Authors: Abin Raj Chapagain, Daniel P. Ames, Iman Maghami – Brigham Young University
Title: Evaluation of the National Water Model’s Retrospective Evapotranspiration Using Eddy-Covariance Flux Tower Measurements across the Continental United States
Abstract: Evapotranspiration (ET) accounts for approximately 70% of precipitation recycling across the Continental United States (CONUS). However, accurate simulation of ET is a significant challenge in hydrologic modeling due to sparse monitoring stations and complex environmental variabilities. In this study, we evaluated the accuracy of ET simulations from the National Oceanic and Atmospheric Administration (NOAA) National Water Model Version 3.0 (NWM V3.0) Retrospective in predicting ET on a 1km grid scale. NWM simulated ET values were compared against observational data from AmeriFlux eddy-covariance flux towers distributed across the CONUS. Statistical analyses, including t-tests, identified substantial regional differences in model performance, with significant underestimations occurring particularly in the California-Nevada River Forecast Center (RFC) region and other areas exhibiting extreme climatic and hydrologic conditions. The findings underscore the need for further NWM enhancements to improve ET simulation accuracies, which are critical for refining hydrological forecasting capabilities across the CONUS.