Spatiotemporal dynamics of population change in flood risk zones of the Pearl River Delta (1985–2024)

The increasing likelihood of extreme adverse impacts driven by climate change has significantly impeded regional sustainable development, with flood-induced losses emerging as a critical challenge. This study selects six flood return periods, namely the 10-year, 50-year, 100-year, 200-year, 500-year, and 1000-year ones, to establish a complete gradient of low, medium-high, and extreme flood risks, breaking the limitation that existing studies mostly focus on the 100-year return period flood risk. By matching dynamic factors such as population size changes and flood control project upgrades in the Pearl River Delta (PRD), it quantifies the chain reaction law of "elevation of return period levels → shrinkage of safe zone scope → expansion of population size in flood risk zones" and reveals the dynamic evolution characteristics of flood risks, thereby providing precise scientific support for regional differentiated flood prevention and control. This study explores the spatiotemporal characteristics and regional disparities of population changes in flood risk zones and identifies the commonalities and specificities of such changes across different cities based on the scope of flood risk zones and exposed population, by adopting population distribution data from 1985 to 2024 and flood maps under six return period levels, to provide more robust and precise theoretical support for disaster prevention and mitigation in the Pearl River Delta in the future. As indicated by the cumulative growth rate, except for the scenario of a 10-year flood return period, the population growth rate within the extreme high-risk zone is significantly higher than that within the low-risk, moderate-risk and high-risk zones. the population growth rate within flood risk zones has exceeded that of the entire region, and in 8 cities except Shenzhen, the population growth rates within the high-risk and extreme high-risk zones have generally been higher than those within the medium-risk and low-risk zones; external conditions have influenced human activities during the change of return period grades, leading to distinct regional characteristics.