http://197.159.135.214/jspui/handle/123456789/977 2026-06-24T14:52:52Z http://197.159.135.214/jspui/handle/123456789/1250 Title: Modelling the Potential Impacts of Forestation on Extreme Climate Events over West Africa Authors: Odoulami, Romaric Christel Abstract: Previous studies on climate change projections over West Africa did not include the influence of on-going forestation activities on future climate extremes over the region. The present study aimed to examine the potential impacts of a large scale forestation activity on the future characteristics of extreme climate events (extreme rainfall and heatwaves) over West Africa using Regional Climate Models (RCMs). The specific objectives of the study were to: (i) examine RCMs ability to simulate extreme climate events over West Africa; (ii) investigate the potential impacts of climate and forestation on extreme rainfall events over West Africa; and (iii) examine the potential impacts of climate and forestation on heatwaves characteristics over West Africa. The study applied two RCMs (RegCM and WRF) to simulate the present day (PRS, 1970-2004) and the future (2030-2064) climates, with and without forestation (GHG and FRS, respectively). The simulations account for the potential impacts of forestation over the Savannah zone (8°N - 12°N) in West Africa. In this study, an extreme rainfall event is said to occur when the daily rainfall amount exceeds a threshold value (i.e. 95th percentile of the daily rainfall) and a Widespread Extreme Rainfall Event (WERE) is defined as the simultaneous occurrence of extreme rainfall that covers at least 50% of a given area. Heatwaves are identified using two metrics: the excess heat factor (EHF) and a percentile based index (TXI: 90th percentile of daily maximum temperature). The RCMs ability to simulate the characteristics of extreme events for PRS is assessed against observed datasets: the Global Precipitation Climatology Project (GPCP) and Tropical Rainfall Measurement Mission (TRMM) for extreme rainfall events analysis; and the Princeton University Global Meteorological Forcing Dataset (PGFD) for heatwaves analysis. The results show that both RCMs reproduce well the extreme rainfall threshold values (95th percentile) over West Africa and WEREs over Savannah in comparison with the observation datasets (GPCP and TRMM), though with some notable discrepancies. The RCMs generally overestimate the threshold of extreme rainfall over coastal areas and highlands, and simulated WEREs earlier than observed. For heatwaves, the two methods (EHF and TXI) generally produce similar patterns of heatwave characteristics over West Africa, except that heatwave number and days are substantially greater with TXI than with EHF. Also, the models give a realistic simulation of extreme temperature thresholds and heatwave characteristics over West Africa, although with some apparent biases. The results agree with previous studies that the Representative Concentration Pathway (RCP4.5) emission scenario would increase the frequency and intensity of extreme climate events over West Africa in future. In fact climate change would increase the frequency of extreme rainfall events over parts of the Guinea coast (and lower it over the Sahel zone), and heatwave number, days and duration over the whole region in future. The results further indicate that forestation would enhance the characteristics of extreme events over West Africa in future. Forestation generally increases the frequency and intensity of extreme rainfall events over the forested zone and decreases it elsewhere. Also, both models suggest that forestation would increase WERE frequency in parts of the Savannah zone. Similarly, forestation would also increase heatwave number and days over the forested area as the forestation would decrease surface albedo which during the dry season would increase the net solar radiation making more energy available at the surface. The outcomes of the present study suggest that the use of forestation to mitigate the impacts of climate change over West Africa might induce undesirable climatic impacts (increase in extreme rainfall and heatwave events) over some locations of the subcontinent, thereby increasing the climatic risk on human health and security. Therefore, the results of this study may guide decision makers in improving the resilience of West African countries to the consequences of climate and weather extremes and also in choosing appropriate climate change mitigation and adaptation options. Description: 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 2016-06-01T00:00:00Z http://197.159.135.214/jspui/handle/123456789/1055 Title: Uncertainties in Global and Regional Climate Change Projection of Summer Monsoon Temperature and Precipitation over West Africa Authors: Nikiema, Pinghouinde Michel Abstract: 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. Description: 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 http://197.159.135.214/jspui/handle/123456789/1053 Title: Modeling the Climate and Hydrology of the Tono Basin in Ghana, West Africa Authors: Naabil, Edward Abstract: 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. Description: 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 http://197.159.135.214/jspui/handle/123456789/164 Title: Simulation of Rainfall Distribution over West Africa using Regional Climate Models Authors: Kouadio, Kouakou Abstract: 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. Description: 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