A GIS Based Water Balance Study of Africa - Physical Land Resources

46areas of Cental-West Africa. The high runoff values on our map around east and centralAfrica is justified by its higher elevation. At the arid regions where runoff is almostnegligible coincide on both maps. South of the Sahel, around 12 0 – 15 0 N, the situation is stillsimilar with values from 10-50mm/yr. It would therefore appear that the region with the mostdiscrepancy is the area around the equator. One would tend to agree more with their higherestimates around the Congo basin because the soils there tend to be heavier owing to themuch higher precipitation they receive. This kind of texture would generally act againstinfiltration thus favouring runoff.Groundwater rechargeWetSpass vs. Döll et al. (2002)Our groundwater recharge map seems not to perfectly align with that of Döll et al. (2002).Though the ranges of recharge values do agree it is the exact location that changes. The highregions of recharge with values of 400-2000mm/yr seem to have been shifted a bit awayfrom the area around the equator (Congo and Gabon) toward the West of Africa aroundCameroon or Nigeria on our map (Fig 4.6). The other regions with lower recharges of lessthan 50mm/yr do however, agree on both maps.NUMERICAL VALUESSeveral attempts have been made by various researchers to numerically quantify the longtermannual values of Precipitation (P), Evapotranspiration (ET) and Surface runoff (Ro) forthe Continent of Africa.