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u RIS KPRO'S SESOIL for Windows User's Guide evapotranspiration algorithm has been modified from the original work,of Eagleson (1978) to include seasonal changes in°average monthly radiation (before, radiation was a constant function ' of latitude). Hetrick (1984) observed that hydrology predictions of the original SESOIL were insensitive to seasonal changes in meteorological data. To model the hydrology more ' realistically, an algonthm from the AGTEHM model (Hetrick et al ; 1982) which computes daily potential radiation (incoming radiation for cloudless skies) for a given latitude and Julian date (December 31 = 365) is now used The middle day of the month is used in the algorithm and ' the effect of cloud cover is calculated with the following expression (Hetrick et al., 1982): S = S [ ( 1-C) + kC] (4) where. S = the average monthly radiation S = the potential radiation ' LL C _" the fraction of sky covered by clouds - k = the transmission factor of cloud cover The value for k used in the model is 0 32, suggested by Hetrick et al (1982). Since latitude and" monthly cloud cover are required input for SESOIL, no-new input data are needed to support this modification There are now more pronounced monthly changes in evapotranspiration predictions'(see Hetrick et al , 1986) w Although SESOIL does produce_monthly_results for soil moisture content of the root zone, i defined in the model as the first i00 cm depth from the surface, this option has not been fully -- developed -Thus; values-fonsoil-moisture for-the root zone-will_usually-be identical-to those-for the entire soil column, and only very dry climates may cause a difference (M Bonazountas, personal communication to David Hetrick, 1986)- - - - ' ,' SESOIL modelusin redictions ( the monthly option) of watershed hydrologic components have P g been compared with those of the more data intensive terrestnal ecosystem hydrology model AGTEHM (Hetrick et al., 1982), as well-asto empirical measurements at a deciduous forest ' watershed and a_grassland watershed (see Hetrick et al , 1986)' Although there were some differences in monthly results between the two models, good agreement was obtained between model predictions for annual values of infiltration, evapotranspiration, surface runoff, and groundwater runoff (recharge) Also, SESOIL model predictions compared well with the empirical measurements at the forest stand and the grassland watersheds ' Page 12 ' i