Evaluation and Zoning of Agricultural Water Demand Supply Ratio Index (AGWS) using SWAT (Case Study: Gunbarchay basin)

The agricultural water demand supply ratio (AGWS) is the actual evapotranspiration ratio to the potential evapotranspiration in an agricultural area during the crop growth period. Determination of this ratio is very important to planning and management properly in an area. In this regard, the index and its zoning in the agricultural areas of Gunbarchay basin were determined in this study. To achieve this purpose, the comprehensive SWAT hydrological-plant model for the basin was adjusted, calibrated and validated. Then, the actual runoff and evapotranspiration values were simulated for the sub-basins of the studied basin during the period 1987-2017. The results indicated that the volume of potential evapotranspiration, in all irrigated lands of the basin during the crop growth period in 2016 is 25.41 MCM. In addition, the simulations showed that the amount of actual evapotranspiration from the total irrigated agricultural lands of Gunbarchay basin during the crop growing season in 2016 is 19.1 MCM. Based on the results, the value of agricultural water supply ratio in Gunbarchay basin in 2016 varies between 0.63 and 0.79. So that the value of this index is more in the northern and western sub-basins of the basin than its eastern sub-basins. According to the results, in Gunbarchay basin, the amount of water supply in the agricultural sector is much less than the amount of demand, especially in the eastern sub-basins, which should be addressed with proper management of agricultural water demand and consumption.