Modelling the impacts of climate change on hydrology and water resources in the Niger-South Sub-Catchment of the Niger River Basin, Nigeria
The Niger River Basin (NRB), located between latitudes 4–7.5o N and longitudes 4.5– 7o E, is a trans-boundary basin which transverses about nine countries of West and Central Africa with a total active area of about 925,796 km2, of which about 60% is an agricultural rain-fed and irrigated area. I...
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/71101/1/FK%202017%2019%20-%20IR.pdf |
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| Summary: | The Niger River Basin (NRB), located between latitudes 4–7.5o N and longitudes 4.5–
7o E, is a trans-boundary basin which transverses about nine countries of West and
Central Africa with a total active area of about 925,796 km2, of which about 60% is
an agricultural rain-fed and irrigated area. In addition, various hydropower stations are
currently in operation along the course of the main river. Hence, there is a growing
concern that any unfavourable climate change impact in the basin might have
consequential impacts on the socioeconomic lives of the people of the country.
To assess these possible impacts of future climate change on the water resources in
the NRB, a sub-catchment of the Nigerian part, hereafter referred to as Niger-South
Basin (NSB) is chosen in the present study. Statistical, trend and drought analyses
were performed on some hydro-climatic variables to ascertain the direction of change
in climate and as well the occurrence of drought with a view to evaluating the likely
impacts on hydrology and water resources in the basin. The results showed a relatively
uniform increase in warming and drying over the entire landscape (1948-2008). While
the decade 2000s and year 1983 were the driest, average annual rainfall was dominated
by August (15%), with the summer season (June, July and August; JJA) also
contributing the highest (40%). Although, only 15% was significant (α < 0.1) ,
rainfall trend was generally negative, with about 8 months exhibiting downward trend,
while only JJA showed significant upward trend.
Similarly, warming over the basin was relatively uniform; while the period between
1978 and 1979, and year 1998 were the warmest (mean temperature = 27.8 oC), the
warmest season was in spring (March, April and May). Significant increasing trends
were observed for all series (minimum; TMIN, maximum; TMAX and mean
temperature; TMEAN) and on monthly, seasonal and annual bases, but trends were
strongest in TMIN and in autumn. However, average warming over the entire landscape was 0.83 oC per annum. Drought analysis indicated pockets of wet and dry
conditions of varied severities since 1970, with meteorological droughts observed
during 1973 to 1977 and 1982-1984, while the decade 1980s showed between
moderate and extreme droughts. Increased warming influenced hydrological drought,
especially during the 1990s, given the relatively higher correlation between the
Standardised Precipitation Evapotranspiration Index (SPEI) and the Standardised
Runoff Index (SRI), while a strong 2-year periodic power was found during the late
1970s and early 1980 controlling drought. Although a moderately wet basin has been
observed, with increased warming, a reversal of the situation might be experienced in
the future.
For the hydrological modelling, a hydrological model, Soil and Water Assessment
Tool (SWAT) was set up to evaluate the impacts of the likely future climate change
on the hydrology and water resources in the NSB. Calibration and validation of the
model was done using the discharge data for the period 1980-1989 and 1990-1999,
respectively. With Nash-Sutcliffe (NS) of 0.82 (calibration) and 0.73 (validation), the
model indicated good performance and robustness. Thereafter, five bias-corrected
General Circulation Models (GCMs) (CNRM, GFDL, CCCma, ICHEC and NCC)
were downscaled and used to drive the model for the future (2040-2059 and 2070-
2089) hydrological parameters simulations. The results showed declines in average
annual precipitation, runoff, baseflow, streamflow and potential evapotranspiration
(PET) of about 16%, 65%, 2%, 23% and 1.7%, respectively during the mid-century
(2040-2059), and 14%, 60%, 0.3%, 20% and 0.8% for precipitation, runoff, baseflow,
streamflow and PET during the late-century (2070-2089). Notwithstanding the
uncertainty observed during the study, the results showed that the basin is highly
sensitive to climate change. Therefore, adoption of good water resources management
and adaptation strategies are needed to ensure sustainable water supply in the basin
especially during the mid-century. |
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