15 October 2010
Population trends, not climate, causing increased flood fatalities in Africa
Posted by Michael McFadden
Receding flood waters outside Khartoum, Sudan, August 2009 (image by sidelife on Flickr, used under a Creative Commons license)
Guest post by Anne Jefferson, assistant professor at the Department of Geography and Earth Sciences, UNC Charlotte, and science blogger at Highly Allochthonous
In August 2009, unusually heavy rains lasting six hours deluged the city of Khartoum in Sudan. Higher, wealthier parts of the city were relatively unaffected, but in the vast shanty towns that surround the city center, people lost their possessions, homes, and lives. Twenty-seven people died, and over 20,000 homes were damaged or destroyed.
Sadly, the flooding in Khartoum is not an isolated incident. The number of flood deaths in Africa has gone from fewer than 2000 in 1950-1969 to more than 15,000 between 1990 and 2009. In addition, the number of lives affected and the amount of economic damage have dramatically increased.
What’s behind this trend? Is it a reflection of climatically-driven increases in the intensity of precipitation and magnitude of floods? Is it simply that there are more people in Africa now to be affected by floods? Or are there socio-economic patterns at work that have magnified flood risks?
According to a paper in press in Geophysical Research Letters, climate is not to blame for the increase of flood deaths in Africa.
In the new study, Giuliano Di Baldassarre and co-authors examine the hydrologic data on African floods in the 20th century and tease out the causes and consequences of flooding, while pointing to ways that future flood risks could be lessened. Watersheds with long streamflow records and little land-use change can be good indicators of climatic influences on the water cycle. So that’s where the authors started their research.
They identified 79 rivers around the African continent with decades’ worth of good data on flood discharges and minimal changes to watershed land-use, including the Niger, Congo, and Nile. Using two different methods, the authors looked for trends in the flood discharge data. When the data were aggregated, there were no statistically significant trends in flood discharge. When each river was examined individually, 65 rivers showed no statistically significant trend, 10 rivers trended toward smaller floods, and only four rivers trended toward larger floods. Based on these results, the researchers conclude the climatic influences cannot explain the troubling rise in African flood fatalities.
After eliminating a climatic cause for flood fatality increases, the authors turned to population patterns. The total population of the African continent has increased by about a factor of 4 four since 1950, but flood fatalities have increased much more dramatically. When the authors compared the increase in flood deaths to the growth in urban populations, the numbers began to match .
In the last 50 years, Africa has undergone intense urbanization. Cities and large towns are now 10 times more populated than they were half a century ago, and flood fatalities have risen just as fast. The authors also show the geographic association of population growth and deadly floods. While floods occurred in many parts of the African continent between 1985 and 2009, the floods that killed people are strongly concentrated in areas with high population growth. Floods over the past few years in places like Dakar (Senegal), Lusaka (Zambia), and Ouagadougou (Burkina Faso), illustrate the problem. Poor migrants from rural areas to cities end up living in unplanned and informal shanty towns and slums, often in the lowest-lying and most flood-prone areas. These settlements frequently have poor drainage, so flood waters pond, turn stagnant, and become breeding places for disease, increasing the number of deaths that result from the floods (although those numbers would not be counted directly as flood fatalities).
Given that the urban population of Africa is still rapidly growing, what can be done to lessen future flood risks? Di Baldassarre and his colleagues point to examples from around the world where the development of flood forecasting and early warning systems have saved many lives by getting people out of flood-prone areas before the waters rise. But, the researchers caution, getting people out of harm’s way when the rains come should be accompanied by building of effective local institutional capacities for urban planning, and discouraging settlements in areas at high risk of floods. Di Baldassarre’s team concludes that these are “effective and socially sustainable actions that should be pursued with priority in the African continent.”
– Anne Jefferson is an assistant professor at the Department of Geography and Earth Science, UNC Charlotte. She blogs at Highly Allochthnous.
Giuliano Di Baldassarre, Alberto Montanari, Harry Lins, Demetris Koutsoyiannis,, & Luigia Brandimarte, Günter Blöschl (2010). Flood fatalities in Africa: from diagnosis to mitigation Geophysical Research Letters
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It’s not strictly true to say that population trends are responsible for increasing flood fatalities, any more than you wd say that population trends are responsible for the damage to the Everglades in Florida. It’s true that the population of Africa’s cities has exploded–but the key word is “poor”. Florida’s population has also exploded, but we don’t frame the Everglades crisis as a “population” issue. Instead, we look at for example a lax regulation regime and a climate of political corruption. Poor governance is also a big factor in Africa. This is important, because the way we frame the problem indicates the solution. We don’t talk about “population control” in Florida!
Hi Alex,
I hope my writing didn’t imply that it was the increased flood mortality was the fault of the poverty-stricken urban dwellers with little choice as to where they live.
I think I was fairly clear in the last few paragraphs of the post that inadequate land use planning and enforcement and hazard preparedness are the real culprits and the places where real solutions will need to be based.
In more general terms though, hazards (African floods) and environmental damage (Everglades) are problems because of the trajectories of human population growth and land use patterns. A flood in a river valley is simply a natural disturbance until people live in it, when a flood becomes a hazard. Similarly, environmental degradation occurs because human activities push an ecosystem out of its natural equilibrium. The greater the population in an area and the more intensive their land-use, the more likely hazards and degradation are to occur and to be severe. So, ultimately, it is about population. But again, given the population dynamics of a region, the solutions are effective use of resources and hazard preparedness and mitigation.
Around web some people are using this study to imply climate change won’t be so bad. But this paper – I can only read the abstract – does not seem to be about future impacts of human caused climate change. The tangible impacts of climate change are just now becoming apparent, so a study about flooding over the 20th century would not have any relevance here. The more recent floods you mention may or may not be come to be seen as connected to climate change.
Of course, regional climate changes caused naturally and by a variety human actions exist, and the study does show that they were not the cause of the increase in flood deaths.
Mike: Good points.
I made the following comments to a reporter last weekend, but I think they are worth reposting here (especially since I have no indication that the reporter intends to use my comments):
“Just because Di Baldassarre’s team did not find a climate change signal in the historical streamflow record does not mean that changes to African river and flood flows are not going to happen in the future. The methods of this study can’t tell us anything about future climate and hydrology. However, their findings that flood fatalities are linked to poorly planned urban development does provide a framework for mitigating current and future hazards, because it appears that the most important step to reducing flood fatalities is to limit settlement of flood-prone areas. As other studies help refine how big future floods may be, urban planners will need to pay heed to the changes to the amount area at risk of inundation.
Also, the Di Baldassarre study did not look at water shortages and droughts, which may be even more critical at present and in the future to protecting Africa’s lives and economies. The strategies necessary to cope with current and future droughts are very different than for floods, so mitigating flood risk in African cities in no way comes close to a full solution to Africa’s climate change adaptation needs related to water.
The larger lesson is that when we look at natural phenomena in terms of loss of human life or economic damages, the answers are almost always going to be found in the people. Populations grow and shift locations very quickly relative to even fast climatic processes, so it is not at all surprising that Di Baldassarre and colleagues found their answers in population and not climate. “
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