Flooding is one of the most devastating natural disasters, often causing significant loss of life and property. Even smaller, frequent floods can accumulate over time, substantially impacting communities. Despite their importance, these smaller floods are often overlooked as traditional methods focus primarily on extreme events.

To better understand flooding worldwide, we developed a new method using millions of satellite images collected from 2018 to 2023. This allowed us to map flooding events in greater detail than previously possible. Applying our dataset to urban areas, we found that over 80% of the world's largest cities, home to about 1.45 billion people, experience flooding more frequently than nearby rural areas. Coastal cities and those in the Global South are especially flood-prone.

Although our approach has limitations, such as cloud cover and satellite revisit intervals of about five days, it still provides the most detailed and continuous global flood map currently available, particularly useful for chronic flooding. Our dataset is also suitable for mapping extreme flood events such as tropical cyclones. These maps can help communities prepare for floods, guide infrastructure improvements, and ultimately reduce future risks to human life and property.