Advancing evapotranspiration estimation in Arizona: evaluating the performance of Priestley-Taylor JPL and Penman-Monteith models using flux tower observations
Abdul Wahed Nab1, Muhammad Jawad1, Ali Behrangi1, Guo-Yue Niu1
1Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, AZ
Accurate estimation of evapotranspiration (ET) is essential for managing water resources in arid and semi-arid regions such as Arizona, where agricultural and ecological systems heavily depend on limited water supplies. In this study, we evaluate and compare the performance of two widely used ET models, the Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) model and the Penman-Monteith (PM) model across multiple flux tower sites in Arizona. Data from eddy covariance flux towers, located in diverse ecosystems, were used to drive both models with consistent meteorological and vegetation datasets, including air temperature, humidity, radiation, wind speed, and leaf area index. The PT-JPL model, based on the Priestley-Taylor equation, estimates ET using biome and environmental constraints on energy availability and moisture conditions, whereas the Penman-Monteith model explicitly incorporates aerodynamic and surface resistance parameters to estimate ET components based on energy and mass transfer principles. Model outputs were validated against observed latent heat fluxes from the flux towers. Preliminary results indicate that both models capture seasonal trends in ET but differ in magnitude. Statistical metrics such as Kling–Gupta efficiency skill error (KGEss), Nash–Sutcliffe efficiency, and coefficient of determination (R2) were used to quantify each model’s accuracy. Our findings highlight key differences in model performance, offering insights into optimal modeling approaches for water management strategies in semi-arid and arid regions. Future work includes expanding the study to additional sites and refining model parameterizations for improved accuracy.