Potential Impacts of Climate Change and Population Growth on Water Resources in Guinea Savanna Ecological Zone of Nigeria

Abstract

The variability and uncertainty of water resources associated with climate change are critical issues in so many regions of the world as projected climate change portend increase in water scarcity risks at a peak level. Hence, this study attempted to examine potential impacts of climate change along with population growth dynamics on the water resources of the Guinea Savanna Ecological Zone (GSEZ) of Nigeria. To this end, three catchments (Kainji lake catchment (KLC), Asejiri lake catchment (ALC), and Shiroro lake catchment (SLC)) spanning the ecological zone were used; the choice of these catchments was informed by the availability of long and continuous hydrometeorological data. To achieve the aim of the study, water availability analysis was done through the instrumentality of the web-based Royal Netherland Meteorological Institute (KNMI) Climate Explorer. For effective analysis, annual water yield scenarios (short-term, medium-term, and long-term) were generated for future periods using the multi-model ensemble mean of coupled model intercomparison project 5 (CMIP 5 GCMs). These were under three Co 2 emission trajectories based on Representative Concentration Pathways (RCP); here, RCP 2.6, 4.5, and 8.5 were adopted. Results obtained based on regional trend analysis revealed absolute water scarcity in the GSEZ. on the other hand, using climate change-population growth scenarios for the respective RCPs, the results indicated variable water stress conditions across the sub-basins or catchments. Under changing climate with stagnant population growth, the cumulative decrease in per capita water stood at 26847 cumec, and 8906 cumec, respectively for KLC and ALC; i.e., between the baseline period (2007-2008) and long-term projection, Similarly, for varying population growth dynamics with constant climate regime, the per capita water was found to be 70678 cumec/year for KLC while both SLC and ALC had a total water availability of 7.0 BCM/year with per capita water reduced to 21853 cumec/year and 18902 cumec/year for KLC. However, for combined climate change-population growth scenario, the results revealed varying spatial trend for the projected future periods under different RCPs in terms of per capita water situations; this connotes variable impact pattern across the GSEZ. It suffices to note that though the CMIP 5 ensemble model is robust, the disparity in its ability to reproduce annual rainfall regime as well as the distribution of variability in processes like evapotranspiration perhaps might have contributed to the nature of the overall results. Therefore, it is imperative to surmise that projected water scarcity on the long-term could largely be attributable to climate change and passively to population growth dynamics.