Potential areas of groundwater discharge were delineated for the Humboldt River Basin to estimate groundwater evapotranspiration from phreatophyte vegetation, the primary component of natural groundwater discharge in the region. The boundary that defines the potential area of groundwater discharge represents the maximum spatial extent of groundwater discharge by phreatophyte vegetation, and areas within this boundary may discharge little to no groundwater where bare soil or sparse vegetation is the primary land cover. The boundaries are based on the original delineations of phreatophyte vegetation published in Reconnaissance Series Reports and Water Resource Bulletins for the state, which have also been included in this database with the filename "Historical_recon_and_wrb_phreatophyte_boundaries.shp".

Potential areas of groundwater discharge by phreatophyte vegetation were delineated based on a combination of previously published phreatophyte boundary maps and datasets, digital elevation model (DEM), gSSURGO soils data (USDA, 2017), high resolution aerial imagery of the NAIP, Landsat land surface temperature and vegetation indices, USGS and NDWR groundwater level data, and field investigations. These boundaries were further refined and divided into ET Units consisting of playa/bare soil, phreatophyte shrubland, meadow, riparian, and cropland.