A new radar system can show us exactly how much rain is falling in a given spot.

In June, as rain flooded Paris, scientists from the Ecole des Ponts ParisTech huddled around their laptops to read data from a sensor atop a campus building. The scientists were creating the most detailed map of urban flooding in existence. And they did it using a state-of-the-art rainfall detection system being tested in Paris and Rotterdam, in the Netherlands.

Site of the dual-polarization X-band radar in Rotterdam, on top of the Nationale-Nederlanden insurance building. Image courtesy of Flickr user wisigreter.

Here's how it works -- scientists perch dual-polarization X-band radars on top of semi-tall buildings. (This is the same technology used to measure oncoming short-range missiles in combat.)

These radars constantly emit energy pulses that accurately detect how much water is falling on a given street, and whether the precipitation is rain, snow, sleet, or something else. This, in turn, makes it possible to precisely map how much water is collecting in different parts of a city or town, says Marie-Claire ten Veldhuis, coordinator of the project in Rotterdam.

As a result, officials can identify what parts of a city are going to flood real-time, and can get water pumps and pathways in place. It will also help cities warn drivers about closed roads or residents about potential evacuations.

ten Veldhuis hopes to have the experiments fully operational by the end of this year.

A map of the rainfall rate in mm/hr, within a 15-kilometer radius around a dual-polarization X-band radar in Cabauw, The Netherlands. Image courtesy of Cesar Observatory

Rainfall rate in mm/hr, within a 15-kilometer radius around a classic radar in De Bilt, The Netherlands. Image courtesy of the Royal Netherlands Meteorological Institute

London is investigating whether shortening the energy pulses from their classic radars would achieve a similarly detailed map, while Leuven, in Belgium, is testing an older X-band radar that doesn't use dual-polarization. These radars are less exact than the ones in Paris and Rotterdam but also require less financial investment. Scientists hope that they can use these study results to design cost-effective flood management alternatives for municipalities that are not able to afford the latest X-band radars. The four cities are collaborating with a host of academic and civic institutions under an EU-funded project that they call RainGain.

A similar experiment is underway in the United States, but scientists there are using X-band radars to predict all kinds of weather events, like tornadoes and dust storms. Plus, the US systems aren't specifically designed to map out urban jungles. The European project is focused solely on improving individual cities’ preparedness for flooding.

An example of radar rainfall rate differences in the same location. Left: X-band radar. Right: Classic radar. Credit: Marie-Claire ten Veldhuis.

Top image: Brian A Jackson/

About the Author

Most Popular

  1. A young refugee from Kosovo stands in front of a map of Hungary with her teacher.

    Who Maps the World?

    Too often, men. And money. But a team of OpenStreetMap users is working to draw new cartographic lines, making maps that more accurately—and equitably—reflect our space.

  2. POV

    The Gateway Project Doesn't Need Trump's Approval

    The $30 billion rail tunnel project may be a victim of President Trump’s feud with Democrats. But New York and New Jersey could still save it.

  3. Equity

    The Austin Bombings Are Terrifying. But Are They 'Terrorism'?

    Absent a motive, the serial bombing attacks in Texas hadn’t been labeled with the term. Now, police say the suspect has been killed.

  4. A woman at a homeless encampment in Anaheim, California

    The Unhappy States of America

    Even with the economy humming, Americans are feeling more anxious, depressed, and dissatisfied with their lives than they did in 2009.

  5. A self-driving Volvo SUV in Scottsdale, Arizona. The company has halted testing of its autonomous vehicle program in the wake of a fatal crash on Sunday.

    How the Self-Driving Dream Might Become a Nightmare

    What will happen if we just accept that a certain number of pedestrian deaths are an inevitable part of adopting autonomous vehicles?