Comparison of the NLDAS Weather Forcing Model to Agrometeorological Measurements in the western United States

Diverse topography and climate in the American West have stymied efforts to accurately quantify the flux of water on the land surface at a high spatial resolution. Observations of the processes governing the earth’s water budget and energy balance are generally from disparate point measurements on the ground and have lower frequency, distinction, or confidence when remotely sensed. Combined, these terrestrial and aerial sources can offset the other’s inherent weaknesses. At a local scale, methodologies have been developed to estimate evapotranspiration. A systematic approach to calculating reference evapotranspiration at a regional scale over the western United States was explored by comparing the drivers of the North American Land Data Assimilation System weather forcing model to 704 agriculturally representative, electronic weather stations at an hourly time step. Parameters of solar radiation, air temperature, humidity, and wind speed were analyzed to identify any uncertainties and biases. Initial inspection of the weather parameter comparisons revealed unsatisfactory performance of one or more of the NLDAS parameters in several regions, but this was mollified in the calculation of reference evapotranspiration for all but the southerly portions of the study area.