Quantifying the Role of Agricultural Groundwater Use for Drought Mitigation
Washington State University
Quantifying the role of agricultural groundwater use for drought mitigationThe 2015 drought in Washington State had a severe impact on the more than 300 crops grown in the state, including an initial estimated loss of $86.52 million on the iconic Washington apple industry alone [Washington State Department of Agriculture, Interim Report: 2015 Drought and Agriculture, 2015]. The full agricultural impact of the Washington drought has yet to be assessed. Groundwater plays an important role in drought mitigation in Washington’s agricultural industry, just as it does in California’s Central Valley. However, a key difference is Washington’s requirement for permit applications to use emergency drought wells, only after the governor makes an official drought declaration. This contrasts with an overall historical lack of regulatory structure for groundwater use in California, though this will change with the 2014 Sustainable Groundwater Management Act. In either location, the decision to use supplemental groundwater is rooted in a farmer’s cost-benefit analysis that may be a function of crop types, seniority of water rights holdings, and capital cost to access groundwater. The cost-benefit analysis is dynamic in time and space, and will likely change as a function of groundwater availability. Climate change is predicted to decrease the availability and accessibility of surface water supplies into the future, leading to greater dependence on groundwater. As a result, an improved understanding of how today’s groundwater mitigation for drought impacts groundwater availability into the future is necessary for sustainable groundwater planning. The goal of this study is to create a baseline to quantify the value of groundwater for drought mitigation in agricultural regions, with a comparison of Washington and California’s recent droughts. An analysis is conducted to estimate the total amount of groundwater use in the Columbia River Basin in Washington based on a combination of drought well permits, provided by the Washington State Department of Ecology for 2001, 2005, and 2015, and additional observation wells. In addition, we assess the potential for value-added information on groundwater use with NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite mission to understand regional scale impacts. By comparing the increased reliance on groundwater during drought in the Central Valley and Columbia River Basin, we can better understand how groundwater dependence changes as a function of drought severity, drought length, and crop distribution. Ultimately, this work lays the foundation to assess the economic value of groundwater to mitigate crop losses in agricultural regions, especially into the future with changing regulatory structures and climate change.