Institute of Meteorology and Climate Research

Flash floods in megacities of Africa and Southeast Asia

The megacities of Africa and Southeast Asia are showing rapid growth. But lack of urban planning and infrastructure increase the risk of severe flood disasters in times of climate change.

In West Africa, there have been a number of extreme rain events over the last few years, affecting major cities and costing lives, but also causing major property damage. Disastrous examples, which happened not a long time ago, are the flooding in 2017 in Freetown (Sierra Leone), 2012 in Dakar (Senegal) or 2009 in Ouagadougou (Burkina Faso). There hasn’t been any special warning for Freetown, the capital of Sierra Leone, by the state weather service in August 2017. Yet 450 people lost their lives through landslides and mudslides caused by the extreme rainfalls.

For this reason, on the one hand the IMK-TRO and local partners are researching the meteorological process chains that lead to these extreme events. On the other hand, the researchers are testing the predictability of these extreme events with the help of numerical and statistical weather forecast models. Are there any differences? What is more promising: a look into the past or the application of physical weather models? In terms of predictability for a few days, the results are sometimes sobering: a recent study for West Africa found that neither individual nor the total of nine global weather forecast models had more predictive quality than prediction derived from past observations. For the event in Ho Chi Minh City, even with high-resolution models, it has not been possible to predict the extreme rain for the next day. In this context, it seems astonishing that the extreme event in August 2015, which haunted the coast of Northeast Vietnam, has been well predictable as early as three days ago.

In which weather situations, however, are sufficient early warning times of about three days given? Are there any alternative methods for predicting with physical models? These are important aims of the research at the IMK, which are partly embedded in the Transregio Waves2Weather funded by the German Research Society.

For more details, have a look at the ESKP-special topic “Metropolises under pressure (in german)”:

Further Literature:
Vogel, P., P. Knippertz, A.H. Fink, A. Schlueter, and T. Gneiting, 2018: Skill of Global Raw and Postprocessed Ensemble Predictions of Rainfall over Northern Tropical Africa. Wea. Forecasting, 33, 369–388,

[Working group: Atmospheric Dynamics]