Estimation of Net Irrigation Requirement of the Crop Pattern in Kermanshah Plain and Comparison with the Data in the National Water Document

To prepare the National Water Document of the country, a 25-year statistical period of 1970-1995 has been used to calculate daily potential evapotranspiration. Due to the climate changes that have taken place in recent years, updating this national valuable work is necessary. Since so far there has been no study on determining the changes in irrigation requirement of plants of cropping pattern in Kermanshah plain in the current climate conditions compared to the values presented in NETWAT software, this subject was investigated. In this study, to calculate crops water requirement, the meteorological data of 2006-2007 to 2015-2016 were used. In order to estimate the net irrigation requirement for cropping pattern in Kermanshah plain, ET0 calculator software was used to calculate evapotranspiration of reference crop. Then, the evapotranspiration values of the cropping pattern, the effective rainfall and, eventually, the amount of net irrigation requirement of the crops were calculated. The comparison between the values obtained in this research with available values in NETWAT software indicate that, for most plants, the obtained values in this study are on average 1.2 times the amounts presented in the NETWAT software. This ratio is about 2 for wheat and barley and about 1 for clover, cantaloupe, pea, and almond. The results of lysimeteric researches in the study area confirms the correctness of the performed calculations in this study.