Water-balance subregions (WBSs), soil types, and virtual crops for the five land-use time-frames used in the Central Valley Hydrologic Model (CVHM)

This digital dataset defines the model grid, water-balance subregions (WBSs), soil types, and virtual crops for the five land-use 
time-frames in the transient hydrologic model of the Central Valley flow system. The Central Valley encompasses an approximate 
50,000 square-kilometer region of California. The complex hydrologic system of the Central Valley is simulated using the USGS 
numerical modeling code MODFLOW-FMP (Schmid and others, 2006a, b).  This simulation is referred to here as the Central Valley 
Hydrologic Model (CVHM) (Faunt, 2009). Utilizing MODFLOW-FMP, the CVHM simulates groundwater- and surface-water flow, 
irrigated agriculture, land subsidence, and other key processes in the Central Valley on a monthly basis from 1961-2003.  The 
total active modeled area is 20,334 square-miles on a finite-difference grid comprising 441 rows and 98 columns. Slightly less 
than 50 percent of the cells are active. The CVHM grid has a uniform horizontal discretization of 1x1 square mile and is oriented 
parallel to the valley axis, 34 degrees west of north (Faunt, 2009). The 21 WBSs initially were identified by the California Department 
of Water Resources (CA-DWR) and Bureau of Reclamation (BOR) as numbered "Depletion Study Areas" (California Department of 
Water Resources, 1977).  The WBSs are used as accounting units for surface-water delivery and for estimation of groundwater 
pumpage. The boundaries generally represent hydrographic rather than political subdivisions, particularly in the San Joaquin and 
Tulare Basins.  The soils were simplified into sandy loam, silty clay, and silt from the State Soil Geographic Database STATSGO 
(U.S. Department of Agriculture Natural Resources Conservation Service, 2005b).  The soil type covering the maximum area of each 
cell was assigned to each cell. The land-use attributes are defined in the model on a cell-by-cell basis and include urban and agricultural 
areas, water bodies, and natural vegetation. The land use, referred to as "virtual crops," that covered the largest fraction of each 1 
square mile model cell was the representative land use specified for that cell. Land-use maps were developed for five different time 
frames during the 42.5-year simulation period. The CVHM is the most recent regional-scale model of the Central Valley developed 
by the U.S. Geological Survey (USGS).  The CVHM was developed as part of the USGS Groundwater Resources Program (see 
"Foreword", Chapter A, page iii, for details).

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Organization: Department of the Interior