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The journey to becoming a greener city has many steps, one of them being the implementation of effective instruments for environmental monitoring. In Hamburg, CLEVER Cities is conducting an assessment of how urban nature is changing in the Neugraben-Fischbek district, and evaluating different tools and methods to support local monitoring activities.

New green roofs will be constructed in the area to test their potential to retain rainwater and to provide more recreational green spaces to residents, leading to reduced temperatures in summer and improved well-being.

As green roofs are difficult to see from the street level, the CLEVER Cities team in Hamburg is exploring the option of using aerial photographs (remote sensing) for monitoring purposes. A first evaluation was conducted using a Geographic Information System (GIS), a framework that allows users to capture and analyse spatial and geographic data.

In partnership with Hamburg’s GIS Academy, four project participants have developed different GIS tools. Investigation goals were defined in consultation with representatives of the Ministry of Environment, Climate, Energy and Agriculture (BUKEA) that can contribute to the CLEVER Cities Monitoring Strategy and be transferred to other project areas or the entire city.

The first evaluation has determined the degree of vegetation coverage in the project area based on aerial photographs taken in 2019. In this context, it is also possible to specifically search for green roofs and thus determine the percentage of newly greened rooftops.

A second evaluation examined the potential for installation of new green roofs. The data collection was based on high-resolution information on the shape of buildings and the inclination of their rooftops. From this data, it can be deduced whether a roof is suitable as a green roof location and thus a green roof potential register can be created. In addition, different parameters such as rain retention capacity were calculated for each potential green roof site.

First results have shown that about 56% of the roof areas in Neugraben-Fischbek would be suitable for a green roof. In another 43%, the roof is too steep, meaning a green roof could only be installed with great technical effort. The remaining 1% are areas smaller than 20 m² that were not considered in the calculation. Since the small roofs are mostly carports and garages, a green roof would be relatively easy to implement.

The calculation tools are available to the CLEVER Cities team in Hamburg and will be used to inform urban planning decisions, as well as communication materials about green roof potential in Neugraben-Fischbek.