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RISKPRO'S SESOIL for Windows User's Guide Each process in Eqs (1) and (2) is written in terms of the soil moisture content, and solution of the equations is accomplished by aerating on soil moisture until the calculated value for precipitation is within 1.0% of the measured value input by the user When this iteration is complete, the components such as infiltration, evapotranspiration, etc , in Eqs (1) and (2) are known SESOIL uses this procedure in both the annual and monthly routines The monthly routine is an extension of the annual routine, both are discussed further below 3.3.1 Annual Cycle ' The annual water balance routine is based on Eagleson's (1978) theory It encompasses one year, so multiple years have to be simulated as separate cycles This routine simply determines the soil moisture content based on solution to equations (1) and (2) using annual climatic I parameters When the value for soil moisture content is arrived at through the iteration technique, the various processes described in equations (1) and (2) are known Note that storage effects in the soil are not considered in the annual option. The theoretical basis for the annual ' dynamic hydrologic cycle used in SESOIL has been validated by Eagleson (1978). Annual model predictions were compared with empirical observations for five years of precipitation data at both a subhumid and an and climate location, with close agreement 3.3.2 Monthly Cycle The monthly water balance routine is based on the same theory as the annual routine, with modifications made to the details of moisture transfer from month-to-month (handling of I moisture storage), and to the radiation effects The initial value for soil moisture content is calculated in SESOIL by summing up the appropriate monthly climatic input data (for the first year) to obtain annual values and then by using the annual cycle algonthm. Then for each ' month, the monthly input values for precipitation, mean storm number, and mean length of the rain season are multiplied by 12 in order to again obtain "annual" values Equations (1) and (2) are solved to compute the soil moisture content, and the results for the components (infiltration, ' evapotranspiration, etc ) are divided by 12 to attain average monthly values Note that if long-term average climatic data are used as input for each year (input for each ' month is the same from year to year), one would expect that the results for the hydrology for each month would be identical from year to year However, since the initial soil moisture content is computed as stated above for the first month (of the first year), this value will be ' different from the soil moisture calculated for the twelfth month (which is then used for the first month of the following year) Thus, although hydrology results will not be identical for the first two years, they will be identical thereafter ' le in SESOIL does account for the chane in moisture storage The monthly cycle g a from month to g month, incorporating the work of Metzger and Eagleson (1980). Also, the SESOIL ' Page 11