When addressing climate change, focus is usually placed on rain forests, melting ice caps, and deserts. But in the future, the urban climate between buildings, in backyards, and in green areas will also be subject to change, bringing the topic right into the cities, where increasing numbers of people live. As both the victims and the perpetrators of climate change, cities are largely responsible for greenhouse gas emissions and suffer on a rising scale from summertime heat waves and pollution in the air.

So what can cities do to combat the impacts of climate change? And what must they do to ensure they remain a comfortable place to live? A team of researchers have set out to find the answers to questions like these. Working on the Urban Climate Under Change project funded by the German Federal Ministry of Education and Research (BMBF) with a budget of 13 million euros for the next three years, the project partners will develop an urban climate model to simulate the climates of entire cities. In the future, using data from the project, urban planners will be able to make informed decisions when accounting for the effects of climate change. For example, they can plant hedges as barriers to absorb fine particles, and they can plan pavements and footpaths to ensure that elderly people are less exposed to air pollution and heat.

The BMBF project comprises three modules with a total of 30 subprojects involving scientists from Humboldt Universität, Technische Universität, and Freie Universität. The modules are all closely interlinked: in one, researchers in Hamburg, Stuttgart, and Berlin collect data on the weather, the climate, and local air pollution levels. In another, potential users provide input on what they hope to gain from the urban climate model. The third involves the actual programming of the model which has yet to be developed.

“Over the past ten years, awareness has developed that cities need to adapt to the local impacts of climate change,” says project coordinator Dieter Scherer, Chair of Climatology at Technische Universität Berlin. Nonetheless tools and instruments are still needed to calculate how, for example, a construction project will affect the climate in a specific urban district or quarter. In the models used to date, cities have been a blind spot, according to Scherer, who says, “Monitoring stations are traditionally designed to help us forecast the weather. That’s why efforts are made to keep them out of the inner city, away from so-called urbanization effects.” Other models, such as those used by architects, work on too small a scale as they only monitor buildings themselves and not the urban environment around them.

The new urban climate model – PALM-4U – holds the key. Measuring the interactions between temperature, humidity, air turbulence, UV radiation, and air chemistry over certain periods of time at different locations and based on differing climate change scenarios, it will be able to calculate an urban climate all the way down to an individual address. “It’s a huge challenge,” says Sabine Banzhaf from the Working Group on Tropospheric Environmental Research (Arbeitsgruppe Troposphäreische Umweltforschung) at Freie Universität Berlin’s Institute of Meteorology. “The model must be equally suited for use in answering complex research questions and for the everyday measurements and calculations done by urban planners. Rather than running on powerful computers only, it must be configurable so it can be used on laptops as well.”

First, the developers fill the blind spots with existing climate models, feeding in as much urban data as they can: development planning, tree registers, satellite photos documenting land use and local emission levels. When developing a new model, each of the project partners brings in their particular strengths. In Banzhaf’s case, it’s her knowledge of transport and conversion of chemical pollutants in the air. The urban climate model must also consider possible interactions such as these. “Urban greening is generally a good way to combat the effects of urban heat islands,” says Banzhaf. “But in urban canyons, trees hinder ventilation and that can lead to more pollution.” Plants also give off precursors of ozone, potentially increasing existing levels. A preliminary version of the model will be tested at the end of 2017 when the developers will feed in the various model scenarios using real climate data collected in advance.

Christoph Schneider is a climate geographer at Humboldt Universität Berlin. His particular contribution to the project is his fine-particle expertise. His team is developing the URBMOBI 3.0. mobile sensor, which can measure air pollutants such as fine particles, ozone, and nitrogen, and adds GPS coordinates to the measurements it takes. In the future, the sensor could be installed on buses that move through the city and send continuous, location-specific measurements straight to an online server.

Air pollution data collected at street level are then enhanced by Dieter Scherer and his team at the Department of Climatology at Technische Universität Berlin. They add vertical measurements taken at heights of one to two meters to ensure that all air pollutants are recorded.

The temperature ranges within a city are measured by a working group headed by Sahar Sodoudi, a junior professor of urban climate at the Institute of Meteorology at Freie Universität. The meteorologist and her team have set up 20 new monitoring stations in Berlin – in housing settlements with a mix of tightly packed and more spaciously located buildings, on grassy areas and lawns, in fields, and in woodlands. They have also placed monitoring stations in the city’s parks, big and small, and at the Müggelsee, Tegeler See, and Wannsee lakes to measure the cooling effects that parks and water bodies bring.

“In the summer temperatures can differ by as much as eight degrees between the different stations,” says Sodoudi. “In the city, where the air hardly moves and there is less ventilation and air exchange, the heat can become intense on really hot days and especially during heat waves.”

It is, of course, impossible to measure every square meter of Berlin during the project’s three-year life cycle, so the researchers combine longitudinal monitoring at permanent stations with short-term, but intensive measuring activities in which all the teams work in a small area all at the same time. Christoph Schneider is full of enthusiasm when talking about days like these: “Augsburg University’s drone flies up and down in a vertical line above Ernst Reuter Square. Technische Universität Berlin uses its masts to measure the wind at different heights. And there are two or three groups who take measurements on bikes or in a monitoring van.” These are all complex and costly measurements that none of the teams could perform or afford in their own right. “But as a joint team,” Schneider continues, “we can develop a holistic model and produce monitoring data for use in evaluation that none of us could ever tackle on our own.”

And as Scherer adds, “We’ve created a situation where everyone involved is a much-needed player and there is no opportunity or need to compete. And although we selected the most suitable project partners, there is a certain element of luck involved as well.”

The new urban climate model will be ready in 2019 and will be validated using the project’s monitoring data. With the necessary basic data such as development plans, tree registers, and satellite photos, the model can then be used by cities around the world to develop new forms of building and greening in their efforts to combat the negative effects of climate change.