Differential signal of change among multiple components of West African rainfall

Abstract

Rainfall components likely differ in the magnitude and direction of their long-term changes for any given location, and some rainfall components may carry a greater regional signal of change than rainfall totals. This study evaluates the magnitude of change of multiple rainfall components relative to other components, and the greatest regions of change across all rainfall components in West Africa. Hourly rainfall data from the ERA5 reanalysis dataset was used to derive twelve rainfall components, which were evaluated for long-term means, interannual variability, and long-term changes.For rainfall totals and rainfall intensity, the central Sahel is witnessing increasing trends while the western Sahel is experiencing signi cant decreasing trends. In general, decreasing trends predominate in the study domain, especially in the northwestern Congo Basin, where annual rainfall is decreasing by 120mm per decade. Importantly, rainfall frequency accounts for 49% of all signi cant grid-point trends for the whole domain. In contrast, rainfall totals account for 26% of all combined signi cant trends across the domain, while rainfall intensity (12.6%), rainy season length (9.5%), and seasonality (3.3%) account for the remaining signals of change. Most of the changes among the rainfall components are in the Tropical Wet and Dry regions (59% of all signi cant trends); the Saharan and Equatorial regions account for the least changes. This study nds evidence that rainfall frequency is changing more across the regions compared to rainfall totals and should be explored as rainfall inputs in climate models to potentially improve regional predictions of future rainfall.

Era5 Reproduces Key Features of Global Precipitation Change in a Warming Climate

“…Decreasing precipitation trends in the Congo Basin have been reported in many studies in the last two decades (Hua et al, 2016;Jiang et al, 2019;Obarein & Lee, 2022). Other proxies, such as rainforest greenness (Zhou et al, 2014) and cloud cover (Lee, 2020), have also shown decreasing trends.…”

“…Reanalysis datasets can mitigate these problems by providing homogenous and consistent long-term data on regularly spaced temporal and spatial intervals. Most evaluations of ERA5 reanalysis precipitation dataset show high performance in outperforming other reanalysis and satellitebased products (Centella-Artola et al, 2020;Gleixner et al, 2020;Jiao et al, 2021;Malayeri et al, 2021;Nogueira, 2020;Obarein & Lee, 2022;Randriatsara et al, 2022;Wang & Zhao, 2022, and others). This high performance has led to the growing use of the ERA5 dataset in precipitation trend analysis (e.g., Boisvert et al, 2023;Box et al, 2019;Chinita et al, 2021;Yu & Zhong, 2021).…”

“…Changes in precipitation primarily emphasize precipitation totals, but other components of precipitation are expected to differ in sign and magnitude (Donat et al, 2016;Obarein & Lee, 2022). For example, although global climate models simulate increases in global mean precipitation (IPCC, 2014;Masson-Delmotte et al, 2021;Salzmann, 2016), these increases are not as robust as in extreme precipitation events (Adler et al, 2017;Emori & Brown, 2005;Sun et al, 2012).…”