Evaluating Regional Corn Crop Coefficients with Satellite Evapotranspiration

Regional crop coefficients are widely used to estimate agricultural consumptive use, but their ability to represent water use across commercial fields is rarely tested. This study evaluated regional corn crop coefficients in Colorado’s South Platte River Basin against six years (2020–2025) of satellite-derived evapotranspiration from 12,430 field-years processed with the AgroET model. The benchmark is itself AgroET-derived, so the analysis assesses consistency with a field-scale satellite benchmark rather than independently validated accuracy. If applied to the full commercial population, a previously developed regional curve representing near-potential corn water use would exceed observed aggregate consumptive use by 14.0% (10.9% by volume, about 134,000 acre-feet relative to the benchmark); equivalently, commercial fields realized about 88% of near-potential use on a depth basis and 90% by volume. Refitting the same formulation to the quality-screened commercial population reduced the difference to 4.0%; this ten-point separation varied only from 9.1 to 11.1 points under ±10% benchmark rescaling. Stratifying by processing region or season changed bias by about 1 point for the tested partition. A trajectory derived from the published Colorado Agricultural Meteorological Network (CoAgMET) algorithm, never calibrated to these retrievals, was near zero in aggregate depth (−1.0%; −3.6% by volume), reflecting partial cancellation between densely and sparsely observed field-years. Field-scale errors remained substantial under every coefficient; in well-observed seasons, 90% of within-season pools met ±10% at five to eight pooled fields. Multi-year satellite records can thus be used to evaluate whether regional coefficients remain representative of commercial water use.