J. Ross Wight
USDA-ARS800 Park Blvd.Suite 105Boise, ID 83712
Telephone : 208-334-1363
FAX : 208-334-1502
ERHYM - II is a deterministic simulation model which simulates daily water-balance and calculates annual yield indices based on the ratio of actual to potential transpiration. The model runs on a daily time step with daily inputs of maximum and minimum air temperatures and solar radiation. Water added to the soil profile is the difference between precipitation and runoff. The SCS curve number procedure as described in CREAMS is used to estimate runoff. As each soil layer is filled to its water holding capacity, water is cascaded down to the next soil layer. When the profile is full, surplus water becomes drainage.
Potential ET is calculated by the Jensen-Haise method. Actual soil and plant evaporation are based on potential ET, soil water content, average site yield, and a relative growth curve. A soil temperature routine from EPIC and the maximum-minimum air temperature and solar radiation generating routines from SPUR are included.
Input data include daily precipitation, maximum and minimum air temperatures and solar radiation, field capacity and permanent wilting water contents for each soil layer, initial soil water content, average site herbage yield at peak standing crop, and dates for start of growing season, peak standing crop, and end of growing season. The model calculates daily values of potential and actual soil and plant evaporation from each soil layer, daily soil water contents, and cumulative actual and potential transpiration. The spatial scale is range site specific.