# Exploring the Impact of Multitemporal DEM Data on the Susceptibility Mapping of Landslides
## 2 Study Area  
### Study Area and Landslide Data  
The southern area of Sichuan province in China is a region with frequently occurring landslides. The study area covers the three districts of Panzhihua, Liangshan, and Ya'an (Figure 1). The area is located at a latitude of 26\({}^{\circ}\)03\({}^{\prime}\)-30\({}^{\circ}\)56\({}^{\prime}\) north and a longitude of 100\({}^{\circ}\)03\({}^{\prime}\)-103\({}^{\circ}\)52\({}^{\prime}\) east. The area also belongs to the Sichuan Basin, adjacent to the Qinghai-Tibet Plateau in the west. It has a complex topography mainly composed of plains, hills, mountains, and plateaus; furthermore, the relative elevation is more than 3200 m.  
The climate in the study area is a typically humid subtropical monsoonal climate that is hot in summer and mild and humid in winter, with plentiful rainfall and mist. The vertical climate differs greatly, and the annual average temperature distribution gradually increases from northwest to southeast. The average temperature ranges from 5.3 to 15.7 \({}^{\circ}\)C, with annual average rainfall ranging from 1500 to 1800 mm. The study area is, therefore, extremely rainy. The rainfall is mainly concentrated from June to October, which accounts for approximately 70%-75% of the annual rainfall. The maximum daily precipitation reaches 300-500 mm. Meanwhile, part of the study area is located in the Himalaya earthquake zone, which suffers from permafrost, avalanches, and landslides. The stratum of the study area is complete (from Archean to Quaternary). The dominant lithology is sedimentary rock, majorly consisting of dolomite, limestone, siliceous rock, shale, and sandstone [33]. The surface water system is developed, and there are many tributaries of the Yangtze River. The groundwater is distributed widely and buried shallowly, which is affected significantly by the rainfall and landform [34].  
The Chinese Geological Environment Monitoring Institute collected the landslides information in this region through the China Geological Survey, including locations and occurrence times, and released it to public in its Bulletin of National Geological Hazards [35]. The annual total number of historical landslide events is shown in Figure 2. More than 85% of the historical landslide events were induced by natural environmental factors, such as rainfall and earthquakes, while only a few events were induced by human factors, such as mining and slope cutting. As the source data in the Bulletin of National Geological Hazards are not distinguished by landslide type, the general landslides analyzed in the study are of various types.  
Figure 1: Location of the study area: (**a**) Sichuan province in China; (**b**) the study area; (**c**) an aerial photograph of the study area.  
In this study, the total number of historical landslide events from 2000 to 2016 and the number of those hazards in various years after 2004 are obtained. However, we can only obtain the total number of historical landslide events for the period between 2000 and 2004. Thus, to better analyze the impact of a DEM on susceptibility assessment, we divide the historical landslide events into two broad types: the landslide events during the period ranging from 2000 to 2009, and the period ranging from 2010 to 2016. The historical landslide events in the study area from 2000 to 2009 and from 2010 to 2016 (Figure 3) can be obtained from the China Geological Environment Information database ([[http://www.cigem.cn](http://www.cigem.cn)]([http://www.cigem.cn](http://www.cigem.cn))). A total of 341 historical landslide events from 2000 to 2009 and 218 historical landslide events from 2010 to 2016 were recorded.  
Figure 3: Locations of historical landslide events.  
Figure 2: Number of historical landslide events in various years.