Browsing by Author "Egbebiyi, Temitope Samuel"

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    Future changes in extreme rainfall events and African easterly waves over West Africa
    (2016) Egbebiyi, Temitope Samuel; Abiodun, Babatunde Joseph
    This study examines the relationship between African Easterly Waves (AEWs) and extreme rainfall events over West Africa, and investigates how climate change could alter this relationship in the future. Satellite observations, reanalysis data, and regional climate model (RCA4) simulations (forced with eight global climate simulations) were analysed for the study. The study used the 95th percentile of daily rainfall as a threshold to identify extreme rainfall events, and applied spectral analysis to extract 3-5 days and 6-9 days AEWs from 700hPa meridional wind component over West Africa. The capability of RCA4 to reproduce the rainfall climatology, extreme rainfall events, the characteristics of AEWs and the contribution of AEWs to extreme rainfall events over the region during the past climate (1971-2005) was examined and quantified using statistical analysis. The future changes (2031-2065) in these parameters were projected for the RCP4.5 and RCP8.5 climate-change scenarios. The results of the study show that RCA4 gives a realistic simulation of the West African climate, including the annual rainfall pattern, the structure of AEWs, and the characteristics of the African Easterly Jet that feeds AEWs. The bias in the simulated threshold of extreme rainfall is within the uncertainty of the observed values. The model also captures the link between the structure of AEWs and the rainfall pattern over West Africa, and shows that the percentage contribution of AEWs to extreme rainfall events over the region ranges from 20 to 60%, as depicted by reanalysis data. For the RCP4.5 and RCP8.5 scenarios, the RCA4 ensemble mean projects a future increase in annual rainfall and in the frequency and intensity of extreme rainfall events over the sub-continent, but the increase is generally higher for the RCP8.5 scenario. It also projects a decrease in the frequency of rain days, no changes in the structure of the AEWs, and an increase in the variance of the waves. However, the simulations from the ensemble mean shows no substantial changes in the contribution of AEWs to the extreme rainfall events, suggesting that the increase in the frequency and intensity of the extreme rainfall events may not be attributable to the changes in AEWs. The study's application is in understanding and mitigating the future impact of climate extremes over West Africa.
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    Spatio-temporal effects of projected climate on future crop suitability over West Africa
    (2020) Egbebiyi, Temitope Samuel; Crespo, Olivier; Lennard, Chris
    Future climate is projected to deviate from present-day by unprecedented measure, hereafter climate departure, with direct consequences on food security. West Africa, one of the hotspots for climate departure globally, has suffered significantly from climate change impacts via extreme events with large impacts on food production. A better understanding of the impact of climate departure on crop growth suitability and planting season is still unknown and is highly needed in West Africa, owing to its high vulnerability and low adaptive capacity. This thesis developed a methodology aimed at defining the cropping system to investigate the projected timing of climate departures from historical variability and their impact on crop growth suitability over West Africa. For the study we used 4 statistically downscaled Global Climate Models, GCMs at station level for the period 1951- 2100 under RCP8.5 across the three AgroEcological Zones (AEZs) of West Africa for eight crops, cassava, maize, mango, orange, pearl millet, plantain, pineapple and tomato. Climate variables minimum mean monthly temperature and total monthly precipitation were used as input crop suitability model, Ecocrop to develop a new approach to define and characterise cropping systems departure from their normal regime, called crop-climate departure (CCD), to better understand the timing of future changes in crop suitability. Also, the concept of CCD was defined, tested and applied in West Africa for five different crops types, using 10 GCMs downscaled by regional climate model, RCA4 as input into crop suitability model Ecocrop. The downscaled GCMs were also employed to examine the impact at the different global warming levels, 1.5, 2.0 and 3.0oC on crop suitability over West Africa. Using the GCMs at station level, we develop the concept of crop-climate used in characterizing the suitability of different crop across the three AEZs of West Africa. The result highlights the constraint, a reduction in suitable area, of growing cassava and pineapple only in the Guinea zone by mid and end of century. In contrast, there is an observed and projected opportunity, increase in suitable areas, of growing maize in southern Sahel by the end of the century while mango remains suitable across the three West African AEZs. The application applying the concept crop-climate departure on different crop types showed in decrease suitable areas for most crops by the end of century with horticultural, cassava and cereals respectively are the crops mostly affected. The changes in crop-climate relationship suggests a future constraint in crop suitability could be detrimental to future food security over West Africa. Finally, our findings from the impact of different global warming levels, 1.5. 2.0 and 3.0oC highlights the potential of sustained suitability for all the crops and improved food security under 1.5oC global warming for all the six crops but a contrast under 3oC over West Africa except for cowpea and groundnut. Our findings for cowpea and groundnut showed an increase suitable area into the southern Sahel with increasing global warming level. The study holds great value at regional scale where improved preparedness and regional cohesion could make the difference in making decision for a food secure Africa. Further studies to explore associated short and long-term adaptation options to changes in crop-climate relationship are recommended.