GREAT BRITAIN–(ENEWSPF)–1 December 2010. A new Oxford and LSE study published in Philosophical Transactions of the Royal Society A has analysed the extent of water scarcity in some of the world’s largest river basins in the next 50 years, under contrasting climate change scenarios of global mean temperature rises of two or four degrees Celsius.
Even if climate policy is successful in limiting global warming to two degrees Celsius, the study suggests water supplies will dwindle in most river basins because of the increased demands for water from the world’s growing populations. However, in a four degree Celsius world, the study suggests that the impacts of climate change would become the biggest threat to water availability as climates become warmer and drier. The study also points out that the problem of water scarcity in most river basins will be compounded if global warming proceeds more rapidly and large climate impacts coincide with a peak in world population.
The research team assessed the effect of a two degree and four degree rise in global mean temperature on water basins, compared to the present day. Using more than 1500 climate models (from the Climateprediction.net experiment and 22 CMIP3 climate models*), they analysed the likely impact of climate change on river basins. They then compiled a water scarcity index by comparing river basin runoff with the total population of the river basin. Runoff in river basins is fed by rainfall, groundwater seepage and melt-water released along the edges of snowfields and glaciers. The population scenarios were developed for 112 major river basins, using population projections for the 2030s and 2060s based on data from the United Nations Development Programme.Oxford and LSE researchers say the projections suggest that in a world that is two degrees warmer, some river basins will become drier and some wetter. An increase of four degrees Celsius will amplify those changes even more. However, future scenarios about possible water shortages also need to take into account the varied projections about population growth around each of the river basins.
Their study finds that the future of water scarcity in the River Danube in Europe is finely balanced. In a two degree Celsius warming scenario, projected water availability depends largely on the size of the population with some projections suggesting it might decrease. However, in a four degrees Celsius world, the study projects reduced water availability in the Danube river basin, irrespective of the size of population.
The Mississippi and the Amazon are also likely to get drier, according to the study’s projections.In contrast, according to model projections the basin of the River Ganges would get wetter if global temperatures rose by four degrees Celsius because of large increases in South Asian monsoon rainfall. The projections suggests that in the Ganges, water availability will increase despite large projected population growth in India and Bangladesh over coming decades, but that seasonal water shortages will increase.
Lead author Dr Fai Fung, from the School of Geography and the Environment at Oxford University, said: ‘Our study is the most comprehensive assessment of global water availability using over 1500 climate models. The projections suggest that if policy makers fail to limit global mean temperatures rising by two degrees Celsius and allow a rapid warming of four degrees, this will have a severe effect on water availability particularly as it may coincide with a peak in world population.