On a hot summer day, it can be excruciatingly hot in some parts of the city while the trees of the parks offer a nice coolness in other parts of the city. That there can be large temperature differences in a city is not news -- but being able to locate the really hot spots has become increasingly urgent in recent years as temperatures have increased. The really hot places are called urban heat islands, “heath islands” and on hot days these environments can create big problems.

An urban heat island is a metropolitan area that is noticeably warmer than its surroundings. As a rule, the temperature difference is greater at night than during the day, and greater in winter than during summer. Factors that play a role are mainly the height, location and materials of buildings, the proportion of hardened surface, as well as both the proportion of vegetation and the type of vegetation.

Lund Municipality works according to Lundaeko, the municipality's plan for ecological sustainability, and includes climate adaptation. One way to adapt to climate change is to have a preparedness to deal with extreme weather events.

- Climate work due to extreme heat has two parts; firstly that we should work preventively with the physical environment to be better equipped and secondly we should be able to minimize the consequences when there is a heat wave, says environmental strategist Linda Birkedal. This project has the potential to help with both of these parts. The technology could detect areas where vulnerable groups such as young children or the elderly live and where temperatures are relatively higher than in other areas. When detecting such places, the Service Administration would be able to see what can be done to make the place cooler. And when we have a heatwave, we can give advice in real time — like recommending the city park as a place to cool off.

During the summer of 2021, the municipality of Lund deployed humidity and temperature sensors at 19 locations in Lund with the help of the Lund company Sensefarm, which was part of the Smart Public Environments (SOM) project. Most of the sensors were placed adjacent to activities such as kindergartens and old people's homes. In the project, some sensors were also installed in some public places in the city to provide a comparison material.

- During the summer of 2021, there were some short-term heat waves, so we had the opportunity to test and learn about the technology, continues Linda Birkedal. We have previously had a very long time series with measurements of the temperature at a site in Lund from SMHI. This is very valuable — but the measurements with sensors have made it clear that we need to measure in more places than one to get a better overview.

In the survey, it was found that the temperature varied greatly in different places in Lund, sometimes more than five degrees. Since so far there has only been one sensor per site, the values cannot be the basis for any direct action, but they nevertheless gave indications of locations where it might be interesting to continue with measurements. Low temperature values on the sensor that had been placed in the city park also supported the possibility of recommending the park as a cool place to visit on hot days.

How will you continue the work now?

- Right now we are considering making a heat map for the whole of Lund. This would mean that we not only measure but also model, including by using GIS tools (GIS means Geographic Information Systems). In this way, the information can be linked to geographical locations.

The municipality has already started a study of how much shade the trees provide through a crown cover analysis both inside Lund and in some of the villages. It is done by the municipality taking photos of the trees and their shade with drones to see where there is a lack of shade and where there are likely to be heat islands. It showed that the need to take measurements can generally be said to be greater in Lund than in, for example, Veberöd, which has a larger crown coverage.

- We could continue the crown coverage analysis to get more clues to where the heat islands are located, says Linda Birkedal. In such places, improvements could be made, for example by planting out trees or putting green roofs where possible. In general, it can be said that trees and greenery lower the temperature while hardened surfaces raise it. Wind conditions are also an important factor.

Sensefarm, the company that sets up the sensors, has previously participated in the SOM project by connecting plantings with sensors, including the large newly planted tree at Katte secondary school. The sensors are then connected to the LoRa network that Kraftringen has been providing in Lund since a few years ago.

- Technically, the work with humidity and temperature sensors in the heating project has worked beyond expectations, says Anders Hedberg at Sensefarm. We learned a lot about the sensors that were deployed at the cathedral and at Kristallen at the start of the SOM project, and we have been able to bring those experiences to this sub-project.

The SOM project (Smart Public Environments) is part of the Strategic Innovation Programme for the Internet of Things, IoT Sweden, funded by Vinnova. The project started on 1 September 2017 and was mostly completed by the end of 2020.

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Facts subproject Heat metering in the city

Project Time: 2020-06-01 - 01/01/2022

Project Manager: Adam Wadsten and Linda Birkedal, Lund Municipality

Partnerschappen: Lund Municipality, Sensefarm, Sensative

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In the big picture: Erik Wapner from Sensefarm screws up a sensor at Bantorget. Photo: Anders Hedberg