Abstract
Forest evapotranspiration (ET) is a major component of hydrologic budget, which regulates runoff, soil water storage, groundwater recharge, biogeochemical cycles, biodiversity, and the global climate system. Ecohydrologic models have been developed in past decades for quantifying forest ET to improve various hydrological research and applications. Prediction of forest ET and its components (e.g., canopy evaporation, transpiration, and forest floor evaporation) in response to a changing environment is essential for understanding interactions between the atmosphere, soil, and vegetation and impacts of forest-water management practices. However, gaps in knowledge and data have limited our ability to accurately simulate and validate ET components. This chapter reviews seven widely used ecohydrologic models (DRAINMOD-FOREST, MIKE SHE, PIHM, RHESSys, SWAT, WaSSI, and WEPP) with their current algorithms for simulating forest ET processes and associated parameters, as well as model limitations, challenges, and uncertainties. In addition, we briefly outlined potential opportunities, including the advances in the eddy covariance related ET fluxes and high resolution spatial and temporal remotely sensed ET data sets.