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.
