WASCAL Scholar Collection:

Influence of the Quasi-Biennial Oscillation on Rainfall Producing Systems over West Africa

Sun, 01 Sep 2019 00:00:00 GMT

Title: Influence of the Quasi-Biennial Oscillation on Rainfall Producing Systems over West Africa Authors: Ballo, Abdoulaye Abstract: Rainfall is a major ingredient for economic development for most West African countries. It has serious implications on the socio-economic activities because more than 95% of its agricultural activities are rainfed and rain-fed agriculture serves as the main source of income for most of the economies. Therefore, rainfall variability in terms of amount and time can lead to good or poor agricultural production as either too much rainfall causes floods and water logging or very little rainfall results in inappropriate agricultural planning and activities. This study used ERA-Interim reanalysis and observational GPCP v2.2 to investigate the seasonal rainfall variability and relationship with the tropospheric jets. This work focuses on the Influence of the Quasi-biennial Oscillation on Rainfall Producing Systems over West Africa. This study analyses the relationship of the sub-tropical westerly jet (STJ) with the West African monsoon and its associated tropospheric jets. The association and relative influence of the low-level West African Westerly Jet (WAWJ), the AEJ and TEJ during wet and dry situation were also examined. Results showed that the sudden appearance of the TEJ in June and the intensification of the AEJ are linked to the weakening and disappearance of the stratospheric easterly flow (QBO) and the fast poleward retreat of the STJ. A close association between the northward movements of the AEJ core and rainfall belt was found. However, no clear relationship was seen between the northward advance of the rainfall distribution and the TEJ slow movement, as this jet core always lags the rainfall maximum. By considering rainfall variability causes, results also showed that the Sub-tropical jet (STJ) retreated poleward faster while the TEJ, WAWJ and ascending motion were all stronger, resulting in higher rainfall during wet years than dry. Furthermore, it was found that the so-called monsoon jump and the reversal of the shape of the monsoon layer both occur in May/June and that this may be linked to the weakening of the QBO and the sudden poleward retreat of the sub-tropical jet in the same months. The influence of stratospheric quasi-biennial oscillation (QBO) on the African Easterly Jet, Tropical Easterly Jet and West African precipitation was investigated through simulations using the Global Climate Model (GCM) using the Coupled Models Intercomparison Project Phase 5 (CMIP5). The performance of the CMIP5 models in reproducing the quasi-biennial oscillation was evaluated while the influence of the QBO on West African rainfall precipitation was studied using wavelet analysis over each zone of region (Sahel, Savannah, Guinea). Also, the composite of the effect during QBO and non-QBO years as well as of the QBO phases on rainfall variability were studied. The results show that all the models capture the general structure of the QBO but with some biases while HadGEM2-CC produced results closer to observation (ERAINT). It was also found that there is good coupling between QBO and precipitation over all zones of West Africa. The wavelet coherence analysis gives confirmation of the results. From this study it is concluded that the quasi-biennial oscillation has an important influence on West Africa precipitation that could lead to improved rainfall prediction over West Africa. Description: A Thesis submitted to the West African Science Service Center on Climate Change and Adapted Land Use and Université Joseph KI-ZERBO, Burkina Faso in partial fulfillment of the requirements for the Master of Science Degree in Informatics for Climate Change

Potential of Wind and Solar Energy Gerneration over West Africa in a Changing Climate

Sun, 01 Sep 2019 00:00:00 GMT

Title: Potential of Wind and Solar Energy Gerneration over West Africa in a Changing Climate Authors: Windmanagda, Sawadogo Abstract: Many West African countries are plagued with a poor electricity supply. However, an abundance of solar irradiance and sufficient wind speed over the region makes solar and wind energy attractive solutions to the problem, but there is a dearth of information on how ongoing global warming may alter the solar energy potential and wind power density over the region in the future. Moreover, there is a lack of information on how accurately numerical weather prediction models simulate the shortwave radiation flux over the region. This study thus investigates, on the one hand, the impact of climate change on photovoltaic power generation potential (PVP) and on wind power density (WPD) over West Africa under various global warming levels (1.5°C; 2.0°C; 2.5°C and 3.0°C) under the RCP8.5 climate change scenario. On the other hand, this study assesses the shortwave radiation flux over West Africa. For the PVP study, fourteen regional climate model simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX) were analysed. Eleven multi-model multi-ensemble simulation datasets, also from the CORDEX project, were analysed for the WPD study. The model simulations for the reference climate (1971-2000) were compared with surface wind speed from weather stations data: Accra (1986 - 2000), Bobo-Dioulasso (1986 - 2016), Ouagadougou (1986 - 2016) and Tamale (1986 - 2000) and two examples of reanalysis data (ERA-INTERIM and ERA20C). In addition, this study also investigated how the Weather Research and Forecasting (WRF) model radiation schemes (Cam, Dudhia, Goddard, New Goddard and rrtmg) simulate the surface downwelling solar radiation (Rs) over West Africa. We modified the Dudhia shortwave radiation physics by making the water vapour absorption varies with temperature and pressure according to levels. Furthermore, we run a short-term simulation (one-year) with WRF different shortwave radiations schemes and a long-term simulation (thirty-years) with the WRF Dudhia shortwave radiation scheme and the modified one. All the WRF output were compared with satellite data (SARAH). The results show that the CORDEX simulation ensemble correctly captures the spatial distribution of climate variables (surface downwelling solar radiation, air temperature, wind speed and relative humidity) and PVP over West Africa, albeit with a few biases. The simulations and observations agree that PVP over West Africa varies from 8% along the Guinean zone to 25% over the Sahel zone and that the annual cycle of PVP is influenced by the seasonal variation of the monsoon system. The simulation ensemble projects a decrease (up to 3.8%) in PVP over West Africa in the future and indicates that the magnitude of the decrease grows with warming levels. The decrease in PVP is attributed to a decrease in Rs (solar dimming; up to 3 W/m2) and an increase in ambient temperature (up to 3.5°C) induced by global warming. A decrease in projected PVP is also projected over all the West African countries. Nevertheless, the spatial and temporal distribution of the PVP changes are more influenced by Rs changes than by Ts changes, such as at GWL1.5, an increase in PVP is projected over all zones during the rainy season when an increase in Rs is projected. A decrease in projected PVP is also projected over all the countries. Nevertheless, the maximum decrease in PVP projected over any country or zone in the region is less than 3.8% even at GWL3.0. Hence, the study suggests that ongoing global warming may have an influence on PVP over West Africa. Description: A Thesis submitted to the West African Science Service Center on Climate Change and Adapted Land Use and Université Joseph KI-ZERBO, Burkina Faso in partial fulfillment of the requirements for the Master of Science Degree in Informatics for Climate Change

Modelling the Potential Impacts of Climate Change and Variability on Electricity Demand in Republic of Niger

Sun, 01 Sep 2019 00:00:00 GMT

Title: Modelling the Potential Impacts of Climate Change and Variability on Electricity Demand in Republic of Niger Authors: Bonkaney, Abdou Latif Abstract: This study investigates the potential impact of climate change and variability on electricity demand under different Global Warming Levels (GWL1.5, GWL2.0, GWL2.5, and GWL3.0). First, to assess the sensitivity of electricity demand to climate variables, the Wavelet Transform Coherence (WTC) as well as Principal Component Analysis (PCA) were used. Secondly, to establish the relationship between electricity demand and climate variables, Multiple Linear Regression (MLR) and Artificial Neural Network (ANN) models have been used. Prior to the model development, the electricity demand data was de-trended to isolate only the influence of climate variables. Thirdly, to project the impact of climate change at specific GWL, the climate data from the reference period (1971-2000) was subtracted from that of GWL period. Results show that the electricity demand (DED) in Niger is positively correlated to Temperatures (Tmean, Tmax, Tmin), Cooling Degree-Days (CDD), and Heat Index (HI) and negatively correlated with Wind Speed (WSP) and Solar Radiation (SR). However, the electricity demand is more sensitive to temperatures, CDD, HI than SR and WSP. The regression models are able to adequately predict the electricity demand with a high coefficient of determination R2 (>0.8) and a relatively low Root Mean Square Error (RMSE<150MWh/day). In addition, the residual analysis reveals that the models comply with the basics assumptions of regression models. Furthermore, the results also show that the CORDEX simulations give a realistic representation of all the necessary climate variables used to model the electricity demand in Niger. The simulations project a robust increase in electricity demand at all the GWLs over Niger and indicate that the magnitude of the projection grows with increasing GWLs. Indeed, an increase of 4-16% of DED is projected depending on the magnitude of the warming. It is also worth noting that the magnitude of changes also differs with season, with the highest increase observed in March-May (MAM) and June-August (JJA) while December-February (DJF) displayed the lowest increase. For instance, the Regional Climate Models (RCMs) ensemble median project an increase of about 18% increase in DED for MAM and JJA while for DJF season, it only projects about 5% increase at GWL3.0. In addition to the increase in mean DED, simulations also project an increase in extreme electricity demand due to the increase of extreme temperatures and heatwaves over the country at all the GWLs. The study showed that climate change will affect both mean and peak DED at all the GWLs, with the magnitude of change growing with increasing GWLs. However, the study suggests the investigation of the roles of other factors to further the research, such as population change, future energy policy, urbanization, and economic growth that may also determine the future electricity demand for more robust projections. Description: A Thesis submitted to the West African Science Service Center on Climate Change and Adapted Land Use and Université Joseph KI-ZERBO, Burkina Faso in partial fulfillment of the requirements for the Master of Science Degree in Informatics for Climate Change

Impact of Natural and Anthropogenic Aerosols on Clouds and Radiative Properties over West Africa

Sun, 01 Sep 2019 00:00:00 GMT

Title: Impact of Natural and Anthropogenic Aerosols on Clouds and Radiative Properties over West Africa Authors: Dajuma, Alima Abstract: Using a high-resolution regional climate model COSMO-ART, the impact of natural and anthropogenic aerosols loads on radiative and cloud optical properties over West Africa is assessed through sensitivity experiments. Based on a monthly climatology, model simulations compare satisfactory with wind fields from reanalysis data, cloud observations, daily average particulate matter (PM), temperature, relative humidity and satellite retrieved CO mixing ratio. However, COSMO-ART shows a slight overestimation of spatial distribution of CO mixing ratio compared to satellite observation. Regarding the atmospheric composition, COSMO-ART shows good representation with the observation of aerosol mass concentration in upwind marine and urban outflow, whereas it underestimates the observed aerosols in the regional background. Evaluating two emission inventories datasets; simulation conducted with DACCIWA emissions performed better than with EDGAR emissions for the chemistry. However, aerosols compounds are mostly underestimated by COSMO-ART except for NO3 using EDGAR inventory. Focusing on a case study of 02 July 2016, using CO as an indicator for biomass burning plume, individual mixing events south of the coast of Côte d’Ivoire due to midlevel convective clouds injecting parts of the biomass burning plume into the boundary layer were identified. Idealized tracer experiments suggested that about 20% of the CO mass from the 2–4km layer are mixed below 1km within two days over the Gulf of Guinea. Quantifying the impact of biomass burning aerosols on cloud and radiation, it is found that 27% increase of cloud droplets number concentration (CDNC) over the Gulf of Guinea and 7.5% over the whole simulated domain spatially averaged. A reduction of 50 W m-2 of surface shortwave (SW) radiation and 20 W m-2 respectively over the Gulf of Guinea (3–4ºN; 9 ºW –1ºE) and over the study domain (3–11ºN; 9 ºW –1ºE) spatially averaged for all sky conditions. The maximum increase of surface concentration for 05- 06 July 2016 case study due to biomass burning aerosols is 154 μg m-3 for CO, 27 μg m-3 for O3 and 6–7 μg m-3 for PM which agrees with WRF-CHEM simulation. Same investigation was done to quantify the impact of local source anthropogenic aerosols on clouds and radiation. 90% of the CDNC are from anthropogenic aerosols and a shift of median clouds radius from 12 to 10 μm as result of anthropogenic aerosols. Regarding the surface SW, a decrease of up to 60 W m-2 is simulated over the study domain as a result of anthropogenic aerosol. A reduction of monsoon wind speed of about 1.2 m s-1 occurred as a result of anthropogenic aerosols. The impact of future anthropogenic emissions increase is examined under two RCP 2.6 8.5 scenarios. All pollutants are projected to increase more or less, over the whole West African region except for BC which shows some decrease in Nigeria part of Ghana and Niger. Looking at local scale, coastal cities (Abidjan and Accra) is predicted to exceed the World Health Organization (WHO) with respect to NOx and O3. In conclusion, the results of this study underscore the need to investigate the impact of aerosols (anthropogenic, biomass burning) on the cloud properties and radiative budget on a longer time scales and a need for air quality monitoring over the region especially over the coastal cities. 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