basin efficiency in the base year is calculated as the ratio of the net irrigation water demand to the total irrigation water depletion estimated from records shiklomanov the projection of irrigation water demand depends on the changes in irrigated area and cropping patterns basin efficiency and effective rainfall global climate change affects future irrigation water demand through changes in precipitation and temperature along w ith other meteorological variables that affect crop evapotranspiration irrigation demand in the fpu is calculated for a given cropping pattern after taking into account the basin efficiency of the irrigation system