northern part of the area where soil is mostly sandy loom in nature and less in the
central part where the soil dominated by clay.
The sub-district level map of crop evapotranspiration from Boro rice field is shown
in Fig. 7. The crop evapotranspiration in the area varies between 423 and 483 mm
with an average of 452 mm. The map of effective precipitation during the irrigation
period is shown in Fig. 8. The spatial distribution of effective precipitation follows
the similar pattern of total precipitation in the study area (Fig. 2a).
The maps of land preparation, percolation and seepage losses, evapotranspiration
and effective precipitation are integrated using GIS to prepare the maps of irrigation
water demand in northwest Bangladesh. The irrigation water demand of each subdistrict
of the integrated layer is calculated using by Eq. 1. The sub-district level
map of irrigation water demand of northwest Bangladesh is shown in Fig. 9. The
irrigation water demand in the study area varies between 839 and 1,210 mm with an