Effective Rain Zoning In Khuzestan Province under Autumn Rainfed Wheat Cultivation

The meteorological data of 12 synoptic stations of Khuzestan province with a 20-year statistical period (1999-2018) were used to perform the present study. First, using CROPWAT software, the effective rainfall was estimated from three methods USDA, FAO and the developed experimental formula. Using AquaCrop software, real transpiration evaporation of rainfed wheat in the study area was calculated and effective rainfall amount was obtained. Then, using ArcGIS software, effective rainfall zoning at the stations studied was drawn in November, December, January, February and March. Relative error (RE) results showed that in the three most rainy months of November, December and January, the best estimation of rain was the experimental method with mean error of -8.8 percent, FAO with -21.7 percent and experimental with 12.9 percent, respectively compared to the inverse solution method. In the low rainfall months of February and March, the USDA method had the best estimation of the effective rain of these three methods with the inverse solution method with -48.6 percent and -51.6 percent, respectively. The zoning map of the estimated effective rainfall also showed that in the rainy months and when the plant is in early growth, the amount of effective rainfall increases by moving from the north side of the province to the southern part. The overall results show that the percentage of confidence in the experimental methods is low and by calculating the effective rainfall and changing the date of cultivation at the country level can increase the productivity and production of rainfed crops.