Abstract
Abstract. Empirical evidence from the humid tropics shows that informal housing can increase the occurrence of rainfall-triggered landslides. However, informal housing is rarely accounted for in landslide hazard assessments at community or larger scales. We include informal-housing influences (vegetation removal, slope cutting, house loading, and point water sources) in a slope stability analysis. We extend the mechanistic model CHASM (Combined Hydrology and Stability Model) to include leaking pipes, septic tanks, and roof gutters. We apply this extended model (CHASM+) in a region of the humid tropics using a stochastic framework to account for uncertainties related to model parameters and drivers (including climate change). We find slope cutting to be the most detrimental construction activity for slope stability, and we quantify its influence and that of other destabilising factors. When informal housing is present, more failures (+85 %) are observed in slopes that would otherwise have had low landslide susceptibility and for high-intensity, short-duration precipitations. As a result, the rainfall threshold for triggering landslides is lower when compared to non-urbanised slopes and comparable to those found empirically for similar urbanised regions. Finally, low cost-effective “low regrets” mitigation actions are suggested to tackle the main landslide drivers identified in the study area. The proposed methodology and rainfall threshold calculation are suitable for data-scarce contexts, i.e. when limited field measurements or landslide inventories are available.
Highlights
Global and regional landslide records reveal an increase in rainfall- and human-triggered landslides during the last century, mainly in economically developing countries with rapid population growth and urbanisation (Kirschbaum et al, 2015; Froude and Petley, 2018)
We demonstrate that informal housing increases landslide hazard and that slope cutting is the most detrimental construction activity when compared to vegetation removal, lack of roof gutters, and presence of water leaks
The presence of informal housing modifies the relative role that natural slope angle, soil cohesion, and soil thickness have in maintaining stable slopes, with increased hazard occurrence for low values of these three main landslide drivers
Summary
Global and regional landslide records reveal an increase in rainfall- and human-triggered landslides during the last century, mainly in economically developing countries with rapid population growth and urbanisation (Kirschbaum et al, 2015; Froude and Petley, 2018). This increase might be partly due to continuing improvements in landslide recording, but it indicates the growing impact of climate and urban pressure on landslide occurrence (Larsen, 2008). The natural landslide susceptibility of these regions coupled with the lack of urban planning and regulations can increase risk in terms of vulnerability and exposure and hazard. We use the term “informal housing” to refer to the combination of these urban modifications which influence slope stability by altering its geometry, hydrology, and material strength (Fig. 1)
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