Flood Hub

Flood Hub is a flood-forecasting website built by Google. Think of it as taking the flood warning sign at the edge of a town and moving it onto an online map. It shows, in color, how much a river is expected to rise over the coming days and which areas are likely to end up underwater as a result.

Building the map takes two steps. First, data on rain, temperature, and terrain is gathered to calculate how much water will flow through a river. Then that calculation is used to draw exactly which land will be flooded. If the first step figures out what's happening to the river, the second step translates that into a map of the land where people actually live. Because the system is designed to make predictions even in places without real gauge records — by pulling in weather and surface data from around the world — it can produce forecasts for towns that have no monitoring station at all.

But not every forecast shown carries the same weight. Points verified against real observed data and points filled in purely by calculation, with no gauge nearby, sit side by side on the same map — meaning information of very different reliability can appear right next to each other on the same screen.

The article reports that, as of the time in question, Flood Hub had grown to cover nearly 250,000 forecast points, with the population able to receive forecasts rising from 460 million to 700 million. One number that's easy to misread here is 2 billion people across 150 countries — that's the total population across all the areas Flood Hub attempts to forecast for, a mix of forecasts verified with real observed data and ones that haven't been verified yet. Appearing on the map doesn't mean every point has the same level of accuracy.

1. Open the Flood Hub website in a web browser.
2. Type the name of a river or region you're interested in into the map search box.
3. Check the water-level forecast graph and the expected flood extent for that location.
4. Look at the accompanying notes to see whether the point shown is based on a real gauge or filled in by calculation.