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Abstract:
Understanding the space-time variations of extreme rainfall plays an important role in the management of water-related disasters in Sahel countries. This study investigates temporal changes in rainfall characteristics and explores the link between Atlantic Sea surface temperature and extreme rainfall in the southern part of Burkina Faso. We find substantial spatial heterogeneity in rainfall trends across the study area. In contrast to national and supra-national studies that found predominantly increasing trends in extreme rainfall, we detect more downward than upward trends, particularly for indices representing extreme rainfall. This difference is presumably a consequence of the high spatial variability in rainfall trends that can only be detected with sufficiently dense climate networks. We use the Poisson-General Pareto (Poisson-GP) distribution to quantify the frequency and intensity of extreme rainfall. Our comparison of the traditional, stationary Poisson-GP model with the nonstationary version where rainfall depends on Atlantic SST shows that the nonstationary model outperforms the traditional approach. This finding suggests that the assumption of stationary nature must be considered with care when modeling the frequency and intensity of extreme rainfall in the study area. Overall, our results suggest that the recent increase in flood disasters in Burkina Faso is rather caused by land use and land cover changes and population and urban growth and not by increasing rainfall extremes.
