A dataset representing the percent of precipitation contributing to recharge was developed for Napa County using output from the U.S. Geological Survey’s Basin Characterization Model ( USGS BCM)(Flint et al., 2021). The BCM is a grid-based, regional water balance software package developed and maintained by the USGS and is widely applied throughout California as a foundational tool for water resource planning, climate change vulnerability assessments, and sustainable groundwater management. The model simulates physical processes in performing water-balance calculations across a high-resolution rectangular grid system with a square cell size of approximately 270 meters by 270 meters. While the published version of BCM utilizes input datasets for underlying geology derived from generalized regional geologic mapping data, to improve the representation of geologic conditions in the model, inputs relating to the underlying geology in the BCM were updated using local geologic data consistent with the surficial geology used in the California Department of Water Resources approved 2022 Napa Valley Subbasin Groundwater Sustainability Plan (GSP). Simulated annual recharge output on a cell-by-cell basis from the adjusted BCM for a 10-year period spanning water years (WY) 2012 through 2021, were used to calculate the average percentage of annual precipitation that contributes to groundwater recharge.

A dataset representing the percent of precipitation contributing to recharge was developed for Napa County using output from the U.S. Geological Survey’s Basin Characterization Model ( USGS BCM)(Flint et al., 2021). The BCM is a grid-based, regional water balance software package developed and maintained by the USGS and is widely applied throughout California as a foundational tool for water resource planning, climate change vulnerability assessments, and sustainable groundwater management. The model simulates physical processes in performing water-balance calculations across a high-resolution rectangular grid system with a square cell size of approximately 270 meters by 270 meters. While the published version of BCM utilizes input datasets for underlying geology derived from generalized regional geologic mapping data, to improve the representation of geologic conditions in the model, inputs relating to the underlying geology in the BCM were updated using local geologic data consistent with the surficial geology used in the California Department of Water Resources approved 2022 Napa Valley Subbasin Groundwater Sustainability Plan (GSP). Simulated annual recharge output on a cell-by-cell basis from the adjusted BCM for a 10-year period spanning water years (WY) 2012 through 2021, were used to calculate the average percentage of annual precipitation that contributes to groundwater recharge.