Assessing future shifts in the water supply sources of South Asian irrigated agriculture using a coupled high-resolution cryosphere-hydrology-crop model

Abstract:

Irrigated agriculture in South Asia depends on melt water generated in the high mountain ranges of Asia, rainfall-runoff supplied by the Asian summer monsoon, and groundwater abstracted from the Indo-Gangetic Basin alluvial aquifer system. Climate change leads to changing hydrological regimes in Asia’s high mountains and shifts in the seasonality and magnitude of water supply from upstream to downstream. Simultaneously, socioeconomic development on the Indo-Gangetic plain leads to shifts in agricultural water demand. Here we use a coupled high-resolution cryosphere-hydrology-crop model forced with an ensemble of climate change and socioeconomic projections to assess how the future magnitude and sources of agricultural water supply in the region may shift during the 21^st century. We find a general shift from the use of melt water to unsustainably abstracted groundwater for most scenarios. However, we also identify season- and crop-specific increased melt water dependence, in particular in the Indus river basin. Furthermore, the increasing interannual variability in both melt water and groundwater as sources of irrigation water supply indicates a growing importance of both sources as supplement to rainfall-runoff. These findings provide important directions for climate change adaptation policy making in this global climate change hotspot.