Accounting for Climate Change and Drought in Implementing Sustainable Groundwater Management

Groundwater provides close to 40% of California’s overall water supply under average hydrologic conditions. It is a critical source of backup during drought when increased pumping occurs to compensate for reduced surface supplies and decreased soil moisture. The conundrum is that in regions of the state where groundwater dependence is already high and rates of recharge are low, over the long term the volume withdrawn, particularly during droughts, generally exceeds replenishment in many regions. The result is overdraft - ongoing declines in groundwater levels over the long-term. To facilitate the reduction or cessation of long-term groundwater overdraft, this paper proposes that sustainable groundwater management must include the development of a drought reserve. The reserve, ideally sourced, sited and used locally, would encompass sufficient water for use during a drought such that the increased withdrawals during a drought do not result in unrecoverable groundwater declines and concomitant negative impacts. The objective is to reduce vulnerability to the state’s periodic droughts, as opposed to mitigating seasonal variations in precipitation. This paper first summarizes the issues associated with developing drought reserves, and then examines in detail how two California groundwater management agencies approach establishing and implementing a drought reserve.