Changes in critical geographical features (including water-bodies and ice-caps) and the effects of such changes
"Water is essential to life and is central to society's welfare and to sustainable economic growth. Plants, animals, natural and managed ecosystems, and human settlements are sensitive to variations in the storage, fluxes, and quality of water at the land surface – notably storage in soil moisture and groundwater, snow, and surface water in lakes, wetlands, and reservoirs, and precipitation, runoff, and evaporative fluxes to and from the land surface, respectively. These, in turn, are sensitive to climate change." Source: U.S. Climate Change Science Program, 2008
Human efforts to alter the hydrological cycle date back to ancient times. Prayer, dances, human and animal sacrifices, and other rituals have been tried to bring rain. Cloud seeding is a more scientific, but still uncertain, attempt to induce precipitation. Although it is questionable whether any of these intentional efforts have significantly altered precipitation patterns, the balance of evidence now suggests that humans are influencing the global climate and, thereby, altering the hydrological cycle, however inadvertently.
The most recent scientific assessment by the Intergovernmental Panel on Climate Change (IPCC) concludes that, since the late 19th century, anthropogenically induced emissions of gases such as carbon dioxide (CO2) that trap heat in the atmosphere in the manner of a greenhouse have contributed to an increase in global mean surface air temperatures of about 0.3 to 0.6oC. Moreover, based on the IPCC’s mid-range scenario of future greenhouse gas emissions and aerosols and their best estimate of climate sensitivity, a further increase of 2oC is expected by the year 2100.
The vast majority of the Earth's water resources are salt water, with only 2.5% being fresh water. Approximately 70% of the fresh water available on the planet is frozen in the icecaps of Antarctica and Greenland leaving the remaining 30% (equal to only 0.7% of total water resources worldwide) available for consumption. From this remaining 0.7%, roughly 87% is allocated to agricultural purposes (IPCC 2007).
These statistics are particularly illustrative of the drastic problem of water scarcity facing the world. Water scarcity is defined as per capita supplies less than 1700 m3/year (IPCC 2007).
There are four main factors aggravating water scarcity according to the IPCC:
· Population growth: in the last century, world population has tripled. Water use has been growing at more than twice the rate of population increase in the last century, and, although there is no global water scarcity as such, an increasing number of regions are chronically short of water.
· Increased urbanization will focus on the demand for water among a more concentrated population.
· High level of consumption: as the world becomes more developed, the amount of domestic water used by each person is expected to rise significantly.
· Climate change will shrink the resources of freshwater.
The Hydrological Cycle
The hydrological cycle begins with evaporation from the surface of the ocean or land, continues as the atmosphere redistributes the water vapor to locations where it forms clouds, and then returns to the surface as precipitation. The cycle ends when the precipitation is either absorbed into the ground or runs off to the ocean, beginning the process over again.
Key changes to the hydrological cycle (associated with an increased concentration of greenhouse gases in the atmosphere and the resulting changes in climate) include:
- Changes in the seasonal distribution and amount of precipitation.
- An increase in precipitation intensity under most situations.
- Changes in the balance between snow and rain.
- Increased evapotranspiration and a reduction in soil moisture.
- Changes in vegetation cover resulting from changes in temperature and precipitation.
- Consequent changes in management of land resources.
- Accelerated melting glacial ice.
- Increases in fire risk in many areas.
- Increased coastal inundation and wetland loss from sea level rise.
· Effects of CO2 on plant physiology, leading to reduced transpiration and increased water use efficiency.
Climate Change Impact on Water Resources
Climate change has the potential to substantially alter river flow regimes and thereby surface water availability. Globally there has been a discernible and contrasting change in the pattern of runoff: the regions lying in the higher latitudes have been experiencing an increase, while parts of west Africa, southern Europe, and southern Latin America have had a decrease.
Groundwater is an important source of water in many parts of the world, and for centuries it has been considered a reliable source of water supply for the human society. However, the overexploitation of this resource has cast serious aspersions on its sustainable use especially because a majority of the groundwater resources are non-renewable on meaningful time scales. Climate change effects- reduced precipitation and increased evapotranspiration- will reduce recharge and possibly increase groundwater withdrawal rates. More importantly because of variations in the volume of snowmelt and distribution of rainfall, the timing of recharge will be affected: typically with a shift in seasonal mean and annual groundwater levels. The FAO (2011) describes some obvious climate-related impacts in general terms, listed hereafter:
· If flooding increases, aquifer recharge will increase, except in continental outcrop areas.
· If drought frequency, duration and severity increase, the cycle time will lengthen and abstraction will require better balance, with less in sequences of wet years and more in dry years.
· If snowmelt increases, aquifer recharge rates should increase, but this is dependent on permafrost behavior and recharge patterns, which largely remains unknown.
Increase in sea-level has serious implications for both human security (increased flood-risks, degraded groundwater quality, etc.) and ecosystems (impact on mangrove forests and coral reefs, etc.), especially so in coastal regions. Coastal cities in developing regions are particularly vulnerable to sea-level rise because of high population densities and often inadequate urban planning and the added burden due to urban migration.
There has always been a steady increase in the global sea-level, but because of accelerated glacier melting in Greenland and the Antarctic, the rise has been quite rapid in the last decade and is projected to rise at a greater rate in the twenty-first century.
The World Bank (2013) reports that as much as 100 cm sea-level rise may occur if emission increases continue and raise the global average temperature to 4○C by 2100 and higher levels thereafter.
Floods and droughts cause significant damages every year and are responsible for a large fraction of water-related disasters. While droughts are a creeping disaster, in which the effects are felt over a longer duration of time, flooding phenomenon is usually more rapid in nature especially in urban areas because of the imperious nature of the ground surface. The IPCC (2012) projects that the frequency of heavy precipitation or the proportion of total rainfall from heavy falls will increase in the twenty-first century over many areas of the globe. The increase will be more intense in the high latitudes and tropical regions and in winter in the northern midlatitudes. Additionally the maximum daily temperatures are projected to increase globally, while extremes in low temperatures will reduce.
Although the risk of flooding is a global concern, coastal and deltaic regions are particularly vulnerable because of the high numbers of exposed people. Climatic change exacerbates the risk of flooding through extreme precipitation events, higher peak river flows, accelerated glacial melt, increased intensity of the most extreme tropical cyclones, and sea-level rise. These changes are already being experienced in many parts of the world today and are expected to further increase the frequency and magnitude of flood events in the future. Among the flooding events, there are wide range of flooding events that can be influenced by climate change, which include flash floods, inland river floods, extreme precipitation causing landslides, and coastal river flooding, combined with the effects of sea-level rise and storm surge-induced coastal flooding.
In addition to floods and landslides, the Himalayan regions of Nepal, Bhutan and Tibet are projected to be exposed to an increasing risk of glacial lake outbursts.
Drought is multifaceted and is broadly categorized into three major types. A meteorological drought is defined by a prolonged period of low or insufficient precipitation, an agricultural drought is defined by soil moisture deficit, and a hydrological drought is characterized by flow reductions in rivers, and from reservoirs, with reduced groundwater levels. A fourth type, socioeconomic drought, is also sometimes considered especially in policy development and associates the supply and demand of economic goods with elements of meteorological, hydrological and agricultural drought. Socioeconomic drought occurs when the demand for any economic good is not met because of shortage of water caused by elements of weather.
Hegerl et al. (2007) point out to the strong possibility that anthropogenic activities have contributed to the increase in the droughts observed towards the end of the twentieth century. Global trends of drought correspond well with trends of precipitation and temperature, which are consistent with expected responses to anthropogenic forcing.
Changes in surface water quality have implications on human and ecological health. While groundwater is relatively free of organic and other contamination, surface water is more prone to pollution. The IPCC (2007) suggests that two main drivers of climate change- higher water temperature and variations in runoff- are likely to produce adverse changes in water quality affecting human health, ecosystems, and water use. Higher surface water temperatures will promote algal blooms and increase microbial content, while more intense rainfall will lead to an increase in suspended solids (turbidity) in lakes and reservoirs due to increased soil erosion and contaminant transport (e.g., pesticides, heavy metals, and organics). These effects will especially be a source of major concern in water bodies where water levels are expected to reduce.
Climate change, coupled with anthropogenic influence, will impact groundwater quality through the influence of recharge, discharge, and land use on groundwater systems. The coastal regions, in particular, are vulnerable to degraded groundwater quality due to climate change impacts, which affect recharge (sea-level rise, changes in precipitation patterns and timings, and evapotranspiration), and increased groundwater pumping, which will result in aggravated salinity intrusion in many coastal regions. Decreased groundwater levels caused due to reduced recharge of groundwater may lead to an increased rate of pumping to meet demands. This is more likely to further degrade groundwater quality by disturbing the balance of the freashwater/saline water boundary, resulting in saline water intrusion in not only coastal basins but inland aquifers as well. Nutrient transport rates, particularly nitrogen (N) and phosphorus (P), beneath agricultural lands may also be sensitive to climate change.
Introduction to glaciers and ice caps
Glaciers and ice caps are among the most fascinating elements of nature, an important freshwater resource but also a potential cause of serious natural hazards. Because they are close to the melting point and react strongly to climate change, glaciers are important indicators of global climate.
Glaciers and ice caps form around the world where snow deposited during the cold/humid season does not entirely melt during warm/dry times. This seasonal snow gradually becomes denser and transforms into perennial firn (rounded, well-bonded snow that is older than one year) and finally, after the air passages connecting the grains are closed off, into ice. The ice from such accumulation areas then flows under the influence of its own weight and the local slopes down to lower altitudes, where it melts again (ablation areas). Accumulation and ablation areas are separated by an equilibrium line, where the balance between gain and loss in the ice mass is exactly zero.
Glaciers, landscapes and the water cycle
Glaciers are among the best natural indicators of climate change. Their development can be observed by everybody – and the physical process, the melting of ice under the influence of warmer temperatures, can intuitively be understood. The impacts of accelerated atmospheric warming are thus changing the public perception of glaciers: they are increasingly recognized as a warning signal for the state of the climate system.
Continued atmospheric warming will inevitably lead to the deglaciation of many currently glacierized landscapes, especially in low-latitude mountain chains. In many places, lakes have already started to form. Such lakes may replace some of the lost landscape attractiveness, but their beauty may come at a dangerous price. On slopes, vegetation and soils take decades and even centuries or sometimes millennia to follow the retreating ice and cover the newly exposed terrain. As a consequence, the zones of bare rock and loose debris will expand. Vegetation (especially forests) and ice both have a stabilizing effect on steeply inclined surfaces. During the expected long transitional period between glacier vanishing and forest immigration, erosion (including large debris flows) and instability (including large rock falls and landslides) on slopes unprotected by ice or forest will increase substantially.
The perennial ice of glaciers is an important part of the water cycle in cold regions. It represents a storage component with strong effects on river discharge and fresh water supply. Such effects indeed make high mountain chains ‘water towers’ for many large areas and human habitats. Climatic change will lead to pronounced changes in this system. At time scales of tens and hundreds of millennia, the growth and decay of continental ice sheets, large ice caps and glaciers during periodical ice ages profoundly affect the global water cycle. Within annual cycles of temperature and precipitation, glacial meltwater feeds rivers during the warm/dry season. In the Andes of Peru, the Argentinean Pampas or the Ganzhou Corridor of China, this contribution to river flow is the predominant source of freshwater for large regions surrounding the corresponding mountain areas. Meltwater from glacierized mountain chains with rugged topography is also intensively used for hydropower generation.
The shrinking and even vanishing of mountain glaciers in scenarios of atmospheric temperature rise is likely to cause both small and large meltwater streams to dry out during hot and dry summers. This drying out may become more frequent at mid-latitudes, where human populations are often dense and the need for fresh water is growing. Earlier snowmelt and perhaps also reduced snow cover from wintertime could result in severe consequences for both ecosystems and related human needs: decreasing river flow, warmer water temperatures, critical conditions for fish and other aquatic forms of life, lower groundwater levels, less soil humidity, drier vegetation, more frequent forest fires, stronger needs for irrigation water, and rising demands for energy (such as air conditioning) coupled with reduced hydropower generation and less river cooling for nuclear power plants. These consequences are all likely to be interconnected and related to growing conflicts of interest.
Perhaps the most critical regions will be those where large populations depend on water from glaciers during the dry season, such as in China and other parts of Asia, including India, together forming the Himalaya-Hindu Kush region, or in the South American Andes. But it will also affect mountain ranges which are densely populated and highly developed, such as the European Alps and the regions in the vicinity of its rivers. Glacier changes, as important and pronounced parts of climate-induced changes in mountain landscapes, are not only the clearest indication of climate change – they also have the potential of having a strong impact on the seasonal availability of fresh water for large, densely populated regions and, hence, on the fundamental basis of ecosystem stability and economic development.
References:
Websites:
1. http://www.climate.org/topics/water.html
2. http://water.epa.gov/scitech/climatechange/Water-Impacts-of-Climate-Change.cfm
3. http://www.unep.org/geo/geo_ice/PDF/GEO_C6_B_LowRes.pdf
4. http://www.rff.org/rff/Documents/RFF-CCIB-03.pdf
Books:
Climate Change and Water Resources: Edited by Dr. Sangam Srestha, Prof. Mukand S. Babel, Dr. Vishnu Prasad Pandey
