http://197.159.135.214/jspui/handle/123456789/11 2026-06-24T14:00:16Z 2026-06-24T14:00:16Z Gaba, Olayèmi Ursula Charlène http://197.159.135.214/jspui/handle/123456789/293 2021-08-05T13:10:39Z 2016-01-01T00:00:00Z

Title: Improvement and comparative assessment of a new hydrological modelling approach to catchments in Africa and the USA Authors: Gaba, Olayèmi Ursula Charlène Abstract: 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. Description: 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 Badjana, Hèou Maléki http://197.159.135.214/jspui/handle/123456789/289 2021-08-05T13:10:39Z 2015-01-01T00:00:00Z

Title: River Basins Assessment and Hydrologic Processes Modeling for Integrated Land and Water Resources Management (Ilwrm) in West Africa Authors: Badjana, Hèou Maléki Abstract: The integrated assessment of river basins based on a holistic system analysis approach is of high relevance for sustainable water resources management. In this study, the climate variability especially rainfall patterns and land use changes were analyzed and assessed between 1950-2012 and 1972-2000 respectively in the Kara River basin (Togo and Benin). Then, the catchment hydrologic characteristics and its rainfall-runoff dynamics were assessed. The methodological approach consisted in fitting statistical distributions to annual maximum rainfall, cumulative annual rainfall and annual number of rainy days for climate variability analysis. To assess changes in land cover, an object-based image analysis approach combined with GIS techniques were used. Catchment characteristics and its runoff generation mechanism were assessed using statistical methods and hydrologic models (the lumped conceptual metric model IHACRES and the distributed model J2000). The results show no significant trend in annual maximum rainfall except at two locations with decreasing trend. The cumulative annual rainfall is decreasing while annual number of rainy days is increasing except at one station. The results also reveal that annual maximum and annual total rainfall which depend on West African monsoon dynamics are highly likely to be also influenced by local relief and topography. It is also evident that the peak of the rainy season shifted from September to August since the 1980s. Also there has been a drought from 1970s which was intensified in 1980s leading to the shift in isohyets downwards all over the basin. From 1990s to 2000s, there has been an increasing trend but the amount of rainfall received still remains less than that of 1960s over the basin. The results also indicate that the basin has experienced important changes with significant decrease in natural vegetation. Agricultural expansion and deforestation appear to be the dominant driving forces. In fact, agricultural land has doubled between 1972 and 2000 by increasing from 19% to 43% of the total basin area while savannah decreased from 63% to 45%. Forest land increased by 1.6% from1972 to 1987 but showed a decrease of 6% from 1987 to 2000, while woody savannah decreased by 3.4% and human settlements increased during the same period. Changes occurred between 1987 and 2000 were found to be very important in comparison to the period between 1972 and 1987. The same analysis in the neighbouring Binah River catchment between 1972 and 2013 revealed the similar changes with agriculture expansion as the dominant driving force. The assessment of catchment characteristics and its rainfall-runoff dynamics reveal that the three nested sub-catchments that constitute the basin have similar rainfall-runoff dynamics and the runoff generation processes, i.e. volume and timing, are controlled by topographic gradient, soils, geology and rainfall distribution. The two models was calibrated and validated for the basin and its sub-catchments and, modelling results indicate that the two models simulate discharge volume and timing for the given period adequately. Results further indicate that runoff generation mechanism is dominated by interflow and saturation excess overland flow and the runoff response to rainfall is very sensitive to climate and land cover changes. It is also shown that combining IHACRES and J2000 modelling is efficient in reproducing the basin hydrology, but also that applying a calibrated process-driven model offers the potential to assess climate and land management impacts on water resources for their sustainable management. Moreover, a river basin information system containing available data and the first results was established in order to facilitate the access and sharing of information and data for decision making but also support future research. This study, which is a first direct assessment of the basin, provides for not only the basin but also other sub-catchments of the Volta basin and in general in West Africa, good information and guidelines for the integrated land and water resources management (ILWRM), an appropriate approach to strive for sustainable management of water resources and to adapt to global change impacts. Description: 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

2015-01-01T00:00:00Z Mbaye, Mamadou Lamine http://197.159.135.214/jspui/handle/123456789/288 2021-08-05T13:10:39Z 2015-10-01T00:00:00Z

Title: Assessment of Climate Change Impact on Water Resources in the Senegal River Basin at Bakel Authors: Mbaye, Mamadou Lamine Abstract: In this study we assess the impact of climate change on water resources by using uncorrected and bias corrected data from the regional climate model REMO simulations over the Senegal River Basin (SRB). Both simulations were used as input of the Max Planck Institute for Meteorology – Hydrological Model (MPI-HM) over the Upper Senegal Basin (USB). Applying the bias correction simulations of present day climate (1971-2000) substantially improved for both temporal and spatial variations of the analyzed climate parameters (precipitation, temperature) when compared to interpolated gridded observations and station data. Additionally, the bias corrected input give better representation of the mean river flow, the low flows (10th percentile) and the high flows (90th percentile) at the outlet of the USB. For the future, the regional climate model projections for precipitation show a general decrease by the end of 21st century (2071-2100) for both scenarios (Representative Concentration Pathways RCP4.5 and RCP8.5) and datasets in the majority of the basin, except the Guinean highlands where a slight increase is found. In case of the potential changes of the maximum consecutive number of dry days and wet days, the northern basin is likely to face the most pronounced increase of dry days and decrease of wet days, although a slight increase of heavy rainfall is found with similar spatial patterns in both data. Higher decadal variability of the maximum 5-day precipitation with the uncorrected data in RCP8.5 is projected, while uncorrected and bias corrected data depict similar temporal variability for extremely wet days. Furthermore, a general temperature increase is projected over the entire basin for both scenarios, but more pronounced under the RCP8.5 scenario. Warm night’s percent is found to be higher than warm day’s percent. As for the potential changes of the basin’s hydrology, a general decrease of river discharge, runoff, actual evapotranspiration, soil moisture is found under RCP4.5 and RCP8.5 in all simulations. The decrease is higher under RCP8.5 with uncorrected data in the northern basin. However, there are some localized increases of runoff in some parts of the basin (e.g. Guinean Highlands). Furthermore, the available water resources are projected to substantially decrease by more than -50% in the majority of the basin for all data, except the southern basin in Guinea where no change is projected. The impact of the bias correction on the projected climate change signal, affects mainly the magnitude of the signal rather than its direction of change although some modifications may occur in particular months and localities. Description: 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

2015-10-01T00:00:00Z Oyerinde, Ganiyu Titilope http://197.159.135.214/jspui/handle/123456789/287 2021-08-05T13:10:39Z 2016-01-01T00:00:00Z

Title: Climate Change in the Niger Basin on Hydrological Properties and Functions of Kainji Lake, West Africa Authors: Oyerinde, Ganiyu Titilope Abstract: The Niger River Basin - home to over 100 million people - is a vital and complex asset for West Africa. Since the 1970s, the basin has been characterized by hydro-climatic changes with significant impacts on water resources. Climate change could potentially have large impacts on water availability in the basin, but its effective simulation is hampered by inadequate and diminishing number of reliable observation stations. Climate simulations in the basin have also been difficult to handle with existing models due to the complexity and diversity of processes to be represented. No consistent trend for either decreasing or increasing precipitation emerged from global climate model (GCM) products. Countries in the Niger River basin (West Africa) are planning to invest millions of dollars in the expansion of hydropower in the nearest future. With the impacts of climate change in the basin already occurring, there is a need to comprehend the influence of future hydro-climatic changes on water resources and hydro-power generation in the basin. This thesis integrates opinions of local populations with scientific approach in the evaluation of impacts of climate change on water resources in the Niger basin. The consistency of indigenous perceptions and adaptive responses to rainfall and river discharge observations was evaluated in the Niger Basin. Socioeconomic data were collected from 239 households in 30 communities across two settlements in the Niger basin. Historical data on rainfall and river discharge from 1950-2010 were analyzed and agreement with local perceptions assessed. Future climate trends were assessed with 8 GCMs and two emission scenarios (RCP4.5 and RCP8.5) from the Coordinated Regional Downscaling Experiment (CORDEX - CMIP5) framework. Future trends (2010-2100) and influence of bias correction on projected climate patterns from the 8 GCMs were also evaluated. Consequently, a hydrological model was adapted and used to evaluate impacts of climate change on runoff under present and future conditions. To determine impacts of climate change on hydropower production, a hydro electricity model based on gauged observations from the largest hydroelectricity dam (Kainji) in the Niger basin was developed. There was close agreement between observations and perceptions. Indigenous perceptions gave good indication of the most vulnerable sectors as well as communities who displayed the greatest willingness to combat climate change. Climate change will drive about 5-10% ensemble median increase in precipitation with high spatial variability in the Niger basin. Larger parts of this increase in precipitation will be experienced in the Sahelian region. Close GCM agreement on projected precipitation pattern shows great confidence in the CMIP5 projected precipitation pattern across the Niger basin. Bias correction improved the quality of rainfall projections from the 8 GCMs by improving their fitness to the observed. Means of 0.74(NSE), 0.92(d), 0.80 (md), 0.89(r), 0.79(R2) and 0.76(KGE) were recorded for climatological comparison between GCMs and satellite modeled observed precipitation before bias correction while means of 0.86(NSE), 0.97(d), 0.86 (md), 0.93(r), 0.87(R2) and 0.92(KGE) were witnessed after bias correction. The improved IHACRES hydrological model presented in this thesis showed high suitability for the basin based on recorded high calibration (0.73(NSE), 0.92(d), 0.74 (md), 0.85(r), 0.73(R2) and 0.81(KGE)) efficiency coefficients. Climate change will drive increase in precipitation, temperature, PET on the Niger basin and runoff at Kainji and Malanville. Close GCM agreement on projected increasing runoff pattern in the basin shows great confidence in the modeling framework presented in this study. The invented hydropower model displayed high calibration (0.81(NSE), 0.94(d), 0.81 (md), 0.95(r), 0.90(R2) and 0.75(KGE)) efficiency coefficients between observed and simulated Kainji lake reservoir level which gives great potential for its applicability in the basin. Climate change will drive about 50MW (RCP4.5) and 100MW (RCP8.5) ensemble median annual average increase in hydropower production in the Niger basin. This potential could be positively exploited by expanding water storage for hydropower production, in parts of the basin where there will be significant increase in discharge as witnessed upstream the Kainji lake. Description: 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