Densely populated floodplains downstream of Asia’s mountain ranges depend heavily on mountain water resources, in particular for irrigation. An intensive and complex multi-cropping irrigated agricultural system has developed here to optimize the use of these mountain water resources in conjunction with monsoonal rainfall. Snow and glacier melt thereby modulate the seasonal pattern of river flows and, together with groundwater, provide water when rainfall is scarce. Climate change is expected to weaken this modulating effect, with potentially strong effects on food production in one of the world’s breadbaskets. Here we quantify the space-, time- and crop-specific dependence of agriculture in the Indo-Gangetic Plains on mountain water resources, using a coupled state-of-the-art, high-resolution, cryosphere–hydrology–crop model. We show that dependence varies strongly in space and time and is highest in the Indus basin, where in the pre-monsoon season up to 60% of the total irrigation withdrawals originate from mountain snow and glacier melt, and that it contributes an additional 11% to total crop production. Although dependence in the floodplains of the Ganges is comparatively lower, meltwater is still essential during the dry season, in particular for crops such as sugar cane. The dependency on meltwater in the Brahmaputra is negligible. In total, 129 million farmers in the Indus and Ganges substantially depend on snow and glacier melt for their livelihoods. Snow and glacier melt provides enough water to grow food crops to sustain a balanced diet for 38 million people. These findings provide important information for agricultural and climate change adaptation policies in a climate change hot spot where shifts in water availability and demand are projected as a result of climate change and socio-economic growth.
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All SPHY and LPJmL output data generated in this study (discharge, irrigation water use by crops and crop yields), as well as the data that support the findings of this study are available from the corresponding author on reasonable request.
The source codes of SPHY and the adjusted LPJmL version used in this study can be obtained from the corresponding author on reasonable request.
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This work was carried out by the Himalayan Adaptation, Water and Resilience consortium under the Collaborative Adaptation Research Initiative in Africa and Asia with financial support from the UK Government’s Department for International Development and the International Development Research Centre, Ottawa, Canada.
This work was also partially supported by core funds from ICIMOD contributed by the governments of Afghanistan, Australia, Austria, Bangladesh, Bhutan, China, India, Myanmar, Nepal, Norway, Pakistan, Switzerland and the United Kingdom. W.W.I. has been supported by the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 676819) and by the research programme VIDI (project no. 016.161.308), which is financed by the Netherlands Organisation for Scientific Research.
The views expressed in this work are those of the creators and do not necessarily represent those of the UK Government’s Department for International Development, the International Development Research Centre, Canada or its Board of Governors, and are not necessarily attributable to their organizations.
The authors declare no competing interests.
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Supplementary methods, Supplementary Figs. 1–6, Supplementary Tables 1 and 2, Supplementary references 1–36
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Nature Sustainability (2019)