Streamflow Map Forecasts Water Flows for 7 Million Stream Reaches

Although floods are the most common weather-related natural disaster, they can be difficult to predict. Flooding can be driven by events upstream. But their impacts tend to be localized and depend on the unique hydrology of an area.

An updated model from the Group on Earth Observations global water sustainability initiative GEOGLOWS offers a new approach to flood forecasting. This interactive map from Esri uses the GEOGLOWS model to forecast streamflow over the next 10 days for seven million global stream reaches.

The interactive map is multiscale and reveals more rivers and streams as you zoom in. Rivers and streams are symbolized in two important ways. The thickness of the map’s river stroke reflects the volume of water. The color indicates the likelihood of high-water flows using the hydrological concept of a return period. Normal and low flows are mapped in blue, while extreme flows (with a 2% chance of occurring in a typical year, or once in a 50-year event) are shown in purple. Hydrologists typically expect floods anytime flows exceed volumes from once in 10-year event. In the map, rivers and stream reaches in orange, red, and purple can be expected to cause various levels of flooding.

A key distinction of the map is the way it treats streams that naturally carry different volumes of water. A high volume of water in the Amazon River may not lead to flooding due to its normal flow capacity. In contrast, a lower volume of water may cause a smaller stream to flood. A thick, blue line on the map is a river that normally carries a lot of water but isn’t at risk of flooding. A thin red line represents a smaller stream that is likely to flood.

You can step through the 10-day forecast using the time slider at the bottom. You can move to a specific point in time, or “play” the map to animate the forecast. As time passes, the map updates to show flows and return periods. It’s a fascinating way to watch the cycle of streams swelling with water before returning to normal flows.

You can click any stream on the map to see its name and current flow. The map also generates an interactive chart showing forecasted flows over the next 10 days. Zooming in or hovering over a point in time reveals forecasted flows and ranges. The chart reflects the colors from the map, so you can see when a given stream is approaching levels that may cause flooding. Moving the time slider with the chart open will also animate the chart over time.

These kinds of specific, local forecasts can help communities prepare for flood events. But they’re also useful for understanding impacts to agriculture, energy generation, logistics, and recreation. With maps like this, we should be able to better understand and anticipate floods before they happen.