The 2010 flash floods in Madeira Island: characteristics and the role of soil water repellency in future events

Abstract

On the morning of February 20, 2010, a storm triggered flash floods and shallow landslides on the surrounding hillslopes of Madeira’s capital city Funchal causing 46 deaths and an estimated 210 million Euros of rebuilding costs. Funchal is located in a coastal basin that drains three major streams. These streams are in deeply incised valleys and drain sediment and water from the centre of the island to the shore. On February 20, the cumulative rainfall exceeded 300mm within hours in different parts of the Island initiating surface runoff that eroded and entrained loose sediments into the streams and generated the flash floods. The loose, coarse nature of the volcanic soils, together with sparse vegetation at altitudes above 1500m and the rugged geomorphology may have contributed towards the scale of the disaster. The paper presents an historical overview of natural hazards in Madeira, followed by a description of the main event, with a focus on rainfall data, sediment transport dynamics, deposits characteristics, and impacts on built infrastructure. Particular attention was given to the occurrence of soil water repellency after wildfires and its impact on future flash floods.