PROJECTION ANALYSIS OF DROUGHTS CHARACTERISTICS AND CLIMATE EXTREMES OVER WEST AFRICA USING RCA REGIONAL CLIMATE MODEL

Abstract

The impacts of climate change and extreme climate events are now a major concern globally, especially in West Africa, where human exposure and vulnerability to climate extremes are high. Formulating reliable policies to adapt to these climate change and extreme events requires an understanding of the impacts at regional and national levels. This study presents projected drought characteristics and climate extremes over West Africa by using Standardized Precipitation Index (SPI; precipitation-based index), Standardized Precipitation Evapotranspiration Index (SPEI; climatic water balance-based index), Consecutive Wet Days (CWD) and Consecutive Dry Days (CDD). The datasets used is simulated daily maximum and minimum temperature and rainfall of Rossby Center for Atmospheric Regional Model (RCA) covering periods of 1976-2005 and 2011- 2100 obtained from the Coordinated Regional Climate Downscaling Experiment (CORDEX) archive. RCA model performance evaluation over West Africa was done using the Climate Research Unit (CRU; version 4.01) datasets, and the correlation between SPI and SPEI was also examined using six stations (two from each agro-climatic zone) using the historical period (1976- 2005). The results show that RCA4 reproduce West African climate pattern well and higher correlation exist between the climatic variables of CRU and RCA datasets. A strong correlation exists between SPI and SPEI that increases with time scale and decreases with latitude at a 95% confidence level. SPI and SPEI at 3-, 6-,and 12-months projects a distinct humid period that will occur from 2011 till early 2060s and dry period from early 2060s till the end of the century under RCP4.5 and 8.5 with the later more severe as a consequence of exceeding global warming level (GWL) of 2℃ by the end of 2050 decade. The projection of drought characteristics shows an increasing trend and noticeable change in the area to be affected with time. Drought duration projected to increase from 2011 till 2100 with the duration of 12-months timescale greater than 6- vi months timescale and 3-months timescale by 2071-2100. While the coastal area and its extension projected to experience shorter drought duration under RCP4.5 and RCP8.5 by both SPI and SPEI from 2071-2100, a noticeable longer drought duration will prevail over the northern part. Likewise, both SPI and SPEI under RCP4.5. Under RCP4.5, northern and western parts of West Africa were projected to have higher drought intensity from 2071-2100 and 2041-2071 by SPEI and SPI, respectively. Also, South of 12oN projected by SPI to have drought intensity between 1.2-1.6 compared to the north of it by 2071-2100 and may further extend to 16oN at 12-months timescale under RCP8.5. Annual consecutive wet days projection shows a decreasing trend while annual consecutive dry days projected to increase over West Africa under RCP4.5 and RCP8.5. The discrepancies between SPEI and SPI projection and robustness of SPEI necessitate a combination of the two indices to overcome the underestimation of drought magnitude in mitigating and quantifying impacts of future drought risk. This study result can be applied in decision making to choose and implement timely autonomous and planned adaptation and mitigation strategies (such as reducing greenhouse gases, avoiding deforestation, increasing bio-energy usage and increasing CO2 capture and usage) for future droughts and climate change occurrences in West Africa.