70
P. Sagna et al.
In the event of an increase in the duration and frequency of dry seasons and
decrease in rainfall in the upper basin of the Ouémé River and the Beninese Niger
River basin as reported by MEHU (2011) and Lawin et al. (2013), there will be
a negative impact on the availability of water resources. For example, a decrease
in rainfall can lead to a decrease in runoff. This could also be accompanied by a
reduction in the amount of water stored in natural or constructed reservoirs into
which seasonal rivers flow. Hence, there is a likelihood of recurrent drying of water
reservoirs as was the case in 2014 for the Djougou reservoir. In the Beninese part of
the Niger River basin and in the central and southern regions, a decrease in rainfall
could lead to a decrease in runoff. The late onset of rainy seasons could introduce a
delay in the occurrence of high-flow periods.
Runoff decreases with rainfall in the Burkinabe parts of the Niger and Volta
basins (El Vilaly and El Vilaly 2013). In the Dapola basin, there was a 1.5% decrease
in decadal discharges after 1971. Yira et al. (2017) used a set of six regional and
global climate models (RCMs and GCMs) to predict future rainfall and runoff in the
Dano basin. The data are then integrated into the Water Flow and Balance Simulation
Model (WaSiM). Two scenarios of greenhouse gas concentrations (the Representative
Concentration Pathways RCP 4.5 and RCP 8.5) were selected. Findings show that
there are uncertainties about the rainfall and runoff relationship in the basin over the
period 2021–2050 compared to the period 1971–2000.
In the Senegal River basin, the relatively dry period from 1960 to 1996 resulted
in a decrease of 30–40% in water availability following a decrease of 20% in
rainfall (Oyebande and Odunuga 2010). In the upper basin, the average discharge
during 1971–2010 (after the rainfall break) decreased by 34–54%, depending on the
waterway, compared to 1904–1969 discharges (before the break). The HadRM3P and
RCA climate models and the GR2M hydrologic model allow us to estimate climatic
and hydrologic changes. They show a general downward and cyclical trend of flows
for the 2030, 2060, and 2090 horizons compared to the 1961–1990 period (Diakité
2017). In fact, variations in flows are twice as high as changes in rainfall (Le Lay and
Galle 2005). Magistro and Lo (2001) find a halving of the flows of the Senegal River
between the 1950s and the 1990s. Bodian et al. (2013) used four 2007 models by the
IPCC and a hydrologic model (GR2M) to study the impact of climate change on the
upper Senegal River basin. According to three climate models (CSMK3, HadCM3
and MPEH5), there will be a gradual decrease in discharge from 2030 to 2090 (Bodian
et al. 2013). Mbaye et al. (2015) used the regional climate model REMO as input to
the Max Planck Institute Meteorology-Hydrology Model (MPI-HM) to simulate flow
rates, runoff, soil moisture, and evapotranspiration. They found a drastic decrease
of 50% in water resources in the upper Senegal River basin. The decrease is more
pronounced toward the North. To the South (Guinean Highlands), models do not
show any variation in water resources. Decline in water resources is related to the
decrease in rainfall and the increase in potential evapotranspiration (Mbaye et al.
2015).
P. Sagna et al.
In the event of an increase in the duration and frequency of dry seasons and
decrease in rainfall in the upper basin of the Ouémé River and the Beninese Niger
River basin as reported by MEHU (2011) and Lawin et al. (2013), there will be
a negative impact on the availability of water resources. For example, a decrease
in rainfall can lead to a decrease in runoff. This could also be accompanied by a
reduction in the amount of water stored in natural or constructed reservoirs into
which seasonal rivers flow. Hence, there is a likelihood of recurrent drying of water
reservoirs as was the case in 2014 for the Djougou reservoir. In the Beninese part of
the Niger River basin and in the central and southern regions, a decrease in rainfall
could lead to a decrease in runoff. The late onset of rainy seasons could introduce a
delay in the occurrence of high-flow periods.
Runoff decreases with rainfall in the Burkinabe parts of the Niger and Volta
basins (El Vilaly and El Vilaly 2013). In the Dapola basin, there was a 1.5% decrease
in decadal discharges after 1971. Yira et al. (2017) used a set of six regional and
global climate models (RCMs and GCMs) to predict future rainfall and runoff in the
Dano basin. The data are then integrated into the Water Flow and Balance Simulation
Model (WaSiM). Two scenarios of greenhouse gas concentrations (the Representative
Concentration Pathways RCP 4.5 and RCP 8.5) were selected. Findings show that
there are uncertainties about the rainfall and runoff relationship in the basin over the
period 2021–2050 compared to the period 1971–2000.
In the Senegal River basin, the relatively dry period from 1960 to 1996 resulted
in a decrease of 30–40% in water availability following a decrease of 20% in
rainfall (Oyebande and Odunuga 2010). In the upper basin, the average discharge
during 1971–2010 (after the rainfall break) decreased by 34–54%, depending on the
waterway, compared to 1904–1969 discharges (before the break). The HadRM3P and
RCA climate models and the GR2M hydrologic model allow us to estimate climatic
and hydrologic changes. They show a general downward and cyclical trend of flows
for the 2030, 2060, and 2090 horizons compared to the 1961–1990 period (Diakité
2017). In fact, variations in flows are twice as high as changes in rainfall (Le Lay and
Galle 2005). Magistro and Lo (2001) find a halving of the flows of the Senegal River
between the 1950s and the 1990s. Bodian et al. (2013) used four 2007 models by the
IPCC and a hydrologic model (GR2M) to study the impact of climate change on the
upper Senegal River basin. According to three climate models (CSMK3, HadCM3
and MPEH5), there will be a gradual decrease in discharge from 2030 to 2090 (Bodian
et al. 2013). Mbaye et al. (2015) used the regional climate model REMO as input to
the Max Planck Institute Meteorology-Hydrology Model (MPI-HM) to simulate flow
rates, runoff, soil moisture, and evapotranspiration. They found a drastic decrease
of 50% in water resources in the upper Senegal River basin. The decrease is more
pronounced toward the North. To the South (Guinean Highlands), models do not
show any variation in water resources. Decline in water resources is related to the
decrease in rainfall and the increase in potential evapotranspiration (Mbaye et al.
2015).