Portugal

Avalanches, Landslides and Rock fall Portugal

Vulnerabilities Portugal - Now

Mainland Portugal

In Portugal, during 1865-2010 1,621 disastrous floods and 281 disastrous landslides were recorded that led to casualties or injuries, and missing, evacuated or homeless people (Azores and Madeira were not considered). These occurrences were responsible for 1,251 casualties. More than half of this number of casualties was due to a single flash flood event in the Lisbon region in November 25–26, 1967. During 1865-2010 no increase in the number of events in time can be observed (3).

The majority of cases (85.2 %) were floods that caused 81 % of total casualties. Clusters with high density of flood cases are observed in the Lisbon region and the Tagus valley, in the Oporto region and the Douro valley, in the Coimbra region and the Mondego valley and along the Vouga river Valley. Most floods occurred in November to February (75.6 % of total flood cases), while landslides tend to concentrate from December to March (73 % of total landslide cases). Floods and landslides are mostly concentrated in the western coastal zone from Setúbal to Oporto, where natural conditions are favourable to floods and landslides, and population density is high (3).

Madeira Island

Natural disasters by landslides and floods are frequent events on Madeira Island, a Portuguese archipelago in the North Atlantic; they are usually of single spatial occurrence and interminable to record over time (1). Heavy rainfall on February 20, 2010, triggered numerous shallow rapid landslides the Island. At high elevations, rainfall up to 383 mm was recorded in a 24-h period, which is approximately two-thirds of the annual amount of precipitation for Madeira Island. Intense flooding followed the heavy rainfall. The rainfall triggered landslides throughout the island which blocked and damaged roads, isolating communities and delaying emergency responses. Debris flows washed out river beds and channels and buried low-lying urbanized areas with woody debris and sediments. At least 42 people died. Property loss was estimated to be 1.4 billion € (2).

Due to anthropogenic influences caused by urban development and population expansion, the event demonstrated the increased vulnerability of the island’s infrastructure. Three main factors contributed to the triggering of the landslides due to the heavy rainfall event in February 2010: the characteristic soil type, the land cover and the slope gradient. Furthermore, the anthropogenic impact on the extent of the hazard becomes obvious due to poor settlement planning and drainage system modification (1).

References

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