# ERS-1/2 and Sentinel-1 SAR Data Mining for Flood Hazard and Risk Assessment in Lima, Peru
## 5 Conclusions  
The Rimac River basin in the city of Lima in Peru is susceptible to flooding as demonstrated by the history documented in the natural disaster catalogues, due to both its intrinsic hazard factors (natural, geological and anthropogenic) and geographic location, which together lead to greater exposure to hydro-meteorological events triggered by the El Nino.  
The present study of the flooding events occurred in 1997-1998 and 2017-2018 demonstrates that the radar signal amplitude information extracted from ERS-1/2 and Sentinel-1 satellite SAR images can allow the identification of changes in the territory and, consequently, can be used as an objective information to improve the assessment of susceptibility to flooding hazard and corroborate what is known from in-situ observations and mapping of damage on the ground. By integrating the information mined from the SAR scenes with ancillary data on land cover, urbanized areas extent and geological information, the various sectors and zones of the Rimac River basin were classified in relation to the potential impact of flooding on the built environment and urban infrastructure, in light of the recent natural hazard events and urban development. Therefore, we developed a map of flooding risk classification at basin scale that, compared to existing hazard maps, has the advantage of using SAR data to enhance areas at high risk based on the evidence that they were already flooded during recent events, and warn about the consequent likelihood to be flooded again, should no risk mitigation measures have been put in place and events of equal severity occur in future.  
The comparison with the official map product that was generated by the Copernicus EMS during the Risk and Recovery Activation EMSN-038 for flood delineation and damage mapping of the same flooding event that happened in mid-March 2017 proves the accuracy and reliability of our change detection method, and reassured us that it provides a robust and validated input to the risk classification.  
The hydraulic risk mapping carried out in this study was developed _a posteriori_, that is, after the 1997-1998 and 2017-2018 flood events had already happened. However, the methodological approach presented in this paper can be applied in future for regular monitoring of the Rimac River basin, with the aim of updating the knowledge and understanding of flood risk factors and the consequent susceptibility. The SAR-based methodology is indeed suitable to be iteratively applied, should newly acquired SAR images be analyzed and/or other events occur. In this regard, it is worth recalling that such regular mapping of changes (either natural or anthropogenic) is a key element in the framework of disaster risk management, as it contributes to preparedness, resilience building and reduction of impacts of such natural hazard events on socio-economic levels.  
Conceptualization, D.T. and F.C.; methodology, N.A.R.; formal analysis, N.A.R.; resources, D.T. and F.C.; data curation, N.A.R.; writing--original draft preparation, N.A.R.; writing--review and editing, D.T. and F.C.; supervision, D.T. and F.C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
This research was carried out during the internship of [PERSON] at the Italian Space Agency (ASI) under the supervision of [PERSON] and [PERSON], in the framework of the II Level Master in Space Science and Technology at the University of Rome Tor Vergata (Italy). Copernicus Sentinel-1 and Sentinel-2 data were sourced from the European Space Agency (ESA)'s Copernicus Open Access Hub, while ERS-1/2 data were accessed through EOLi-SA (project ID 45250). Google Earth images (c) 2020 Maxar Technologies) were sourced and analyzed from Google Earth Pro. Global Urban Footprint (GUF) product over Lima was provided by the German Aerospace Center (DLR).  
The authors declare no conflict of interest.