Evaluation of landslide risk drivers to define risk management strategies at the municipal level

Nowadays it is essential to develop new methodologies to quantify landslide risk, which contribute to the landslide risk management at the municipal level. In this work, a Landslide Risk Index (LRI) is computed for the 278 Portuguese municipalities, which are ranked and characterized according the landslide risk drivers. Landslide risk index was assessed as the product of hazard, exposure and physical vulnerability of buildings scores.

The landslide hazard includes the landslide susceptibility evaluated at the national scale using the Information Value method and further validated with prediction-rate curves (Zêzere et al., 2018). Additionally, a weather and climate events index (WCE) was computed using a multicriteria analysis that included the annual frequency of circulation weather types associated to damaging landslides and an extreme precipitation susceptibility index (Santos et al., 2020). Exposure  was evaluated for each municipality using the population density (inhabitants/km²) and the road density (km/km²). The physical vulnerability of the buildings was computed using four statistical variables obtained from the official Census: (i) construction technique and construction materials, (ii) reinforced structure, (iii) number of floors and (iv) conservation status. Variable classes were empirically weighted.

Exposure is the main driving force of LRI in the metropolitan areas of Lisbon and Porto, whereas the hazard is more relevant in the NW municipalities and the physical vulnerability is the major driving force in the south of the country.

For each municipality a landslide risk profile was built, based on the combination of the three driving forces, which can be compared and ranked. Therefore, the landslide risk management strategies at the municipal level must be adjusted to the corresponding dominant drivers in order to reduce landslide impacts.

Municipalities with high values of hazard are sensitive to changes on the other risk components, which should draw additional efforts concerning land use management and emergency planning. On the exposure, planning instruments should consider the negative effects on LRI from measures that promote the expansion of people and economic activities towards hazardous zones. On the physical vulnerability, public policies should be aware of the increasing physical vulnerability of buildings in time due to age and lack of maintenance and to public works involving embankments and earthworks.

This work contributes to context-oriented strategies of landslide risk management that still lacks in most of the national and regional levels of risk governance processes.

 

Acknowledgements:

This work was financed by national funds through FCT—Portuguese Foundation for Science and Technology, I.P., under the framework of the project BeSafeSlide—Landslide Early Warning soft technology prototype to improve community resilience and adaptation to environmental change (PTDC/GES-AMB/30052/2017) and by the Research Unit UIDB/00295/2020. Pedro Pinto Santos is funded by FCT (project reference CEEIND/00268/2017).

 

References:

Santos, P.P.; Pereira, S.; Zêzere, J.L.; Tavares, A.O.; Reis, E.; Garcia, R.A.C.; Oliveira, S.C. (2020) A comprehensive approach to understanding flood risk drivers at the municipal level. Journal of Environmental Management (in press).

Zêzere, J.L., Oliveira, S.C., Pereira, S., Garcia, R.A.C., Melo, R., Vaz, T., Tavares, A.O., Bateira, C., Santos, P.P., Meneses, B., Quaresma, I. (2018) Construction of a National Landslide Susceptibility Map for Portugal. Geophysical Research Abstracts, Vol. 20, EGU2018-4541.