13 Assessment of Hydrological Impacts …
279
the large basins of the Gambia, at Gouloumbou (Ardoin-Bardin et al. 2009; Stanzel
et al. 2018) and Mako (Bodian et al. 2018), project a reduction in water resources in
the Gambia of between −4 and 26%, but these studies do not provide disaggregate
projections at the level of each sub-basin of the Gambia. It is essential to assess the
sensitivity of water resources to future climate change at finer spatial scales in order to
understand fluctuations, given the significant uncertainties of hydroclimatic models
(Brulebois 2016; Stanzel et al. 2018). In addition, the local analysis provides a basis
for integrating climate into sustainable water resource management and exploitation
policies (e.g., water management design, hydroelectric development, the definition
of appropriate adaptation strategies to reduce the vulnerability of ecological systems
to irregular rainfall and flow variability).
Two models of RS Minerve (GR4J and SAC-SMA) were compared to evaluate
the hydrological impacts of climate change on the Diarha river basin. The CORDEX
approach among three regional climate models (IPSL -CM5A-LR, INM-CM4 and
GFDL-ESM2G) that best reflects the rainfall-runoff relationship during the crossvalidation phase (1975–1992 and 1998–2003) will be applied to project flows of the
Diarha in the near future (2020–2050).
2 Materials and Methods
2.1 Study Area
The Diarha catchment is a tributary of the left bank of the Gambia River. It extends
between the parallels 12°26’ and 12°63’ and the meridians −12°86’ and −12°57’.
The physical environment of the basin has been described in earlier work (Thiaw
et al. (2017)). With an area of 759.3 km
2 and a perimeter of 145.1 km, the Diarha
extends 45 km upstream-to-downstream. Geologically, the basin lies entirely in the
Paleozoic and Proterozoic formations of the Birrimian basement, which has given
rise, as a result of the physicochemical alteration of the rocks, to low permeability
and very fragile soils. Its Sudano-Guinean climate is marked by the spatial and
temporal variability of precipitation since the 1967 climate break. From that time to
the year 2014, precipitation in the catchment has decreased by 10.5%. This decrease
in precipitation is attributable to the drought of the 1970s, which has been continuous
since 1968 for all the rainfall stations studied, and the magnitude of which, analyzed
by the Standardized Precipitation Index (SPI), is greater than that of the offsetting wet
period (1921–1967) (Thiaw 2017). In addition to changing its hydrological regime
and increased water erosion problems (Thiaw and Dacosta, 2017), this drought has
resulted in diminished rainfed and dry season farming systems, now threatening food
self-sufficiency. However, a slight return of rainfall conditions has been noted over
the last two decades (1991–2010) (Thiaw 2017) which also implies potential changes
in the hydrological behavior of the watershed.
279
the large basins of the Gambia, at Gouloumbou (Ardoin-Bardin et al. 2009; Stanzel
et al. 2018) and Mako (Bodian et al. 2018), project a reduction in water resources in
the Gambia of between −4 and 26%, but these studies do not provide disaggregate
projections at the level of each sub-basin of the Gambia. It is essential to assess the
sensitivity of water resources to future climate change at finer spatial scales in order to
understand fluctuations, given the significant uncertainties of hydroclimatic models
(Brulebois 2016; Stanzel et al. 2018). In addition, the local analysis provides a basis
for integrating climate into sustainable water resource management and exploitation
policies (e.g., water management design, hydroelectric development, the definition
of appropriate adaptation strategies to reduce the vulnerability of ecological systems
to irregular rainfall and flow variability).
Two models of RS Minerve (GR4J and SAC-SMA) were compared to evaluate
the hydrological impacts of climate change on the Diarha river basin. The CORDEX
approach among three regional climate models (IPSL -CM5A-LR, INM-CM4 and
GFDL-ESM2G) that best reflects the rainfall-runoff relationship during the crossvalidation phase (1975–1992 and 1998–2003) will be applied to project flows of the
Diarha in the near future (2020–2050).
2 Materials and Methods
2.1 Study Area
The Diarha catchment is a tributary of the left bank of the Gambia River. It extends
between the parallels 12°26’ and 12°63’ and the meridians −12°86’ and −12°57’.
The physical environment of the basin has been described in earlier work (Thiaw
et al. (2017)). With an area of 759.3 km
2 and a perimeter of 145.1 km, the Diarha
extends 45 km upstream-to-downstream. Geologically, the basin lies entirely in the
Paleozoic and Proterozoic formations of the Birrimian basement, which has given
rise, as a result of the physicochemical alteration of the rocks, to low permeability
and very fragile soils. Its Sudano-Guinean climate is marked by the spatial and
temporal variability of precipitation since the 1967 climate break. From that time to
the year 2014, precipitation in the catchment has decreased by 10.5%. This decrease
in precipitation is attributable to the drought of the 1970s, which has been continuous
since 1968 for all the rainfall stations studied, and the magnitude of which, analyzed
by the Standardized Precipitation Index (SPI), is greater than that of the offsetting wet
period (1921–1967) (Thiaw 2017). In addition to changing its hydrological regime
and increased water erosion problems (Thiaw and Dacosta, 2017), this drought has
resulted in diminished rainfed and dry season farming systems, now threatening food
self-sufficiency. However, a slight return of rainfall conditions has been noted over
the last two decades (1991–2010) (Thiaw 2017) which also implies potential changes
in the hydrological behavior of the watershed.