What our alerts mean

Every month, each reservoir grows or shrinks by a normal amount. For example, many fill up in the rainy season.

We send an alert when a reservoir changes much more, or much less, than normal for that month.

If a lake shrinks more than normal, the dam may have let more water out downstream. Or less rain may have flowed in. We cannot always tell which.

Each alert has a level: MODERATE or STRONG. It also says how sure we are. Alerts at small dams are less sure.

An alert is a reason to look closer, not a flood warning. For safety, always follow your local and official warnings.

Translations are machine-drafted and need review by a native speaker.

How satellites measure dams · Accuracy · Methods