Extreme Rainfall and Streamflow in Niamey City: Trends and Relationship Between Higher Streamflow and Rainfall

Abstract

Increasing rainfall frequency and intensity, which causes floods, is one effect of climate change. Recent heavy rains have caused regular flooding in several major towns in West Africa. ln order to comprehend the cyclical patterns of flash floods and very high rainfall occurrences in Niamey, Niger, between 1982 and 2021. The National Meteorological Direction, the Regional Centre AGRHYMET, as well as the Niger Civil Protection General Direction, provided the flood disaster data used in this research. Five rainfall extreme indices created by the Expert Team for Climate Change Detection Monitoring and Indices (ETCCDI) were studied to define severe rainfall intensity and frequency indices. The Gumbel extreme value distribution was used to estimate the return period of flood and extreme rainfall throughout the period of 5 to 100 years based on the annual maximum daily rainfall. All five severe rainfall indices had an increased trend, except for the continuous wet days (CWD), which revealed a diminishing tendency. During the study period, it was shown that extreme rainfall had both increased in frequency and intensity. An analysis of the flood reports from 1990 to 2020 showed an increase in Niamey. We discovered that a daily maximum of 1-day rainfall and a daily maximum of continuous 5-day rainfall might both reach 163 and 182.2 mm in 100 years from 2020, respectively. Regarding QMax and QX5day, the maximum discharge over five days and the peak discharge may exceed 2722.2 and 14287 m3 /s, respectively. According to the study's findings, floods often occur in Niger, requiring mitigation and adaptation strategies.