Redefining flood hazard and addressing emerging risks in an era of extremes
Mohammad Shamsudduha
Abstract
Globally, floods are becoming more frequent and increasingly destructive, driven by the accelerating impacts of anthropogenic climate change (increasing hazards), urbanization with growing settlements in floodplains, and aging infrastructure (increasing exposure and vulnerability) 1 . Between 1990 and 2022, floods affected 168 countries, impacting over 3.2 billion people, causing more than 218,000 deaths, and leading to economic losses exceeding 1.3 trillion US dollars 2 . In 2024 alone, floods have affected over 23 million people worldwide from the Global South to the Global North. In August–September 2024, devastating floods resulted in deaths, destruction, and economic losses across Bangladesh, Nepal, Nigeria, Sudan, Thailand, and several countries in Central Europe. Bangladesh, one of the most flood- and cyclone-prone countries in the world 3 , experienced devastating flash floods in August 2024, claiming 42 lives and affecting over 5 million people 4 . Similarly, flash flood events of September 2024 in Central Europe – particularly in Austria, the Czech Republic, and Poland – were described as the worst in decades, taking at least 24 lives. In October 2024, the Valencia region of Spain faced catastrophic flash floods, with torrential rainfall exceeding 250 mm in some areas in less than 24 hours, leading to a human death toll of over 200 and causing extensive damage to homes, infrastructure, and agricultural lands 5 . A common factor in these disastrous flood events was the escalating scale, intensity, and rapid onset of flood hazards. These events highlight the severe impacts of extreme weather driven by anthropogenic climate change 6 , which not only influences hazard frequency and intensity but also interacts with increased human exposure and vulnerability in our societies. Intensified and widespread flood hazards increase human exposure and vulnerability globally with 2 billion people living on floodplains including 1.4 billion on the 100-year floodplain 7 . Asia is the region with the highest number of people exposed to flooding, with 1.5 billion individuals residing on floodplains, accounting for 35% of the continent’s total population 7 . Floods disrupt agricultural production, damage crops, and contaminate surface water sources, undermining food security gains and complicating freshwater management systems. Therefore, understanding emerging global flood risk and assessing population exposure are essential for evaluating impacts and developing strategic measures to reduce future flood disasters 8 .