D. R. Archer et al. discuss the impact of climate change on resources in the Indus River basin. The Indus River drains the highest mountain ranges in the world and contains the greatest area of perennial ice outside the Polar Regions. Since Pakistan is highly dependent on water resources originating in the upper Indus, any impact through climate change that stresses these resources could have a drastic impact on food security and the environment. Possible sources of damage include declining reservoir storage, the impact of waterlogging and salinity, and reallocations for environmental remediation. The impact of climate change in the Upper Indus is dependent upon three hydrological systems, which are a nival regime dependent on melting of winter snow, a glacial regime, and a rainfall regime dependent on concurrent rainfall. However, historical trends show no strong evidence implying that climate trends will reduce water resources via any of these hydrological systems.—Maddy Busacca
Archer, D. R., Forsythe, N., Fowler, H. J., Shah, S. M., 2010. Sustainability of water resources management in the Indus Basin under changing climatic and socioeconomic conditions. Hydrology and Earth System Sciences Discussions 7, 1883-1912.
Climate changes projected in the Indus region would decrease river flow and have a huge effect on irrigated agriculture in Pakistan. Although mean annual temperatures are generally rising, summer temperatures, the key time for glacial melt, have been falling in the Pakistan mountain ranges from 1961 to 2000. This decreasing trend in summer temperatures contrasts with the prediction of shrinking glaciers.
The climate of the Upper Indus is dependent upon the disposition and height of mountain ranges. Generally lower elevations, 2500 m, receive 200mm of rain per year while higher elevations, 500 m, receive 1500mm of annual rain. Since the valleys receive significantly less rainfall than the higher elevations, the lower elevations rely on the main hydrological activities of melt of seasonal snow and glaciers to contribute to river runoff.
Water stress is defined as either the ratio of withdrawals to long-term average annual runoff rising above 0.4 or per capita water availability falling below 1700 m3 per year. According to both definitions, the Indus River is water stressed. The per capita definition of water stress accounts for population growth; a predicted population of 246–335 million people in Pakistan for 2025–2050 results in per capita estimates of only 711 to 522 m3 per year. The issue is that as Pakistan’s population continues to increase at about a rate of 4 million people per year, demand for water increases, but the supply does not.
Evidence of the potential impact of climate change on water resources is conflicting. The expectation of a severely reduced resources is based on two assumptions: that the effect of rising temperature on glacier melt is the primary impact on water resources, and that temperatures in the Upper Indus will rise in line with global climate change projections. However, Archer et al. question these assumptions and show that river flow in the Indus does not primarily depend on glacier melt but on three distinct regimes relating climate to river flow.
The first regime is a nival, meaning growing in snow, regime at middle altitudes where flow is dependent on the melting of seasonal accumulated snow. Summer runoff is correlated to winter precipitation, not summer temperature.
The second regime is a glacial regime at very high altitudes where river flow is closely dependent on summer temperature. Unlike in the middle altitudes, at very high altitudes there is a high and positive correlation between summer runoff and summer temperature, but no correlation between summer runoff and winter precipitation. As temperatures increase, summer runoff will initially increase but, with declining glacier mass, ultimately decrease severely. However, Archer et al. found that summer temperatures have actually been falling and furthermore expect potential glacial surges at the highest elevations.
The third regime is a rainfall regime dependent on runoff from concurrent rainfall during the monsoon season. Runoff resulting from monsoon rainfall is more intense than that from glacial and nival sources. The impact of climate change on monsoon precipitation trend in the Indus Basin is unknown due to the region’s complex topography and marine influences, and a lack of clarity over the effects of the El Niño Southern Oscillation, a quasi-periodic climate pattern that occurs across the Pacific Ocean about every five years causing extreme weather disturbances.
The analysis of the three regimes shows little evidence for substantial reductions in runoff. However, uncertainty over the meteorological origins of climate trends, links between climate, glacial accumulation and runoff , and why the Upper Indus should differ in its response to climate change from other mountain regions in the world remains.