Trees with grassy areas soften summer heat

Study on the cooling effect of black locust and linden trees in cities.

One location was the Lehrer-Wirth-Strasse in Munich, where measuring instruments were attached to Robinia below the foliage. (Picture: F. Rahman/ TUM)
One location was the Lehrer-Wirth-Strasse in Munich, where measuring instruments were attached to Robinia below the foliage. (Picture: F. Rahman/ TUM)

Trees are considered to be nature’s air conditioners, making them the most practical way of alleviating the heat in cities. Trees cool their environment and “heat islands”. In a recent study, scientists at the Technical University of Munich (TUM) compared two species of urban trees.

The Bavarian capital is the third-largest and the most densely populated city in Germany. It has an air temperature up to six degrees Celsius warmer than its rural surroundings. A team from the Chair for Strategic Landscape Planning and Management and the Chair of Forest Growth and Yield Science at TUM has now used combined sensor and storage devices (data loggers) to investigate how the microclimate develops below urban treetops in particular.

The examination was carried out during summer days with varying temperatures at different locations in Munich — close to the East Station of Munich and Messestadt Riem. With the Little-leaved linden, the 2016 tree of the year, and the dark insect — otherwise called false acacia — they chose two well known however differentiating urban tree species to break down the mind-boggling transaction of area factors, current climate conditions, and tree write. In light of environmental change, the attention was on the cooling impact on extremely hot days.

Black requires less water and therefore better suited for cities. With the Little-leaved linden, the 2016 tree of the year, and the dark beetle — otherwise called false acacia — they chose two famous however differentiating urban tree species to investigate the unpredictable exchange of area factors, current climate conditions, and tree compose.

The study progresses toward becoming clearer by correlation: The yield of a mechanical aeration and cooling system is in the vicinity of one and ten kilowatts (kW) that of a linden tree up to 2.3 kW. This cooling limit is encouraged by different procedures, for example, the thick treetops that give shade. Or on the other hand the way that the leaf surfaces mirror the short-wave beams of the sun and furthermore utilize them for transpiration.

These cooling systems are normal in all plants including grass. Notwithstanding, with greater and denser shelters alongside higher water misfortune from the stomata of their leaves, linden trees utilize a vast level of the caught radiation to vaporize them, thus cooling the encompassing little-scale atmosphere better.f environmental change, the emphasis was on the cooling impact on exceptionally hot days.

Be that as it may, there are a few contrasts to the richly blossoming dark beetle: Its crown is less thick, the leaf surface is littler, and subsequently the transpiration is lower. That influences the linden to tree more viable with regards to cooling on gentle summer days. Be that as it may, the dark beetle needs less water than the linden tree, which removes more water from the dirt amid the high warmth.

In this manner, if there should be an occurrence of grass gardens extra cooling capacity from the grass surfaces under dark insect trees appear to be more powerful. With the environmental change and quickening dry spell it is possible that we need to water the grass yards for having a higher cooling impact under the tree species, for example, linden or less water requesting species should be found. Then again, for cleared surfaces better cooling from the thick shade of linden trees are more compelling.

Reference:

Mohammad A. Rahman, Astrid Moser, Anna Gold , Thomas Rötzer and Stephan Pauleit: Vertical air temperature gradients under the shade of two contrasting urban tree species during different types of summer days, Science of the Total Environment 2018.
DOI: doi.org/10.1016/j.scitotenv.2018.03.168