http://197.159.135.214/jspui/handle/123456789/969 2026-04-23T15:11:17Z http://197.159.135.214/jspui/handle/123456789/303 Impact of Climate Change and Urbanization on the Continental Terminal Aquifer Recharge in Aghien Lagoon Area (Abidjan, Côte D’ivoire) Kouakou, Koffi Abdelaziz 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. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Universite Abomey Calavi, Cotonou, Benin, in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Climate Change and Water Resources 2019-04-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/301 Modeling the Impacts of Climate Change, Land Use Change and Dam Management on Water Resource in West Africa: Case of the Mono River Basin, Togo-Benin Koubodana Houteta, Djan’na A good understanding of climate change, land-use change and dam management impacts on water balance components must enable the development of sustainable water resources strategies in West Africa. The Mono River Basin (MRB) in West Africa is a river basin shared with Togo and Benin Republics. Its contributions to the socio economic development of the region are needless to emphasize. But its course has been lately subject to several human activities such as dam construction that may have modified its functions. The present study objectives are to analyze the accuracy of CILSS, ESA and Globeland30 land cover datasets between 1975 and 2013, to investigate climate change detection via trend analysis on the hydro-climatic datasets over the period of 1961 to 2016, to simulate and compare discharge using empirical lumped, and to assess water balance component changes using semi- distributed hydrological models over two baseline periods in the Mono River Basin. The methodological approaches consist in land cover reclassification and accuracy evaluation. The three datasets were used to predict future LULC changes between 2020 and 2027 using the Terrset Land Change Modeler. Afterward, the non-parametric Mann Kendall (MK) trend analysis of historical hydro-climatic data was applied, and these data sets were used as inputs for the lumped models, GR4J (Génie Rural à 4 paramètres Journaliers), IHACRES (Identification of unit Hydrographs and Component flows from Rainfall, Evapotranspiration and Stream data) and SWAT (Soil, and Water Assessment Tool) simulations are undertaken. The results indicate for the accurate CILSS data set, there are an increase of 30.97% of cropland area, the losses of (6.91%) of forest area and the decrease of (25.59%) of savanna between 1975 to 2013 and are explained by the increase in population and their food demand. The climate change detection analysis reveals positive and negative trends of hydro-climatic data over MRB from 1961 to 2016. Mean temperatures increase at α = 0.01 and 0.05 significance levels in the three stations investigated whereas a negative non-significant trend is noticed for average rainfall. Meanwhile, the discharge presents a significant seasonal and annual trend for three gauge stations investigated. An acceptable accuracy (R2 ≥ 0.9) of validated ensemble climate models allow the computation of extreme climate indices under RCP4.5 and RCP8.5 scenarios which shows a significant annual trend of some climate extreme indices of rainfall and temperature at three selected stations between 2020 and 2045. The hydrological modeling analysis indicates that the two lumped models discharge predictions are acceptable with evaluation efficiencies over pre-dam period (1964 – 1986) and more and less acceptable during post-dam period (1988-2010). IHACRES model was found to underestimating extreme high runoff in the downstream of MRB (1964-1986). Finally, the simulation with SWAT semi distributed model performances and uncertainty analysis show that there are good model performances (Calibration_1964-1975; R2> 0.60; KGE ≥ 0.70 et PBIAS ≤ ± 4.5; validation_1976 - 1986: KGE ≥ 0.50 and PBIAS ≤ ± 3.40) and acceptable parameters values range between 1964 and 1986. Conversely, there are poor model performances (calibration_1988-2000: KGE ≥ 0.60 and PBIAS ≤ ± 20); validation_2001-2011: KGE ≥0.24 and PBIAS ≤ ± 17.20) during the second period (1988-2010). An individual assessment of surface runoff, evapotranspiration and water yield components shows that its seasonal and annual variability depends on different land-use type change, climate conditions and also on the presence or not of reservoir in the watershed. This indicates that the implementation of the dam on the MRB in 1987 has affected the hydrological system of the river. Land use land cover change with the amplification of climate change are the others drivers accelerating this change. The study has proposed effective strategies for better planning and management of water resources in MRB such as land use management, climate change adaptation basin and Nangbéto reservoir reliable managements. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Universite Abomey Calavi, Cotonou, Benin, in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Climate Change and Water Resources 2020-02-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/300 Integrated Hydrological Modelling of Climate Change Impacts in Semi-Arid Urban Watershed of Niamey, Niger Boubacar, Abdou Boko The Niger River is the sole permanent surface water used for agriculture and drinking water supply for the area of Niamey, Niger, West Africa. Given that the water distribution network does not cover the entire populated area, and because of recurrent droughts, the River cannot cover the total water demand in the area. Groundwater is pumped through open wells and boreholes to provide water to more than 35% of 1.3 million of people of the city. Groundwater demand for drinking and agriculture purpose is increasing as a result of rapid population growth and urbanization. Simultaneously, episodes of extreme low flows have become more frequent due to increasing demand, sedimentation of the River bed, and increased variability in streamflow upstream of Niamey. The minimum environmental flow for Niamey, set to 55 m3/s over 10 days, is therefore often not available. In this context, this study investigates ground water surface interactions and the whole hydrological system response under climate change. An equivalent porous medium approach was used to define a hydrogeological conceptual model to understand the hydrodynamic of the fractured aquifer system, and quantify the integrated interaction between this system and surface water resources as well as the climate change impacts. Combined used of hydrochemicals and isotopes have shown that the major source of both groundwater and surface water is provided by silicate weathering. The isotopes signals of water are exempt from strong evaporation influence, implying that groundwater recharge process is strongly dominated by rapid and localized infiltration. A large scale, high resolution fully-integrated hydrologic model was built and calibrated using HydroGeoSphere with a sequential approach of increasing levels of temporal resolution: 1) steady state average conditions; 2) dynamic equilibrium with repeating monthly normal forcing data; and 3) fully transient conditions. Simulations results show that exchange flux between groundwater and surface water are important processes in the basin. The basin average water balance highlights the importance of plant transpiration (58 % of total rainfall) over surface evaporation (8%), with groundwater recharge of up to 5% of total rainfall. Overland flow and infiltration account for 11% and 16 % of the total annual rainfall respectively, and groundwater discharge to the river is 2% of the total rainfall. Historical (1980-2005) and projected (2020-2050) climate scenario derived from the outputs of three regional climate models (RCM), under the RCP 4.5 scenario, were statistically downscaled using the multiscale quantile mapping bias correction method. The durations of the Minimum Environmental Flow (MEF) conditions, required to supply drinking and agriculture water were found to be very sensitive to changes in runoff resulting from climate changes. MEF occurrences and durations are likely to be greater for the first decade (2020-2030) of the mid-century, and then they will be reduced for the last two decades (2030-2050) of the mid-century period. All the three RCMs consistently project a rise in groundwater table of more than 10 meters in topographically high zones where the groundwater table is deep and an increase of 2 meters in the shallow groundwater table. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Universite Abomey Calavi, Cotonou, Benin, in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Climate Change and Water Resources 2020-03-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/299 Integration of Land Surface Modeling, Data Assimilation and Climate Change in Assessing Past and Future Hydroclimatic Conditions over Burkina Faso, West Africa Tall, Moustapha Estimating climate change impacts on water resources in West Africa has been challenged by hydrological data scarcity and inconsistencies in the available climate projections. In this thesis, an integrated approach involving land surface modelling, data assimilation and multi-model ensemble of the most recent regional climate model output is used to simulate the hydroclimatic impacts of climate change over Burkina Faso. To this end, high-resolution simulations from theCO2-responsive versions of the Interactions between Soil, Biosphere, and Atmosphere (ISBA), the global Land Data Assimilation System (LDAS-Monde) and a multi-model ensemble based on the most recent version of the Regional Climate Model (RegCM4) under two Representative Concentration Pathways (RCP4.5 and RCP8.5) are used.ISBA estimates are assessed throughits forcings (ERA5 and ERA-Interim reanalyses) for precipitation and solar radiation variables. First, it is shown that both reanalyses present a good performance in representing precipitation variability and incoming solar radiation (with better score for ERA5). This highlights a good calibration and the potential of ISBA to provide good quality estimates of land surface estimates such as Leaf Area Index (LAI) and Surface Soil Moisture (SSM). Then, within LDAS-Monde,SSMandLAIobservationsfromtheCopernicus Global Land Service (CGLS) are assimilated with a simplified extended Kalman filter (SEKF) using ISBA over a long period (2001-2018). Results of four experiments are then compared: Open-loop simulation (i.e., model run with no assimilation) and analysis (i.e., joint assimilation of SSM and LAI) both forced by either ERA5 or ERA-Interim. After jointly assimilating SSM and LAI, sensitivity study of the model to the observations permits to notice that the assimilation is able to impact soil moisture in the first top soil layers (mainly up the first 20 cm), but also in deeper soil layers (from 20 cm to 60 cm and below), as reflected by the structure of the SEKF Jacobians. The benefit of using ERA5 reanalysis over ERA-Interim when used in LDAS-Monde is highlighted. The assimilation is able to improve the simulation of both SSM and LAI: the analyses add skills to both configurations, indicating the good behaviour of LDAS-Monde. For LAI in particular, the southern region of Burkina Faso (dominated by a Sudan-Guinean climate) highlights a strong impact of the assimilation compared to the other two sub-regions of Burkina Faso (dominated by Sahelian and Sudan-Sahelian climates). In the southern part of the domain, differences between the model and the observations are the largest, prior to any assimilation. These differences are linked to the model failing to represent the behaviour of some specific vegetation species, which are known to produce leaves before the first rains of v the season. The LDAS-Monde analysis is very efficient at compensating for this model weakness. Evapotranspiration estimates from the Global Land Evaporation Amsterdam Model (GLEAM) project as well as upscaled carbon uptake from the FLUXCOM project and sun-induced fluorescence from the Global Ozone Monitoring Experiment-2 (GOME-2) are used in the evaluation process, again demonstrating improvements in the representation of evapotranspiration and gross primary production from assimilation. Finally, the impact of anthropogenic climate change in the hydroclimatology of Burkina Fasofor the middle (2041– 2060) and late (2080–2099)21stcentury has been investigated with regard to the historical period (2001-2018). The results indicate that an increased warming, leading to substantial increase of atmospheric water demand, is projected over all Burkina Faso areas. In addition, mean precipitation unveils contrasting changes with wetter conditions (for all three climatic zones) by the middle of the century and drier conditions during the late twenty-first century(mostly for the Sahelian zone). Such changes cause more/less evapotranspiration and soil moisture respectively during the two future periods. Furthermore, surface runoff shows a tendency toincrease and decrease along with short spatial gradients regardless whether the region receives more or less precipitation. Finally, it is found that while dry and semi-arid conditions develop in the RCP4.5 scenario, generalized arid conditions prevail over the whole Burkina Faso for RCP8.5. It is thus evident that these future climate conditions substantially threaten water resources availability for the country as well asagricultural activities. Therefore, strong strategedies are needed to help design response options to cope with the challenges posed by the projected climate change for the country. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Universite Abomey Calavi, Cotonou, Benin, in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Climate Change and Water Resources 2020-01-01T00:00:00Z