High-impact weather and urban flooding in the West African Sahel – a multidisciplinary case study of the 2009 event in Ouagadougou

On September 1st 2009 an extreme high-impact weather event occurred in Burkina Faso that had significant impacts upon the capital city Ouagadougou and its inhabitants. Subsequent reporting and research has however not focused on the contributing socio-economic and hydrological factors and the role of global warming and climatic change remains uncertain. This reflects a paucity of evidence attributing such extreme weather events to climate change for the West Africa region and limits the knowledge base for urban planning to climate-related risks which pose serious threats. This case study provides a holistic assessment of the most extreme urban hydrometeorological event recorded in the West African Sahel, that links synoptic conditions to climate change and through to hydrological impacts on vulnerable urban populations. The intention is to inform regional decision-makers on climate change and flood-generating high-impact weather events at the urban scale and to bridge the gap between what scientists understand as useful and decision-makers view as useable at the city scale by providing interdisciplinary answers to key questions raised by local stakeholders. Such an approach was shown to foster enhanced dialogue and engagement with stakeholders, while also providing a focus for communicating science at variable time- and spatial scales and between disciplines to improve understanding of how global processes have localised consequences. This reveals that Ouagadougou remains vulnerable to climate change and that such extreme weather events will become more frequent. But it is also demonstrated the complexity of attributing extreme events at such localised ‘urban’ scales to atmospheric phenomena affected by global climate change. Regional climate models are evolving and becoming more able to represent such extreme weather phenomena at suitable scales, enabling improved representation of climate-driven changes on such events, improving the ability for short-range forecasts in the future. Frameworks for managing flood risks however remain weak and under-resourced and there is limited capacity to manage flood risk from such events, particularly when rapid urbanisation amplifies vulnerability concerns. Recommendations are made to improve flood-resilience to future storms