TO: Technical Advisory Group for the Napa County Groundwater Sustainability Agency
FROM: Brian D. Bordona - Director of Planning, Building and Environmental Services
REPORT BY: Jamison Crosby, Natural Resources Conservation Manager
SUBJECT: Update on Spring 2024 Groundwater Conditions
RECOMMENDATION
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Provide an update on the start of the Water Year 2024 with a focus on change in storage and future climate impacts.
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BACKGROUND AND DISCUSSION
A core charge of the Technical Advisory Group (TAG) is to provide guidance on Napa County Groundwater Sustainability Agency responses to groundwater conditions occurring in the Napa Valley Subbasin. This update is to inform TAG members and public of the current groundwater conditions across the Napa Subbasin in response to precipitation events occurring during the first half of Water Year (WY) 2024 (October 1, 2023 through April 30, 2024).
Leading up to WY 2024 (October 1, 2023 through September 30, 2024), WY 2023 experienced total precipitation of 32.91 inches, or 128 percent of average. Temperatures and atmospheric demand were less than the historical average in WY 2023 and groundwater pumping was near the sustainable yield. All of these conditions led to higher groundwater levels and general recovery of groundwater storage throughout the Subbasin.
Precipitation in WY 2024 included near or above average precipitation from December 2023 through March 2024. Overall, as of April 26, 2024, the total precipitation is 22.19 inches, or 89 percent of water year average (24.86 inches). If no other precipitation falls during WY 2024, it will be classified as a Normal (below average), analogous to WY 2016 and WY 2021.
Groundwater storage is estimated based on spring water level data. Groundwater level data are interpolated from wells that are screened primarily or exclusively in the alluvial aquifer. The saturated thickness is calculated by comparing the interpolated groundwater elevation to the depth of the alluvial...
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