## 2 Materials and Methods
### Landslides Inventory and Related Triggering Rainfall Events  
The main task of this research was to test the suitability of aggregated regional landslide archives in the evaluation of landslide susceptibility assessment. For this reason, a set of independent available debris flows/slides archives were exploited for training and validating a regional landslide susceptibility map. Archives from five different sectors of the El Salvador territory were considered, which, even in the same sector, were considered as un-uniform in terms of operators, methods (field/remote), and epoch (which means grouping debris flows/slides linked to multiple and/or different extreme rainfall). These landslide inventories were prepared in the framework of different studies (master's degree thesis, PhD thesis and so on, see Author Contributions), many of which have been part of the RIESCA project (Proyecto Regional de Formacion Aplicada a los Escenarios de Riesgos con Vigilancia y Monitoreo de los Fenomenos Volanicos, Sismicos e Hidrogeologicos en Centro America). For this reason, the study areas were not a priori limited and as mentioned above, they were restricted to the sectors affected by the activation of  
Figure 1: Setting of the study area. the inventoried debris flows/slides: the Ilopango (ILO), Coatepeque (COA), San Miguel (SMG), San Vicente (SVC), and San Salvador (SSV) areas. The ILO and the COA inventories were mapped through systematic remote analysis and integrated by some random file checks, consisting of 38,525 and 1895 debris flows/slides, respectively. The SVC inventory included 4975 phenomena, which were remotely recognized according to an irregular spatial scheme. The debris flows/slides of the SMG (233 cases) were extracted by a historical simplified archive inventory, whilst the SSV inventory (382 cases) merged the results of some spot field surveys. At the same time, the expertise and perspective of the operators were different, with ILO and COA having been mapped in the framework of scientific research, all the other inventories coming from civil protection tasks and SMG collecting a number of historical reports. The main triggering events for these landslide scenarios were Hurricane Ida and the tropical depression 12 E (TD12 E). The tropical-humid climate setting of El Salvador produces, in the rainy season between May and October, very high rainfall amounts (above 1846 mm, on average) that, usually, occur in the form of intense storms. Therefore, rapid saturation of the regolithic mantle and powerful surface runoff trigger a huge number of landslides even in the case of a normal rainfall season [5]. Between November 7 th and 8 th, Hurricane Ida, and the low-pressure system 96 E, simultaneously struck the central area of El Salvador, with cumulated rainfall exceeding 300 mm/24 h in the Ilopango and San Vicente villages [5; 6; 27; 28]. Floods and landslides lashed these areas, causing around 200 deaths and huge economic losses [9], with damages to cropland, rural houses, and roads. In particular, the most devastating debris flows were triggered from the north-western flank of the San Vicente Volcano, hitting the villages of Verapaz and Guadalupe [5; 7]. Tropical depression 12 E affected El Salvador during the period from the 10 th to 20 th October. With a cumulative maximum of 1513 mm, equivalent to 42% of the mean annual rainfall of the period 1971-2000 [28], DT12 E was classified as the most severe meteorological event recorded in the region. Additionally, in this case, with 10% of the national territory affected, especially along the coastal plains and the volcanic mountains, El Salvador was heavily hit by the related floods and landslides, reporting 35 victims and an economic loss of more than USD nine hundred million [10; 28]. The Coatepeque debris flows were triggered by the tropical depression (TD) 12 E in 2011. The same extreme rainfall event activated the debris flows/slides of the San Salvador dataset.