Scientists from Southern Federal University, together with colleagues from Moscow and Yekaterinburg, have found out that greenery alone is not enough. For a roof to truly benefit the city, it is important to take into account the climate, soil composition, and even the specific features of the region.

In the context of rapid urbanization, cities continue to lose natural green spaces. Therefore, increasing attention is being paid to nature‑oriented solutions that can make the urban environment more sustainable. One such solution is green roofs.

According to Sergey Gorbov, a professor at the Department of Botany at the Southern Federal University’s Academy of Biology and Medicine, today green roofs are no longer seen as merely an ornamental element of architecture, but as an important part of modern urban infrastructure.

“Green roofs are considered an important element of modern urban infrastructure, as they contribute to increasing the environmental sustainability of cities. Currently, green roofs are viewed not just as a decorative element, but as one of the key nature‑oriented solutions for urban green infrastructure,” noted Sergey Gorbov.

Such structures help solve several urban problems at once. They retain a significant portion of precipitation, reducing the load on storm drainage systems. Vegetation and substrate reduce the heating of roofs and buildings, mitigating the effect of the urban heat island and can help reduce energy costs for cooling indoor spaces during the summer. In addition, green roofs create additional habitats for plants and animals, supporting urban biodiversity, improve the microclimate, and make the city more comfortable to live in.

However, the impact of green roofs on the carbon balance has so far remained a subject of scientific debate. It is commonly believed that plants absorb carbon dioxide during photosynthesis, which means that any green roofs automatically help combat climate change. Scientists have an opportunity to verify this claim, because checking the carbon balance is a secondary objective of the experiment.

The study was conducted in three cities in Russia at once — Yekaterinburg, Moscow, and Rostov‑on‑Don. They are located in different climatic zones and differ significantly in terms of temperature regimes and precipitation levels. This made it possible to assess how the same structures perform under different natural conditions and to what extent the climate affects their ecological functions.

To ensure that the results could be objectively compared, the same experimental design was used in all three cities. Experimental plots were set up on the roofs, with two types of substrate — a universal one and a local one, developed taking into account the specific characteristics of the region. In addition, two substrate thickness options were compared — 15 and 25 centimeters. Sedums were grown in the experimental plots (approx. a genus of succulent plants belonging to the Crassulaceae family) and local herbaceous plants. In total, 18 experimental plots were created in each city.

During the first season after construction, researchers measured carbon dioxide emissions twice a month using dynamic closed chambers. At the same time, the temperature and humidity of the substrate were continuously recorded, which made it possible to track the impact of weather conditions on the performance of green roofs.

The results obtained showed that average carbon dioxide emissions varied noticeably between cities. The lowest values were recorded in Yekaterinburg, while in Moscow and Rostov‑on‑Don they turned out to be approximately twice as high.

At the same time, scientists found that the reasons for the differences depend on the region. In Yekaterinburg and Moscow, the seasonal dynamics of emissions were determined mainly by air temperature and substrate temperature. In Rostov‑on‑Don, the decisive factor turned out to be substrate moisture, which underscores the special role of the water regime for the southern regions.

No less interesting were the results of comparing different types of substrate. A universal substrate is a specially formulated mixture of organic and mineral components that can be used in various climatic conditions. It provides good moisture retention, air permeability, and contains a sufficient amount of nutrients for plants. A local substrate, by contrast, is created taking into account the natural characteristics of a specific region and includes materials available in that area. Its composition is maximally adapted to the local climate and regional plant species.

The study showed that the type of substrate was one of the main factors determining the carbon balance of green roofs. Universal substrates containing more compost provided more intensive plant growth, but at the same time released significantly more carbon dioxide than local ones. As a result, the increase in plant biomass did not compensate for the additional emissions. At the same time, the species diversity of plants had virtually no effect on the level of carbon dioxide emissions.