Evapotranspiration in Southeast Arizona Semi-Arid Watersheds: Walnut Gulch and Cienega Creek

Abstract

Two simple evaporation models, the Priestley-Taylor model, and a Penman Monteith based model, were calibrated using data from meteorological-flux stations in the USDA-ARS experimental watershed. The residual eddy covariance technique employed propeller vertical anemometers for measurement of sensible heat. These limited frequency response instruments significantly underestimated the sensible heat flux, resulting in an overestimation of the latent flux. By adjusting the sensible heat frequency response correction factors the energy balance evaporation estimates were more closely matched to the mass-balance estimates. The models performed well during calibration, but poorly for the validation period. The two simple models were also calibrated to BA TS-modeled latent heat fluxes at a site in the Tucson mountains. With calibration, they reproduced the BATS output reasonably well. Finally, the two models were applied to the CienegaCreek watershed, and their results support the assumption of earlier investigators that the precipitation and evaporation essentially balance for the basin's desert grasslands.