Modelling crop evapotranspiration and potential impacts on future water availability in the Indo-Gangetic Basin

Abstract

In this research, we modelled crop actual evapo-transpiration (AET) of the Indo-Gangetic Basin (IGB) to better understand the use of water by cropland at the administrative region scale. By using the WaterWorld Policy Support System (WWPSS), we estimated baseline crop AET for the year 2000. We compared this baseline AET with AET under a plausible expansion of cropland for 2050 and explored the likely implications for future water availability. The scenario assumes all factors other than the land use (i.e. climate and crop water management practices) remain the same between the baseline and the scenario. Where cropland is increased it is assumed that it replaces the year 2000 cover of natural forest and grassland as defined by the MODIS Vegetation Continuous Fields product. The total crop water requirement increases due to higher AET under cropland compared with the current sparse vegetation cover. This AET would need to be supported by irrigation. A significant increase in crop AET would occur in upland regions such as Chhattisgarh (111.3%), Nepal (100%), Madhya Pradesh (62.2%), Jharkhand (60.6%), Uttarakhand (58.9%), Himachal Pradesh (58.8%) and Khyber Pakhtunkhwa (40.4%). Moderate to low growth in crop AET also occurs in lowland regions such as Rajasthan (33.5%), West Bengal (32.7%), Bihar (18.1%), Punjab (Pakistan) (16.6%), Uttar Pradesh (14.5%), Punjab (India) (8%) and Haryana (6.9%). Increased crop water use in the upland regions would affect water availability locally and in the regions affecting agriculture as well as other hydrological ecosystem services, especially in the water deficient north-west regions of the basin. If croplands were to increase in this way, more efficient use of freshwater would be essential to avoid serious water deficits within the basin.