Understanding the drivers of groundwater use for drought mitigation in Washington State

Additional use of groundwater is just one of multiple mitigation options available to farmers during droughts, but one with the potential to have a long-term impact on future water availability. The choice to use groundwater versus other options, such as fallowing or increasing surface water storage, is likely driven by a diversity of factors. The 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 Dept. of Agriculture, Interim Report: 2015 Drought and Agriculture, 2015], but the extent to which groundwater played a mitigating role has yet to be fully explored. Washington State has a specific regulatory mechanism to utilize additional groundwater supplies solely during drought via emergency groundwater permits. These permits were utilized in the 2001, 2005, and 2015 droughts. Despite similar levels of drought severity, the extent to which groundwater was used to mitigate these droughts varied over multiple orders of magnitude based on permit application records. This study aims to understand the combination of drivers that lead farmers to use groundwater for drought mitigation in Washington. We look at the volume of groundwater authorized for use from the emergency groundwater permits, drought characteristics, crop and irrigation types, institutional structure, and geographic location as possible drivers. We use VIC-CropSyst, a coupled hydrology-cropping systems model, to evaluate drought characteristics. Institutional structure and permit records are analyzed from the Washington State Dept. of Ecology's Water Rights Tracking System. On-farm characteristics are analyzed with a combination of Washington State Dept. of Agriculture's agricultural land use data and Ecology place-of-use records. Preliminary findings show that emergency groundwater is used to irrigate predominantly high-value crops and the introduction of a cost associated with emergency groundwater applications likely deterred additional users. The results of this study will allow for estimating the economic contribution of groundwater to drought and evidence for improving future groundwater management as droughts become more severe and intense with climate change.