Detecting rainfall in urban areas

What amount of rainfall causes flooding in urban areas? No one actually knows. In order to gain more knowledge of the impact of rainfall, TU Delft and international partners are trying to find answers by cooperating in the RainGain project. They use new radars and measuring systems on rooftops and the ground - even trams collect data.

Unknown how much rain falls in the city. (Photo: Mariska van Rijswijk)

Weather forecasting institutes traditionally built measuring system to detect rainfall as far away as possible from obstacles, like buildings and trees. In Rotterdam, a system is located at the airport, for example. This will make it easier to accurately know how much rain has actually fallen. “But the downside is that we do not know how much rain falls in the city,” says assistant professor of urban drainage, Marie-Claire ten Veldhuis.

In order to fill this knowledge gap, Prof. Ten Veldhuis is cooperating with 13 international local authorities and academic and business partners in the RainGain project. In four cities (Rotterdam, London, Paris and Leuven) the rainfall will be intensely measured. On the 16 of April the partners will come together to share information and best practices at an international workshop in Leuven.

TU Delft will detect the rainfall in Rotterdam, where there are now measurement systems on rooftops, the ground and even on top of trams. “We will also use a new radar that accurately detects rain in an area of 30 kilometres. It will see the shape and direction of the raindrops, and will be placed on the Nationale Nederlanden building near Rotterdam Central Station. The radars currently used to detect rain in the Netherlands give less detailed information.” Delft can learn a lot from scientists in Leuven, where an older version of the radar was placed in 2008.

RainGain will also focus on how to deal with the amount of rainfall in order to prevent flooding. Interestingly enough, the cities use different approaches. “Paris has many hills and uses large basins underneath the city. Rotterdam is a polder area and almost flat, has less basins and is thinking about storing water on squares in a controlled way in case of an emergency. London focuses on early warning systems and informing inhabitants what they can do by installing barriers at house level. The different circumstances and approaches will provide a fascinating overview of rainfall and flooding in urban areas.”

The project will go on for at least four years and an international workshop will be held every six months in one of the four cities.