Estimation of crop evapotranspiration and water requirement over different agro-climatic conditions (Case study: Qom province)

Estimates of water requirement in areas such as Qom province have always been a difficult task due to their different agro-climatic zones and latitudinal ranges, and low density of weather station network. In this study, estimation of evapotranspiration and water requirement of major crops was studied in Qom province. Initially, the studied area was divided into four sub-areas of Qom, Saveh-Tafresh, Saveh and Garmsar which have different climatic conditions. Then, the climate parameters were amended using the obtained regression equations from the elevations in each sub-area and the net irrigation requirement was calculated in each sub-area at various altitudes. The results showed that the amount of net irrigation requirement of all selected crops in Saveh was higher than other zones. The minimum net irrigation requirement of winter (wheat, barley, and canola) and spring (cotton, alfalfa, corn) crops was in the Garmsar and Saveh-Tafresh zone, respectively. Average net irrigation requirement of wheat, barley and canola in Saveh zone was 743.7, 647.3 and 743.7 mm more than Garmsar zone, respectively. This amount for cotton, corn and alfalfa in Saveh was 811.5, 354.7 and 1.875 mm more than Saveh-Tafresh zone, respectivelyIt was concluded that cultivation of winter crops in Saveh zone is not suitable due to higher virtual water compared to other areas and cultivation of spring crops is recommended in this zone.