Abstract
This study analyzed trends in extreme precipitation based on daily rainfall data provided by Bénin Méteo Agency for the Upper Ouémé valley in Benin over the period 1951–2014. Eleven indices divided into two groups were considered. The first group consists of frequency indices: number of heavy rainfall days, very heavy rainfall days and extremely heavy rainfall days; and maximum number of Consecutive dry days and wet days. The second group concerns intensity: daily maximum rainfall (RX1day), maximum five-day rainfall (RX5day), annual total wet-day rainfall (PRCPTOT), simple daily intensity index (SDII), very wet day (R95P) and extremely wet day rainfall (R99P). The non-parametric Mann-Kendall test was used to assess trends in those indices. The results show that only 30% of the stations experienced decreasing trends for the number of heavy rainfall days (R10mm) and daily maximum rainfall (RX1day). For the annual total wet-day rainfall (PRCPTOT), the simple daily intensity index (SDII) and the very wet day rainfall (R95P), 20% of stations faced significant negative trends. In addition, the decreasing trends are observed for 10% stations considering the number of very heavy rainfall days (R20mm), the maximum five-day rainfall (RX5day) and the extremely wet day rainfall (R99P). About the increasing trend, 10% stations are identified for the number of consecutive dry days (CDD), very heavy rainfall days (R20mm), the daily maximum rainfall (RX1day), the simple daily intensity index, and the extremely wet day rainfall (R99P). These results show the absence of clear trend of climate indices evolution in almost all stations. Consequently, uncertainties in the evolution of rainfall indices must be taken into account in the definition of adaptation strategies for flood or drought risks. Similarly, these results show a slight drop in the dry sequences of the 1970s and 1980s revealed in the region by previous studies.
Highlights
In recent decades, the accentuation of climate variability has sometimes induced catastrophic floods in many countries over the world, and longer or shorter droughts
Several extreme rainfall indices are established by the World Meteorology Organization (WMO) [22] and widely used throughout the world [1,8,10,20,23,24]
Significance threshold, no clear trend at annual time scale is detected over the study period for all the frequency indices in most stations except R10mm, R20mm and consecutive dry days (CDD) index, respectively, in three, two and one of the stations
Summary
The accentuation of climate variability has sometimes induced catastrophic floods in many countries over the world, and longer or shorter droughts. The consequences of changes in the frequency and intensity of extreme rainfall and atmospheric electrical activity have been violent winds, lightning and floods. These phenomena seriously impede the socio-economic development of nations and especially poor countries. In Africa, the last decade has been characterized by frequent floods (notably in the west), which have not even spared the Sahelian countries, such as Senegal, Mali, Burkina Faso, and Niger. The African continent was hit in 2007 by floods which affected more than two million lives
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