Abstract
Increased knowledge of future changes in rainfall variability is needed to reduce vulnerability to potential impacts of global warming, especially in highly vulnerable regions like West Africa. While changes in mean and extreme rainfall have been studied extensively, rainfall variability has received less attention, despite its importance. In this study, future changes in West African summer monsoon (WASM) rainfall variability were investigated using data from two regional climate models that participated in the Coordinated Regional Climate Downscaling Experiment (CORDEX). The daily rainfall data were band-pass filtered to isolate variability at a wide range of timescales. Under global warming, WASM rainfall variability is projected to increase by about 10–28% over the entire region and is remarkably robust over a wide range of timescales. We found that changes in mean rainfall significantly explain the majority of intermodel spread in projected WASM rainfall variability. The role of increased atmospheric moisture is examined by estimating the change due to an idealized local thermodynamic enhancement. Analysis reveals that increased atmospheric moisture with respect to warming following the Clausius–Clapeyron relationship can explain the majority of the projected changes in rainfall variability at all timescales.
Highlights
Variability as used is essentially defined as the fluctuation of climate variables from the mean state, such as the deviation of temperature and precipitation at different timescales from the mean state
West African summer monsoon (WASM) rainfall variability will amplify under global warming is crucial for mitigation and adaptation strategies for climate change
The stippling in the figures represents grids where there is added value in the extreme rainfall indices from the regional climate model (RCM) compared to the indices from the driving GCMs
Summary
Variability as used is essentially defined as the fluctuation of climate variables from the mean state, such as the deviation of temperature and precipitation at different timescales from the mean state. The West African region (0–20°N, 20°W–20°E) has experienced large fluctuations in seasonal rainfall over the years[1], with pronounced variability across a range of temporal scales These range from synoptic and intraseasonal variations, which are critical for rain-fed agriculture, hydroelectric power generation, and water resource management[2,3], to annual, interannual, and decadal variabilities that have important implications for long-term water availability. West African summer monsoon (WASM) rainfall variability will amplify under global warming is crucial for mitigation and adaptation strategies for climate change. West African summer monsoon rainfall in a warmer climate are rare, even though this region has experienced substantial changes and variability in rainfall during the past century at different. We study the global-warming-induced changes in summer monsoon rainfall variability using data from two CORDEX regional climate models
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