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that a time series is homogeneous between two given dates and according to two laws of different distributions. On the one hand, these tests are known for their robustness but do not allow the detection of more than one break in a time series. On the other hand, Hubert’s test gives the year of the different breaks observed in the series with the means and standard deviations of the different segments. This method has been the subject of numerous publications in different regions of Africa (Ardoin et al., 2003; Bodian et al., 2011; Servat et al., 1999) and in Central Africa (Nguimamet & Orange, 2020). These tests have not been applied to the Uele time series, which are series inferred from the surrounding basins.

      6.3.3. Calculation of River Depletion Coefficients

      The river depletion coefficients of the Ubangi at Mobaye and the volume mobilized by the basin aquifer were calculated from daily data (according to Cosandey et al., 2003; Goula et al., 2006; Nguimalet & Orange, 2019; Savané et al., 2001). However, numerous gaps in the 1960s with exceptional rainfall and after 1976 shortened the series. This approach makes it possible to assess the contribution of surface runoff on aquifer recharge, by homogeneous hydropluviometric period in this deficit context.

      The mathematical expression for the river depletion coefficient is written:

      (6.3)normal upper Q Subscript normal t Baseline equals normal upper Q 0 normal e Superscript negative k t

      where Qt = discharge at time t, Q0 = initial discharge (discharge at the beginning of the depletion), and k = Maillet depletion coefficient. Maillet’s law is modeled on a single reservoir, which corresponds to all the aquifers contributing to flows in the watershed under study (Goula et al., 2006; Nguimalet & Orange, 2019). The integration of this equation over the interval [0, +] gives an estimate of the volume mobilized from the aquifers in the watershed, i.e.:

      (6.4)equation

      6.4.1. Interannual Evolution of Rainfall and Annual Flows of the Ubangi River at Mobaye

Hydrological basins Interannual average (mm) Pettitt Lee and Heghinian Segmentation of Hubert (mm) Standard Deviation Hydro‐climatic trends P divided by interannual average (%)
Ubangi at Mobaye (403,800 km2) 1,506 1969 1969 1938–1968: 1,568 1969–2006: 1,436 2007–2013: 1,583 109 88 81 Wet Dry Wet +4 –5 +5
Mbomu at Bangassou (115,000 km2) 1,491 1970 1951–1994: 1,851
Mbomu at Zemio (29,300 km2) 1,421 1970 1951–1994: 1,748
Kotto at Kembe (77,500 km2) 1,348 1969 1969 1948–1980: 1,458 1981–1991: 1,306 1992–1993: 1,577 94 89 32 Wet Dry Wet +2 –8 +11
Kotto at Bria (61,500 km2) 1,348 1967 1967 1948–1966: 1,436 1967–1991: 1,267 1992–1993: 1,515 94 105 83 Wet Dry Wet +7 –7 +12
Schematic illustration of rainfall index and flow index of the Ubangi basin at Mobaye, 1938–2015.

      6.4.2. Interannual Evolution of Rainfall and Annual Flows in Sub‐Basins of the Ubangi at Mobaye

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