The Influence of Tropical Cyclones on Mixed-Population Flood Frequency Analysis

Abstract Floods induced by tropical cyclones (TCs) and their frequency analysis have received much attention at the regional scale, but little is known about the role of TCs in the mixed flood frequency analysis at the global scale, which is the key for hazard management. Here, we investigated the influence of TCs on the upper tail of flood frequency estimates using discharge observations at 3883 stations influenced by TCs alongside global discharge simulations from the second phase of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2a). Our results show that TC-induced floods in inland areas are not always found along the TC path but can be located about 1000 km ahead, which is linked to TC-induced predecessor rain events. Extreme floods associated with TCs are generally larger in coastal areas compared to those in inland areas, whereas TC-induced floods in some inland areas tend to be more extreme relative to their local flood magnitude. The flood peaks generated by TCs and other mechanisms compose a mixed population flood series. However, the largest flood peaks in coastal areas are usually affected by TCs. These large TC-induced flood peaks play an important role in making the upper tail of the flood frequency curve heavier. In regions affected by TCs, the flood magnitude with an n -yr return period is greater when estimated from TC-induced floods only. Therefore, regions (especially inland regions) should thoroughly consider the extremity of TC-induced flooding when improving hydraulic infrastructures to ensure a more conservative design, thereby enhancing the safety of these hydraulic projects. Significance Statement Tropical cyclones (TCs) are responsible for extreme floods in coastal and inland areas influenced by TCs, which may play an important role in the flood frequency analysis and flood risk management. In this study, we investigated how TCs affect the upper tail of flood frequency estimates at the global scale. We find that extreme floods associated with TCs are generally higher in coastal areas, whereas TC-induced floods in some inland areas tend to be more extreme relative to their regional flood magnitude. These anomalously large TC-induced flood peaks control the upper tail of the flood frequency curve in coastal and inland areas and make the upper tail heavier. Globally, the flood magnitude once in n years is generally greater, estimated from only TC-induced flood peaks than that estimated from all flood peaks. Therefore, regions (especially inland regions) should thoroughly consider the extremity of TC-induced flooding when improving hydraulic infrastructures to ensure a more conservative design, thereby enhancing the safety of these hydraulic projects.