Role of groundwater in buffering irrigation production against climate variability at the basin scale in South-West India.

The basaltic aquifers of the Upper Bhima River Basin in India are highly utilized for irrigation but the sustainability of groundwater withdrawals and the agricultural production systems they support is largely unknown. Here we used hydrogeological data, supported by secondary data, to assess the effects of water scarcity over a decade-long period (1998�2007) on the groundwater resources at the regional basin scale. This reveals no evidence of systematic declines in total groundwater availability over the period; only shorter-term losses/gains in storage associated with successive dry/wet years. The clearest indicator of stress comes from the more widespread drying out of wells following lower rainfall years throughout the basin and especially in upland areas where aquifers are least developed and most easily drained. Groundwater in the basin offers an adaptive mechanism to climate variability to some degree, but the buffering capacity is constrained by low aquifer storativity and average residence times of just a few years. Around 40% of the basin is currently at a level of development that is of concern, and the number of irrigation wells is growing rapidly. However recent evidence of conversion from high to low water use crops indicates the adaptive capacity of farmers to water-related stresses. Surplus surface water flows may provide opportunities to enhance groundwater recharge but requires careful trade-off analysis of the downstream impacts.