Intercomparison of methods for calculating potential evaporation in regional and global water balance models

Five methods (Thornthwaite, Hamon, Jensen-Haise, Turc, and Penman) for estimating potential evaporation for a reference surface (PEr) were compared to four methods (Priestley-Taylor, McNaughton-Black, Penman-Monteith, and ShuttleworthWallace) for estimating surface-dependent potential evaporation (PEs) using three cover types at each of seven locations from Fairbanks, Alaska, to San Juan, Puerto Rico. For annual PE the PEs methods generally agreed with the PEr methods, but for many locations, differences among methods were hundreds of millimeters per year. No methods were consistently low or high. Three of the PEs methods depend strongly on maximum leaf conductance, for which Körner [1994] provided satisfactory values by cover type. Potential interception (PEi) can only be estimated appropriately for all cover types by the Shuttleworth-Wallace method. Use of 5-day or monthly input data did not greatly degrade results, so use of monthly data to generate PE estimates appears warranted in global water balance models.