Читать книгу Congo Basin Hydrology, Climate, and Biogeochemistry - Группа авторов - Страница 87

The rainfall break of the 1970s was less marked in Central Africa than in West Africa. Nevertheless, it has largely impacted the hydrological regimes of the region’s major rivers (Laraque et al., 1998, 2001; Nguimalet & Orange, 2013; Olivry et al., 1998; Orange et al., 1997; Paturel et al., 1998, 2007; Servat et al., 1999; Sighomnou et al., 2007; Wesselink et al., 1996). On the Ubangi River at Bangui, a large savannah‐dominated basin, the slight drop in rainfall of 5 to 6% resulted in a 21% runoff deficit over the period 1983–2013 (Orange et al., 1994). On the Congo River, Laraque et al. (2013) noted that after a hydrological deficit observed in the 1980s, the runoff has returned to normal since 1990. According to Nguimalet & Orange (2019), the rainfall amount in the Ubangi basin at Bangui has shown a significant increase since 2009, but still without any real hydrological impact on the course of the Ubangi River at Bangui. Recently, Nguimalet and Orange (2020) showed that hydrological behaviors in small basins of 2,500 to 5,000 km² in the north of the Central African Republic, in the Sudanian savannah zone, were all impacted by the 1970 drought, at different levels and without any common hydroclimatic period. It remains to be seen whether this is specific to the northern basins with savannah vegetation, in contrast to the southern basins under equatorial forest. Therefore, we propose here to study the hydropluviometric evolution of the Ubangi basin at the outlet of Mobaye and its constituent hydrological sub‐basins, Mobaye being located 380 km upstream from Bangui with no large tributaries between these two hydrological stations (Orange et al., 1995). The Ubangi basin at Mobaye is without any anthropogenic influence. Half of it is covered by savannah drained by two large rivers (the Kotto and the Mbomu), and half by dense forest drained by the Uele (Orange, 1996).

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.