http://197.159.135.214/jspui/handle/123456789/11 2026-04-23T15:11:11Z http://197.159.135.214/jspui/handle/123456789/293 Improvement and comparative assessment of a new hydrological modelling approach to catchments in Africa and the USA Gaba, Olayèmi Ursula Charlène Assessing water resources is still an important issue especially in the context of climatic changes. Although numerous hydrological models exist, new approaches are still under investigation. In this context, we investigate a new modelling approach based on the Physics Principle of Least Action. A first version of a Least Action based hydrological model, in its deterministic version has already given very good results in simulating the Bétérou catchment in the Ouémé basin, Benin. The thesis presents new hypotheses to go further in the model development with a view of widening its application. The improved version of the model MODHYPMA was applied on 21 subcatchments in Africa, in Bénin, Côte d’Ivoire, Ethiopia; and in the USA. Its performance was compared to two well-known lumped conceptual models, the GR4J and HBV models. The model was successfully calibrated and validated; it showed a good performance in most catchments. The analysis revealed that the three models have similar performance and timing errors. But in contrary to other models used in this study, MODHYMA is subject to a less loss of performance from calibration to validation. The parameter uncertainties were analysed using the GLUE methodology. It is concluded that model uncertainties are higher during high flows and that uncertainty analysis should include the uncertainty of the discharge data. In order to explore the possible transferability of our model for ungauged basins studies, we then intended to investigate how model parameters could be estimated from the physical catchments characteristics. We relied on statistical methods applied on calibrated model parameters to deduce relationships between parameters and physical catchments characteristics. These relationships were further tested and successfully validated on gauged basins that were considered ungauged. 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 2016-01-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/292 Modelling the Impact of Climate and Land Use/Land Cover Change on Streamflow and Sediment Yield in the Black Volta River Basin Aziz, Fati This study investigated the impacts of climate change and the sensitivity of land use/land cover (LULC) changes on river flow and sediment yield in the Black Volta River Basin (BVRB) using a modelling approach, with the aim of providing water resources and basin managers with science-based evidence of impacts of global change at basin level to inform sustainable planning and management of water resources in the basin. Climate change impact and sensitivity of LULC change on streamflow and sediment yield in the studied basin were assessed using the Soil and Water Assessment Tool (SWAT) model. Sensitivity analysis, calibration, validation and uncertainty analysis of the SWAT model were performed in SUFI-2 algorithm of SWAT-CUP. Calibration and validation were done at monthly time step for river flow and total sediment yield at Bui and Chache, respectively. Due to lack of long term data of good quality, calibration of flow was limited to 6 years (1995-2000) while that of total sediment yield was from 2000 to 2004 (5 years). Validation of flow was for 5 years (2002-2006) and for sediment, 3 years (2005-2007). The calibrated SWAT model was driven with three RCM/GCM pairs (RCA4/MPI-ESM-LR, RACMO22T/ICHEC-EC-EARTH and RCA4/CanESM2) of downscaled rainfall and temperature data analyzed in this study. The model was also driven with the ensemble mean values of the RCM/GCM pairs. The RCM/GCM data were obtained from the CORDEX archives and consisted of data forced by two IPCC emission scenarios- Representative Concentration Pathways (RCPs) 4.5 and 8.5 for two future time slices: 2051-2075 - representing the late 21st century (the 2060s) and 2076-2100 - representing the end of the 21st century (the 2080s). The period 1984- 2010 was set as the baseline. The sensitivity of streamflow and sediment yield to changes in LULC in the BVRB was assessed based on the basin’s LULC maps of 1990 and 2000. The SWAT model results showed that the curve number (CN2) and canopy storage (CANMX) were, respectively, the most and least sensitive model parameters, with respect to streamflow. The model performance in reproducing monthly streamflow and sediment yield of the basin during calibration was rated as “good”. The Nash-Sutcliffe efficiency (NSE), coefficient of determination (R2), percent bias (PBIAS) and root mean square error (RSR) values for streamflow calibration were 0.85, 0.86, 8.1% and 0.38 respectively. Sediment calibration results yielded NSE of 0.68, R2 of 0.74, PBIAS of 27.5% and RSR of 0.59. In general, the model validation results were “satisfactory” for both flow and sediment yield. The NSE, R2, PBIAS and RSR values for streamflow validation were 0.60, 0.62, 20.1% and 0.64 respectively while that for sediment yield were 0.66, 0.74, 39.1% and 0.59 respectively. The p- and r-factor values for the model calibration and validation indicated that low levels of uncertainties existed in the model results. The projected precipitation over the basin by the ensemble members of the models showed a mixed pattern of positive and negative trends. However, both the positive and negative future trends in the rainfall were statistically non-significant. Analyses of the average annual, intra-annual and seasonal precipitation indicated high uncertainty regarding the direction of the future rainfall. Mean annual precipitation change for the late 21st century ranged between -16% and +6% under the RCP4.5 scenario and between -27% and +14% under the RCP8.5 scenario. The end of the 21st century projections showed changes in mean precipitation amounts ranging between -23% and +2% and between -33% and +13% under the RCP4.5 and RCP8.5 scenarios, respectively. With regards to temperature, average annual projections by the ensemble runs showed increases over the basin under both RCP scenarios and for both time periods. Warming over the basin is projected to be higher under the RCP8.5 scenario than under the RCP4.5 scenario, with the end of 21st century period being warmer than the late 21st century. Average annual mean temperature increase across the model run ranged between 2.2oC and 2.6oC under the RCP4.5 scenario and between 3.5oC and 3.7oC under the RCP8.5 scenario for the end of the 21st century. Analysis of dry - (November to March) and wet - (August to October) period streamflow and sediment yield showed mainly increases for the 2060s and 2080s under both scenarios. The model runs also projected increases in mean annual streamflow and sediment yield for the basin. The change in streamflow is projected to range between +40% and +42%, and between +100% and +143% for sediment yield during the late 21st century under the RCP4.5 scenario. For the end of the 21st century, the projected change ranges between -6% and +78% while sediment yield is between +100% and +216%. Under the high emission RCP8.5 scenario, streamflow is projected to range between +48% and up to +148% across the models. For sediment yield the projected change ranges from +249% to +335%. The end of century projections of flow is between +69% and +243% while total sediment ranges between +358% and 412% across models. Analysis of the trends in the future annual flow and sediment yield indicated that the increasing trends observed are statistically significant at the 5% level of significance. Sensitivity analysis of streamflow in the basin based on a 10-year land use/land cover change showed statistically insignificant changes. 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 2017-07-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/291 Impacts of Climate Change on Water Resources in Lake Guiers, Senegal Djiby, Sambou Lake Guiers is a shallow reservoir located in the north-western part of Senegal. Its water is used both for irrigating crops and as a drinking water resource for urban centres, including Dakar, the capital of Senegal, as well as for the local population and animal herds. During the last three decades, increasing population, changing patterns of water demand has pressurized Lake Guiers's freshwater resources. To address the challenges that climate change and population growth poses in Lake Guiers water resources, it is necessary to consider its potential impacts on di erent dimensions of water resources. Therefore, this research aim to assess recent and future patterns on climate and future water situation (water availability and demand) in Lake until 2030. To achieve the objectives of this research, Lake Guiers climatic simulations based on the representative concentration pathways (RCPs) 4.5 and 8.5 has been analyzed and future water availability and demand has been modeled under scenarios of climate change and population growth by applying the Water Evaluation And Planning System model (WEAP). The results show that the basin of Lake Guiers experiences an increase of temperature of about 1, 2 C and an elevated warning, leading to signi cant increase of atmospheric water demand is projected. In addition an increasing trend in precipitation (+6.1mm/year) has been observed from 1988-2011 and precipitation projections reveal changes an increase trend ranging between 5 and 48% in Lake Guiers area in the near-future (2050s). However, at the end of the century (2100s) an decrease of precipitation for RCP 4.5 and RCP 8.5.scenarios is projected. The changes in evapotranspiration mostly follow those from the mean precipitation and temperature with more evapotranspiration during the near future and decrease in the late century. In terms of water availability and demand, water stored in the reservoir (Lake Guiers) will be su cient when all projects are implemented however, the pressure on Lake's water resources will increase, leading to greater competition between agriculture and municipal demand sites. Decreasing in ows scenario via taouey canal due to climate change will aggravate this situation. 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 2017-08-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/290 Multi-Model Evaluation of Blue and Green Water Availability under Climate Change in Four-Non Sahelian Basins of the Niger River Basin Badou, Djigbo Félicien A proper estimation of future water availability is vital information for water planners. However, most contemporary quantitative hydrological predictions are mostly streamflow-centred which makes them fundamentally uncertain. Since, total streamflow represents only 35% of the total incoming rainfall at the global scale and even less than that in regions like West Africa, an alternative of using soil moisture and evapotranspiration is a possibility. This study explored these alternative avenues for more accurate hydrological prediction. From a theoretical perspective, water resources were treated as blue water (BW, sum of streamflow and deep aquifer recharge) and green water (GW, sum of actual evapotranspiration and soil moisture). The theoretical aspect also addressed the uncertainties associated with the use of a single hydrological model and adopted a multi-model evaluation instead. This theoretical framework was applied to the Benin Portion of the Niger River Basin, a conglomerate of four understudied and poorly gauged basins, Coubéri, Gbassè, Yankin, and Kompongou. This area provides a number of ecosystem services whose sustenance requires better hydrological knowledge. To this purpose, four objectives were addressed in order to assess the impact of climate change on future BW and GW availability in the study area. The first objective was to identify within a set of hydrological models the most suitable ones to better simulate streamflow and soil moisture. The performance of four hydrological models (HBV-light, UHP-HRU, SWAT and WaSiM) to simulate daily streamflow and the ability of three of these models (UHP-HRU, SWAT and WaSiM) to reproduce daily remotely-sensed soil moisture dynamic were compared. The results showed that none of the hydrological models clearly outperformed the others in the simulation of streamflow in all the basins. While WaSiM was the most suitable to simulate streamflow in the Yankin and Kompongou basins, HBV-light was the best for the Coubéri and Gbassè basins. However, regardless of the basin, UHP-HRU was the most adequate model to simulate soil moisture. The second objective dealt with the downscaling of three regional climate models outputs (HIRHAM5, RCSM, and RCA4) under RCP4.5 and RCP8.5 for the historical period (1976-2005) and the future (2021-2050). To this end, the Statistical DownScaling Model (SDSM) was used. The results suggested that rainfall will increase (1.7 to 23.4%) for HIRHAM5 and RCSM under both RCPs but will show mixed-trends (-8.5 to 17.3%) for RCA4. Mean temperature will also increase (-0.1 to 0.48°C) for HIRHAM5 and RCSM but decrease for RCA4 (-0.37 to 0.1°C). On the basis of the results of the two previous objectives, the third objective was to quantify the future BW only with the models found robust to simulate streamflow and future GW solely with the models found suitable to simulate soil moisture. It was found that GW will increase in all the four investigated basins while BW will only increase in the Kompongou basin. The last objective was about the quantification of the overall uncertainty associated with the evaluation of future BW and GW. This was done by computing the inter- quartile range of the total number of model realizations for each basin. The results show that BW evaluation is associated with larger uncertainty than GW quantification. To cope with the projected decrease in BW that could adversely impact livelihoods and food security of the local population, some recommendations for the development of adequate adaptation strategies including the rational use of BW are briefly discussed. 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 2016-09-01T00:00:00Z