The Hydrology of the Congo River Basin: A GIS-Based Hydrological Water Balance Model

A GIS-based hydrological model, namely HATWAB — Hybrid Atmospheric and Terrestrial Water Balance (Alemaw, 2006), was developed to compute water resource availability, simulating its spatial and temporal distribution over the CRB. HATWAB model simulates the Integrated Moisture Convergence (C), soil moisture (SM), Actual Evapotranspiration (AET) and Runoff (ROF). The spatial distribution of the simulated parameters shows a strong correlation with the rainfall pattern, especially in the high rain fed region (Effective Rainfall >1100 mm/year), corresponding to the heart of the equatorial forest which extend between 5 and –5 degrees of latitude; whereas some disturbances are observed in the lowest rain fed (Effective Rainfall <1000 mm/year) regions of the basin located the southeastern and the up-north part of the CRB. The Evapotranspiration Ratio (ETR) defines two main climatic regions, ETR close to 1 for region 1 and ETR < 7, with an intermediate zone between (07 < ETR < 0.8). The Annual average SM varies between 0 and 400 mm while the AET varies between 400 and 1700 mm/year with highest values on the water bodies. The total annual grid ROF varies between 0 and 1400 mm. Swamps are characterised by 0 to 40 mm values while highest runoff (> 900mm) are computed on the rivers and lakes. The inland grid ROF varies between 50 and 900 mm per year with an average of 324 mm/year. The accumulated ROF computed final outlet reaches 44700m³/second which is within an error margin of 5 % compared to the observed discharge. The HATWAB model still proved its ability of simulating water balance for large scale basins such as the CRB if input data are available and well prepared at acceptable resolution.