Abstract
Natural hazards are indeed counted as the most critical challenges facing our world, represented in floods, earthquakes, volcanoes, hurricanes, and forest fires. Among these natural hazards, the flash flood is regarded the most frequent. In this work, we utilized two Sentinel-2 satellite images, before and after the flash flood, SRTM and photos captured by using a helicopter. This paper aims at three prime objectives. Firstly, the flood influence is determined on the city of Ras Ghareb, Egypt, based on analyzing free satellite data (Sentinel-2 images). Secondly, fuzzy the analytical hierarchy process (FAHP) method and a geographical information system (GIS) are integrated for flood risk analysis and evaluation in the flood-prone area. Finally, such a flood vulnerability map is used as an index to assist the decision-makers prepare for probable flooding. FAHP is preferable as it can cater to the uncertainties in data and analysis. As a result, FAHP is appropriate to determine the flood-vulnerable area in cities especially due to the matching with the most destroyed areas identified by the change detection between the two Sentinel-2 images. Then, the decision-maker can depend on Sentinel-2 images to estimate the flood influence through a regional scale or applying the FAHP on cities susceptible to flash floods in case of unavailable satellite images to contribute in establishing an early warning system enough to the evacuation of the risky areas.
Highlights
Urban flooding has been recently one of the most critical problems in the world due to its frequent occurrence which leads to infrastructure damage and people death. e flash flood in an urban area is identified by the comparatively short period of ephemeral water flow, scarcely takes more than one day [1]. e first step of flood management is the obtainment of the latest update of the hazard maps
All available data like geolocated photos or derived information provided by social media and the Internet [20, 21] or by volunteers [22, 23] can be very beneficial to improve the mapping of the flooded areas. erefore, we have searched in the Internet webpages, and we have found precious images, images captured by using a helicopter and terrestrial images by a geographic information volunteer. ese images significantly contribute to determine the area inundated and preknowledge of the classification results
Six LULC classes were specified as sea water, bare soil, buildings, roads, desert, and quarry area. e classification results of the pre- and post-flash flood images are illustrated in Figure 8. e flash flood has caused massive damage to infrastructure
Summary
Urban flooding has been recently one of the most critical problems in the world due to its frequent occurrence which leads to infrastructure damage and people death. e flash flood in an urban area is identified by the comparatively short period of ephemeral water flow, scarcely takes more than one day [1]. e first step of flood management is the obtainment of the latest update of the hazard maps. Spaceborne radar is the active sensor which emits a radar pulse and records the land surface backscatter at the satellites It has some merits over optical satellites; the ability of data collection through cloud cover and during the night [9, 10] and it has the ability of continuous observation of flood events for accurate, rapid, and costeffective flood mapping. Aerial remote sensing technology has abundant merits such as low flight altitude, which is not affected by clouds and, the very high spatial resolution (decimeter levels) which allows monitoring and assessment of flood impacts in the complex urban area compared with spaceborne observations. (1) e flash flood impacts on Ras Gharib city are monitored based on free satellite data (Sentinel-2) and mapping the destroyed areas. The local government is seeking hard to implement protective actions
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