A Mechanistic Approach to Include Potential Urbanisation and Climate Change in Landslide Susceptibility Maps

Empirical evidence shows that climate, deforestation and informal housing (i.e. unregulated construction practices typical of fast-growing developing countries) can increase landslide occurrence. These environmental changes have not been considered jointly and in a dynamic way in regional or national landslide susceptibility assessments. Considering simultaneously both rainfall and land cover changes in large areas requires a sound a computationally effective model. We suggest a new method that uses a hillslope-scale mechanistic model to generate regional susceptibility maps under changing climate and urbanization, which also accounts for existing uncertainties. An application in the Caribbean shows that the landslide susceptibility estimated with the new method and associated with a past rainfall-intensive hurricane corresponds well with hillside areas where landslides were observed after that event. We subsequently demonstrate that the hypothetical expansion of informal housing (including deforestation) increases landslide susceptibility more (+20%) than intensified rainstorms due to climate change (+6%). However, we find that their combined effect would lead to a much greater landslide occurrence (up to +40%) than if the two drivers were considered independently. Results demonstrate the importance of including both potential land cover and climate change in landslide susceptibility assessments. Furthermore, by modelling mechanistically the overlooked dynamics between urban growth and climate change, our methodology can provide quantitative information of the main landslide drivers (e.g. quantifying the impact of deforestation vs informal urbanisation) and locations where these drivers are or might become most detrimental for slope stability. Such information is often missing in data-scarce developing countries but is key for supporting national long-term environmental planning, for targeting financial efforts, as well as for fostering national or international investments for landslide mitigation.