Considering the Impact of Atmospheric Rivers on Groundwater using In-Situ Well Data and GPS-Derived Surface Subsidence

Atmospheric Rivers (ARs) have been shown to significantly impact precipitation, snowpack and streamflow along the western United States. This study examines whether there is a detectable response in groundwater and the lag of the impact based on in-situ records of precipitation, streamflow and groundwater elevation - via direct well measurements and inferred from GPS subsidence measurements - from central California. For the well data in northern-central California, the results show that groundwater local to the precipitation event increases in response to ARs, with the maximum response occurring about 4-6 days after the AR event. The lag-response analysis, computed from 8 isolated AR events overlapping available daily well-water records, shows well-water heights increasing about 9-10 cm 4-6 days after AR events, with local streamflow indicating a smaller lag time of 1-2 days and showing an increase of about 55 m3 s-1. Further examination of GPS-derived surface subsidence observations provides similar information regarding the time lag for the maximum response to the AR precipitation. These findings indicate the important role of ARs in helping to establish local fresh water availability in regions they impact; additional implications and caveats are discussed.