Water use estimates are valuable to the Navajo Nation in adjudicating water rights and informing other environmental policy decisions. Estimates of actual evapotranspiration (ETa), precipitation (PP), and consumptive use (CU) of riparian vegetation assist decision making by natural resource managers. The objectives of this project were to estimate the riparian land cover area for trees and shrubs, calculate their corresponding daily and annual water use, and derive riparian CU in acre-feet (AF). Select riparian reaches of Little Colorado River tributaries, streams, and springs were delineated into a tree and shrub map using a 2019 summer scene from the National Agriculture Imagery Program (NAIP) (1-meter resolution), which was then rasterized using Landsat 8 (30-meter resolution) to estimate ETa for 2014–2020. To determine potential evapotranspiration (ETo) and PP, U.S. Geological Survey scientists used indirect remote sensing methods based on two sources of gridded weather data: Daymet (1-kilometer resolution) and PRISM (4-kilometer resolution). Measurements of vegetation greenness were derived from Landsat 8 data using the 2-band Enhanced Vegetation Index (EVI2). Estimates of annual potential ET were calculated using the Blaney-Criddle method, and riparian land cover ETa was then quantified using the Nagler ET(EVI2) approach.
Vector and raster estimates of tree, shrub, and total riparian area made it possible to produce the first remotely sensed measurements of CU for this region. Using Daymet data, the ‘conservative’ estimate of CU data was 31,648 AF while the ‘best-approximation’ estimate was 36,983. Using PRISM data, the ‘best-approximation‘ estimate of CU was 41,585 AF. The range of 31,648 AF to 41,585 AF refines earlier published predictions (25,387—46,397 AF) and aligns with previous CU estimates for the Hopi Reservation, which is contained within the Navajo Nation. The associated manuscript is available here.
The Little Colorado River and tributaries’ riparian vegetation comprised of trees and shrubs used to measure ETa and CU with Landsat 8 and ET(EVI2) from 2014 through 2020. EVI2 is a two-band Enhanced Vegetation Index. The associated manuscript is available here.
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