News

Managing river flows in turbulent times

Variation of rainfall in the Ganges basin will increase over the coming years, producing both floods and dry spells that will impact agriculture. Photo: CGIAR Challenge Program on Water and Food.

    Cliquez pour la version française

    by Sonja Vermeulen

    “Ever-changing, ever-flowing, and yet ever the same” is how Jawaharlal Nehru described the Ganges. Already home to more than half a billion people, the Ganges basin is expected to have a population of 720 million by 2025. Water will be the primary medium through which climate change will have an impact on their livelihoods, argues Freshwater, climate change and adaptation in the Ganges River Basin, by Heather Hosterman, Peter McCornick, Elizabeth Kistin, Bharat Sharma and Luna Bharati. Management of water must therefore be at the forefront of adaptation.

    Water use in agriculture is startling. Globally, irrigated farming accounts for about 68% of water abstraction and 93% of consumption (PDF) – domestic and industrial end-uses make up the remaining 7%. The Ganges basin is at the higher end of such statistics: agriculture accounts for 96% of withdrawals in Bangladesh and Nepal, and 86% in India. But water supplies must also be managed for other, sometimes competing, uses. Hosterman and co-authors consider the likely impacts of climate change, and arising implications for adaptation policy, across the interconnected sectors of agriculture, energy and ecosystems. 

    Aside from overall quantity and quality of water, the timing of flows will be a major challenge under climate change to both farming and hydropower.  Among the more robust predictions for the Ganges basin is that variation in rainfall will increase between years and within years. Both floods and dry spells threaten future agricultural production. For example, the major flood of 2007 caused losses in rice yields in the order of a million tonnes in Bangladesh.

    Furthermore, the Himalayan glaciers that account for about 9% of flow in the Ganges are receding, despite the distraction of the misquoted data in the last IPCC report. One anticipated outcome is a rise in the frequency of Glacial Lake Outburst Floods – “GLOFs” to the experts – in which meltwater collected behind a moraine dam suddenly bursts through. The biggest recorded GLOF in the Ganges basin, in 1985 in Nepal’s Bhote Kosi, released 2000 cubic metres per second at peak discharge, causing mass damage to crops and infrastructure, and destroying a new hydroelectric project. The risk of these events is one of the reasons that Nepal exploits only 2% of its hydropower potential.

    Managing increasing variability in water flows, including extreme events like GLOFs, is going to be important for both agriculture and energy. Proposed engineering solutions include updates to the existing infrastructure of reservoirs, dams, canals and pumping plants, as well as ambitious new ideas such as managed aquifer recharge systems based on large underground water banks.  Technology is not enough, however.  Hosterman and co-authors show just how critical it will be to strengthen cross-sectoral institutions to enable difficult decisions – such as whether to allocate a fixed volume of water for life-support to natural river ecosytems, even if this means foregoing food production. Policy-makers in the Ganges basin need both creativity and collaboration to ensure that the ever-changing river remains the font of life that it has been for millennia.  

    Links

    This is the March 2012 installation of AgClim Letters, a monthly e-bulletin on science and policy written by Sonja Vermeulen, Head of Research for CCAFS. Sign up to receive AgClim Letters bulletin and read past bulletins. Your comments are welcome below.