Abstract
Based on daily precipitation from the Global Precipitation Climatology Project (GPCP) data during April–October of the 1997–2014 period, the daily extreme rainfall trends and variability over West Africa are characterized using 90th-percentile threshold at each grid point. The contribution of the extreme rainfall amount reaches ~50–90% in the northern region while it is ~30–50% in the south. The yearly cumulated extreme rainfall amount indicates significant and negative trends in the 6°N–12°N; 6°N–12°N; 17°W–10°W and 4°N–7°N; 4°N–7°N; 6°E–10°E 4°N–7°N; 6°E–10°E 4°N–7°N; 6°E–10°E domains, while the number of days exhibits nonsignificant trends over West Africa. The empirical orthogonal functions performed on the standardized anomalies show four variability modes that include all West Africa with a focus on the Sahelian region, the eastern region including the south of Nigeria, the western part including Guinea, Sierra Leone, Liberia, and Guinea-Bissau, and finally a small region at the coast of Ghana and Togo. These four modes are influenced differently by the large-scale ocean surface and atmospheric conditions in the tropical Atlantic. The results are applicable in planning the risks associated with these climate hazards, particularly on water resource management and civil defense.
Highlights
Rainfall is one of the most usable weather parameters that allows determining climate variability, in West Africa [1, 2]
They seem to define areas of high values as, for instance, in the regions 6∘N–12∘N; 17∘W–10∘W and 4∘N–7∘N; 6∘E–10∘E where the maximum reaches ∼25 mm
This work aims to study trends and variability of daily extreme rainfall in West Africa. It analyses the relationships between these rainy events and the large-scale ocean surface and atmospheric conditions in the tropical Atlantic
Summary
Rainfall is one of the most usable weather parameters that allows determining climate variability, in West Africa [1, 2]. In the last several decades, alteration of periods with extreme rainfall events with dry conditions has led to a succession of flood/drought years [4]. The spatiotemporal distribution of the extreme rainfall events is not homogenous in West Africa They can cause flooding or drought that have negative impacts by increasing environmental disasters. Flood periods can have dramatic consequences in poor countries of West Africa Such situation was observed in 1994 when the runoff of the Bagre Dam in Burkina Faso reached 2050 m3 s−1 instead of the initial project runoff of 1520 m3 s−1 [8]. The southern region of West Africa has experienced social and economic impacts due to flooding, as, for instance, the episodes that caused many deaths in Abidjan (Cote d’Ivoire, 39 deaths in 2014 and 16 deaths on June 22, 2015; see http://www.rfi.fr/afrique/ 20150621-cote-ivoire-bilan-victimes-intemperies-pluies-abidjan)
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