Spatial Patterns of Storm-Induced Landslides and Their Relation to Rainfall Anomaly Maps

Storm-induced landslides are a common hazard, but the link between their spatial pattern and rainfall properties is poorly understood, mostly because hillslope stability is modulated by under-constrained, spatially variable topographic, hydrological, and mechanical properties. Here, we use a long-term rainfall data set from the Japanese radar network to discuss why the landslide pattern caused by a major typhoon poorly correlates with the event rainfall but agrees with the event rainfall normalized by the 10-year return period rainfall amount, that is, a rainfall anomaly. This may be explained if the variability in hillslope properties has coevolved with the recent climate and can be accounted for with such normalization. Further, rock types seem to respond to rainfall anomalies at various timescales, favoring specific landslide geometries, and suggesting various hydrological properties in these zones. The computation of rainfall anomalies for multiple timescales may pave the way toward operational landslide forecasts in case of large storms.