The influence of antecedent conditions on flood risk in sub-Saharan Africa

Most flood early warning systems have predom- inantly 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) be- fore the event. The 7-day precipitation preceding a flood event (PRE7) and the standardized precipitation evapotran- spiration 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 pro- vides evidence that bringing together weather and seasonal conditions can lead to improved flood risk preparednes