CLIMATE CHANGE IMPACT ON WATER RESOURCES AVAILABILITY IN THE GUINEA AND SUDANO SAHELIAN ECOLOGICAL ZONES, NIGERIA

Abstract

Water resources have been threatened in the Guinea and Sudano-Sahelian ecological zones by the persistent impact of climate change. Many previous studies in the area were based on historical trend analysis or hypothetical assumptions in projecting climate change impacts on water resources. Considering the sensitivity of the hydrological system to climate change, there is the need to adopt the current global paradigm shift from the use of historical trend analysis to the use of General Circulation Models (GCMs) with Representative Concentration Pathways (RCPs). This is yet to be adopted within the study area, which constitutes the research gap this thesis has identified. Thus, the aim of the thesis was to examine the impact of climate change on water resources availability in the Guinea and Sudano-Sahelian ecological zones of Nigeria. The objectives were to: analyse the sensitivity of the Guinea and Sudano-Sahelian ecological zones of Nigeria to climate change; determine the potential impact of climate change on water yield; identify the trend in the occurrence of extreme rainfall indices; and estimate the water stress resulting from climate change in the study area. The data used (observed and simulated) were from the archive of the Royal Netherlands Meteorological Institute Known as the KNMI Climate Explorer. The respective coordinates of each basin were used to derive the observed and simulated data. Mann Kendal statistical test was used to analyses trends in all the time series at the 0.05 significance levels. Projections were produced for three future periods namely: 20192048, 2049-2078 and 079-2100 using the multi-model ensemble mean of CMIP5 GCMs under RCP2.6, RCP4.5 and RCP8.5. The metrics were root mean square error (RMSE), Mean Absolute Error (MAE) and Nash-Sutcliffe Efficiency (NSE). The errors between the observed and simulated were within the acceptable threshold. Regional trend analysis of seasonal and annual temperature confirm significant positive trends for (2019-2048), (2049-2078), and (2079-2100) with respect to highest emission trajectories. On the other hand, seasonal and annual rainfall projections for the same time horizons confirm high level of variability unlike temperature. However, regional trend analysis confirms that Guinea and Sudano-Sahelian ecological zones of Nigeria will experience decreasing dry season water yield. As for wet season, it reveals that under 2019-2048 period there are no significant increasing trends. This is with respect to high emission scenario (RCP8.5) but significant in low and middle emission scenarios (RCPs 2.6 and 4.5). Furthermore, it is evident that regional trend analysis of maximum 5- day rainfall demonstrated that under 2019-2048 period there will be no significant positive trend. Regional trend analysis of heavy rainfall days point out that there will be no significant positive trends for RCP2.6 with respect to the three projected periods but significant with respect to 2049- 2078 for RCP4.5 as well as RCP8.5. Regional trend analysis of CWD established that there will be no significant negative trends. Conversely, CDD will increase within the range of 2-5 days and 6-10 days for all the three RCPs under the two baseline periods of (1959-1988) and (19892018) respectively. However, regional trend under the influence of population growth at constant climate observed that there will be significant positive trends in water stress for the three projected periods. This implies that future water scarcity is imminent and will be primarily caused by population growth and only secondarily by climate change in the Guinea and Sudano-Sahelian ecological zones of Nigeria. It was recommended amongst others that future research should explore the comparative analysis of CMIP5 and CMIP6 in reproducing historical seasonal as well as annual temperature and rainfall in the Guinea and Sudano-Sahelian ecological zones of Nigeria. This will facilitate a robust climate projection for the study area