A Computer Model Based on Soil-Water Balance for Estimating The Effective Rainfall in Dryland Wheat Crop (The Case Study of Fars Province)

The estimation of effective rainfall is an important technique for exploiting the rainwater resource، planning for irrigation in irrigated agriculture، and determining changes in dryland wheat products for country''s macroeconomic management. In this research، a two-layer soil-water balance model based on a new approach has been formulated to estimate the effective rainfall in dryland wheat crop. In this model، it is assumed that، in addition to the soil moisture retained on root zone on before day، also that part of water saved between the previous and current root-zone development add to the effective rainfall at current day. Greater ability of current approach to determine changes in wheat yields، which can be justified by changes in effective rainfall، confirms superiority of the current approach. Besides that، In order to estimate the effective rainfall in dryland wheat crop by this approach، daily climatic records during statistical period (1999-2000 till 2008-2009) from 12 meteorological stations of Fars province were collected. Results indicated that among the studied stations the amount of mean annual effective rainfall in dryland wheat crop changes from 296. 4 (mm) in Doroodzan dam station to 112. 6 (mm) in Abadeh station. Also، it is assumed that production of dryland wheat crop at north and northwest of Fars province is more success than other parts، due to satisfactory supply of effective rainfall.