Freshwater availability is vital to civilization because it provides drinking water and water for irrigation to feed society. "Observational records and climate projections provide abundant evidence that freshwater resources are vulnerable and have the potential to be strongly impacted by climate change, with wide-ranging consequences for human societies and ecosystems" is the conclusion of Bates, et al. (2008) in Climate Change and Water, a Technical Paper of the Intergovernmental Panel on Climate Change, WG II (2007).
Bates et al. find:
Fig. 1 (IPCC, 2007) shows the impact of human activities on freshwater resources and their management. As one can see climate change is only one of multiple influences on water resources.
In a warmer world, more water vapor can be present in the air and evaporation from the surface increases. This coupling will likely cause increased climate variability - more intense precipitation and more droughts. While temperatures are expected to increase everywhere over land and during all seasons of the year, precipitation is expected to increase globally and in many river basins, but is expected to decrease in some regions. Precipitation may increase in one season and decrease in another. These climatic changes lead to changes in all components of the global freshwater system (Ibid).
Climate-related trends of some components during the last decades have already been observed. For a number of components, such as groundwater, the lack of data makes it impossible to determine whether recent changes are due to climate change or non-climate factors. During recent decades, non-climatic drivers have exerted strong pressure on freshwater systems. This has resulted in water pollution, damming of rivers, wetland drainage, reduction in streamflow, and lowering of the groundwater table (mainly due to irrigation). In comparison, climate-related changes have been small, although this is likely to be different in the future as the climate change signal becomes more evident (Ibid).
Fig. 2 (Oram, 2010) illustrates the various components of the hydrologic cycle.
Fig. 2a (USGRP, 2009) shows the observed water-related changes during the last century in the United States.
Fig. 2b (Ibid) shows the anticipated changes in the water cycle of the United States.
Fig. 3 (IPCC, 2007) shows the observed climate-related trends of the various components of the global freshwater system.
Fig. 4 (Ibid) shows examples of current vulnerabilities of freshwater resources and their management; in the background, a water stress map.
Fig. 5 (Bates et al., 2008) shows the anticipated changes in various components of the water cycle between the years 2080-2099 as compared to the years 1980-1999.
Fig. 6 (IPCC, 2007) shows the mean global river runoff change until 2050 for the SRES A1B scenario from an ensemble of twenty-four climate model runs (from twelve different GCMs).
Almost all model runs agree that runoff change in the high latitudes of North America and Eurasia will increases 10% to 40%. With higher uncertainty, runoff can be expected to increase in the wet tropics. Prominent regions, with strong agreement between models, of decreasing runoff (by 10 to 30%) include the Mediterranean, southern Africa, and western USA/northern Mexico. In general, between the late 20th century and 2050, the areas of decreased runoff expand (Ibid).
Fig. 6a (Bates et al., 2008) shows the anticipated changes in runoff between the years 2090-2099 as compared to the years 1980-1999. Changes greater than 40% relative to 1980-1999 are expected in some regions by the end of the 21st century.
In the United States, precipitation and runoff are likely to increase in the Northeast and Midwest in winter and spring, and decrease in the West, especially the Southwest, in spring and summer as shown by Fig. 6b (USGRP, 2009).
Climate change leads to changes in the seasonality of river flows where much winter precipitation currently falls as snow. This has been found in projections for the European Alps, the Himalayas, all of North America, the entire Russian territory, and Scandinavia and Baltic regions. The effect of seasonal changes is greatest at lower elevations (where snowfall is more marginal), and in many cases peak river flow would occur at least a month earlier. Winter flows will increase while summer flows will decrease (IPCC, 2007).
One-sixth of the Earth’s population rely on melt water from glaciers and seasonal snow packs for their water supply. Glaciers are the source for many rivers, particularly in the Hindu Kush-Himalaya and the South-American Andes. Higher temperatures generate increased glacier melt and as these glaciers retreat due to global warming, river flows are increased in the short term, but the contribution of glacier melt will gradually decrease over the next few decades. In regions with little or no snowfall, changes in runoff are dependent much more on changes in rainfall than on changes in temperature. In the Andes, glacial melt water supports tens of millions of people during the long dry season. Many small glaciers, e.g., in Bolivia, Ecuador, and Peru, will disappear within the next few decades, adversely affecting people and ecosystems. The entire Hindu Kush-Himalaya ice mass has decreased in the last two decades. Hence, water supply in areas fed by glacial melt water from the Hindu Kush and Himalayas, on which hundreds of millions of people in China and India depend, will be negatively affected (Ibid).
In a recent study, Immerzeel, et al. (2010) find that climate change will reduce the contribution of glaciers to total run-off while also changing weather patterns, including rain and snowfall. Immerzeel, et al. concluded that the river flow change will range from a decrease of 19.6% for the Brahmaputra to a 9.5% increase for the Yellow River. The authors conclude that climate change will reduce water supplies enough that by 2050, declines in irrigation water are likely to reduce the number of people the region's agriculture can support by about 60 million — 4.5% of the region's present population.
Changes in lake levels are determined primarily by changes in river inflows and precipitation onto and evaporation from the lake. Impact assessments of the Great Lakes of North America show changes in water levels of between -1.38 m and +0.35 m by the end of the 21st century. It is possible that the levels in the Caspian Sea may drop by around 9 m by the end of the 21st century, due largely to increases in evaporation. Levels in Lake Victoria would initially fall as increases in evaporation offset changes in precipitation, but subsequently rise as the effects of increased precipitation overtake the effects of higher evaporation (IPCC, 2007).
Model studies show that land-use changes have a small effect on annual runoff as compared to climate change in the Rhine basin, south-east Michigan, Pennsylvania, and central Ethiopia. In other areas, however, such as south-east Australia and southern India, land-use and climate-change effects may be more similar (Ibid).
The demand for groundwater is likely to increase in the future due to population increases and reduced summer river flows in melt-water dominated basins regions. Climate change will affect groundwater recharge rates, i.e., the renewable groundwater resource, and groundwater levels. However, even knowledge of current recharge and levels in both developed and developing countries is poor. There has been very little research on the impact of climate change on groundwater, including the question of how climate change will affect the relationship between surface waters and aquifers that are hydraulically connected. As a result of climate change, in many aquifers of the world the spring recharge shifts towards winter, and summer recharge declines. In high latitudes, thawing of permafrost will cause changes in groundwater level and quality. Climate change may lead to vegetation changes which also affect groundwater recharge. Also, with increased frequency and magnitude of floods, groundwater recharge may increase, in particular in semi-arid and arid areas where heavy rainfalls and floods are the major sources of groundwater recharge (Ibid).
According to the results of a global hydrological model, groundwater recharge (averaged globally) increases less than total runoff. While total runoff was computed to increase by 9% between the reference climate normal 1961 to 1990 and the 2050s, groundwater recharge increases by only 2%. For the four climate scenarios investigated, computed groundwater recharge decreases dramatically by more than 70% in north-eastern Brazil, south-west Africa and along the southern rim of the Mediterranean Sea (Figure 7). Regions with groundwater recharge increases of more than 30% by the 2050s include the Sahel, the Near East, northern China, Siberia, and the western USA (Ibid).
Figure 7: Simulated impact of climate change on long-term average annual diffuse groundwater recharge. Percentage changes of 30 year averages groundwater recharge between present-day (1961 to 1990) and the 2050s (2041 to 2070), as computed by the global hydrological model WGHM, applying four different climate change scenarios (climate scenarios computed by the climate models ECHAM4 and HadCM3), each interpreting the two IPCC greenhouse gas emissions scenarios A2 and B2.
Climate change-linked sea level rise leads to intrusion of salt water into the fresh groundwater in coastal aquifers which adversely affects groundwater resources. Fig. 8 (USGS, 2008) illustrates a coastal freshwater aquifer.
Under natural conditions, the seaward movement of freshwater prevents saltwater from encroaching coastal aquifers, and the interface between freshwater and saltwater is maintained near the coast or far below land surface. This interface is actually a diffuse zone in which freshwater and saltwater mix, and is referred to as the zone of dispersion (or transition zone). Saltwater intrusion decreases freshwater storage in the aquifers, and, in extreme cases, can result in the abandonment of supply wells. Rising sea levels forces the zone of dispersion inland which can render freshwater wells useless thus limiting freshwater supply for the regional population (Ibid). Fig. 9 (Ibid) shows areas along the Atlantic coast where saltwater has intruded freshwater aquifers. Projected future growth in population along the coastal areas of the United States combined with sea level will likely increase stresses on coastal aquifers and on the ecosystems that depend upon freshwater discharges from these aquifers (Ibid).
New York City, Philadelphia, and much of California’s Central Valley obtain some of their water from portions of rivers that are slightly upstream from the point where water is salty during droughts. If sea level rise pushes salty water upstream, then the existing water intakes might draw on salty water during dry periods (EPA, 2010). Loáiciga & Pingel (2008) modeled saltwater intrusion in two of California's most productive aquifers - Oxnard Plain aquifer in Ventura County and the Salinas Valley coastal aquifer in Monterey County. Their model showed that by 2106 saltwater had intruded into the aquifer by 1.5 km due to combination of sea level rise and well extraction (Fig. 10).
Floods and Drought:
A warmer climate, with its increased climate variability, will increase the risk of both floods and droughts (IPCC, 2007).
Droughts have become more common, especially in the tropics and sub-tropics, since the 1970s. It is likely that the area affected by drought has increased since the 1970s, and it is more likely than not that there is a human contribution to this trend (Ibid). Decreased land precipitation and increased temperatures are important factors that have contributed to more regions experiencing droughts as shown by the Palmer Drought Severity Index (PDSI) in Fig. 11 (Ibid).
The PDSI is a prominent index of drought. Red and orange areas are drier (-PDSI) than average and blue and green areas are wetter (+PDSI) than average. The smooth black curve shows decadal variations. The PDSI curve reveals widespread increasing African drought, especially in the Sahel. Note also the wetter areas, especially in eastern North and South America and northern Eurasia.
The regions where droughts have occurred seem to be determined largely by changes in sea surface temperatures, especially in the tropics, through associated changes in the atmospheric circulation and precipitation. In the western USA, diminishing snow pack and subsequent reductions in soil moisture also appear to be factors. In Australia and Europe, direct links to global warming have been inferred through the extreme nature of high temperatures and heat waves accompanying recent droughts (Bates et al., 2008)
There has been a large drying trend over Northern Hemisphere land since the mid-1950s, with widespread drying over much of Eurasia, northern Africa, Canada and Alaska. In the Southern Hemisphere, land surfaces were wet in the 1970s and relatively dry in the 1960s and 1990s, and there was a drying trend from 1974 to 1998, although trends over the entire 1948 to 2002 period were small. Decreases in land precipitation in recent decades are the main cause for the drying trends, although large surface warming during the last 2–3 decades is likely to have contributed to the drying. Globally, very dry areas (defined as land areas with a PDSI of less than -3.0) more than doubled (from ~12% to 30%) since the 1970s, with a large jump in the early 1980s due to an ENSO-related precipitation decrease over land, and subsequent increases primarily due to surface warming (Ibid). In the U.S. much of the Southeast and West has had reductions in precipitation and increases in drought severity and duration, especially in the Southwest (USGRP, 2009). Fig. 11a (Ibid) shows the observed drought trends since 1958.
According to Dai (2010) and as described in the Climate Progess blog post titled: New study puts the ‘hell’ in Hell and High Water, global warming could lead to drought conditions worse than the 1930s Dust Bowl in many parts of the world including much of the United States. In Fig. 11b (Dai, 2010) red to pink areas are extremely dry (severe drought) conditions while blue colors indicate wet areas relative to the 1950–1979 mean. Values are based on the PDSI where -4 is considered extreme drought.
By the 2030s, some regions in the world could experience severe drought conditions with PDSI values -4 to -6 in much of the central and western United States as well as several regions overseas, and -8 or lower in parts of the Mediterranean. By the end of the century, many populated areas, including parts of the United States, could face readings in the range of -8 to -10, and much of the Mediterranean could fall to -15 to -20. These values are unprecedented.
As temperatures rise, the likelihood of precipitation falling as rain rather than snow increases, especially in areas with temperatures near 0°C in autumn and spring. Snowmelt is projected to be earlier and less abundant in the melt period, and this may lead to an increased risk of droughts in snowmelt-fed basins in summer and autumn, when demand is highest.
Droughts affect rain-fed agricultural production as well as water supply for domestic, industrial and agricultural purposes. Some semi-arid and sub-humid regions, e.g., Australia, western USA, southern Canada, and the Sahel have suffered from more intense and multi-annual droughts (Bates et al., 2008).
The 2003 heat wave in Europe, attributable to global warming, was accompanied by annual precipitation deficits up to 300 mm. This drought contributed to the estimated 30% reduction in gross primary production of terrestrial ecosystems over Europe. Many major rivers (e.g., the Po, Rhine, Loire and Danube) were at record low levels, resulting in disruption of inland navigation, irrigation and power plant cooling. The extreme glacier melt in the Alps prevented even lower flows of the Danube and Rhine Rivers (Ibid).
Models agree in their estimates that by the 2070s, a 100-year drought of today’s magnitude would return, on average, more frequently than every 10 years in parts of Spain and Portugal, western France, the Vistula Basin in Poland, and western Turkey as shown in Fig. 12 (IPCC, 2007).
Globally, the number of great inland flood catastrophes during 1996–2005 was twice as large, per decade, as between 1950 and 1980, while related economic losses increased by a factor of five. Socio-economic factors such as economic growth, increases in population and in the wealth concentrated in vulnerable areas, and land-use change were significant contributors. Floods have been the most reported natural disaster events in many regions, affecting 140 million people per year on average. In Bangladesh, during the 1998 flood, about 70% of the country’s area was inundated (compared to an average value of 20–25%). Because flood damages have grown more rapidly than population or economic growth, other factors must be considered, including climate change. The weight of observational evidence indicates an ongoing acceleration of the water cycle. The frequency of heavy precipitation events has increased, consistent with both warming and observed increases in atmospheric water vapor (Ibid).
The flooded area in Bangladesh is projected to increase at least by 23-29% with a global temperature rise of 2oC. Up to 20% of the world’s population live in river basins that are likely to be affected by increased flood hazard by the 2080s in the course of global warming (Ibid).
Fig. 13 (Bates et al., 2008) shows possible impacts of climate change due to changes in extreme precipitation-related weather and climate events.
In the past century, averaged over the United States, total precipitation has increased by about seven percent, while the heaviest one percent of rain events increased by nearly 20 percent. This has been especially true in the Northeast, where the annual number of days with very heavy precipitation has increased most in the past 50 years, as shown By Fig. 13a (USGRP, 2009). Extended periods of heavy precipitation have also been increasing over the past century, most notably in the past two to three decades in the United States (Ibid)
Zhang et al. (2007), IPCC (2007), and Held and Soden (2006) conclude that global warming due to human activities is increasing the severity of drought in areas that already have drought and causing more rainfall in areas that are already wet.
Zhang et al. considered three groups of global climate model simulations and compared those simulations to the observed precipitation between 70o north and 40o south as shown in Figure 14 below.
This clearly shows that the ALL simulations (a and d) do a much better job of matching observed precipitation trends than either ANT (b and e) or NAT (c and f) alone. In fact, the correlations: ALL = 0.83, ANT = 0.69 and NAT4 = 0.02. It is for this reason that Zhang et al. (2007) conclude that changes in precipitation trends cannot be explained by natural forcing only and it certainly parallels what the IPCC WGI and WGII reports suggest.
Fig. 15 shows that the models do not predict the mid-latitude trends at all. Regional precipitation pattern predictions are NOT a strong suit of the models which modelers have stated. What this image does show however, is that areas of green and yellow show where the model trends match those of the observed trends and the models do a decent job of forecasting the correct trends in most regions.
Higher water temperatures, increased precipitation intensity, and longer periods of low flows are projected to exacerbate many forms of water pollution, including sediments, nutrients, dissolved organic carbon, pathogens, pesticides, salt and thermal pollution. This will promote harmful algal blooms and increase the bacterial and fungal content of the water. This will, in turn, impact ecosystems, human health, and the reliability and operating costs of water systems (Bates et al., 2008).
More intense rainfall will lead to an increase in suspended solids (turbidity) in lakes and reservoirs due to soil erosion and pollutants will increase. The projected increase in precipitation will enhanced transport of pathogens and other dissolved pollutants (e.g., pesticides) to surface waters and groundwater; and in increased erosion, which in turn leads to the mobilization of adsorbed pollutants such as phosphorus and heavy metals. In addition, more frequent heavy rainfall events will overload the capacity of sewer systems and water and wastewater treatment plants more often. An increased occurrence of low flows will lead to higher pollutant concentrations, including pathogens. In areas with overall decreased runoff (e.g., in many semi-arid areas), water quality deterioration will be even worse (Ibid).
Water-borne diseases will rise with increases in extreme rainfall. In regions suffering from droughts, a greater incidence of diarrhoeal and other water-related diseases will mirror the deterioration in water quality (IPCC, 2007).
Impacts of climate change on costs & other socio-economic aspects of freshwater:
People living in snowmelt-fed basins experiencing decreasing snow storage in winter may be negatively affected by decreased river flows in the summer and autumn. The Rhine, for example, might suffer from a reduction of summer low flows of 5–12% by the 2050s, which will negatively affect water supply, particularly for thermal power plants (Ibid). The Rio Santo in Peru depends almost entirely for its dry-season runoff on glacial melt. This river supports 5% of Peru's electricity and much of its agriculture. More than a million people in the coastal cities of Chimbote and Trujillo depend on this river for their drinking water. By 2050 the glaciers that feed the Rio Santo will have shrunk by 40% to 60%. Lima, home to more than eight million people, will also experience drastic water shortages as the climate warms and glaciers retreat to higher and higher elevations (Lynas, 2008). In western China, earlier spring snowmelt and declining glaciers are likely to reduce water availability for irrigated agriculture (Bates et al., 2008).
According to the Water Security Risk Index, released by Maplecroft (2010), a firm specialising in corporate risk intelligence, Somalia (1), Mauritania (2), Sudan (3), Niger (4), Iraq (5), Uzbekistan (6), Pakistan (7), Egypt (8), Turkmenistan (9) and Syria (10) are the countries with the least secure supplies of water (Fig. 16).
The report states that countries in the extreme risk category, including the emerging economies of Pakistan, Egypt and Uzbekistan, are already experiencing internal and cross-border tensions due to limited water resources. Furthermore, as the global climate changes, water stress is predicted to become more acute in these regions and has the potential to threaten stability. For more information view the full report.
As reported in The Sunday Times story (June, 2010), War clouds gather as nations demand a piece of the Nile, countries along the Nile River have signed an agreement to possess more of the water from that river. Egypt is already sabre rattling and the Foreign Minister has described the Nile waters as a matter of national security and a “red line” not to be crossed. Some Egyptian newspapers even discussed tactics that would prove effective if war erupts. Boutros Boutros Ghali, Egypt’s former Foreign Minister who later became the UN Secretary-General, warned: “The next war in our region will be over water, not politics.”
Iraq, Syria, and Turkey may fight over Turkey’s control of the headwaters of the Tigris and Euphrates Rivers, further destabilizing the fragile Middle East. Arab countries may increase their nuclear capabilities to desalinate water and, in doing so, proliferate nuclear weapons to protect their dwindling resources (Dyer, 2008). Rivers fed by glaciers in the Tibetan Plateau (Indus, Ganges, Brahmaputra, Salween, Mekong, Yangtze, and Yellow) will initially flood due to rapid glacial melt but will eventually dwindle thus causing water shortages to billions of people during summer when needed most. This will lead to food shortages and cross-border conflicts between NUCLEAR nations such as China, India, and Pakistan (Ibid). Will India redirect water away from Pakistan to feed its own people? Will Pakistan use nukes to rest this resource back?
Many locations in the United States are already in conflict over water resources and these conflicts are projected to increase toward the year 2025 as shown in Fig. 17 (USGRP, 2009).
For an aquifer in Texas, the net income of farmers is projected to decrease by 16–30% by the 2030s and by 30–45% by the 2090s due to decreased irrigation water supply and increased irrigation water demand (Bates et al., 2008).
If freshwater supply has to be replaced by desalinated water due to climate change, then the cost of climate change includes the average cost of desalination, which is currently around US$1.00/m3 for seawater and US$0.60/m3 for brackish water. The cost for freshwater chlorination is approximately US$0.02/m3. In densely populated coastal areas of Egypt, China, Bangladesh, India and south-east Asia, desalination costs may be prohibitive.
Average annual direct flood damage for three Australian drainage basins was projected to increase four- to ten-fold under doubled CO2 conditions. In selected U.S. cities, the mean and standard deviation of flood damage are projected to increase by more than 140% if the mean and standard deviation of annual precipitation increase by 13.5%. In the metro Boston area in the north-eastern USA, both the number of properties damaged by floods and the overall cost of flood damage may double by 2100, relative to what might be expected if there was no climate change.
Climate-change is likely to alter river flows which in turn will impact hydropower generation. Hydropower impacts for Europe have been estimated using a macro-scale hydrological model. The results indicate that by the 2070s the electricity production potential of hydropower plants existing at the end of the 20th century will increase (assuming IS92a emissions) by 15–30% in Scandinavia and northern Russia, where currently between 19% (Finland) and almost 100% (Norway) of electricity is produced by hydropower. Decreases of 20–50% and more are found for Portugal, Spain, Ukraine and Bulgaria, where currently between 10% (Ukraine, Bulgaria) and 39% of the electricity is produced by hydropower. For the whole of Europe (with a 20% hydropower fraction), hydropower potential is projected to decrease by 7–12% by the 2070s (Ibid).
Fig. 18 (Ibid) is and illustrative map of future climate change impacts related to freshwater which threaten the sustainable development of the affected regions.
Fig. 19 (USGRP, 2009) highlights the water-related impacts by sector in the United States.
Asia is in the grip of a water crisis that could set back the region's robust economic growth if left unresolved, according to a top Asian Development Bank (ADB) official, Arjun Thapan, special adviser to ADB president Harukiko Kuroda on water and infrastructure issues. Thapan stated "We believe that the estimate recently made about Asia having a 40 percent gap between demand and supply by 2030 is a reasonable estimate." With 80 percent of Asia's water used to irrigate agricultural lands, the shortage could have serious implications for food supplies, he warned. Between 10 and 15 percent of Asia's water is consumed by industry. Thapan said that the efficiency of water usage in agriculture and industry has improved by only one percent a year since 1990. Thapan said that if left unresolved, the water crisis "has the potential of slowing down" Asian growth. Another problem is the volume of used water in Asia that remains largely untreated, leading to massive pollution of water sources like rivers. Of the 412 rivers in the Philippines, 50 are biologically dead, he said. Between $2 billion and $2.5 billion dollars is needed to clean up Manila Bay and Pasig River in Manila alone. In China, India, and the Philippines, among other Asian countries, the total availability of water per person per year has fallen below 1,700 cubic metres -- the global threshold for water stress, a situation where water demand exceeds the available amount during a certain period. About 50 percent of China's Yellow River is so polluted it cannot support agriculture, and over 50 percent of the surface water in the country's Hai river basin is not fit for any use, Thapan said (Abbugao, 2010).
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Last updated: 10/23/10