http://197.159.135.214/jspui/handle/123456789/977 2026-04-23T15:09:38Z 2026-04-23T15:09:38Z Nikiema, Pinghouinde Michel http://197.159.135.214/jspui/handle/123456789/1055 2026-02-13T10:14:46Z 2016-06-01T00:00:00Z

Uncertainties in Global and Regional Climate Change Projection of Summer Monsoon Temperature and Precipitation over West Africa Nikiema, Pinghouinde Michel This study aims at investigating climate change scenarios over West Africa with the associated uncertainties to improve the value of climate information to end-users for informed decision making. For the present day (1982-2005), the mean climatology, intermodel variability and spatio-temporal patterns of temperature and precipitation over West Africa from CMIP5, CMIP5_SUBSET (ensemble of GCMs driving CORDEX) and CORDEX multimodel ensembles (MMEs) were first evaluated and intercompared for the monsoon season (June-September). While CORDEX failed to outperform the simulated mean climatology of temperature by the CMIP5 ensembles, it substantially improved precipitation and provided more realistic fine-scale features tied to local topography and landuse. This improved performance over the region depend more on the internal models physics than the driving boundary conditions and results from a more consistent and realistic simulation of monsoon precipitation across the various Regional Climate Models (RCMs). Rotated Empirical Orthogonal Function (REOF) analysis indicated that the CORDEX ensemble captures better the spatio-temporal variability of both temperature and precipitation (first REOF mode), in particular depicting the warming and Sahel precipitation recovery in recent decades over West Africa. On the other hand, the spatial patterns and associated time series of the last two REOF modes in CORDEX mostly follow the CMIP5_SUBSET pointing towards a strong role of the boundary forcing in the RCM simulation of precipitation variability. For the future climate 2070-2099 relative to 1976-2005, a Bayesian model was applied to the three sets of models (CMIP5, CMIP5_Subset and CORDEX) and PDFs of Temperature and precipitation change for two sub region (Sahel and Guinea Coast) were derived. For temperature change over the Guinean Coast, CMIP5_S models under RCP8.5 has a lot of uncertainties showing more bias and less agreement among models but the CORDEX seems to reduce those uncertainties. Over the Sahel, only CORDEX under RCP4.5 scenario shows more agreement and less bias. CMIP5 and CMIP_S show multi modal PDF pointing out some uncertainties and less agreement among models. For precipitation change over the Guinean Coast under RCP8.5 and RCP4.5 uncertainties still remain in CORDEX model with an increasing precipitation trend for the late century. There is no significant difference on precipitation change between RCP4.5 and RCP8.5. CORDEX has a wide PDF curve under RCP4.5 and RCP8.5 scenario showing the persistence of uncertainties. Two sources of uncertainty in climate projection from CMIP5, CMIP5_Subset and CORDEX were also examined for temperature and precipitation. An ordinary least square was used to fit each decadal anomalies prediction of CMIP5, CMIP5_Subset and CORDEX with a fourth-order polynomial over the years of 2006-2099 for the two scenarios RCP45 and RCP85. The anomalies were computed with the reference period of 1976-2005. The new generation of models had an added value compare to the driving GCMs (CMIP_S) and CMIP5 MMEs by reducing the Internal and Inter Model Variability over the West African region. Inter Model Variability was the dominant source of uncertainties and is explaining up to 90 % of total uncertainty. The study conclude that for temperature under the two scenarios, the change is robust (Signal to Noise ratio greater than one) over most of West African countries with more spatial details and improved signal to noise ratio with CORDEX MMEs compare to CMIP5 and CMIP5_S MMEs. Over West Africa, CORDEX under RCP4.5 has a signal to noise ratio greater than one with an increasing trend of precipitation while the noise dominates the signal under RCP8.5, in CMIP5, CMIP5_S and CORDEX. An assessment of climate change information over West African region needs to rely on the careful evaluation and compounded information deriving from multiple sources. Adapted Land Use and the Federal University of Technology, Akure, Nigeria, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree in West African Climate Systems

2016-06-01T00:00:00Z Olusegun, Christian Funmilola http://197.159.135.214/jspui/handle/123456789/1054 2026-02-13T09:56:36Z 2016-05-01T00:00:00Z

Simulating the Impact of Agri-Silviculture on the Future Climate of West Africa Olusegun, Christian Funmilola The study investigated the influence of agri-silviculture on the projected future climate in West Africa using regional climate model (RegCM4). The performance of the model in the representation of surface processes over West Africa was evaluated and validated. Thereafter, the future climate change over West Africa was projected using the validated model. Investigation of the influence of different percentages cover of trees/shrubs and crops on the future climate of West Africa was also examined. Eleven numerical agri-silviculture experiments with time-invariant vegetation and dynamic vegetation were used to simulate the historical and future climates of West Africa. The first three experiments simulated the historical climate of West Africa from 1979-2004 using time invariant vegetation (PRES), dynamic vegetation in a smaller Africa domain (PRESd1) and dynamic vegetation in a larger Africa domain (PRESd2). The next three experiments projected the future climate from 2029-2054 with time-invariant vegetation (FUTU), dynamic vegetation in a smaller Africa domain (FUTUd1), dynamic vegetation in a larger Africa domain (FUTUd2). The next experiments were carried out using different percentages cover of trees/shrubs and crops along Guinea Savanna zone using time-invariant vegetation (GUSAG), dynamic vegetation in a smaller Africa domain (GUSAGd1) and larger Africa domain (GUSAGd2) in order to represent agri-silviculture. The last two agri-silviculture experiments were carried out along the West Africa coast using time-invariant vegetation (COAG) and dynamic vegetation (COAGd1). All future climate experiments were carried out under Representative Concentration Pathways 4.5 Scenario (RCP4.5). Model performance was evaluated by comparing historical climate simulations with gridded Climate Research Unit (CRU) datasets and Era-Interim reanalysis atmospheric data products. Generally, the historical simulation reproduces the seasonal evolution of precipitation and temperatureregimes very well with correlations greater than 0.8 but with a cold and wet bias of 1 -2°C and 1 mm/day respectively. However, a narrow monsoon flow and weaker Jets were simulated in August. Widespread warming is projected in the near future across most parts of West Africa which range from an increase of 0.5°C along the coastal and orographic regions from June to August with an increase of more than 1.5°C over the continent in other seasons. Other parts of West Africa were projected to have positive/negative changes in precipitation not exceeding 1 mm/day during the monsoon and post monsoon seasons. The impact of the different simulated agri-silviculture experiments on the future climate of West Africa varied. The GUSAG experiment induces cooling of about 0.5 - 2°C over most areas along the agrisilviculture zone (Nigeria, Ghana, Cote d’Ivoire and Cameroon, Togo, Benin Republic and Ghana) in all seasons. However, the induced cooling does not necessarily translate to more precipitation, except over Ghana where precipitation increases by 0.5 - 1.8 mm/day during MAM and JJA seasons. On the other hand, GUSAG experiment enhances the warming over Liberia and Sierra Leone by about 2°C in all seasons, which intensifies the drying condition to about 1.8 mm/day. The GUSAGd2 experiment induces cooling of about 2°C in areas within 8°E and 16°E along the agri-silviculture zone in all seasons but increases the warming by more than 0.5°C outside this area. Generally, agri-silviculture practice along the coast (COAG and COAGd1) does not necessarily have a large-scale impact on temperature and precipitation over the entire West Africa region. The study concluded that agri-silviculture could be used to mitigate the projected future warming and drying across most West African countries except Liberia and Sierra Leone. Therefore, it is recommended that agri-silviculture practice should be adopted as a land-based strategy to combat food insecurity, deforestation due to agricultural expansion and ameliorate the impacts of climate change in West Africa. Adapted Land Use and the Federal University of Technology, Akure, Nigeria, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree in West African Climate Systems

2016-05-01T00:00:00Z Naabil, Edward http://197.159.135.214/jspui/handle/123456789/1053 2026-02-13T09:46:24Z 2016-05-01T00:00:00Z

Modeling the Climate and Hydrology of the Tono Basin in Ghana, West Africa Naabil, Edward The study focused on the Tono basin in the Kessena municipality in the Upper East Region of Ghana. Due to poor data collection at the basin, there has not been any hydrological and climatic assessment of the basin. To address these challenges the study explored the potential of using a state of the art hydrological model (WRF-Hydro) in a coupled mode to assess these water resources, particularly the Tono basin in Ghana. A 2-domain configuration was chosen: an outer domain at 25 km horizontal resolution encompassing the West African Region and an inner domain at 5 km horizontal resolution centered on the Tono basin. The infiltration partition parameter (kdtref) and Manning’s roughness parameter (MannN) of the Hydrological model were calibrated to fit the simulated discharge with the observed one. The simulations were done from 1999-2007, using 1999 as a spin-up period. The results were compared with TRMM precipitation, CRU temperature and available observed hydrological data. A standalone WRF model was run for the same period to assess whether the coupled model (WRF/WRF-Hydro) provides an improvement in estimating climate variables, e.g. precipitation and temperature. Theforcing data used to drive the model runs were, ERA interim reanalysis and ECHAM6. The WRF/WRF-Hydro forced with ERA-I demonstrated a precipitation pattern of correlation with observed (TRMM) data of about 0.91 and its centered RMS error of 2.4 mm/day, whereas WRF only forced with ERA-I produced a precipitation pattern of correlation of about 0.82 and a RMS error of 3.6mm/day. For temperature, WRF/WRF-Hydro produced a pattern of correlation with observed (CRU) data of about 0.94 and a RMS error of 0.6 0C, whereas WRF-only produced a pattern of correlation of about 0.87 and a RMS error of 1.2 0C. Similar characteristics were demonstrated by ECHAM6 model data; however, ECHAM6 produced the worst results especially for the coupled approach. These variations in model performance can be attributed to the optimum physics option chosen, which may not be the optimum in the Tono basin (microscale effect) and also applying the same calibration for different models (coupled or uncoupled). The WRF-Hydro model demonstrated strong signal of streamflow estimate; with Nash-Sutcliff efficiency (NSE) of 0.78 AND Pearson’s correlation of 0.89. Further validation of model results was based on driving the output from the WRF-Hydro to a water balance model to simulate the dam levels. The model-derived dam levels were in good agreement with the observed dam levels with a correlation (R2) of 0.71. The deficiency in the modelled dam levels could be attributed to the models’ over estimation of evaporation. Regarding climate change impact on the Tono dam, two climate change emission scenarios were applied (i.e. RCP4.5 and RCP8.5). Both scenarios did not agree on the signal of change with respect to precipitation but both indicated a warmer condition. RCP4.5 indicated an annual rainfall projection increase of +7%, which implies a future increase in flows of about 14% and RCP8.5 indicated rainfall projection decrease by -9.6%, implying about 20% reduction in flows. There is therefore the need to put in place adaptation measures to ensure the sustainability of the Tono dam in the face of climate change. A Thesis submitted to the West African Science Service Centre on Climate Change and Adapted Land Use and the Federal University of Technology, Akure, Nigeria, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree in West African Climate Systems

2016-05-01T00:00:00Z Kouadio, Kouakou http://197.159.135.214/jspui/handle/123456789/164 2026-01-30T10:42:12Z 2016-06-01T00:00:00Z

Simulation of Rainfall Distribution over West Africa using Regional Climate Models Kouadio, Kouakou This research work focused on the thorny problem of the representation of rainfall over West Africa and particularly in the Gulf of Guinea and its surroundings by Regional Climate Models (RCMs). The first part of the study assessed the ability of RCMs from a set of simulations from AMMA-ENSEMBLES project in their representation of the rainfall pattern over West Africa and specifically over Cote d’Ivoire. The skills of the RCMs in the simulations for the periods 1990- 2005 was evaluated using meteorological stations data from the National Meteorology Office of Côte d’Ivoire. Time series and statistical scores are analysed. A second period (2010-2013) was used to evaluate the ability of these AMMA-ENSEMBLES simulations to predict the near future using the same ground-based observations. Furthermore, the sensitivities of Weather Research and Forecasting (WRF) Model are tested for changes in horizontal resolution (convective permitting versus parameterized) on the replication of West African Climate in year 2014 and also changes in microphysics (MP) and planetary boundary layer (PBL) schemes on June 2014. The results indicate that the skills of the RCMs vary from one station to another and from one season to another. None of the models considered presents a good performance over the entire country and during all the seasons. Generally, the ensemble mean of all the models presents better results when compared to the observations. These results suggest that the choice of any model to be used for precipitation outputs over the country may depend on the focus of interest: intensity or variability of the rain and also on the area of interest. The future climate simulated by the same RCMs for 2020-2040 over West Africa indicates an unrealistic modification of the seasonal cycle over Guinea Coast and surroundings. However, the absence of common period for the simulations driven by ERA-Interim (1990-2005) and by GCMs (from 2010) did not allow to determine the origin of this change (climate change signal or unsuitable GCMs information). The sensitivity to horizontal resolution study show Both runs at 24km and 4km (explicit convection) resolution fairly replicate the general distribution of the rainfall over West African region. The analysis also reveals a good replication of the dynamical features of West African monsoon system including Tropical Easterly Jet (TEJ), African Easterly Jet (AEJ), monsoon flow and the West African Heat Low (WAHL). Some differences have been noticed between WRF and ERA-interim outputs irrespective to the spectral nudging used in the experiment which then suggest strong interactions between scales. The link between the seasonal displacement of the WAHL and the spatial distribution of the rainfall and the Sahelian onset is confirmed in this study. The results also show an improvement on the replication of rainfall with the very high resolution run observed at daily scale over the Sahel while a dry bias is observed in WRF simulations of the rainfall over Ivorian Coast and in the Gulf of Guinea. Generally, over the Guinean coast the high resolution run did not provide subsequent improvement on the replication of rainfall. The sensitivity of WRF to MP and PBL on rainfall replication study reveals that the most significant added value over the Guinean coast and surroundings area is provided by the configurations that used the PBL Asymmetric Convective Model V2 (ACM2) suggesting more influence of the PBL compared to MP. The change on microphysics and planetary boundary layer schemes in general, seems to have less effect on the explicit runs into the replication of the rainfall over the Gulf of Guinea and the surroundings seaboard. A Thesis submitted to the School of Postgraduate Studies, in Partial Fulfillment of the Requirement for the award of the Degree of Doctor of Philosophy in Meteorology and Climate Science of the Federal University of Technology, Akure, Ondo State in Nigeria

2016-06-01T00:00:00Z