Flooding affects more people than any other environmental hazard and hinders sustainable development^1,2. Investing in flood adaptation strategies may reduce the loss of life and livelihood caused by floods³. Where and how floods occur and who is exposed are changing as a result of rapid urbanization⁴, flood mitigation infrastructure⁵ and increasing settlements in floodplains⁶. Previous estimates of the global flood-exposed population have been limited by a lack of observational data, relying instead on models, which have high uncertainty^{3,7,8,9,10,11}. Here we use daily satellite imagery at 250-metre resolution to estimate flood extent and population exposure for 913 large flood events from 2000 to 2018. We determine a total inundation area of 2.23 million square kilometres, with 255–290 million people directly affected by floods. We estimate that the total population in locations with satellite-observed inundation grew by 58–86 million from 2000 to 2015. This represents an increase of 20 to 24 per cent in the proportion of the global population exposed to floods, ten times higher than previous estimates⁷. Climate change projections for 2030 indicate that the proportion of the population exposed to floods will increase further. The high spatial and temporal resolution of the satellite observations will improve our understanding of where floods are changing and how best to adapt. The global flood database generated from these observations will help to improve vulnerability assessments, the accuracy of global and local flood models, the efficacy of adaptation interventions and our understanding of the interactions between landcover change, climate and floods.

与其他任何环境危害相比，洪水对人的影响更大，并且阻碍了可持续发展^1,2。投资于洪水适应战略可能会减少洪水造成的生命和生计损失³。^{由于快速的城市化4}、防洪基础设施⁵和洪泛区定居点的增加⁶ ，洪水发生的地点和方式以及受灾人群正在发生变化。先前对全球受洪水影响的人口的估计受到缺乏观测数据的限制，而是依赖于具有高度不确定性的模型^{3,7,8,9,10,11}. 在这里，我们使用 250 米分辨率的每日卫星图像来估计 2000 年至 2018 年 913 次大型洪水事件的洪水范围和人口暴露情况。我们确定总淹没面积为 223 万平方公里，有 255-2.9 亿人直接受洪水影响. 我们估计，从 2000 年到 2015 年，卫星观测到的洪水地区的总人口增加了 58-86 百万。这意味着全球遭受洪水的人口比例增加了 20% 到 24%，是之前的 10 倍估计⁷. 对 2030 年的气候变化预测表明，受洪水影响的人口比例将进一步增加。卫星观测的高空间和时间分辨率将提高我们对洪水变化的地方以及如何最好地适应的理解。从这些观测中生成的全球洪水数据库将有助于改进脆弱性评估、全球和地方洪水模型的准确性、适应干预措施的有效性以及我们对土地覆盖变化、气候和洪水之间相互作用的理解。