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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 20, issue 5 | Copyright
Hydrol. Earth Syst. Sci., 20, 1971-1982, 2016
https://doi.org/10.5194/hess-20-1971-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 17 May 2016

Research article | 17 May 2016

Crop-specific seasonal estimates of irrigation-water demand in South Asia

Hester Biemans1, Christian Siderius1,2, Ashok Mishra3, and Bashir Ahmad4 Hester Biemans et al.
  • 1Alterra, Wageningen University and Research Centre, Wageningen, the Netherlands
  • 2Environmental Economics and Natural Resources Group, Wageningen University, Wageningen, the Netherlands
  • 3Agricultural and Food Engineering Department, IIT Kharagpur, Kharagpur, India
  • 4Pakistan Agricultural Research Council, Islamabad, Pakistan

Abstract. Especially in the Himalayan headwaters of the main rivers in South Asia, shifts in runoff are expected as a result of a rapidly changing climate. In recent years, our insight into these shifts and their impact on water availability has increased. However, a similar detailed understanding of the seasonal pattern in water demand is surprisingly absent. This hampers a proper assessment of water stress and ways to cope and adapt. In this study, the seasonal pattern of irrigation-water demand resulting from the typical practice of multiple cropping in South Asia was accounted for by introducing double cropping with monsoon-dependent planting dates in a hydrology and vegetation model. Crop yields were calibrated to the latest state-level statistics of India, Pakistan, Bangladesh and Nepal. The improvements in seasonal land use and cropping periods lead to lower estimates of irrigation-water demand compared to previous model-based studies, despite the net irrigated area being higher. Crop irrigation-water demand differs sharply between seasons and regions; in Pakistan, winter (rabi) and monsoon summer (kharif) irrigation demands are almost equal, whereas in Bangladesh the rabi demand is  ∼ 100 times higher. Moreover, the relative importance of irrigation supply versus rain decreases sharply from west to east. Given the size and importance of South Asia improved regional estimates of food production and its irrigation-water demand will also affect global estimates. In models used for global water resources and food-security assessments, processes like multiple cropping and monsoon-dependent planting dates should not be ignored.

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This study presents crop-specific seasonal estimates of irrigation-water demand in South Asia resulting from the typical practice of multiple cropping. We show that crop irrigation-water demand differs sharply between seasons and regions; in Pakistan, winter and summer irrigation demands are almost equal, whereas in Bangladesh the demand in winter is much higher. Insight in where and when sufficient irrigation water supply is critical to sustain food production, is essential to plan adaptation.
This study presents crop-specific seasonal estimates of irrigation-water demand in South Asia...
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