Physiogeographic features of the Oubangui catchment and environmental trends reflected in discharge and floods at Bangui 1911-1999, Central African Republic

Varying discharges of large rivers observed over long periods can reflect environmental trends like 'climate change' within the catchment (e.g. ongoing aridification results in a reduced discharge). The present study on the Oubangui River in Central Africa first lines out some physiogeographic features of the almost 500 000 km2 large catchment situated on the vast north equator rise. Subsequently, a discharge record from 1911-1999 of Qmax. and Qmin., covering data for 73 years from the gauge station Bangui, is examined. Annual variability of Oubangui floods is generally high and shows over the past years, especially since the mid to end 1960s, a less significant trend to a slight depletion of maximum discharge. Frequency analysis (Gauss, Gumbel, Weibull) of floods resulted in return periods between 7 and 35 years. Distributions calculated after Gumbel generally gave the best results. No linear and simple evidence exist of the tendency of the river to reduce discharge because of a depletion of rain fall as the Oubangui's floods are again increasing since the mid 1990s. Finally, the consequences of Oubangui flood hazards for the growing town of Bangui are discussed. Flooding of urban areas from exceptional high Qmax. discharge is spatially reconstructed for the floods in 1916, 1962, and 1999.