Analysis of factors affecting evapotranspiration zoning

Reference evapotranspiration (ET_o) has a significant role in water resource planning and management as well as analysis of crop production and other agricultural tasks. Methods for estimating ET_o may require diurnal/monthly assessments to perceive the consequences of climatic changes on local regions. The spatial and temporal patterns of ET_o were analyzed in the current work using data from 340 weather stations in Iran. The entropy theory was used to assess the uncertainty of the utilized variables and the modified Kendall test was applied for temporal trend analysis. The interpolation (e.g., kriging) and ordinary least squares (OLS) methods were used for spatio-temporal ET_o classification/modeling. The spatial analysis demonstrated that the OLS method with a good fit measure (R² = 0.985) successfully simulated the spatial relationships of ET_o with climatic parameters. After examining error indices, the cokriging method with an exponential variogram was introduced as the best method of seasonal and annual ET_o classification in Iran. Spatially and temporally calculated ET_o patterns using modified Hargreaves (MHGR) and MODIS methods closely resembled the standard FAO Penman-Monteith (FPM-56) method, all indicating a gradual increase in ET_o. MHGR and MODIS methods serve as suitable alternatives for estimating ET_o in various climatic regions of Iran, provided data availability.