Central Valley Groundwater Map and Forecast
Depth to groundwater across California's Central Valley, monthly since 2005, from about 10,000 DWR monitoring wells. A model trained on those readings (it has no pumping data) forecasts how levels respond to precipitation: the map opens on NOAA's outlook for this water year, and you can pick a drier or wetter scenario.
Each monthly refresh: briefing · what changed, by GSA · track record · valley summary · RSS feed · model card · data releases · API
- Colors are depth to groundwater: blue is shallow, red is deep.
- Pick a drier scenario or a past drought under Scenario, then press Run forecast.
- Click a subbasin for its chart, RMS wells, plan rules and wells at risk. Valley: map layers. GSAs: one agency in detail.
Scenario
Precipitation as a % of the 1991–2020 normal, or a past drought replayed from today's levels. Months 1–24 are tested; later months are a what-if.
More info
The scenario sets valley-floor precipitation at each well as a percentage of its PRISM 1991–2020 monthly normal. This is the same 30-year baseline agencies use when they report “% of normal”. The 2005–2026 record, with two major droughts, averaged about 8% below it.
Most of the valley's water arrives as Sierra runoff, not local precipitation. So the upstream watershed enters only through the surface-water inputs tied to the scenario. These are the Sacramento Valley and San Joaquin Valley water-year indices, CVP and SWP Table A allocations, and river and project-canal flows. The CVP allocations are north- and south-of-Delta agriculture and Friant Class 1. Each one follows the scenario's precipitation, as it did in past years.
Allocations already published for the coming months are kept for those months, unless you set the deliveries control below. The forecast's status line says which months. For forecasts longer than a year, you can set the precipitation water year by water year.
Not represented: reservoir carryover, fallowing in response to allocations, and temperature, ET and NDVI. Each year's allocation follows that year's own precipitation. Crop mix is held at 2025 unless you change it below. Temperature, ET and NDVI are held at each well's 2005–2026 monthly means.
The forecast is monthly. Months 1–12 were tested on two held-out years and the second year on three held-out two-year periods (see Additional info). Beyond 24 months the forecast is a what-if: no period has tested a third year.
After month 12 the value shown keeps each well's usual seasonal cycle.
The NOAA outlook is what the map opens with. It uses the Climate Prediction Center's latest seasonal outlooks for the Sacramento and Fresno areas, updated monthly. The forecast runs the current water year at NOAA's expected precipitation, with NOAA's temperature outlook. In a GSA's chart, thin lines show the forecast if the year lands in the dry third or the wet third of the outlook; the valley's own record (1955–2014) sets how wide that range is. Later water years are normal. Seasonal precipitation outlooks for California have little skill except in strong El Niño or La Niña years: in the 2021 drought NOAA's outlook stayed near normal while about 70% fell.
Replay a past drought runs a past drought month by month from today's levels: one critically dry water year (2008, 2014, 2015, 2021 or 2022) for 12 months, or a multi-year drought water year by water year (2014–15 and 2021–22 for 24 months, 2007–09 and 2013–15 for 36). It uses the drought's precipitation and temperature at each well, and its water-year indices, allocations and river and canal flows. Crops are held at today's mix.
Checked against what happened: in the second year of the 2014–15 and 2021–22 replays the modeled decline matched the observed one within a few feet in Kern / Tulare, Friant and valley-wide. Westside in 2014–15 came out at about half the observed decline. The 2007–09 and 2013–15 replays come close valley-wide but run below the observed decline in the southern valley (2013–15 from its first year). Their third year is a what-if.
Precipitation by water year (% of normal)
Set each water year (October–September) separately. Allocations and river flows follow each year's own precipitation.
Valley summary
Now, and under the scenario on the map. Open a line for the GSAs behind it.
Change map view
DWR readings, kriged between wells.
More info
Show on the map
Turns off the depth colors while on; stays on in every view.
Turns off the depth colors while on.
Valley-wide layers, now or under the scenario on the map. Margins are the GSA panel's (30 ft by default).
More info
Recharge: well-draining soil within 2 km of a canal, where the water table is more than 30 ft down. Domestic: a red dot for each domestic well with under 30 ft of water above its bottom (monitoring wells hidden meanwhile). Record low: wells whose record spans a past drought, at their deepest reading since 2005. RMS: the plans' monitoring wells, red where the level is below the minimum threshold. ISW: the plans' interconnected-surface-water wells against their minimum threshold, and wells within 1 mile of a river with a water table 30 ft down or less, colored by depth. Subsidence is measured by radar, so it does not change with the scenario. Disadvantaged communities: DWR's 2023 layer (Census block groups whose median household income is below 80% of the state's; severely: below 60%); the domestic wells sections count the wells at risk inside them. Dropped-out wells: main-aquifer monitoring wells last read 1–3 years ago in DWR's periodic dataset (the readings this map is built on); the GSA's own network may hold later readings, and wells last read before that are the historical record, not shown.
Now uses the latest month for recharge, the low point of a normal year for domestic wells, and readings from the last 12 months for record lows. This scenario uses the forecast on the map: its shallowest month for recharge (the least room), its deepest month for domestic wells, and wells forecast below their record low in the first 24 months (the tested ones).
RMS wells (the plans' representative monitoring sites): now = the latest reading in the last 12 months against the well's minimum threshold (grey: no reading in that time); this scenario = the forecast's last month (grey: the model has no forecast for the well). Click one to open its GSA. Canals (OpenStreetMap, simplified) show with the recharge layer. Measured subsidence: DWR / TRE ALTAMIRA InSAR, median of the radar points in each cell; unshaded = no radar data.
Each square is one cell of the map's surface, about 5.7 by 4.4 km. The margins (30 ft) are the GSA panel's defaults; changing them there changes these layers too. The same numbers, summed per agency, are in the GSA view.
Bulletin 118 subbasins
Click a subbasin on the map or pick one above. Averages are over the kriged surface (main aquifer only).
Groundwater Sustainability Agencies
Click a GSA. Its panel shows wells below their minimum threshold under this forecast, the status of each RMS well, the change in groundwater storage, and the domestic wells at risk.
Look up a point
Drop a pin, or type coordinates or a well's site code or State Well Number.
Sources & credits
- Groundwater levels: California DWR, Periodic Groundwater Level Measurements (data.cnra.ca.gov)
- GSA boundaries: California DWR, i03 Groundwater Sustainability Agencies (data.cnra.ca.gov, CC BY)
- Groundwater basins: California DWR, Bulletin 118 groundwater basins (i08) and the 2019 critically overdrafted basins list (data.cnra.ca.gov, CC BY)
- Precipitation & temperature: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed monthly (monthly data; “normal” precipitation = PRISM 1991–2020 normals)
- Evapotranspiration: OpenET ensemble v2.1 (etdata.org), CC BY 4.0; sampled at the wells
- Vegetation (NDVI): NASA MODIS MOD13A2 v061 (Didan, K., doi:10.5067/MODIS/MOD13A2.061), via NASA AppEEARS
- Crop cover: USDA NASS Cropland Data Layer
- River flows: USGS National Water Information System
- Project flows & water-year indices: California DWR CDEC
- Allocations: U.S. Bureau of Reclamation (CVP) and California DWR (SWP)
- Sustainability thresholds: the adopted groundwater sustainability plans (per-well minimum-threshold tables) and California DWR, SGMA Portal (GSP Monitoring Data)
- Ground elevation: USGS 3DEP 1/3 arc-second DEM and DWR surveyed station elevations. Data available from U.S. Geological Survey, National Geospatial Program.
- Land subsidence: California DWR / TRE ALTAMIRA InSAR vertical displacement (data.cnra.ca.gov); contains modified Copernicus Sentinel data (2015–2026)
- Recharge soils: Soil Survey Staff (2020). Gridded National Soil Survey Geographic (gNATSGO) Database for the Conterminous United States. USDA Natural Resources Conservation Service. https://nrcs.app.box.com/v/soils (SSURGO / STATSGO), averaged to 800 m as the UC Davis California Soil Resource Lab does; canals: © OpenStreetMap contributors (the recharge layer's canal distances are a Produced Work of OpenStreetMap data, ODbL)
- Rivers (interconnected surface water): from the FlowState CV river network, © OpenStreetMap contributors and USGS National Hydrography Dataset; these river lines are available under the ODbL at api/isw
- Disadvantaged communities: California DWR, i16 Census Block Group Disadvantaged Communities 2023 (ACS 2019–2023), data.cnra.ca.gov, CC BY
- Domestic wells: California DWR, Well Completion Reports (public domain); dry-well reports: California DWR, Dry Well Reporting System (data.ca.gov)
- Precipitation and temperature outlook: NOAA Climate Prediction Center long-lead outlooks
- Basemaps: OpenFreeMap, © OpenMapTiles, data © OpenStreetMap contributors (Streets, Gray streets); USGS The National Map (Terrain, Gray canvas; public domain). Data available from U.S. Geological Survey, National Geospatial Program.
US federal data (USGS, NASA, USDA, Reclamation) are public domain.
© 2026 Will Gray