systems and nerves, causing behavioral
disorder
–Cadmium causes heart disease, high blood pressure and kidney
damage
–Nickel causes lung cancer and respiratory diseases
–Mercury damages nerves, kidneys and the brains
–Asbestos causes lung cancer and a lung disease called asbestosis
–Beryllium damages eyes, lungs and the heart
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128. Effects of Pollutants on Vegetation
•Air pollutants cause:
–destruction of leaf structure, termed as necrosis
–destruction of chlorophyll in leaves, called chlorosis
–dropping of leaves, called abscission
–stunted growth
–death
–etc.
•Pollutants like arsenic deposited on grass can be harmful to
animals
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129. Effects of Pollutants on Materials
•These include the following:
–soiling of painted surfaces (e.g., by dust and soot), which spoils
their appearance
–corrosion of metals (e.g., steel, copper, zinc) by acid mist
–disintegration of leather and fabrics (especially polyesters)
–discoloring of paper
–deterioration of marble and limestone
–degradation of rubber (especially y ozone)
–etc.
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130. Global Effects of Air Pollution
•These include:
–Cloud/fog formation
–Obstruction of sun’s radiation
–Acidification of rain
–Ozone layer depletion
–Greenhouse effect
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131. Cloud/Fog Formation
•Some particulates facilitate the condensation of water vapor to
form clouds and fog
•Such particulates are called cloud condensation nuclei (CCN)
and freezing nuclei (FN)
•An example of CCN/FN is acid mist (e.g., sulphuric acid mist)
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131

132. Obstruction of Sun’s Radiation
•Particles like soot and dust reduce the amount of the sun’s
radiation that reaches the earth’s surface
•Such particles have a cooling effect
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132

133. Acidification of Rain
•Some gaseous pollutants cause acid rain
•For example, sulphur dioxide and sulphur trioxide react with
rain water to form sulphuric acid
•Acid rain may have adverse ecological effects
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133

134. Ozone Layer Depletion
•O
3
layer depletion, is simply the wearing out (reduction) of the amount of O
3
in the
stratosphere
•Industries that manufacture things like insulating foams, solvents, soaps, coolants like ACs,
Refrigerators and ‘Take-Away’ containers use CFCs.
•These substances are heavier than air, but over time, (2-5years) they are carried high into
the stratosphere by wind action
•UV radiation breaks up these CFCs releasing Chlorine atoms
•Chlorine atoms react with O
3, starting a chemical cycle that destroys O
3
•One chlorine atom can break apart more than 100,000 ozone molecules
•Other Ozone Depleting Substances (ODS) include methyl bromide used in pesticides,
halons used in fire extinguishers, and methyl chloroform used in making industrial solvents
•Sadly, there isn’t much humans can do to replenish the depleted Ozone, as it tends to
recover slowly by itself.
•All there is to do is to be more responsible with our manufacturing needs so that we do not
introduce more CFCs into the air.
•Natural production and depletion of ozone balances out
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135. Ozone Layer Depletion
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136. Greenhouse Effect
•Some gases act as insulators of the earth through the so-called
greenhouse effect
•Greenhouse effect may lead to global warming
•Examples of GHGs include CO
2
, N
2
O, CFCs, CH
4
and water
vapor
•How does greenhouse effect lead to climate change???
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137. The End
Thank You for Playing Audience
The next lecture will be on:
“Effects of Climate on
Forms of Construction”
Same Venue! Same Timing!
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138. Effects of Weather and Climate
on Forms of Construction
Lecture Five
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138

139. Weather, Climate, Climate Change (extreme weather),
Built Environment (Construction projects and buildings)
Lecture 5
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139

140. Lecture Content/Outline
•The Weather/Climatic Conditions: Temperature (Hot Conditions & Cold
Conditions), Wet Conditions (Rain & Groundwater), Thunderstorms, Lightning,
Wind and Fog (Visibility)
•Where the Effect is felt: The Site, Paint and Painting, Workers, Building
Equipment, Building Materials, Foundation and the Building itself (Roofing
and Comfort).
•Stages of Operations: Surveying, Site Clearing And Grading, Site Excavation,
Pouring Concrete, Erecting Structural Steel, Exterior Carpentry, Exterior
Masonry, Roofing, Exterior Painting and Landscaping
•Anticipated Impacts of Climate Change and associated alteration in Local
Weather Patterns
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141. Introduction
•The various geographical regions of the world have different
prevailing weather/climatic conditions that are typical to a particular
region (temperature, wind speed, precipitation etc.)
•Long term climate impacts, such as sea level rise, coastal erosion, and
drought; and short-term weather related impacts, such as high winds and
‐
flooding influence the choice of site construction (location), building
techniques, and materials construction workers use (type)
•The potential risk of inclement weather and climate conditions also
influence planning and project completion timelines.
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142. Introduction
•Building professionals need to take suitable measures to eliminate or at least
reduce the effect of weather/climatic conditions
•Buildings ought to be constructed in such a way as to minimize the need for
artificial heating/cooling in order to provide workers (inhabitants) with
adequate comfort (bioclimatic architecture)
•Extreme weather conditions during the time of the operation may reduce
productivity
•The natural climate should be used as widely as possible to avoid the high
cost of man-made climate
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143. Introduction
•Since weather influences the efficiency of the construction industry
over a wide range of elements, and the critical nature of many of these
operations, many aspects of construction must be performed only at
certain times of the year.
•Soil strength and stability are critical in building and civil engineering
•The majority of problems experienced in building industry emanate
from issues of soil moisture content and effects of temperature on the
ground, e.g. frost or ice formation; and precipitation (run-off)
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144. Temperature (hot conditions)
Paint and painting
•Weather can be very detrimental when it comes to the application of
paints and its performance
• During the application of paint, when the surface temperature of the
place to be applied is too high or its relative humidity (too low or
too high), the solvents in the paint evaporate too fast
•This causes the paint not to cure properly with the surface therefore
causing wrinkles, peeling, cracking and even blisters
•Ultraviolet rays also affect the performance of paints ultimately
causing chalking and fading among others
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144

145. Temperature (hot conditions)
Building materials
•Weather has a wide array of effects when it comes to building materials; dry
weather causes water in concrete and masonry mortar to evaporate too fast
•This produces concrete with a lower compressive strength and a finished
concrete that tends to curl upward and to spall
•It also causes the mortar to begin setting prematurely; thus, there may not be
sufficient moisture to ensure the brick absorb the mortar paste properly
•This reduces the bond strength between the mortar and the brick, which is a
major cause of masonry leaks
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145

146. Temperature (hot conditions)
The site
•The actual place where the construction will be erected, is
affected by very many weather conditions that tend to slow down
the time of execution of construction project
•Hot and dry weather is associated with dust
•Dust generates dirt that must be removed from interior surfaces
on a regular basis during and after construction translating to
more costs
•Tanker trucks can be used to spread a water mist over designated
areas to reduce dust
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147. Temperature (hot conditions)
Workers
•Extremes of temperature can directly or indirectly increase the
probability of an accident
•In hot temperatures, workers may suffer from conditions such
as dehydration and sunstroke
•This can affect their judgment and reaction times
•This is particularly perilous when driving a heavy vehicle
around or operating machinery.
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148. Temperature (hot conditions)
Workers
•Workers may also give in to temptation to cool down by not wearing
protective equipment e.g. hard hats or high-visibility jackets
•This increases the odds of them being injured or killed by a moving
object or falling item
•The physical activity that is associated with construction work causes a
very great loss in body fluids, aggravated during hot and dry weather
•This leads to fatigue of workers, slowing down the construction process
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149. Temperature (hot conditions)
Building equipment
•Hot and dry weather conditions affect equipment both in and
outside
•Increased dusty conditions lead to frequent blocking of filters that
may lead frequent premature breakdowns
•Dust can also cause accelerated wear and tear of moving parts
when exposed
•Therefore frequent lubrication and cleaning of these machines
and equipment should be carried out
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150. Temperature (hot conditions)
Building equipment
•High temperatures or the intense glare of the sun can also cause
overheating and fire risks to machinery and flammable material on
site
•Extreme temperatures can cause machinery not to operate correctly
or breakdown completely
•Not only will this cost time and money, but can also be extremely
dangerous if the temperature were to damage or cause a failsafe
feature not to function whilst in use
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151. Temperature (cold conditions)
Building materials
•Cold weather causes the formation of ice crystals that retain
moisture
•This may cause the curing process to slow down.
•In the long run, the slowed down curing process affect
concrete strength, promote spalling, and can ruin the finish
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152. Temperature (cold conditions)
Paints and painting
•Cool temperatures can cause solvents in solvent-
based paints and water in water-based paints to
freeze or even thicken
•This will slow the curing process leading to
filing in paints
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153. Temperature (cold conditions)
Foundation
•The most critical component of every building that needs to be very
firm and strengthened
•Has to be placed below the frost line to prevent heaving
•The colder the climate, the deeper the frost line, and consequently,
the deeper the foundation
•If the foundation is above the frost line, freeze-thaw cycles can
cause excessive structural movement
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154. Temperature (cold conditions)
The site
•Cold conditions can also lead to site freezing.
•When the site freezes water is retained in the earth so that
surface drying is slowed
•This results in prolonged muddy conditions
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155. Temperature (cold conditions)
Workers
•In cold weather workers are required to put on extra clothing
to protect them from the cold
•This clothing is often heavy and poses a risk to the workers as
they become more susceptible to accidents
•Furthermore, this additional clothing restricts their movement
in a way therefore hindering effective productivity
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156. Temperature (cold conditions)
Workers
•In cold conditions the human muscles are not as flexible as they
are supposed to, may result to injury during work when strained
•Moreover, in cold conditions, frost and dew causes wetting of
surfaces such as roofs and floors among others, may cause fatal
accidents
•Extreme cold increases risk of poor visibility through frozen up
windscreens, as well as creating slip hazards from ice
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157. Temperature (cold conditions)
Building equipments
•Water-cooled engines in certain equipments are very susceptible
to cold temperatures
•They may therefore not be very efficient during cold weather
conditions
•Cold lubricants such as water are known not to be effective as the
equipment will be in a state of inadequate or less functioning
•These may cause accelerated wear and tear
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158. Wet Conditions (rain )
The site
•Mud will hinder access to the site since both foot and vehicle traffic
can be restricted
•This will prevent or slow down all building processes such general
earthwork, paving, and foundation work
•Compacted gravel or rock can be used in roadways to establish a firm
base
•The site should be properly graded to ensure positive drainage away
from the structure and to prevent water collection points
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159. Wet Conditions (rain )
Workers
•Apart from being unpleasant to work in, the presence of
heavy or torrential rain will reduce visibility for the
drivers of vehicles
•It will also turn the ground into mud which poses its own
risks to the health and safety of site workers
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159

160. Wet Conditions (groundwater)
The site
•A high water table or excessive rain can increase
groundwater
•Regardless, dewatering provisions for excavations dry
enough to allow steady progress
•Furthermore, including permanent waterproofing for below-
grade spaces in the building design will compensate for high
water table and groundwater conditions
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161. Thunderstorms
Workers
•Thunderstorms sometime give warning of their arrival by the
darkening sky and towering dark clouds
•Other times, they occur suddenly
•They are particularly dangerous to workers
•They should therefore seek inside protection on the ground
floor or basement away from steel, windows and doors
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162. Thunderstorms
The site
•Thunderstorms are also particularly dangerous to tall structures, especially
those in the open
•Straight-line winds, sometime approaching hurricane velocity that usually
accompanies thunder storms can wreak havoc on construction sites
•Construction crew should ensure that materials are properly secured and
protected, construction in progress is properly braced, trash and debris are
in containers that are properly secured, and personal protection measures
are taken
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163. Thunderstorms
The site
•Thunderstorms often include hail and wind.
•Hail can break windows and severely damage exposed materials
such as sheet metal and roofs- especially shingles and single-ply
roofs
•It will dent and deform sheet metal and strip thin paint from
substrates
•Where severe thunderstorms are common, consider roof systems
that are resistant to hail
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164. Thunderstorms
The site
•Occasionally, a thunderstorm produces severe storms- the tornado,
hurricanes (short-lived)
•The tornados suck up anything not properly anchored and spit out
debris all over the place
•Metal buildings are even more prone to tornado damage
•During design and construction, special consideration and attention
must be given to the model building code requirements for these
areas
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165. Lightning
The site/workers
•The abundance of metal on a construction site means that the risk
of lightning is very real, particularly for objects which are tall
and higher up such as cranes and scaffolding
•Acting as conductors, there is a chance they could be struck by
lightning causing electrocution, fires, or explosions as a result
•Therefore, buildings in areas with frequent thunderstorms should
be designed with lightening protection
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166. Strong Winds
•In most instances, wind can dramatically multiply the effects
of the previously discussed elements
•One of the main dangers from strong winds will be to the
people and loose material at a height as it is likely to be more
exposed, and therefore more susceptible to high winds
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167. Strong Winds
Building materials
•Wind increases drying by accelerating the removal of moisture
•It reduces cooling time by accelerating the removal of heat
•Wind drives moisture into the structure by increasing the
pressure on the film of moisture on the surface of the structure
•It makes cold feel colder by accelerating the evaporation of
perspiration
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168. Strong Winds
The site
•Wind damage can vary from removal of a hard hat to rearranging
staged materials to blowing down an unsupported masonry wall
•Since tall, flat walls receive the full impact of wind, it can move tall
sky scrapers several feet off true vertical
•Walls that are structurally braced and do not have provisions for
movement can tumble down in a pile of rubble
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169. Strong Winds
Workers
•People working at a height can be blown to the side, increasing the chances of
them falling if there is insufficient side protection or harnesses to stop them
from falling
•If the wind is strong, there can be a risk of materials such as roof tiles and fast
moving debris striking a person
•Also, the wind can whip up dust which can damage or irritate eyes, as well as
aggravating conditions such as asthma
•Strong winds can also make it difficult to hear properly, so much so that
workers may be oblivious to approaching vehicles if they cannot hear them
coming
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170. Fog (visibility)
Workers
•Fog can be particularly dangerous for workers on a construction site as it
greatly reduces the visibility of everyone
•The drivers will not be able to see very far ahead, may not be able to react
in time if a person or object is in the road way
•The driver may even drive off the road if they cannot see where the edge
is, increasing the chances of them colliding with something g or driving
over the edge of a steep drop
•Workers on the ground will also find it difficult to see approaching
vehicles and get out of the way in time
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171. Effects of weather/climate on buildings
•Weather and climatic conditions not only affect the
construction but also the already set up buildings, the
materials and their occupants
•Effects on the building materials may be short-lived or long-
term and as such some may require frequent replacement
which may be very expensive
•These include roofing such as tiles, thatches and iron sheets,
ventilation, drainage and comfort among others
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172. Effects of weather/climate on buildings
Roofing
•Roofing materials are the most affected by most of the weather
conditions because of their exposure e.g. to rain, wind, sun etc
•They may fade or even get blown off by certain strengths of wind
•Some buildings are designed in such a way that they have flat
roofs
•These however, have their own disadvantages; poor drainage-
stagnation- leads to other hygiene-related problems
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173. Effects of weather/climate on buildings
Comfort
•Human beings can tolerate a fairly wide range of climatic conditions, but comfort in the
climatic sense involves more than just avoiding the extremes of freezing to death and dying of
heat exhaustion.
•Comfort depends on more than temperature; air temperature, humidity, radiation and air
movement all produce thermal effects.
•Changes in weather/climate have adverse effects on the comfort of people inside a building
•Hot and dry weather leads to overheating of buildings as not all of them have proper
ventilation mechanisms
•During the cold weather, some buildings may tend to be too cold and unfit for human
habitation and as such may be forced to use heaters
•This therefore affects the comfort of people in the building
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174. Summary table; Influence of weather on the efficiency of the construction
industry
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175. Impacts of Climate Change on the Built
Environment (Construction and Buildings)
•Climate change attributed due human activities alters the local weather/climate patterns,
thus impacting built environment
•Climate change may affect the project design, construction procedures and even the comfort
of buildings as people spend most of their time in buildings (workplaces and homes)
•The built environment has already been affected by the rapidly changing climate and weather
•Over the past few years, extreme weather events that affect the built environment have taken
place in Kenya and around the world.
•Most of the damage caused has been as a result of floods and storms
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176. Impacts of Climate Change on the Built
Environment (Construction and Buildings)
•These changes have clearly proven that the buildings we live and
work in and also those that are under construction could look totally
different in the future if our climate doesn’t change as predicted
•These changes will continue affecting the way offices, homes and
other constructions are designed and constructed
•The differences and complexities in damages can be compared by
looking at structures in different regions of the country such as
western Kenya and the coast or even different countries in the world
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177. Potential effects of climate change on buildings
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178. Key impacts of climate change on construction
•Weather related impacts: flooding, coastal erosion, subsidence, drainage
systems require new building techniques and materials to withstand
adverse weather conditions; influence the choice of site
•Cost of finance/insurance: Insurance sector beginning to factor impacts of
climate change into premiums. Sector has yet to put systems into place to
discount climate-change related risk mitigation, but could be pushed to do
so through building industry initiatives.
•• Business interruption from wetter winters
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179. General strategies to address climate change in
construction
•Government taxation and regulation e.g. Tax breaks or rewards for energy
efficiency; raised energy efficiency standards for construction and
refurbishments; calls for increased transparency in property energy use
which could effect valuations
•Voluntary targets - Industry sets reporting metrics, individual companies
set targets
•Process/technology innovation
•Switching to lower carbon fuels
•Identifying alternative raw materials (e.g. lower clinker-content cement)
•CO2 capture and sequestration (although very costly)
•Emissions trading
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180. Conclusion/Recommendations
•Weather is always here - It is always around us – It cannot be
controlled
•“everyone talks about the weather, but no one does anything
about it”
•The uncertainties in weather prediction can pose unforeseen
problems and delays
•Even with the most comprehensive project management and health
and safety precautions, there are still risks of injuries and accidents
occurring, which will be greatly increased by the presence of one or
more of the weather conditions discussed earlier
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181. Conclusion/Recommendations
•Although, weather extremes associated with climate change can test building
performance, building professionals can prepare for it and adjust to resulting
conditions
•Adapting building designs for climate change is about managing the unavoidable. There
is growing awareness that design practices need to take into account predictions of
increased risk and intensity of extreme events.
•Proper preparation, adjustment and reaction to local weather will influence the
success of a construction project and the completed building
•“Facilities can be designed, built, operated, and regulated to withstand,
manage, or harness the impacts of weather and climate”
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182. Conclusion/Recommendations
•Having access to relevant and easily understandable weather and climate data is
essential for strategic planning purposes, risk management, and assessing
environmental footprints.
•A changing climate can lead contractors to build smarter structures that are more
energy efficient and cost effective.
•Collaboration between climate scientists and the construction community is
essential in helping to build the necessary bridges that will transform climate science
into information that is relevant and credible.
•Authoritative, timely and reliable information about climate variability and
change opens a world of possibilities to build resilient communities, infrastructure,
and economies.
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183. As individuals and decision makers across all sectors ask how
‐
they can best adapt to prepare their lives, communities and
businesses for the impacts of a changing climate,
Meteorologists, are to provide reliable, easily accessible
climate information to inform state, regional and national
policy decisions.
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184. Conclusion/Recommendations
•Building performance can be improved with insulation, corrosive-resistant
metals, decay-resistant wood, UV-resistant paint and sealant, selective roof
systems, drainage planes, permanent flasing, positive drainage everywhere,
and high performance windows and doors with high performing glass.
•In relation to roofing, building professional should provide the best roofing
systems
•They should be provided with proper training and protection in relation to
weather to prevent injuries and fatal falls
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185. Conclusion/Recommendations
•Proper ventilation mechanisms should also be employed in buildings
to improve comfort
•To curb immobility to and from buildings and construction sites,
both vehicle and foot traffic can be restricted in a certain area
•In addition, compacted rock and gravel can be used in roads to and
from sites to establish a firm base
•The site in addition should be properly drained and graded to ensure
proper drainage away from it so as to prevent water collection points
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186. The End
Thank You for Playing Audience
The next item will be:
“Continuous
Assessment Test”
Same Venue! Same Timing!
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