The-Future-Hydrological-And-Geomorphological-Impacts.pptx

The-Future-Hydrological-And-Geomorphological-Impacts.pptx

1. Chapter 10 : The Future: Hydrological And Geomorphological Impacts ZYVEN JOHANN N. CAVILIZA LOUIE TEPAN FERNANDO

2. Introduction Global Warming will affect hydrological systems and Fluvial geomorphological in a whole range of ways (Arnell, 1996; Jones et al., 1996). Increasing temperatures will tend to melt snow and ice and promote greater evapotranspirational losses. There will be changes in the amount, intensity, duration and timing of precipitation, which will affect river flows and groundwater recharge.

3. Hydrological systems -a system of interrelated components, including the processes of precipitation, evaporation, transpiration , infiltration, groundwater flow and stream flow in addition to those structures and devices that are use to manage the system. Fluvial geomorphological -is concerned with the creation of landforms by river processes through the removal and transfer of materials on Earth’s surface

4. In a warmer world, changes in the type, amount and intensity of moisture received as precipitation, together with increased rates of evapotranspiration, will have major, though sometimes opposite, impacts on the hydrological environment. In addition, the presence of increased levels of carbon dioxide in the atmosphere may affect moisture transpiration by plants. There is evidence that some parts of the world will have more available moisture for stream flow and that other areas will have less.

5. Rainfall Intensity

6. Rainfall Intensity Rainfall intensity- is a major factor in controlling phenomena as flooding, rates of soil erosion and mass movements. The Intergovernmental Panel on Climate Change (IPCC) suggest that extremes of daily precipitation are likely to increase in many regions.

7. Rain Intensity - refers to the rate at which rain falls within a specific area over a certain period. It is typically measured in millimeters per hour or inches per hour. Higher rain intensity values indicate heavier rainfall while lower value indicate lighter rain.

8. Rainfall characteristics Precipitation in arid and semi-arid zones results largely from convective cloud mechanism producing storms typically of short duration, relatively high intensity and limited area extent. Rainfall intensity is defined as the ratio of the total amount of rain, falling during a given period to the duration of the period. The statistical characteristics of high-intensity, short-duration, convective rainfall are essentially independent of locations within a region and are similar in any parts of the world.

9. Changes in tropical cyclones Tropical cyclones are highly important geomorphological agents, in addition to being notable natural hazards, and are closely related in their places of origin to sea temperature conditions. An increase in hurricane intensity and frequency would have numerous geomorphological consequences in low latitude, including accentuated river flooding and coastal surges, severe coast erosion, accelerated land erosion and siltation and the killing of corals.

10. Changes in tropical cyclones

11. An increase in hurricane intensity and frequency would have numerous geomorphological consequences in low latitudes, including accentuated river flooding and coastal surges (Mousavi et al., 2011), severe coast erosion, accelerated land erosion and siltation, and the killing of corals (because of freshwater and siltation effects) (De Sylva, 1986).

12. Figure 10.1 (a) The present frequency of cyclones crossing 500-km long sections of the Australian coast, and an estimate of the frequency under conditions with a 2°C rise in temperature; (b) The area where February sea surface temperatures around Australia are currently greater than 27°C (stippled) and the additional area with such temperatures with a 2°C rise in temperature (hatched) (modified from Henderson-Sellers and Blong , 1989, figures 4.12, 4.14). Reproduced with permission from New South Wales University Press.

13. Figure 10.2 (a) Scatter diagram of monthly mean sea surface temperature and best-track maximum wind speeds (after removing storm motion) for a sample of North Atlantic tropical cyclones. The line indicates the 99th percentile and provides an empirical upper bound on intensity as a function of ocean temperature; (b) The derived relationship between sea surface temperature and potential intensity of tropical cyclones (a and b, modified from Holland et al., 1988, figures 5 and 6. Reproduced with permission).

14. Tropical cyclones Tropical cyclones - also known as hurricanes or typhoons depending on the region, have been changing due to various factors like climate change. Some changes observed in tropical cyclones include: 1 . Intensity – There is evidence suggesting an increase in the intensity of tropical cyclones, with stronger storms becoming more frequent.

15. Tropical cyclones 2 . Frequency : While there isn’t a clear trend in the overall number of tropical cyclones globally, certain regions have experienced changes in cyclone frequency. 3 . Precipitation : Warmer air can hold more moisture, leading to an increase in rainfall associated with tropical cyclones. This can result in more intense and prolonged periods of rainfall, contributing to flooding and other hazards.

16. El Ni ñ o El Ni ñ o can also can also influence the tracks that tropical cyclones follow. In Pacific basin, cyclones during El Ni ñ o years are more likely to occurred northward, impacting different regions than during La Ni ñ a or neutral.

17. El Ni ñ o El Ni ñ o can affect rainfall patterns associated with tropical cyclones. In some regions, El Ni ñ o conditions can lead to increased rainfall and flooding, while in others, it may result in drier conditions.

18. Runoff Response

19. Runoff Response Runoff response refers to how water from precipitation, such as rain or snow moves across the land surface and into streams, rivers, and other water bodies. It is influenced by factors such as soils type, land cover, slope, vegetation, and human activities.

20. Different landscapes and environmental conditions can result in varied runoff responses, including infiltration into the soil, surface runoff, or a combination of both.

21. Factors like urbanization, deforestation, and climate change can also impact runoff patterns and volumes. However, excessive runoff can lead to issues like flooding, soil erosion and water pollution. Highlighting the importance of managing runoff effectively.

22. In areas where snowmelt contributes significantly to runoff, rising temperatures can alter the timing and magnitude of snowmelt. This can lead to earlier snowmelt, which in turn affects stream flow patters and water availability.

23. Understanding and addressing these complex interactions between climate change and runoff response are essential for sustainable water management and ecosystem resilience.

24. Cold Regions

25. Cold Regions In cold regions, the relationship to river flow are significantly influenced by the freezing and melting of ice.

26. Some key points regarding this relationship 1. Seasonal Variability : In cold regions, river flow can exhibit significant due to changes in temperature. During winter, water bodies often freeze, leading to reduced or even halted river flown in some areas. In contrast, during warmer seasons such as spring and summer, melting ice and snow contribute to increased river flow.

27. Some key points regarding this relationship 2. Snowbelt Contribution : The melting of snow, which accumulates during colder months, is a crucial factor in river flow dynamics. The timing and rate of snowmelt can significant impact the volume and speed of river flow. Rapid snowmelt, especially when combined with rainfall, can lead to sudden increase in river discharge, potentially causing floods.

28. Some key points regarding this relationship 3. Human Impacts : Human activities, such as dam constructions, water diversion for irrigation or hydropower generation, and land use changes, can further modify river flow pattern in cold regions. These alternation can have both intended and unintended consequences on water availability, flood risk and ecosystem health. 4. Changes in Precipitation totals may also be significant and in some areas may work in same or opposite direction as warming.

29. Some key points regarding this relationship 5. The other major control on future river flow in cold regions will be melting of glaciers. If this occurs, discharges may initially increase, but as the glacier mass decline through time, so will stream flows.

30. Changes in runoff in the UK Arnell (1996) has studied the likely changes that will occur in the UK as a result of global warming. With higher winter rainfalls and lower summer rainfalls (particularly in the south-east) he forecasts for the 2050s:

31. Figure 10.3 Monthly runoff by the 2050s under two scenarios for six British catchments (modified from Arnell and Reynard, 2000, figure 7.19). Figure 10.4 Effect of a climate change scenario on stream flow in two European snow-affected catchments by 2050s (modified from Arnell, 2002, figure 7.20).

32. 1. An increase in average annual runoff in the north of Britain of between 5 and 15% 2. A decrease in the south of between 5 and 15%, but up to 25% in the south-east 3. An increased seasonal variation in flow, with proportionately more of the total runoff occurring during winter 4. High flows increased in northern catchments and decreased in the south.

33. Werritty (2002) looked specifically at Scottish catchments and noted a particularly marked increase in precipitation in the north and west in the winter half of the year. He predicted that by the 2050s Scotland as a whole will become wetter than at present and that average river flows will increase, notably in the autumn and winter months. He believed that high flows could become more frequent, increasing the likelihood of valley floor inundation. However, a study of the history of valley floors in upland Scotland suggests that they are relatively robust, so that although they may become subject to extensive reworking, they are unlikely to undergo large-scale destabilization ( Werritty and Lees, 2001).

34. Europe

35. Europe Arnell (1999b) modelled potential changes in hydrological regimes for Europe, using four different GCMbased climate scenarios. While there are differences between the four scenarios, each indicates a general reduction in annual runoff in Europe south of around 50°N and an increase polewards of that. The decreases could be as great as 50% and the increases up to 25%. The proposed decrease in annual runoff in southern Europe is also confirmed by the work of Menzel and Burger (2002) in Germany, who also suggest that peak flows will be very substantially reduced. Rising temperatures will affect snowfall and when it melts (Seidel et al., 1998). Under relatively mild conditions, even a modest temperature rise might mean that snow becomes virtually unknown, so that the spring snowmelt peak would be eliminated. It would be replaced by higher flows during the winter. Under more extreme conditions, all winter precipitation would sti still fall as snow, even with a rise in temperature.

36. As a consequence, the snowmelt peak would still occur, although it might occur earlier in the year. In Figure 10.4, for instance, in the Polish example the snowmelt peak is eliminated by the 2050s, whereas in the Ukraine example it is brought forward. One of the most important rivers in Europe is the Rhine. It stretches from the Swiss Alps to the Dutch coast and its catchment covers 185,000 km2 ( Shabalova et al., 2003). Models suggest that the Rhine’s discharge will become markedly more seasonal with mean discharge decreases of about 30% in summer and increases by about 30% in winter, by the end of the century. The increase in winter discharge will be caused by a combination of increased precipitation, reduced snow storage and increased early melt.

37. In the Mediterranean region a number of processes operating in tandem may lead to a severe reduction in available water resources (García-Ruiz et al., 2011). A general decrease in precipitation and a rise in evapotranspiration rates will lead to flow reductions, as will the presence of dams and reservoirs, overexploitation of groundwater, and an expansion of the area that is forested following on from farm abandonment in upland regions.

38. Other examples The Zambezi River at Victoria Falls. 1 Zambezi A study of the Zambezi River in central Africa, using different GCMs, and projecting conditions for 2080 indicates that river flow may decline substantially. Simulations indicate that for three scenarios annual flow levels at Victoria Falls (Figure 10.5) reduce between 10 and 35.5% (Harrison and Whittington, 2002).

39. Susquehanna Susquehanna, eastern USA, and New England The Susquehanna which flows into Chesapeake Bay, the largest estuary in USA, is an example of a river system which will enjoy larger annual flows because of increased precipitation over its catchment (Najjar, 1999). For a 17.5% increase in annual precipitation, and a temperature increase of 2.5°C, the total predicated increase in annual stream flow is 24%. This contrasts with the prediction of future flows for rivers in New England, where Huntington (2003) has suggested that annual stream flow would be reduced by 11–3%.

40. California and the Colorado River 3. California and the Colorado River One of the most pronounced features of some recent GCMs (Hadley Centre and Canadian) is that they show a projected increase in precipitation for California and the south-west. This would be the result of a warmer Pacific Ocean causing an increase mainly in wintertime precipitation (MacCracken et al., 2001). Smith et al. (2001a), using the Hadley and Canadian models, estimated that California runoff will increase by the 2030s by about three-fifths and double by the 2090s (Table 10.3). On the other hand, Maurer and Duffy (2005) believed that there will be decreases in summer flows and increases in winter flows, and a shift to flow earlier in the year. Barnett and Pierce (2009) have suggested that annual runoff in the Colorado River will be reduced by 10–30%.

41. Pacific Northwest of USA Pacific Northwest of USA Wigmosta and Leung (2002) modelled the response of the American River in the Pacific Northwest of the USA. More winter precipitation falling as rain rather than snow, and also leading to more rain-on-snow events, produced a future with greater winter flooding. However, the reduced snowpack caused less flows in the spring and summer.

42. Bangladesh In a warmer world, it is probable that there will be a general increase in precipitation, caused by enhancement in summer monsoon activity. This could be a cause of increased flood risk in areas like Bangladesh. In Table 10.4, from the work of Mirza (2002), four GCM scenarios are presented for changes in temperature and precipitation for three major catchments that create floods in Bangladesh. In addition, predicted mean peak discharges for those scenarios are presented. The current peak discharges (cubic metres per second) are 54,000 for the Ganges, 67,000 for the Brahmaputra and 14,000 for the Meghna. The four GCMs display some differences, as do predicted peak discharge values. However, overall, the discharge values show a range from a modest decline to a substantial increase.

43. sinuosity single channels or braided patterns, increased bank erosion, and more rapid channel migration. Increased magnitude of large floods will result in sudden changes to channel characteristics that may trigger greater long-term instability of rivers. Increased frequency of large floods will tend to keep rivers in the modified and unstable state. Decreased discharge often results in channel shrinkage, vegetation encroachment into the channel, sedimentation in side channels, and channel pattern change toward more stable, single-channel patterns. In entrenched or confined valleys there may be reductions in the stability of the valley walls and, hence, increases in the rate of erosion caused by a greater tendency for streams to erode the valley walls. Increased valley-side erosion will increase sediment delivery to the streams with consequences for stream morphology.

44. Geomorphological Consequences of Hydrological and other Changes

45. It is likely that changes in river flow will cause changes in river morphology, particularly in sensitive systems, which include fine grained alluvial streams. Bedrock streams will probably be less sensitive.

46. The potential impacts of increased discharge include channel enlargement and incision, a tendency toward either higher sinuosity single channels or braided patterns, increased bank erosion and more rapid channel migration.

47. Increased magnitude of large floods will result in sudden changes channel characteristics that may trigger greater long-term instability. Increased frequency of large floods will tend to keep rivers in modified and unstable state.

48. Decreased discharge often results in channel shrinkage, vegetation encroachment into the channel, sedimentation in side channels, and channel pattern change toward more stable, single -channel patterns.

49. In entrenched or confined valleys there may be reduction in the stability of the valley walls and hence, increases in the rate of erosion caused by a greater tendency for steams to erode the valley walls. Increased valley-side erosion will increased sediments delivery to the streams with consequences for stream morphology.

50. Sediment delivery by rivers may also be impacted by climate change. It is of course, likely that climate change will cause farmers to change the ways in which they manage their crops and change the crops they plant

51. Weathering Weathering refers to the process of breaking down and wearing away rocks, soils, and minerals through various physical, chemical, or biological means. It is crucial part of the Earth’s geological process and can occur through mechanism like erosion, abrasion, chemical dissolution and biological activities.

52. Weathering

53. Physical Weathering This process involves the physical breakdown of rocks into smaller fragments without changing their chemical composition

54. Chemical Weathering Processes alter the composition of rocks and minerals breaking them down into different substances

55. Chemical weathering involves the interaction of rock with mineral solutions (chemicals) to change the composition of rocks. In this process, water interacts with minerals to create various chemical reactions and transform the rocks. Chemical weathering is a gradual and ongoing process as the mineralogy of the rock adjusts to the near-surface environment. Secondary minerals develop from the original primary minerals of the rock. In this the processes oxidation and hydrolysis are the most frequent chemical processes that take place. Chemical weathering is enhanced by such geological agents as the presence of water and oxygen, as well as biological agents as the acids produced by microbial and plant root metabolism.

56. Biological Weathering Living organisms contribute to weathering through their activities.

57. Processes of Weathering  Have you ever considered how rock becomes  soil   What would happen to human civilization, food and fiber production if the processes we call  weathering ceased to occur?  The processes of weathering are critical to soil formation. Goal :  Students will understand the  weathering  process and its influence on  soil  formation. Objectives Describe how climatic factors influence the weathering of rocks and minerals. Define and distinguish physical, chemical, and biological weathering processes. How do rocks become soil?  How does the climate in places such as Peru, Alaska, and Algeria influence the weathering of rock?  These questions are critical in understanding the roles weathering processes and climate play in the disintegration of rocks and minerals to begin the process of soil formation.

58. Weathering is the process of disintegration of rock from physical, chemical, and biological stresses. Weathering is influenced by temperature and moisture (climate).  As rock disintegrates, it becomes more susceptible to further physical, chemical, and biological weathering due to the increase in exposed surface area. During weathering, minerals that were once bound in the rock structure are released.

59. The influence of the interaction of temperature and rainfall on processes of physical and chemical weathering. Notice that as annual rainfall and temperature increase, chemical weathering dominates over physical weathering. On the contrary, notice that as the temperature lowers, physical weathering begins to dominate over chemical weathering.  Image courtesy of UNL, 2005 The degree of weathering that occurs depends upon the resistance to weathering of the minerals in the rock, as well as the degree of the physical, chemical, and biological stresses. A rule of thumb is that minerals in rocks that are formed under high temperature and pressure tend to be less resistant to weathering, while minerals formed at low temperature and pressure are more resistant to weathering. Weathering is usually confined to the top few meters of geologic material, because physical, chemical, and biological stresses generally decrease with depth. Weathering of rocks occurs in place, but the disintegrated weathering products can be carried by water, wind, or gravity to another location (i.e., erosion or   mass wasting ).

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