Impact of Climate Change and Urbanization on the Continental Terminal Aquifer Recharge in Aghien Lagoon Area (Abidjan, Côte D’ivoire)

Abstract

This study focuses on the influence of climate and land use/land cover (LULC) change on groundwater recharge over the Continental Terminal catchment (Abidjan aquifer) in the context of urbanization and population growth. The specific objectives of the study were to, (i) assess groundwater recharge regarding the changes in LULC of the Continental Terminal catchment using water balance method, (ii) assess the impact of the Representative Concentration Pathways (RCP4.5) climate change scenario on rainfall, temperature, and groundwater recharge in the near future 2020-2049, and (iii) model and analyze locally impact of climate and LULC change on groundwater balance using MODFLOW model by assessing the interaction between groundwater and surface water. Many data have been used for the study such as, piezometric level data, observations (stations and CHIRPS) climate data, Landsat images (1990, 2000 and 2016) for LULC mapping, Regional Climate Models (RCMs) under RCP4.5 scenario for historical (1982-2011) and near future (2020-2049) period for climate change impact assessment. The results show an increased in built-up and agricultural land, while the forest and shrub areas declined, with water body remaining unchanged over the period 1990-2016. The decline in forest could be imputed to the demographic and socio-economic growth as expressed by the expansion in agriculture and urbanization. Groundwater recharge represents 34%, 21% and 26% of rainfall respectively in 1990, 2000, and 2016. While the runoff during these same years is respectively 20%, 46% and 14% of rainfall total. The ensemble mean projected a warmer climate in the near future (2020-2049) with a 1.73oC increase in mean annual temperature and a 37.32% increase in mean annual rainfall relative to the baseline (1982-2011) period. Groundwater recharge projection was found more depending on climate change parameter, especially changes in rainfall and temperature. Groundwater and lagoon Aghien intaraction show that Aghien lagoon drains the aquifer to 1.104 m3 /day in certain areas where the aquifer is deeper, the lagoon supplies the groundwater by drainage up to 41.103m3/day and all the scenarios made to assess future groundwater water level (2060) reveal a drop of hydraulic head and this could impact surface water reserve.