The importance of Sierra Nevada Mountain snowpack to Central Valley aquifer recharge

Aquifer recharge is an essential component of sustainable groundwater management plans in California. The Sierra Nevada Mountain’s snow pack during winter months is believed to be important for aquifer recharge and studies support that a significant amount of  late winter to spring snow melt infiltrates as mountain front and mountain block recharge. Details of the connections between the Sierra’s mountain groundwater recharge processes to the adjacent Central Valley basin aquifer remain unclear. With the purpose to achieve a better understanding of this connection, we investigate geodetic, hydrologic, and climate datasets. These include total water storage variations from GRACE JPL Mascons and composite hydrology to quantify groundwater storage changes in the Central Valley. We study seasonal variations in this and other groundwater related observables, after isolating them through wavelet multi-resolution analysis of all datasets. The results for valley wide timing and amplitude of the various datasets provide insight into seasonal recharge mechanisms and they indicate that the Sierra Nevada Mountains play a more prominent role in the recharge of California’s deep Valley aquifers than previously assumed. We further support this finding through process-based model experiments. The time that is needed for vertical pressure propagation from the Sierra Nevadas to deep aquifer layers in the Valley is consistent with observed time difference between occurance of maximum water availability for groundwater recharge in the Sierra Nevadas and that of maximum groundwater levels in deep aquifer layers. Based on our findings, we suggest that models used for groundwater management plans need to include the Sierra Nevada Mountains for accurate predictions of human and climate change impacts on the Central Valley’s groundwater resources.