The 20 February 2010 Madeira Island flash-floods: VHR satellite imagery processing in support of landslide inventory and sediment budget assessment

Abstract

On 20 February 2010, an extreme rainfall episode occurred on Madeira Island, which caused an exceptionally strong flash flood and several soil slip-debris flows, producing 45 confirmed deaths and 6 persons declared missing, as well as extensive material damages. In order to understand and quantify the importance of landsliding in routing sediment through mountainous drainage, such as Madeira Island's landscape, it was essential to perform extensive landslide analysis. This study describes the methodology used to semi-automatically detect the landslides, produce the landslide inventory maps and estimate the sediment volume produced during this particular event which ranged from 217 000 m³ to 344 000 m³ and 605 000 m³ to 984 000 m³ for the Funchal and Ribeira Brava basins, respectively. These results contributed to the design and implementation of measures to prevent damages caused by landslides in Madeira Island

Semiautomated object-based classification of rain-induced landslides with VHR multispectral images on Madeira Island

“…The separation of the landslide-affected region into source, transport, and deposition areas is important to support postevent mitigation actions, since sediments deposited by landslides are likely to become source materials in subsequent events (Mondini et al, 2011a;Lira et al, 2013). More generally, the assessment of the volume of sediments produced, displaced, and deposited by landslides is important for susceptibility and hazard evaluation (Guzzetti et al, 2009).…”

“…Madeira Island, where our method was tested, is an example of a region where accurate co-registration was not possible (Chini et al, 2011). We test the approach on a GeoEye-1 multispectral image (0.5 m panchromatic band) acquired 3 days after an exceptionally heavy rainfall episode in February 2010 that triggered thousands of shallow landslides and flash floods across Madeira Island, in the North Atlantic, and claimed 45 lives (Lira et al, 2013). Section 2 describes the imagery and ancillary data used in the study and the preparation of a landslide inventory to evaluate the results.…”

“…1), with a population of 250 000 inhabitants, has a long record of flash floods, with at least 30 flash flood events of significant intensity registered since the beginning of the 19th century (Baioni, 2011;Lira et al, 2013). These flash floods usually last a few hours, during which a large amount of sediment is transported downstream very rapidly and with very high energy.…”

“…These flash floods usually last a few hours, during which a large amount of sediment is transported downstream very rapidly and with very high energy. Large part of the transported material is sourced by shallow landslides triggered upstream by the heavy precipitation (Lira et al, 2013). The combination of rough and steep terrain (mean slope angle 37 %) with intense rainfall provides the conditions for frequent and widespread landslides on Madeira.…”

“…In the first hours of the morning rainfall values reached more than the double of the monthly average, triggering landslides and exceptionally strong flash floods that affected severely the municipalities of Funchal (home to half of the island population) and Ribeira Brava (Lira et al, 2013).…”