Do Energy‐Based PET Models Require More Input Data than Temperature‐Based Models? — An Evaluation at Four Humid FluxNet Sites

It is well established that wet environment potential evapotranspiration ( PET ) can be reliably estimated using the energy budget at the canopy or land surface. However, in most cases the necessary radiation measurements are not available and, thus, empirical temperature‐based PET models are still widely used, especially in watershed models. Here we question the presumption that empirical PET models require fewer input data than more physically based models. Specifically, we test whether the energy‐budget‐based P riestley‐ T aylor ( P ‐ T ) model can reliably predict daily PET using primarily air temperature to estimate the radiation fluxes and associated parameters. This method of calculating PET requires only daily minimum and maximum temperature, day of the year, and latitude. We compared PET estimates using directly measured radiation fluxes to PET calculated from temperature‐based radiation estimates at four humid A meri F lux sites. We found good agreement between P ‐ T PET calculated from measured radiation fluxes and P ‐ T PET determined via air temperature. In addition, in three of the four sites, the temperature‐based radiation approximations had a stronger correlation with measured evapotranspiration ( ET ) during periods of maximal ET than fully empirical H argreaves, H amon and O udin methods. Of the three fully empirical models, the H argreaves performed the best. Overall, the results suggest that daily PET estimates can be made using a physically based approach even when radiation measurements are unavailable.