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Can we predict floods?


© AMNH
Robert Brackenridge at work

Historical records of floodplains help us prepare for floods. Knowing which lands were once under water makes it easier to figure out whether those areas may be prone to future flooding. Many countries record the amount of water passing by gauging stations, but few make maps showing previously underwater lands. Why are maps so important?

Maps pinpoint areas that are safe for development. Large floods hit a specific region approximately every 50 or 100 years. That means we need maps to identify historical floods, not just recent floods. If no maps exist, how do people know which areas are flood-prone?

In many countries, word of mouth is the only way that people know if an area is dangerous. In the United States, for instance, the government uses estimates of flood sizes (the amount of water a flood produces) to estimate how much of the floodplain will be flooded. But predictions are uncertain. When a big flood actually occurs, even carefully prepared maps may prove inaccurate. Why?

Landscapes change over the years. Sometimes they erode, and other times major construction alters a region. Landowners may partially fill or enroach on a river adjoining their property--causing severe flooding upstream. When a river floods, it always changes the landscape. This makes it difficult to predict future floods. But comparing new satellite images with old floodplain maps lets experts see the differences between floods immediately. This makes it easy to keep track of floods around the world. What can this tell us?

Accurate maps that are easy to update help scientists understand the relationship between rainfall and flooding. They can look at a region and see exactly how much rainfall will provoke a flood. Then they can then determine which regions are more susceptible to flooding--and why. The result is smarter city planning, which means fewer catastrophes.