Landslide Societal Risk in Portugal in the period 1865-2015

Open image in new window In Portugal, social impacts caused by landslides occurred in the period 1865–2015 are gathered in the DISASTER database. This database includes social consequences (fatalities, injuries, missing people, evacuated people and homeless people) caused by landslides documented in newspapers. The DISASTER database contains 291 damaging landslides that caused 238 fatalities. In this work we aim to: (i) analyse the spatio-temporal analysis of damaging landslides occurred in the last 150 years; (ii) analyse the frequency and the temporal evolution of fatal landslides; (iii) analyse the spatio-temporal distribution of landslide fatalities; (iv) identify the most deadly landside types; (v) verify gender tendencies in landslide mortality; and (vi) evaluate the individual and societal risk. Individual risk is evaluated computing mortality rates for landslides, which are calculated based on the annual average population and the annual average of fatalities. The societal risk is evaluated by plotting the annual frequency of landslide cases that generated fatalities. The results demonstrate the absence of any exponential growth in time of both landslide cases and landslide mortality in Portugal. The highest number of landslide cases and related mortalities occurred in the period of 1935–1969 in relation to very wet years. Most of landslide fatalities mainly occurred in the north of the Tagus valley where the geologic and geomorphologic conditions are more prone to landslides. The Lisbon area registered a mortality hotspot, which is explained by natural conditions combined with the high exposure of population to landslide risk. Falls and flows were responsible for the highest number of fatalities associated with landslides. Males were found to have the highest frequency of fatalities. In conclusion, the spatial patterns of landslide mortality can be related to the unequal distribution of predisposing conditions to landslides, changes in the land use and exposure and social vulnerability to landslide hazards.


OBJECTIVES
In this work we explore the mortality patterns resulting from damaging landslides occurred in Portugal in the period 1865-2015.

Objectives:
(i) analyse the spatio-temporal distribution of damaging landslides; (ii) analyse the temporal evolution of fatal landslides; (iii) analyse the spatio-temporal distribution of landslide fatalities; (iv) identify the most deadly landslide types; (v) verify gender tendencies in landslide mortality; (vi) evaluate the individual and societal risk.The Disaster database was built under the assumption that social consequences (fatalities, injuries, missing, homeless and evacuated people) of landslides are relevant enough to have been reported by newspapers, which were used as the data source.
Each DISASTER case includes details on the disaster characteristics (landslide subtype, date of occurrence, location, and triggering factor) and damages (structural damages and social consequences [human damage, gender of fatalities, and circumstances surrounding the fatalities]).
Individual risk was evaluated using mortality rates for landslides, which were calculated based on years with population census in Portugal (usually every 10 years).
The mortality rates were computed for each decade using the annual average of fatalities, which were then divided by the annual average population.The result was multiplied per 100,000 to scale it according to the size of population per unit time.
Societal risk was evaluated by plotting F-N curves representing the annual frequency of landslide cases that generated fatalities.Fatalities occurring inside vehicles are increasing in time while fatalities occurring outdoors registered a slightly decrease.

Spatial distribution
Fatalities occurred inside buildings tends to maintain in time.• The total number of fatalities resulting from landslide disasters is certainly underestimated because deaths that did not occur immediately after the landslide would not have been reported, and then it is not possible to asses these features using newspapers as the data source.
• The temporal trends of disaster landslides and corresponding fatalities demonstrate the absence of any exponential growth with time.
• Falls and flows were responsible for the majority of fatalities associated with landslides in Portugal.
• Spatial distribution of landslide mortality can be related to factors other than climate, such as the unequal distribution of predisposing conditions to landslide occurrence (geomorphologic and hydrologic), changes on land use and population exposure to landslide hazard and the evolution of social vulnerability.
Landslide Societal Risk in Portugal in the period 1865-2015 • Landslide fatality victims are mostly male which can be explained by cultural reasons, related to the social role of the breadwinner that exposes men to hazardous occupations and men often assume risk behaviors outdoors and act with a false sense of security when are driving vehicles.
• Frequency of landslide fatalities per gender and period does not evidence any particular regional trend, not allowing for any conclusions regarding territorial inequalities.
Landslide Societal Risk in Portugal in the period 1865-2015 • Despite the increasing quality of the building environment observed in the last decades due to the adoption and use of building construction techniques and codes most fatalities still occur inside buildings.These buildings improvements are not enough to resist very rapid landslides such as falls and flows.Even today these incidents are frequent because buildings are often located on hazardous slopes.

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Landslide Societal Risk in Portugal in the period 1865-2015 2. DATA AND METHODS Landslide societal risk in Portugal (1865-2015) was based on an updated version of the Disaster database until 2015 and updates the work developed by Zêzere et al. (2014) about the Portuguese Disaster database and Pereira et al.(2016) about related landslide fatalities (1865-2010).
in Portugal in the period 1865-2015 Landslide cases and landslide fatalities monthly distribution evidences a clear concentration during the autumn and the winter seasons from December to March.
rates per time period F-N curves In Portugal landslide mortality rate did not show any clear tendency in time.Annual frequency of fatal landslides is highest in the North region and lowest in the south region.The societal risk in Portugal is considered unacceptable for landslides.Landslide Societal Risk in Portugal in the period 1865-2015