Influence of the mapping unit for regional landslide early warning systems: comparison between pixels and polygons in Ca
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Rosa M. Palau I Marcel Hürlimann I Marc Berenguer I Daniel Sempere-Torres
Influence of the mapping unit for regional landslide early warning systems: comparison between pixels and polygons in Catalonia (NE Spain)
Abstract This work presents a prototype landslide early warning system (LEWS) adapted to real-time performance over the region of Catalonia (NE Spain). The system uses high-resolution rainfall information obtained from weather radar observations and susceptibility maps to issue a qualitative warning level at a regional scale. To study the influence of the mapping unit on the LEWS outputs, susceptibility maps obtained for Catalonia based on (i) pixels of different sizes and (ii) hydrological subbasins have been compared. The susceptibility has been derived using a simple fuzzy logic approach combining slope angle and land cover data. The susceptibility maps for the different mapping units have then been employed to run the LEWS for a period of 7 months (warm season of 2010). For each configuration, the performance, interpretability of the warnings, and computational requirements have been compared to assess the suitability of each mapping unit for their use in the LEWS in real time. The configuration using pixels of 30-m resolution as mapping units seems to be the best as a compromise between resolution, performance, and computational cost. However, from an end-user’s real-time perspective, the interpretation of the warnings can be difficult. Therefore, summarizing and visualizing the warnings, which are computed over the highresolution grid, by subbasins is proposed as the best option. Keywords Landslides . Early warning systems . Mapping units . Susceptibility analysis Introduction Rainfall-triggered shallow slides and debris flows represent an important hazard that causes major economic losses and fatalities worldwide (e.g., Jakob and Hungr 2005; Froude and Petley 2018). Although these phenomena are not as widely reported in Catalonia (NE Spain) as they are in other regions, their hazard is still significant (Gallart and Clotet 1988; Portilla et al. 2010a; Hürlimann et al. 2014; Palau et al. 2017). Rainfalls that trigger shallow slides and debris flows are frequently rather short and intense (Guzzetti et al. 2008; Alfieri et al. 2012; Abancó et al. 2016), and its frequency is expected to increase due to climate change (Gariano and Guzzetti 2016). Building reliable early warning systems is of key importance to reduce the risk by increasing awareness and preparedness of communities which may be exposed (Alfieri et al. 2012; UNISDR 2015; Alcántara-Ayala et al. 2017). In the recent years, regional landslide early warning systems (LEWSs) have been developed covering multiple areas worldwide, e.g., Japan (Osanai et al. 2010), Hong Kong (Lloyd et al. 2001), the Chinese Zhejiang province (Yin et al. 2008), Southern California (Baum and Godt 2010), Rio de Janeiro (Calvello et al. 2014), the Italian regions of Emiglia-Romana and Campania (Piciullo et al. 2017; Segoni et al. 2018), Norway (Krøgli et al. 2018), and
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