Comment on nhess-2021-308

doi:10.5194/nhess-2021-308-rc2

Abstract

The co-occurrence of storm tide and rainstorm during tropical cyclones (TCs) can lead to compound flooding in low-lying coastal regions. The assessment of TC compound flood risk can provide vital insight for research on coastal flooding prevention. This study investigates TC compound flooding by constructing a storm surge model and overland flooding model using Delft3D Flexible Mesh (DFM), illustrating the serious consequences from the perspective of storm tide. Based on the probability distribution of storm tide, this study regards TC1415 as the 100-year event, TC6311 as the 50-year event, TC8616 as the 25-year event, TC8007 as the 10-year event, and TC7109 as the 5-year event. The results indicate that the coastal area is a major floodplain, primarily due to storm tide, with the inundation severity positively correlated with the height of the storm tide. For 100-year TC event, the inundation area with a depth above 1.0 m increases by approximately 2.5 times when compared with 5-year TC event. The comparison of single-driven flood (storm tide flooding and rainstorm inundation) and compound flood hazards shows that simply accumulating every single-driven flood hazard to define the compound flood hazard may cause underestimation. For future research on compound flooding, copula function can be adopted to investigate the joint occurrence of storm tide and rainstorm to reveal the severity of extreme TC flood hazards.

Highlights

Flood hazards, especially those happening during tropical cyclones (TCs), have become the most devasting and expensive natural hazards of coastal cities (Patricola and Wehner, 2018; van Oldenborgh et al, 2017; Hallegatte et al, 2013; Adelekan, 2011)
The results indicate that the coastal area is a major floodplain, primarily due to storm tide, with the inundation severity positively correlated with the height of the storm tide
The results show that storm tide is the key driving factor of compound flood inundation in Haikou, and tide level decides the inundation extent

Summary

Introduction

Especially those happening during tropical cyclones (TCs), have become the most devasting and expensive natural hazards of coastal cities (Patricola and Wehner, 2018; van Oldenborgh et al, 2017; Hallegatte et al, 2013; Adelekan, 2011). Lian et al (2017) identified the major hazard-causing factors of compound flooding and classified the floodplains into tidal zone, hydrological zone, and transition zone in Haikou City Studies such as these have investigated the joint risk of hazard-causing factors in compound floods, they seldom pay attention to the compound flooding that occurs during TCs. 72 Most studies concerned with compound flooding rely on historical data, which contains information on hourly storm tide and daily rainfall (Yum et al, 2021; Fang et al, 2020; Zellou and Rahali, 2019; Wu et al, 2018; Lian et al, 2017). The objectives of this study include (1) investigating the probability of storm tide during TCs by modelling TCs influenced Haikou; (2) quantifying the compound effects of rainfall and storm surge under TC events of different return periods; (3) assessing and comparing the flood severity of rainstorm inundation, storm tide flooding, and compound flooding.

Methods

Results

Conclusion