The influence of antecedent conditions on flood risk in sub-Saharan Africa
- 1Institute for Environmental Studies, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, the Netherlands
- 2Royal Netherlands Meteorological Institute (KNMI), De Bilt, 3731 GA, the Netherlands
- 3Global Facility for Disaster Reduction and Recovery (GFDRR), World Bank, Washington DC, USA
- 4International Research Institute for Climate and Society, Columbia University, Palisades, NY 10964, USA
- 5Red Cross Red Crescent Climate Centre, The Hague, 2521 CV, the Netherlands
Abstract. Most flood early warning systems have predominantly focused on forecasting floods with lead times of hours or days. However, physical processes during longer timescales can also contribute to flood generation. In this study, we follow a pragmatic approach to analyse the hydro-meteorological pre-conditions of 501 historical damaging floods from 1980 to 2010 in sub-Saharan Africa. These are separated into (a) weather timescale (0–6 days) and (b) seasonal timescale conditions (up to 6 months) before the event. The 7-day precipitation preceding a flood event (PRE7) and the standardized precipitation evapotranspiration index (SPEI) are analysed for the two timescale domains, respectively. Results indicate that high PRE7 does not always generate floods by itself. Seasonal SPEIs, which are not directly correlated with PRE7, exhibit positive (wet) values prior to most flood events across different averaging times, indicating a relationship with flooding. This paper provides evidence that bringing together weather and seasonal conditions can lead to improved flood risk preparedness.