To calculate the irrigation water demand in Boro rice field in the study area, monthly averaged rainfall and temperature data for the time period 1961–1990 is used.
It is found that potential evapotranspiration in the study area starts to exceed precipitation in the month of November and continues up to April.
This means
that soil moisture deficit starts to buildup in November.
The amount of water required to replenish the soil moisture in the month of December is considered as the water required for land preparation. The map of soil water required for land preparation is shown in Fig. 5.
The figure shows that the water required for land preparation varies between 114 and 128 mm in the study area.