Initial insights from a global database of rainfall-induced landslide inventories: the weak influence of slope and strong influence of total storm rainfall

Abstract

Abstract. Rainfall-induced landslides are a common and significant source of damages and fatalities worldwide. Still, we have little understanding of the quantity and properties of landsliding that can be expected for a given storm and a given landscape, mostly because we have few inventories of rainfall-induced landslides caused by single storms. Here we present six new comprehensive landslide event inventories coincident with well identified rainfall events. Combining these datasets, with two previously published datasets, we study their statistical properties and their relations to topographic slope distribution and storm properties. Landslide metrics (such as total landsliding, peak landslide density, or landslide distribution area) vary across 2 to 3 orders of magnitude but strongly correlate with the storm total rainfall, varying over almost 2 orders of magnitude for these events. Applying a normalization on the landslide run-out distances increases these correlations and also reveals a positive influence of total rainfall on the proportion of large landslides. The nonlinear scaling of landslide density with total rainfall should be further constrained with additional cases and incorporation of landscape properties such as regolith depth, typical strength or permeability estimates. We also observe that rainfall-induced landslides do not occur preferentially on the steepest slopes of the landscape, contrary to observations from earthquake-induced landslides. This may be due to the preferential failures of larger drainage area patches with intermediate slopes or due to the lower pore-water pressure accumulation in fast-draining steep slopes. The database could be used for further comparison with spatially resolved rainfall estimates and with empirical or mechanistic landslide event modeling.

How size and trigger matter: analyzing rainfall- and earthquake-triggered landslide inventories and their causal relation in the Koshi River basin, central Himalaya

“…Our finding regarding similar cutoff values obtained from different inventories created for the same area also supports this argument. This conclusion is also supported by Marc et al (2019), who found similar beta values between ETLs and RTLs, but the cutoff value is much smaller because a correction to remove runout was applied.…”

“…Dahal and Hasegawa (2008) used a dataset of 193 landslides occurring from 1951 to 2006, part of which were from the Koshi River basin, to generate a threshold relationship between rainfall intensity, rainfall du-ration and landslide initiation. The latest research from Marc et al (2019) gives the magnitude of annual landsliding in different High Himalayan valleys.…”

“…This inventory has a limitation that a landslide that occurred and revegetated during 1992 to 2015 could not be identified by the remote-sensing images obtained in 2015. It is impossible to make a complete historical landslide inventory in this region due to a lack of multitemporal high-resolution images (Marc et al, 2019). After the 25 April 2015 Gorkha earthquake, a substantially complete earthquake-triggered landslide inventory was created by Roback et al (2017).…”

“…The problem with the studies indicated above is that rainfall-triggered landslides that occur shortly after a major earthquake are generally following the same spatial patterns, due to the availability of large volumes of landslide materials of the coseismic landslides (Hovius et al, 2011;Tang et al, 2016;Fan et al, 2018a). However, other studies argue that there is not a clear correlation of rainfall-triggered landslides with the coseismic pattern, as only the 20 %-30 % of the RTLs that occurred just after an earthquake are spatially related to ETLs, suggesting limited reactivation of ETLs by RTLs (Marc et al, , 2019.…”

“…They mostly focus on mapping rainfall-induced landslides after an earthquake, such as for the 1999 Chi-Chi earthquake (Lin et al, 2006(Lin et al, , 2008, the 2005 Kashmir earthquake (Saba et al, 2010) or the 2008 Wenchuan earthquake (Tang et al, 2010(Tang et al, , 2016Fan et al, 2018a). A few studies were car-ried out on multitemporal RTL inventories in Taiwan, Papua New Guinea, Japan and Central Nepal before an earthquake, which supplied a good comparison study for RTLs under the effect and without the effect of earthquakes (Marc et al, , 2019. The problem with the studies indicated above is that rainfall-triggered landslides that occur shortly after a major earthquake are generally following the same spatial patterns, due to the availability of large volumes of landslide materials of the coseismic landslides (Hovius et al, 2011;Tang et al, 2016;Fan et al, 2018a).…”