Joint impact of rainfall and tidal level on flood risk in a coastal city with a complex river network: a case study of Fuzhou City, China

Abstract

Abstract. Coastal cities are particularly vulnerable to flood under multivariable conditions, such as heavy precipitation, high sea levels, and storms. The combined effect of multiple sources and the joint probability of extremes should be considered to assess and manage flood risk better. This paper aims to study the combined effect of rainfall and the tidal level of the receiving water body on flood probability and severity in Fuzhou City, which has a complex river network. Flood severity under a range of precipitation intensities, with return periods (RPs) of 5 yr to 100 yr, and tidal levels was assessed through a hydrodynamic model verified by data observed during Typhoon Longwang in 2005. According to the percentages of the river network where flooding occurred, the threshold conditions for flood severity were estimated in two scenarios: with and without working pumps. In Fuzhou City, working pumps efficiently reduce flood risk from precipitation within a 20-yr RP. However, the pumps may not work efficiently when rainfall exceeds a 100-yr RP because of the limited conveyance capacity of the river network. Joint risk probability was estimated through the optimal copula. The joint probability of rainfall and tidal level both exceeding their threshold values is very low, and the greatest threat in Fuzhou comes from heavy rainfall. However, the tidal level poses an extra risk of flood. Given that this extra risk is ignored in the design of flood defense in Fuzhou, flood frequency and severity may be higher than understood during design.

Investigating compound flooding in an estuary using hydrodynamic modelling: a case study from the Shoalhaven River, Australia

“…Studies on compound flooding have been assessed on local scales using hydrodynamic models and joint-probability statistics (Lian et al, 2013;Chen and Liu, 2014;Olbert et al, 2017); and on regional to national scales using joint-probability statistics (Zheng et al, 2013;Wahl et al, 2015). Olbert et al (2017) have investigated the interaction of storm-tide and riverine flooding drivers in the Lee Estuary using a coupled ocean-hydrodynamic model.…”

Bivariate copulas functions for flood frequency analysis

“…Application of copula methods in modeling the joint distribution could relax the limitation of the traditional flood frequency analysis by selecting marginal from different families of probability distribution functions for flood characteristics. It is found that copula based flood frequency analysis performs better than conventional flood frequency analysis [20].…”

“…Its association with a bivariate t-distribution can be illustrated by stating two dependent variables with degrees of freedom and a correlation linear coefficient, (Lian et al 2013). …”

Extreme Events Assessment Methodology Coupling Debris Flow, Flooding and Tidal Levels in the Coastal Floodplain of the São Paulo North Coast (Brazil)

“…As well known, the study of the joint effect between the tide and the rainfall flooding and debris-flow effect is one of the most important areas of the knowledge to be developed in the research community in the new century [2][3][4][5]. However most of these analyses were conducted using numerical modeling and neglecting a detailed statistical analysis between rainfall effects and tide recorded data [5].…”

“…However most of these analyses were conducted using numerical modeling and neglecting a detailed statistical analysis between rainfall effects and tide recorded data [5].…”