Impacts of Climate Change and Population Growth on Groundwater Resources: Case of the Klela Basin in Mali, West Africa

Abstract

Due to the effects of climate change and population growth, global water resources are threatened in terms of quantity and quality. As groundwater is more resilient to climate variability, to date, many studies are addressing the simulation of groundwater dynamics for adaptation purpose. Groundwater on the Klela basin in Mali, a subbasin of the Bani’s basin (one of the main tributaries of the Niger River), is very important for the population because it is required for domestic use, irrigation and livestock. Surface water is limited to seasonal rainfall and runs dry a few months after the rainy season. Therefore, investigations of groundwater resources to understand aquifer system behavior are vital to the inhabitants of the Klela basin. Actually, groundwater resources are sufficiently enough and available to cover the current water demand, but in the face of climate variability and change, growing population and high urbanization rates, this vital resource is being threatened. Therefore, water assessment tools were used to understand the aquifer behavior of the basin. The focus of this study is on estimating the amount of rainwater that replenishes the aquifer, understanding the hydraulic interactions between surface-water and groundwater, and quantifying and evaluating groundwater dynamics in the context of climate change and population growth, using different scenarios. Different approaches such as the water table fluctuation (WTF), chloride mass balance (CMB), simulations using the EARTH model and the Thornthwaite model for recharge estimation, MODFLOW for groundwater modeling, and the WEAP model for evaluating groundwater resources are applied to achieve the study objectives. Climatological, hydrological, geological, hydrogeological, hydraulic and demographic data are collected and used as models input data. The sandstone aquifer in the study area was simulated under steady and transient conditions, and the groundwater budget was computed. Recharge was estimated to be approximatively 635 Mm3/a or 13.9% of the mean annual rainfall for the period 2012-2013. The amount of water discharging the aquifer into the streams was estimated to be approximatively 618 Mm3/a, representing 97% of recharge amount. Currently, the reduction of groundwater storage of about 39 Mm3/a (10.6 mm/a) is mainly due to groundwater extraction by population. Scenarios of climate change, population growth and socio-economic development were developed to assess future groundwater resources. The results reveal that the impacts of climate change on groundwater are greater than that of the socio-economic development. However, the climate scenario RCP8.5 appeared to be the worst for groundwater availability. The overall conclusion of this study is that groundwater recharge, groundwater level and storage are decreasing over time, especially in the 2030s, where the simulated drought events are expected. The greatest impacts on groundwater resources are due to climate change and population growth.