Floods in the Douala metropolis, Cameroon: attribution to changes in rainfall characteristics or planning failures?

With urban populations worldwide expected to witness substantial growth over the next decades, pressure on urban land and resources is projected to increase in response. For policy-makers to adequately meet the challenges brought about by changes in the dynamics of urban areas, it is important to clearly identify and communicate their causes. Floods in Douala (the most densely populated city in the central African sub-region), are being associated chiefly with changing rainfall patterns, resulting from climate change in major policy circles. We investigate this contention using statistical analysis of daily rainfall time-series data covering the period 1951-2008, and tools of geographic information systems. Using attributes such as rainfall anomalies, trends in the rainfall time series, daily rainfall maxima and rainfall intensity-duration-frequency, we find no explanation for the attribution of an increase in the occurrences and severity of floods to changing rainfall patterns. The culprit seems to be the massive increase in the population of Douala, in association with poor planning and investment in the city's infrastructure. These demographic changes and poor planning have occurred within a physical geography setting that is conducive for the inducement of floods. Failed urban planning in Cameroon since independence set the city up for a flood-prone land colonization. This today translates to a situation in which large portions of the city's surface area and the populations they harbor are vulnerable to the city's habitual annual floods. While climate change stands to render the city even more vulnerable to floods, there is no evidence that current floods can be attributed to the changes in patterns of rainfall being reported in policy and news domains.