G. Di Baldassarre, A. Montanari, H. F. Lins, D. Koutsoyiannis, L. Brandimarte, and G. Blöschl, Increasing ﬂood risk in Africa: a climate signal?, European Geosciences Union General Assembly 2011, Geophysical Research Abstracts, Vol. 13, Vienna, EGU2011-5634-1, doi:10.13140/RG.2.2.26541.28648, European Geosciences Union, 2011.
The economic damages caused by ﬂoods, as well as the number of people killed by them has substantially increased in recent decades on the African continent. The number of ﬂood fatalities, in particular, has increased about one order of magnitude during the last 50 years. These ﬁgures call for urgent actions to reduce damages and casualties. To plan these actions, we ﬁrst need to understand the reasons why ﬂood risk has increased so dramatically in Africa. Flood risk can be deﬁned as a combination of the ﬂood probability and the potential adverse consequences. Hence, we investigated both the climatic signatures that may have increased ﬂood probability, as well as the population changes that may have led to increased human vulnerability to extreme ﬂoods. Given the global perception that the severity and frequency of ﬂoods has increased in recent years, we examined if these perceived trends are supported by observational data collected in Africa. In particular, we investigated trends in annual maximum discharge using a large, consistent and quality-assured database from 79 gauging stations in Africa. The related African river basins remain largely undisturbed and are representative of diverse hydro-climatic conditions. Hence, changes in their hydrological response may provide relevant information for detecting spatially and temporally averaged climatic conditions. Based on the results of both continental and at-site data analyses, we found that the frequency and magnitude of African ﬂoods have not signiﬁcantly increased during the Twentieth Century, and that climate, overall, has not been a main factor in the observed increase of ﬂood damages. Having detected no signiﬁcant climate signals, the study focused on ﬂood vulnerability. The African continent, as well as many other areas around the world, has undergone widespread and intensive urbanization. During the last 50 years, while the total population has increased by a factor of 4, the urban population in Africa has increased by one order of magnitude; approximately the same as the increase of fatalities caused by ﬂoods. The study of population patterns at the continental scale showed that most of the recent deadly ﬂoods have happened where the population increases have been largest. At the local scale, we found numerous examples of increased human settlements in ﬂood prone areas. These results provide demonstrable evidence that intensive and unplanned urbanization, and the related population increase on ﬂoodplains has led to an increase in the potential adverse consequences of ﬂoods; particularly of the most serious and irreversible type of consequence, namely the loss of human lives.