For the mapping of spatial extents of evapotranspiration and effective precipitation
from point data kriging interpolation method is used. Geostatistical analysis tool
of ArcMap 9.1 (Environmental Systems Research Institute 2004) is used for this
purpose. Water required for irrigation is calculated within GIS at sub-districts scale.
Therefore, the maps of evapotranspiration, effective rainfall, water required for land
preparation, percolation and seepage losses, etc. are converted to sub-district scale.
Area weighted overlay method is used for this purpose. Area weighted overlay
technique allows integrating dissimilar inputs with diverse values to a common
measurement scale. Preparation of sub-district scale map of effective precipitation
using area weighted overlay technique is described in Fig. 3. To prepare the subdistrict
scale maps of effective precipitation, the raster map of effective precipitation
is first overlaid on the sub-district map of the study area. The rainfall value at each
sub-district is calculated by averaging the area weighted rainfall of all polygons of the
sub-district as shown in Fig. 3.