Congo Basin Hydrology, Climate, and Biogeochemistry. Группа авторов
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Название: Congo Basin Hydrology, Climate, and Biogeochemistry

Автор: Группа авторов

Издательство: John Wiley & Sons Limited

Жанр: География

Серия:

isbn: 9781119656999

isbn:

СКАЧАТЬ 3 National Directorate of Meteorology, Ministry of Transport and Civil Aviation, Bangui, Central African Republic

      ABSTRACT

      The rainfall reduction in the 1970s, less marked in Central Africa than in West Africa, still had a major impact on the hydrological regimes of the region’s large rivers. The study of the hydropluviometric behavior of the Ubangi River at Mobaye has the advantage of being a study of a basin excluding anthropogenic impact. Forest cover and population density have not changed since at least 1970. Statistical analysis of the breaks in the long rainfall time series to Mobaye (1938–2015) confirms a long period of drought from 1969 to 2006, corresponding to a reduction of 8% in rainfall. Also, the study of the corresponding hydrological series indicates a second downward break in 1981, marking an exceptional hydrological drought. Flows increased in 2013, a few years after the rainfall increase. The statistical study of the annual rainfall/flow series of the upstream basins over the period 1951–1995 (the Kotto River in Kembe and Bria, the Mbomu River in Bangassou and Zemio, and the Uele River + Bili hydrographic system) highlights different hydrological behaviors related to the vegetation cover. On the one hand, the savannah basins show a continuous hydrological deficit marked by a runoff coefficient (CE) that fell to only 5% from the 1990s. On the other hand, the basins under forest show a runoff increase since 1990, marked by a CE above 10%. Under savannah, the part of the flow infiltrating to recharge the aquifer would have decreased faster than under forest, which results in a runoff CE very significantly negatively correlated with the savannah area present in the studied watershed.

      The coupled evolution of rainfall (P) and annual flow (Q) over the upstream basin of the Ubangi River at Mobaye is studied in order to discuss the role of the forest compared to the savannah on the hydropluviometric behavior of the Kotto, Mbomu, and Uele basins, and to assess the behavior of aquifers in this hydropluviometric deficit context recorded since 1970 in the region. We approach this analysis by looking for homogeneous hydroclimatic periods of the 1938–2015 sequence on the Ubangi River at Mobaye, and over the 1951–1995 period for its three major tributaries: the Kotto, Mbomu, and Uele rivers.

Schematic illustration of topographic map of the Ubangi basin at Mobaye.

      Source: Based on Orange et al., 1994.

Schematic illustration of vegetation map of the Ubangi basin at Mobaye, the geological bedrock and the hydropluviometric network studied, with the limits of the five studied sub-watersheds.

      Source: Based on Orange et al., 1996.

      In the region, population growth is low: the population in Bangassou on the Mbomu River, the regional capital, increased from 902,205 inhabitants in 2006 to 1,126,730 in 2015, an increase of only 2.5% per year. The entire Ubangi basin at Mobaye thus remains a sparsely populated area, with a population density varying between 10 inhab/km2 and 3.3 inhab/km2. In the Uele basin, the population density was 7 inhab/km2 in 2008 (Haut‐Uélé, СКАЧАТЬ