A GIS Interface Method Based on Reference Evapotranspiration and Crop Coefficients for the Determination of Irrigation Requirements

A GIS approach was developed to utilize spatially distributed and temporally averaged meteorological data and crop distributions and their coefficients in order to estimate irrigation requirements. The irrigation requirements were estimated as the difference between crop evapotranspiration and effective rainfall. Crop evapotranspiration was evaluated as the product of reference evapotranspiration and the crop coefficient. Reference evapotranspiration was calculated using the FAO Penman-Monteith method. Monthly effective rainfall was estimated from total monthly rainfall according to the method developed by the USDA Soil Conservation Service. In order to illustrate the applicability of this approach, a case study for the country of Greece was used. Based on the share of water use in agriculture for irrigation purposes, results obtained from this study indicate an irrigation efficiency of approximately 66 percent for the year 1991. Taking that number into account, the irrigation requirements for the year 2020 are estimated at 8,350 Mm3.