Monitoring the Iran Pol-e-Dokhtar flood extent and detecting its induced ground displacement using sentinel 1 imagery te
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Monitoring the Iran Pol‑e‑Dokhtar flood extent and detecting its induced ground displacement using sentinel 1 imagery techniques Ali Mehrabi1 Received: 12 March 2020 / Accepted: 29 October 2020 © Springer Nature B.V. 2020
Abstract On 25 March 2019, the Lorestan Province, Iran, suffered a heavy rainstorm. This rainstorm flooded the city of Pol-e-Dokhtar and many villages. To elucidate and monitor the nature of the spatial extent during and after the flood event, and to evaluate flood-induced ground displacement, the time series Sentinel 1 images were analyzed using threshold and SBASInSAR techniques. The SAR images were first calibrated, geometrically corrected, and filtered. Then, the threshold method was applied to draw the map of the affected areas. The results showed that flood spatial propagation varies through time. The nature of spatial extent was sinusoidal, so that the flood behavior complied with precipitation periods. Furthermore, the findings of the SBAS-InSAR indicated how an extreme flood can cause ground displacement. Several active movement areas were identified, showing a surface velocity up to −1.1 mm day−1 away from the satellite. The field observations demonstrated that the landslide phenomenon occurred in some of these areas. Therefore, the other identified areas can also be at risk of landslides. Finally, based on the findings, it is evident that SAR data can effectively be used for flood water mapping, flood monitoring, and floodinduced ground displacement. Keywords Flood extent · Threshold method · Ground displacement · SBAS-InSAR method · Pol-e-dokhtar flooding · Iran
1 Introduction Floods have recently increased due to climate change, particularly in densely populated regions of the Middle East (Almasi and Soltani 2016). In March 2019, many provinces of Iran suffered a heavy rainstorm and were affected by flooding. Among them, the city of Pol-e-Dokhtar in Lorestan Province strongly suffered; more than 70,000 people were affected by this flood, in which 15 people lost their lives. Cars and buses were submerged and many buildings were destroyed (Fig. 1). * Ali Mehrabi [email protected] 1
Department of Geography, Faculty of Literature and Humanities, Shahid Bahonar University of Kerman, Kerman, Iran
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Natural Hazards
Fig. 1 Field photographs of flooding hazards in Pol-e-Dokhtar
Although it is impossible to avoid flood hazards or prevent their incidence, it is possible to decrease their effects and the resulting losses (Elkhrachy 2015). A major challenge during the flood is to achieve an overall vision of the event with the accurate extent of the affected area. Flood extent maps can be a guiding source for effective risk management, helping relief organizations and decision-makers to acquire spatially clear information about inundated regions in a time- and cost-efficient manner (Mason et al. 2015). In addition, such maps can supply validation data and precious distributed calibration for the hydraulic models of river flow processes (Dung et al. 2011; García-
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