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 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 3,883 stations influenced by TCs alongside global discharge simulations from the ISIMIP 2a. Our results show that TC-induced floods in inland areas are not always found along the TC path but can be located about 1,000 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 TC, the flood magnitude with n-year return period is greater when estimated from TC-induced floods only. Therefore, regions (especially inland regions) should thoroughly consider the extremity of TC-induced fooding when improving hydraulic infrastructures to ensure a more conservative design, thereby enhancing the safety of these hydraulic projects.