Abstract
This paper examined future trends with change detection in temperature and rainfall over three agro-climatic zones of West Africa. Historical (1961–2000) and projection (2020–2099) data of ensemble-mean of six RCMs that dynamically downscaled five GCMs that participated in CMIP5 obtained from Co-Ordinated Regional Climate Downscaling Experiment (CORDEX) were used. Standard normal homogeneity, Buishand’s, Pettitt’s, and Mann–Kendall test were used for change point detection and trend analysis at 5% significant level. Inter-annual anomaly and projected change in the seasonal cycle relative to historical mean were investigated. The ensemble-mean evaluation performed for the historical period (1961–2000) using CRU dataset revealed that the change point occurred in rainfall and temperature series in the 1970s and 1980s, while a significant increasing trend is observed in temperature in all climatic zones. Change-point detection test projects rainfall series to be homogeneous as significant change point is expected to occur in temperature for all zones under RCP4.5 and RCP8.5 for near (2020–2059) and far-future (2060–2099). For the near-future, an increase in the mean temperature between 0.5–1.30 ℃ and 0.19–1.67 ℃ is projected to occur under RCP4.5 and RCP8.5 respectively. Projected relative change in seasonal cycle shows that winter months may witness increase in rainfall amounts under RCP4.5 but significantly dry under RCP8.5 in near and far-future as temperature is expected to become warmer in all months. Rainfall anomaly projects the Sahel to have a reduced amount of rainfall compared to other zones as temperature anomaly reveals a continuous increase in all the zones under the two RCPs. The results of this study show that climate change will intensify in West Africa in the future.
Highlights
Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) projected a continuous increase in global temperature (IPCC 2007a) as a result of: increasing fossil fuel combustion and greenhouse gases (GHG) emission, significant changes in land-use/land-cover due to industrialization and urbanization and natural processes like earthquake (IPCC 2007b)
This helps to understand the capability of the ensemble mean in replicating seasonal distribution of temperature and rainfall and how it captured temperature and rainfall amplitudes and phases over the three climatic zones compared to Climate Research Unit (CRU) observation
The change point noticed from the CRU and ensemble mean agreed to have occurred in the 1970s and 1980s, these two decades are decades of well know drought in west Africa (Le Barbé et al 2002; Lebel and Ali 2009; Nicholson 2013) that resulted in significant low rainfall amount
Summary
Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) projected a continuous increase in global temperature (IPCC 2007a) as a result of: increasing fossil fuel combustion and greenhouse gases (GHG) emission, significant changes in land-use/land-cover due to industrialization and urbanization and natural processes like earthquake (IPCC 2007b). Non-parametric test such as Pettit’s test (Mauget 2003; Yu et al 2006), Standard Normal Homogeneity (GonzalezRouco et al 2001; Stepanek et al 2009) test, Buishand’s range test (Buishand 1982; Jaiswal and Lohani 2015) and Mann–Kendall trend test (MK; Kendall 1975; Wang et al 2005; Karmeshu 2012) used in this study have the capability to identify an abrupt change and gradual trend superimposed on a climate variables These tests have been widely used to detect change point and examined the trend in series of hydro-climatic variables like temperature, rainfall, wind speed, humidity and sunshine hour (Salarijazi et al 2012; Sivakumar et al 2012; Jaiswal and Lohani 2015; Emmanuel et al 2019; Ajayi and Ilori 2020). The Pettit’s test, SNHT, Buishand’s range test, and MK trend test were used and performed over the three homogeneous agro-climatic zones of West Africa
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