Trends and Conditions
Napa County has several groundwater basins, the largest of which is the Napa Valley Subbasin.
Napa County and other public agencies have been studying our groundwater since the mid-1900s. Although water levels drop during the dry-season and during dry years, they fully recover when we have higher than average rainfall. Infiltration of precipitation has been shown to provide significant groundwater recharge in Napa County, particularly in unconsolidated geologic settings like much of the Napa Valley floor (Kunkel and Upson 1960, LSCE and MBK 2013). Recently, long term precipitation records in Napa County have been used to develop a water year rating system that defines Very Dry, Dry, Normal, Wet, and Very Wet water year types (LSCE 2016, 2NDNATURE 2013). Overall, groundwater levels in the main Napa Valley Subbasin have been relatively stable for decades. Groundwater conditions outside the Napa Valley Subbasin are more variable, such as in the Milliken-Sarco-Tulucay (MST) area.
Overview of Trends and Conditions
Trends and conditions for each subarea in the County are tracked separately. Find information about the latest trends and conditions by visiting the webpage for each groundwater subarea:
- Angwin & Pope Valley
- Calistoga & St. Helena
- Carneros, Jameson/American Canyon, Napa Wetlands
- Eastern & Western Mountains
- Milliken-Sarco Tulocay (MST)
- Napa & Yountville
Follow this link to find annual reports with additional details on groundwater trends and conditions.