Climate Change’s Influence on Water Resource Availability in Nigeria’s Guinea and Sudano Sahelian Ecological Zones
Water resources in the Guinea and Sudano-Sahelian ecological zones of Nigeria are under threat from the persistent impact of climate change. Previous studies in the area have relied on historical trend analysis or hypothetical assumptions to project climate change impacts on water resources. However, considering the sensitivity of the hydrological system to climate change, there is a need to shift towards the use of General Circulation Models (GCMs) with Representative Concentration Pathways (RCPs), which represents the current global paradigm. This shift has not yet been adopted in the study area, creating a research gap that this thesis aims to address.
The objective of this thesis is to examine the impact of climate change on water resources availability in the Guinea and Sudano-Sahelian ecological zones of Nigeria. Specific objectives include analyzing the sensitivity of these zones to climate change, determining the potential impact on water yield, identifying trends in extreme rainfall indices, and estimating water stress resulting from climate change in the study area.
Data used for the study, both observed and simulated, were obtained from the archive of the Royal Netherlands Meteorological Institute known as the KNMI Climate Explorer. Mann Kendall statistical test was employed to analyze trends in the time series at a significance level of 0.05. Projections were generated for three future periods (2019-2048, 2049-2078, and 2079-2100) using the multi-model ensemble mean of CMIP5 GCMs under RCP2.6, RCP4.5, and RCP8.5. The metrics used to evaluate the projections included root mean square error (RMSE), Mean Absolute Error (MAE), and Nash-Sutcliffe Efficiency (NSE), with the errors falling within acceptable thresholds.
The regional trend analysis of seasonal and annual temperature confirmed significant positive trends for all future periods with respect to highest emission trajectories. In contrast, rainfall projections for the same time horizons exhibited high levels of variability, unlike temperature. However, the analysis revealed a decreasing trend in dry season water yield for the Guinea and Sudano-Sahelian ecological zones of Nigeria. For the wet season, there were no significant increasing trends under the 2019-2048 period for the high emission scenario (RCP8.5), but significant trends were observed in the low and middle emission scenarios (RCPs 2.6 and 4.5).
Furthermore, the regional trend analysis indicated that there would be no significant positive trend in maximum 5-day rainfall under the 2019-2048 period. Similarly, there were no significant positive trends in heavy rainfall days for RCP2.6 across all projected periods, but significant trends were observed for RCP4.5 and RCP8.5 in the 2049-2078 period. The analysis of consecutive wet days (CWD) revealed no significant negative trends. However, consecutive dry days (CDD) were projected to increase within the range of 2-5 days and 6-10 days for all RCPs in the baseline periods of 1959-1988 and 1989-2018, respectively.
Additionally, considering the influence of population growth under a constant climate, it was observed that there would be significant positive trends in water stress for the three projected periods. This implies that future water scarcity is imminent in the Guinea and Sudano-Sahelian ecological zones of Nigeria, primarily driven by population growth and secondarily by climate change.
Recommendations include conducting comparative analyses of CMIP5 and CMIP6 in reproducing historical seasonal and annual temperature and rainfall patterns in the study area to enhance robust climate projections.
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