Soil moisture variation is determined as the percentage of the maximum amount of soil moisture available for Evapotranspiration (ET) processes within the plant rooting depth which is equal to soil water content at field capacity minus soil water content at wilting point times the rooting depth.

The monthly variation of soil moisture shown in the maps track the rainfall season, as observed clearly in the eastern Nile, where high soil moisture content starts in June and continue in rise through October and in decrease in November and lowest in February – March. The soil moisture is highest in the three upper southern sub-basins and lowest in the Main Nile and Tekeze-Atbara sub-basins.