## 3 Experiments
### Flood Risk  
Coastal flood risk and adaptation are worldwide concerns [296,297]. Previous studies suggest that about 40 million people living in coastal port cities are likely to be subject to at least one major coastal flooding event each century [298]. Using global re-analysis products of storm surge and extreme sea levels and a hydrodynamic model, [PERSON] et al. [299] estimated 76 million people could be subjected to a once a century flood event. The most significant inundation mainly occurs in the delta regions of Asia and Europe, especially China, the Netherlands, Vietnam, and Egypt, all of which have relatively sensitive flood exposure. European coasts will be strongly impacted by climate-induced flood risk [11]. It has been estimated that by the end of 2100, five million Europeans will be under the threat of a 100-year extreme sea level event [11]. Previous investigations have documented that low-lying river deltas, especially cities, are significant flood risk hotspots [299, 300, 290]. Global climate change and local ground subsidence can significantly increase the exposure to coastal flooding risk. Previous research has employed different approaches (e.g., GIS-based method, RS, hydrodynamic models, etc.) to map and simulate flood inundation in floodplains [302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316]. Various numerical models have also been developed for floodplain delineation/flood inundation and flow simulation [317, 318, 319, 320].  
Satellite RS is a valuable tool for detecting and monitoring flood phenomena [318,321], allowing the differentiation between inundated and non-inundated areas. Flood risk increases due to urban growth, land subsidence, and climate change [322]. Identifying areas that are more prone to extreme floods helps optimize urban planners' civil protection actions and evaluate damage [323]. To reliably estimate the losses in affected regions, comprehensive maps of the flooded areas and the computation of the water level and flow velocity are required [324, 325, 326, 327]. Recent advances in RS technology have allowed the generation of rapid damage prediction maps and associated models helpful in a flood event [e.g., the Copernicus Emergency Management Service ([[https://emergency.copernicus.eu/](https://emergency.copernicus.eu/)]([https://emergency.copernicus.eu/](https://emergency.copernicus.eu/))) (accessed on 1 May 2021)]. Satellite RS data are beneficial to detect the impact of severe floods at distinctive spatio-temporal resolutions, using multispectral [328, 329, 330, 331, 332] or SAR [333, 334, 335, 336, 337, 338, 339] images. SAR data are beneficial for sub-tropical cloud-prone areas, and consecutive SAR time series help a multifaceted understanding of flood regimes. For instance, [PERSON] et al. [321] used ENVISAT ASAR-WSM time series with a spatial ground resolution of about 150 m for analyzing flood dynamics and floodwater progression in the Mekong River Delta. Associated with coastal flooding risk is the growing worldwide occurrence of extreme weather events and rapidly evolving flash floods that overpower the capacity of coastal populations to develop effective responses [340; 341]. RS satellite data are widely used to monitor rapid flash floods' effects and forecast their occurrence and strength. For instance, a recent study has documented a remarkable increasing tendency of extreme rainfall in the vicinity of major Chinese delta rivers, including the cities of Shanghai, Suzhou, and Nanjing, from 1998 to 2015 [342]. Several advanced applications of RS technology for the evaluation of the effects of extreme rainfall have recently been proposed [343; 344; 345; 346]. Finally, it is also worth highlighting that weather radar has assisted predictions for more than 50 years by providing rainfall estimates and helping develop proper hydrological models (see, for instance, [347; 348]).