Green areas in cities as cooling safeguards: the research results 2018

An urban greening of courtyards in high-rise residential districts is crucial in forming a comfortable living environment for citizens. In this research made in Kyiv (July, August 2018), we estimated an adapting potential of urban green areas towards heat waves that much intensified recently in Ukraine due to climate change.

Under a pre-study, we analyzed visual and thermal satellite images of Kyiv to assess distribution of building density, greening density and surface temperature over residential districts. In hot days of 07/24 – 08/04 we explored thermal characteristics of four selected courtyards of a high-rise building residential zone in Kyiv, which had low building density and different level of greening (13%, 21%, 25%, and 33%).

Firstly, we did a continuous air temperature and humidity monitoring (each 10 minutes, for 14 days) with 16 stand-alone portable sensors mounted at 3-4m on lampposts (a “non-shaded” area exposed to a direct sunlight), single trees (an area of a “non-intensive” shadow), and group of trees (a “deep shadow” area). In the morning, a temperature of sensors placed at direct sunlight area was increasing rapidly. Even little shaded locations (in case of a single tree with not so dense canopy) decelerated a heat rise.

Secondly, we performed an aerial thermal imaging of the yards with an UAV DJI matrice 100 and thermal camera Flir, from the height of 100 m with resolution 10-13 cm. Thermal and digital surface maps analysis shown that trees of a middle size planted uniformly are optimal. Shadows of buildings should be considered in a yard infrastructure, and a combination of different types of greening (grasses/shrubs/trees) is more efficient for cooling.

Thirdly, we measured CO₂ fluxes at a leaf level in optimal and hot conditions for 4 local tree species (Linden, Black Locust, Osier, and Maple). Black Locust appeared to be a heat tolerant species. Osiers reduced their photosynthetic activity under the hot air temperatures up to 50%, but were the most productive species. Linden and Maple did not reacted to heat but were not active in CO2 exchange.

Finally, we analyzed Ukrainian legislation on urban greening in terms of planning and planting density requirements.

The research data analysis allowed forming a number of conclusions and recommendations for urban green zones planning and management in Ukrainian cities under climate change impact presented nowadays.

It is important to consider the shadowing from buildings and trees in planning of the yard infrastructure. Optimal combination of tree coverage and shadowing conditions can help to reduce effect of summer heat waves for the locations of common public use, like playgrounds and sports grounds. At the opposite, trees planted in a constant shadow of buildings provide less benefit in terms of microclimate formation. Loans significantly decrease surface temperatures of open areas even under direct sunlight.

More than 30% of trees planting density causes effective cooling even outside of shaded areas. Increasing a plant density for 10% results in decreasing of mean summer surface temperature for 1°С for Kyiv city. According to the Ukrainian State building standards “Б.2.2-12:2018”, a vegetation in the residential districts of cities in Ukraine is supposed to cover not less than 25% of the area. In contrast, “State Sanitary Rules for Planning and Development of Settlements” states that this coverage must be 40%. Thus, an optimal level of greening should be specified and regulations requirements need to be harmonized.

Here you can watch a video about the project performance and a visualization of the results:

The research project was supported by National Geographic Society Explorers Program @insidenatgeo

Research team

1. Oleksandra Khalaim, PhD, Head, NGO “Ukrainian Ecological Club “Green Wave”
2. Taras Kazantsev, PhD, Research Associate, State Institution “Scientific Centre for Aerospace Research of the Earth” of the Institute of Geological Sciences of the National Academy of Sciences of Ukraine
3. Oleksandr Polishchuk, PhD, Senior Researcher, M.G. Kholodniy Botanical Institute of the National Academy of Sciences of Ukraine
4. Ihor Panas, PhD student, Palladin Institute of Biochemistry of the National Academy of Sciences of Ukraine
5. Olena Zabarna, MSc, National University of Kyiv-Mohyla Academy

We are thankful to DroneUA for the technical support.