The effect of spatially distributed meteorological parameters on irrigation water demand assessment

Geographic information systems technology was used to utilize meteorological data and crop distributions 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, while the reference evapotranspiration was calculated via 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. For the purpose of this paper, the island of Crete in Greece was used as a case study. Based on individual meteorological stations as representative stations for the whole island the irrigation water demand was estimated at 362±135 Mm3 for the year 1991. The large variation is caused by the location and number of representative meteorological stations. A combination of up to 10 meteorological stations, chosen for geographical reasons as representatives of different regions of the island, resulted in a significant reduction of this variation. The irrigation water demand for the year 1991 was estimated, based on 10 stations, at 359 Mm3. The station of Lefkogia can be considered the representative station for the island. An increase in irrigation water requirements is projected to be 8–10 Mm3/year for Crete. These analyses should assist in the strategic planning of water use for irrigation, particularly in cases where the number of stations is inadequate, by identifying representative stations for different regions and projecting further irrigation water demand. The accurate estimation of irrigation water demand is also essential for developing a rational policy for sustainable water resources.