The U.S. Geological Survey (USGS), in cooperation with the Water Replenishment District of Southern California, developed a regional groundwater model of the Los Angeles Coastal Plain (LACP) incorporating new data, analyses, and modeling tools to better understand the hydrogeology of the groundwater basins. The LACP covers about 580 square miles and is the largest coastal plain of semiarid southern California. This aquifer is heavily developed with mostly residential, commercial, and industrial use and relies heavily on groundwater for its water supply. There has been a heavy reliance on groundwater from the LACP for many years. The need to replenish the groundwater basins within the LACP was recognized as far back as the 1930s, when spreading grounds were first used to replenish groundwater basins and store water underground during times of water surplus to meet demands in times of shortage. Seawater intrusion resulting from fresh-water pumping became significant in the 1940s. As a result, injection of imported water through wells at what is now the West Coast Basin Barrier Project began on an experimental basis in 1951. Managed aquifer recharge from the spreading grounds and barrier wells is an important part of the LACP's groundwater supply. This study, in cooperation with the Water Replenishment District of Southern California, involved an assessment of the historical and present status of groundwater resources in the LACP and the development of tools to better understand the groundwater system. The Los Angeles Coastal Plain Groundwater Model (LACPGM) developed for this study, represents a major update of a previous groundwater model developed by Reichard and others (https://doi.org/10.3133/wri034065). The LACPGM uses the USGS model code MODFLOW-USG, which enables the use of an unstructured finite-difference grid which contains nodes one-eighth mile (mi; 660 ft) in length and width. The LACPGM incorporates 12 layers for the 13 chronostratigraphic units, with the two bottom units modeled as a single layer. MODFLOW-USG was selected for its ability to effectively represent the discontinuous and faulted chronostratigraphic layers using an unstructured grid. The LACPGM simulates groundwater flow in the LACP using quarterly stress periods from 1971 to 2015. The model was used to predict water levels under future water-management scenarios, base case wet and dry scenarios, increased pumpage wet and dry scenarios, and optimized replenishment wet and dry scenarios. The scenarios include projected future pumping rates and estimate the increases in water spreading and injection that would be needed to maintain water levels. The scenarios simulate expected future pumping rates and estimate needed increases in water spreading and injection in order to maintain water levels. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20215088).

This data release contains monthly 270-meter gridded Basin Characterization Model (BCMv8) climate inputs and hydrologic outputs for Los Angeles (LA). Gridded climate inputs include: precipitation (ppt), minimum temperature (tmn), maximum temperature (tmx), and potential evapotranspiration (pet). Gridded hydrologic variables include: actual evapotranspiration (aet), climatic water deficit (cwd), snowpack (pck), recharge (rch), runoff (run), and soil storage (str). The units for temperature variables are degrees Celsius, and all other variables are in millimeters. Monthly historical variables from water years 1896 to 2019 are summarized into water year files and long-term average summaries for water years 1981-2010. Four future climate scenarios were spatially downscaled from 6 kilometers to 270 meters, and run through the BCMv8 using the same model parameters. The future climate scenarios are all Representative Concentration Pathway (RCP) 8.5 and include: CanESM2, CNRM-CM5, HadGEM2-ES, and MIROC5 from California's Forth Climate Change Assessment. Future climate scenarios span from water year 2007 to 2099, and monthly variables were summarized by water year and the average 2070 to 2099 period. Streamflow for each calibration basin was calculated using a post processing Excel spreadsheet and BCMv8 recharge and runoff, and are provided in tabular comma separated *.csv files. Raster grids are in the NAD83 California Teale Albers, (meters) projection in an open format ascii text file (*.asc).

This data release accompanies the USGS Techniques and Methods report titled: "The Basin Characterization Model - A Regional Water Balance Software Package", and includes all necessary Basin Characterization Model version 8 (BCMv8) inputs and outputs for water years 1896 to 2023. The BCMv8 was refined from the previous BCMv65 version to improve the accuracy of the water-balance components, particularly the recharge estimate. The new version includes seven new features: (1) monthly vegetation-specific actual evapotranspiration (AET) for 65 vegetation types, (2) spatially distributed calibration coefficients for snow accumulation and snowmelt, (3) mapped soil organic matter, (4) soil hydraulic properties calculated from soil texture and soil organic matter (model simulations run using water content at field capacity of –0.01 megapascal (MPa) and wilting point of –6 MPa), (5) soil dry-out below wilting point at a rate driven by average statewide aridity, (6) a switch allowing for the incorporation of urban impermeable surfaces, and (7) internally calculated gaining and losing streams. The model has been run at a monthly time scale to calculate the unimpaired water balance for every 18-acre (270 by 270-meter) grid cell for all of California, including all basins draining into the State for water years 1896–2022. Version 2.0 Changes from previous version: 1) Added BCMv8 climate inputs and outputs for water year 2021 2) Updated climate inputs and outputs for water 2020 to correct error. Version 3.0 Changes from previous version: 1) Added BCMv8 climate inputs and outputs for water year 2022 Version 4.0 Changes from previous version: 1) Added BCMv8 climate inputs and outputs for water year 2023

This dataset represents locations of major inflows to the CA Central Valley. All but the two southernmost locations are associated with CalSim II. CalSim II is an operations model for estimating State Water Project and Central Valley Project Deliveries of surface water. CalSim II was used as part of the CA Water Commission Water Storage Investment Program (WSIP) to estimate projected deliveries associated with projected Climate Change Conditions. The related records are for model results from the 2030 Central Tendency, 2070 Central Tendency, 2070 Dry-Extreme Warming and 2070 Wet-Moderate Warming projections. All projections are based on an ensemble of 10 GCMs using two different emissions scenarios (RCP 4.5 and RCP 8.5).

This dataset represents locations of major inflows to the CA Central Valley. All but the two southernmost locations are associated with CalSim II. CalSim II is an operations model for estimating State Water Project and Central Valley Project Deliveries of surface water. CalSim II was used as part of the CA Water Commission Water Storage Investment Program (WSIP) to estimate projected deliveries associated with projected Climate Change Conditions. The related records are for model results from the 2030 Central Tendency, 2070 Central Tendency, 2070 Dry-Extreme Warming and 2070 Wet-Moderate Warming projections. All projections are based on an ensemble of 10 GCMs using two different emissions scenarios (RCP 4.5 and RCP 8.5).

This dataset represents locations of major inflows to the CA Central Valley. All but the two southernmost locations are associated with CalSim II. CalSim II is an operations model for estimating State Water Project and Central Valley Project Deliveries of surface water. CalSim II was used as part of the CA Water Commission Water Storage Investment Program (WSIP) to estimate projected deliveries associated with projected Climate Change Conditions. The related records are for model results from the 2030 Central Tendency, 2070 Central Tendency, 2070 Dry-Extreme Warming and 2070 Wet-Moderate Warming projections. All projections are based on an ensemble of 10 GCMs using two different emissions scenarios (RCP 4.5 and RCP 8.5).

The hydrologic modeling approach used to predict functional flows relies on daily streamflow data from gages operated by the U.S. Geological Survey (USGS) in California. This dataset contains, for each of 219 gages, a collection of metrics computed on each water year for the period of record to and including Water Year 2016.

The Los Angeles Coastal Plain (LACP) covers about 580 square miles and is the largest coastal plain of semiarid southern California. The LACP is heavily developed with mostly residential, commercial, and industrial land uses that rely heavily on groundwater for water supply. In 2010, the LACP was home to about 14 percent of California’s population and is also a major commercial and industrial hub. There has been a heavy reliance on groundwater from the LACP for many years. Managed aquifer recharge from the spreading grounds and barrier wells is now a substantial component of the LACP’s groundwater supply. The U.S. Geological Survey (USGS) conducted a study in cooperation with the Water Replenishment District of Southern California (WRD) assessing the historical and present status of groundwater resources in the LACP and the development of tools to better understand the groundwater system. The cornerstone of these tools is the development and application of the Los Angeles Coastal Plain Groundwater-flow Model (LACPGM-USG) to simulate past groundwater conditions, estimate groundwater-budget components and flow paths, and approximate future groundwater conditions under different scenarios (https://doi.org/10.3133/sir20215088).

This dataset provides monthly and average annual long-term estimates (water years 1981-2010) of gridded recharge and runoff from water years 1896-2018 for the Anza-Cahuilla Groundwater Basin in southern California. Gridded data are available in flat ASCII files (*.asc) in the NAD83 California Teale Albers projection. This dataset also includes streamflow calibration basins and stations as shape files (*.shp), and a Basin Characterization Model (BCMv8) model archive.

The dataset contain estimates of natural monthly streamflow for 135,118 stream segments in California, USA, from 1950 to 2012. Segments are identified per the medium resolution National Hydrography Dataset (NHD), Version 1. The dataset also contains observed monthly streamflows and estimates of natural monthly streamflows for 894 USGS stream gages in California, USA.