Characterization of the current hydrological drop of the Ubangui River at Bangui, Central African Republic

The Ubangui River in Bangui comes from The Mbomu River, the CAR side and the Uele River from the DRC. Its flow till Bangui in the bottom has 546 kilometers long and has numerous anastomoses, sprinkled with a good deal of islands and strangulations (Palambo and Bangui). Its side basin is influenced by the Sudano-Guinean variable of dumb tropical climate. This paper revisits the hydroclimatic changes of the Ubangui River at the outlet of Bangui in favor of a new hydropluviometric serial data from 1935 to 2015. The annual rainfall and hydrological data series were analyzed using different statistical tests (rainfall index and flow index, breaks research, depletion coefficients). Rainfall series still shows only one break in 1970, which confirms the exceptionality of this climate disruption in Central Africa. However hydrological series identifies four different hydrological periods: 1935-1959, 1960-1970, 1971-1982 and 1982-2013. The last period shows an average deficit of -22% (2 893 m(3)/s) compared to the mean annual flow over the entire study period (3 700 m(3)/s). The average relationship rain/runoff did not change during these well-identified hydroclimatic periods, suggesting that the hydrological functioning of the Ubangui River has not changed because of this climate disruption. It is attributed to the low human impact over this basin and to the small change of the vegetation cover. However the comparison of annual changes in the depletion coefficient with the volume mobilized by the aquifer flows to sustain the Ubangui River flows clearly indicates the relationship change before and after 1970 and after 2000.