Yinxue Liu

Abstract More than one billion people are exposed to flood risk globally, with this number projected to double by 2050. Global flood models underpin risk assessment and adaptation planning, yet typically assume that river bankfull capacity corresponds to a fixed two-year return period, neglecting spatial and temporal variability in channel characteristics.

1 Introduction Flooding is one of the most devastating and costly natural hazards, affecting tens of millions of people each year (CRED, 2023). Flood exposure continues to increase in many regions with population growth and climate change (Ford et al., 2019; Hirabayashi et al., 2021; IPCC, 2023). For example, urbanized areas in floodplains with a 1% annual probability of flooding have almost doubled since 1985 (Andreadis et al., 2022).

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