How Do You Cool a Big City?
Mannheim is currently setting up a network of measuring stations to collect data on the microclimate. The aim: an effective concept for more green spaces - and a city that remains liveable even in the heat.
The sun is beating down, the tarmac almost seems to be melting, there is not a breath of air between the tall buildings. What could be better on a hot summer's day in the city than a cool spot in a park, on the banks of a lake or a river? It has long been recognised that more greenery and unsealed surfaces help to make cities more resilient to climate change. In near-natural landscapes, it is not just us humans who find the microclimate - i.e. the conditions in the air layers close to the ground - much more pleasant. Plants and water surfaces cool through evaporation, trees and shrubs provide shade. Concrete jungles, on the other hand, threaten to become dangerous heat islands on hot days. So plant everything you can in city centres? It's not quite that simple ...
Smart Roots Project
Smart City Mannheim GmbH, a municipal joint venture with MVV Energie AG, intends to work with the city's Climate Protection and Climate Impact Adaptation departments in the Smart Roots project over the coming years to find out how major cities can better arm themselves against climate change. Mannheim is particularly affected by the ongoing warming: The second largest city in Baden-Württemberg is located in the Upper Rhine Plain, a region with particularly warm summers, and is one of the hottest cities in Germany. Together with its sister city Ludwigshafen, Mannheim forms a conurbation with areas that are a good two thirds sealed. The number of annual hot days with temperatures of at least 30 degrees has already risen by 81 per cent to 21 days since 1991.
But how can a large city be cooled effectively: with fresh air corridors, more trees in the pedestrian zone, larger parks or green roofs? ‘We want to find out which measure has which effect,’ says Sven Riffel, Smart City Manager at Smart City Mannheim. The engineer is not a fan of the watering can principle. After all, he points out, a municipality is also about the responsible use of taxpayers' money and reconciling interests. A city not only needs trees but also housing, industrial and commercial space, car parks and much more...
Unsealing and Planting
In the future, reliable data should help the city administration to decide how, where, and to what extent the city needs to be unsealed and planted in order to improve the quality of life during hot spells. "One question is, for example: Do lots of small green spaces also help with connectivity?’ says climatologist Dr Wolfgang Lähne, who is supporting the Smart Roots project. To provide answers, Smart City Mannheim has been building a close-knit climate and environmental monitoring network since 2022. The first sensors have already been installed at a height of three to four metres on street lighting masts in the Neckarstadt district, collecting data on humidity and air temperature as well as wind speed and direction. ‘We are creating a database, not only for Mannheim, but also for third parties,’ says Sven Riff el.
Particularly important: the sensors, which are independent of the power grid, are designed to collect the actual air temperature in real time - regardless of whether the devices are installed under a tree, in the shade of a building or in the blazing sun. ‘We can only find answers to our questions with high-quality data,’ says Wolfgang Lähne.
By the end of the year, Smart City Mannheim will have installed measuring stations at 350 to 400 locations - around three per square kilometre of the city. Each individual site will be examined and selected by climatologist Wolfgang Lähne. One of Smart City Mannheim's co-operation partners is Rhein-Neckar-Verkehr GmbH. Since the spring, a tram has been travelling on lines 1 and 3 as a rolling measuring station in the city as part of a pilot project. The advantage: the public transport vehicle travels the same route at regular intervals - and thus contributes to a detailed climate profile of Mannheim. The technology collects data on wind and precipitation as well as the temperature on the ground. Some of the tram tracks have already been greened, and the travelling measuring station is also intended to show how great the positive effect of this measure is.
A lot Helps a Lot?
This no longer applies to green spaces, especially when the plants that are supposed to cool the city are themselves subject to heat stress and die. In addition to data on climate and air quality, the Smart City Mannheim project team is therefore also collecting data on soil moisture and soil temperature in urban green spaces. ‘We are working closely with our colleagues from the Mannheim Urban Space Service,’ says Sven Riff el. As part of a pilot project, ten trees of different species throughout the city are equipped with sensors in order to derive findings for comparable locations. ‘We want to know which tree needs water and when,’ says the Smart City Manager. In the future, the data collected will help the employees of the urban space service to water the green spaces in Mannheim in a more resource-efficient way.
Climate change is causing extremes to become more frequent. Not only long droughts are a problem, but also when too much precipitation hits sealed surfaces in a short space of time. ‘Our urban drainage system is also interested in the data,’ says Sven Riff el. The climate monitoring network is intended to show how much rain falls in which neighbourhoods. ‘It used to happen that the world virtually ended in one neighbourhood - and the rest of Mannheim didn't even notice,’ says the Smart City Manager. Such weather phenomena, which are limited to a very small area, could become more frequent as a result of climate change, says climatologist Wolfgang Lähne. All the more reason to collect data in the urban area more closely than in the past. In the event of heavy rainfall, for example, the measuring stations could support the fire brigade in planning their operations, which would then know at an early stage where flooding is imminent in Mannheim. The population can also be warned via apps.
Sven Riff el is convinced that it makes sense to take a close look at which measures will really help in the face of climate change. ‘We want to make the city resilient for the future and adapt it to the consequences of climate change.’ That's why he and his colleagues are passionate about the Smart Roots project and the development of the climate measuring network. ‘I believe many other cities can benefit from this.’
