The Analysis of the CROPWAT Model Efficiecy Estimating Water Requirement of Wheat in the West of KermanshahTownships of the Islamabad Gharb, Sarpol Zahab and Ravansar

In this study, the evapotranspiration and water requirement of wheat for the townships Islamabad Gharb, Sarpole Zahab and Ravansar were determiend in 18 years from 1988 to 2005.
At first, using the average of long-term, the period climatogical data (temperature and rainfall) of dry and wet period for three stations were determined. The dry period length in this region which lasts from the early spring to the mid fall is coincided with the harvest time and wheat sensitivity to water shortage.
Thus there is a need to supplementary irrigation. Hence, a large part of this region that are cultivated by rainfall cultivation, has to be irrigated by underground water.
Accordingly, it results in a severe decrease of surface aquifer in the lands of the region.
Then, using the CROPWAT model, the real evapotranspiration of wheat and its water and irrigation requirement in the region was studied.
The arerage of climate data (maximum and minimum temperature, monthly rainfall, wind speed, relative humidity and dally sunshine) as well as, the cultivation model of the crop (including Kc values, stage days, root depth, depletion fraction) and the area planted (0-100% of the total area), soil type, total available soil moisture, initial soil moisture (% of total available moisture) were entered in to the model and in stage the results were represented as chart and graph. Finally the timetable of irrigation was designed
soil moisture deficit in real in the growth period was comparatively obtained.
Further, water requirement, irrigation and evapotranspiration rates were depicted in the growing term as a graph. According to results of the irrigation schedule table station and according to severe aridity and moisture deficit in the soil, two or three supplementary irrigations are needed to prepare the crop for harvesting.