Water resources: the impact of glacier melt
Dr Wouter Buytaert: Grantham affiliated Lecturer in Water Resources and Environmental Change in the Department of Civil and Environmental Engineering, Imperial College London.
The melting and shrinking of glaciers is one of the most visible effects of climate change on water resources. In tropical and subtropical regions, glaciers often compensate for the seasonal variability in the flow of mountain rivers by providing a constant and reliable input of melt water. Given the difficulties with extracting groundwater in mountain regions, rivers are the main source of water for domestic use, irrigation, and hydropower.
As glaciers shrink, they will provide a smaller contribution to the overall river flow. This means water levels in the rivers they feed will be lower and more variable during dry periods. Warmer conditions increase the evaporation of water from land surfaces, and precipitation patterns are also changing, meaning that conditions are getting dryer anyway, adding to any potential water shortage in vulnerable regions.
Research has revealed that these changes in mountain river stream flow are already happening. Global assessments of glacier extent and thickness have shown that several smaller tropical glaciers are on the verge of disappearing or beyond the peak flow caused by their melting. When glaciers lose mass, they initially contribute more water to the rivers they feed whilst they are melting. After this there is a decline in water contributed to the seasonal melt cycle by that glacier. This is increasing the pressure on the water resources of high mountain communities in places such as Peru and Bolivia. Because of their remoteness and difficult living conditions, inhabitants of mountain regions are particularly vulnerable to the degradation of natural resources. The economic development and increase in living standards of the surrounding lowlands often bypasses these regions, resulting in “poverty pockets”. At the same time, these upland regions are in the midst of a perfect storm: ecosystem degradation, soil degradation, deforestation and erosion.
Scientists using field surveys and increasingly detailed remote sensing data are rapidly improving our knowledge of glacier melt. However, evaluating the effect this is having on water resources and poverty is still fraught with difficulties. Most communities lie considerable distances downstream of the glaciers, where other hydrological processes (wetlands and groundwater aquifers) are also important.
Most large cities that receive melt water from glaciers, such as Quito and Lima, are located so far downstream from the glaciers that the contribution of glacier melt to their water supply is only around 5%. The only major tropical cities currently getting a significant proportion of their water from glaciers are La Paz and El Alto in Bolivia. Both get around 30% of their water from melting glaciers, enough to make them vulnerable to changes in the glacier melt signal.
However, in remote regions of Bolivia, Peru, Chile, Argentina, and to a lesser extent Ecuador, tens of thousands of poor rural dwellers rely on glacier-fed river water for irrigation and drinking water. These people are among the most vulnerable to global climate change and risk getting trapped in a vicious cycle of degrading natural resources and increasing poverty.
Glacier dependency. Each of the provinces in Peru that currently get at least some of their water from glaciers are represented by a circle. The area of agricultural land in each province is represented by the size of the circles. The colours represent the percentage of the water supply in each region that currently comes from glaciers, giving an idea of the vulnerability of agriculture in each region.