Urban Heat Island (MWC, or UHI) is a phenomenon that involves significantly higher temperatures in urban centers compared to rural areas. As a result of intensive urbanization, surfaces that would naturally absorb water and give off cooling, such as forests, meadows and fields, have been replaced by concrete and asphalt. This, combined with heat emissions from vehicles, air-conditioning systems, server rooms, and industrial plants, is leading to rising temperatures in cities.
In Europe, the phenomenon is of growing concern because of its impact on public health, energy consumption and overall quality of life in cities. Most of Europe's population lives in cities and suburban areas, and while Europe's overall population is expected to decline in the future, the population in most major cities is expected to increase, leading to a further increase in the percentage of urban residents. What's more - these will tend to be older people. Although many European cities regularly rank high in rankings of the best places to live, the problem of urban heat islands poses a serious threat to many vulnerable groups. Heat waves, which have become more frequent and intense in recent years, are particularly dangerous for the elderly, whose bodies can cope less effectively with extreme temperatures.
The European Environment Agency (EEA[1]) has disguised the intensity of the Urban Heat Island. The phenomenon was estimated for 100 European cities. The intensity represents the spatial intensity of a given city. The index is calculated by subtracting the spatial temperature value from the average map of air temperature corrected for altitude (to exclude the influence of terrain). The map shows quite well that some cities, including Poland, glow red all the way.
Average intensity of urban summer heat island (°C) and predicted number of extreme heat waves in the near future (2020-2052; - The map shows the predicted number of extreme heat waves in the near future across Europe and the intensity of the urban summer heat island effect in 100 European cities.
Summary based on EEA (2019e) and VITO (2019).
If we trace the map of heat wave phenomena in Europe, we find that the most vulnerable areas are southern Europe, such as Madrid. As one of the continent's hottest cities, Madrid is experiencing severe WMC effects. Likewise, Greece's Athens, which faces extreme heat during the summer months. In Central Europe, however, the most "spectacular" example is Paris. Although it is known for its historic monuments, architecture and museums, the city often records temperatures several degrees higher than in its rural surroundings. According to an article published in the journal The Lancet[2], the population there is at the highest risk of death from a heat wave.
Researchers from various European countries examined the risk of heat and cold mortality in 854 cities between 2000 and 2019, and the results were clear. Paris topped the list of heat-related risks in all age groups, with the likelihood of excess deaths from rising temperatures 1.6 times higher than in other European cities.
In the summer of 2003. Europe was ravaged by an unprecedented heat wave, causing the deaths of more than 70,000 people, including 15,000 in France alone. In Paris, temperatures exceeded 40°C for weeks. Hospitals were overflowing with heatstroke and dehydration patients. Authorities were unprepared and were criticized for failing to recognize the heat as a major cause of deaths. A state of emergency was declared, diverting patients to military hospitals and setting up emergency morgues. The elderly suffered the most - half of the victims were over 85 years old, and many lived alone. The crisis highlighted the vulnerability of isolated individuals and marked a turning point in the recognition of the effects of climate change. With the advent of rising temperatures due to climate change, Paris is sure to continue to feel the heat - by 2050, the city's temperature could reach as high as 50°C.
Added to this is the fact that in the past, heat waves have been less frequent in Paris than in other European capitals, such as the aforementioned Madrid. "Cities accustomed to heat waves have adapted to them," - explains Dr. Pierre Masselot, a researcher at the London School of Hygiene & Tropical Medicine.
It is worth adding that pollution also contributes to the urban heat island. Generated mainly by vehicles, they cause a "kind of greenhouse effect" that traps heat and intensifies temperature extremes. "Exhaust fumes are darker, thus reducing the city's albedo (the percentage of incoming solar radiation reflected by various surfaces in the urban environment), trapping more heat," - Masselot explains.
On a hot summer's day
The situation in Poland may be similar to that in France. We, too, are not used to such extreme temperatures. The elderly, young children, people with disabilities or animals have an increased risk of heat stroke. Life in cities is becoming uncomfortable. It is estimated that the increase in the frequency of heat waves in Warsaw will cause a significant increase in mortality, especially in the second half of this century. Taking into account the average risk of death, the increase in mortality by 2040 will be about 36% of the total number of daily deaths, during a heat wave. What will happen after that? Well, after 2040, due to a six-fold increase in the number of 5-day heat waves, mortality will increase by up to more than 225 percent over the current situation[3].
Hot weather puts a strain on our bodies. Heat islands are appearing in every city in Poland. According to Monika Mierczyk-Burke of the Earth Observation Department of the Polish Space Agency, which did the research, the phenomenon was studied in detail in five agglomerations: in Gdansk, Warsaw, Lodz, Krakow and Wroclaw. There are such islands in each of them.
Krakow's heat island
Copernicus platform
The urban heat island is typical of urban areas, but let's keep in mind that it is also coupled with other effects, such as intensification of torrential precipitation, which is most pronounced in large agglomerations, but also appears in medium and small cities, of which Poland has the largest number. The expected increase in the intensity and frequency of extreme precipitation, as well as the occurrence of rainless periods in between, translates into an increase in the risk of urban flash floods. As we can read in the PAN communiqué, "The conventional approach to rainwater management through stormwater and combined sewer systems, which is common in Polish cities, does not solve this problem, and often exacerbates it. Already, rapid rainfall of more than 30 mm causes overloading of combined sewer systems, which were not designed with such a high volume and intensity of rainfall in mind. Meanwhile, we are increasingly seeing daily precipitation exceeding the average monthly precipitation of 50 mm or more. This trend will increase."
In Krakow, the state of air quality has been improving for several years thanks to the city's environmental policy, which includes changing heating sources, reducing car traffic in the center, planting urban greenery, creating green areas and introducing elements of green infrastructure. Although WHO measurements and standards indicate that Krakow's air is good[4], the problem of air pollution remains an important topic of public discussion. Krakow continues to face pollution coming from suburban towns surrounding the city, the so-called "ring road."
The burning problem needs to be cooled down
One solution to improve the current situation is to increase the number of green elements in urban space, such as urban parks (including linear and pocket parks), green tracks, facades, rooftops and green landscaping. This will not only improve air quality, but also lower the city's temperature, reducing the urban heat island effect in Krakow's hottest neighborhoods.
Europe has recognized the urban heat island problem and is actively implementing solutions to mitigate its effects. These solutions focus on expanding green infrastructure, improving urban planning and promoting sustainable practices. The first step is certainly to decongest cities. Increasing vegetation in urban areas helps lower temperatures and provides recreational areas for residents. Planting trees along streets and in parks not only provides shade, but also cools the air through evaporation. Creating rain gardens, facilitating water runoff onto the lawns of parks rather than into drains, is helpful in this regard.
It is also important to use light-colored facade materials. These reduce heat absorption and thus make it easier to maintain lower temperatures in buildings. Urban planning should include the design of ventilation corridors. These are open spaces that allow air to flow through the city, reducing heat buildup as well as pollution.
Paris and Madrid have developed heat action plans to protect vulnerable populations during heat waves. The plans include measures such as cooling centers and public awareness campaigns. Paris has launched a project of street green oases and thousands of new plantings in the city center. Vienna and Paris are promoting the installation of green roofs and walls. These installations help cool buildings, reduce energy consumption and improve air quality. Madrid and Athens are expanding their city parks and green spaces.
The urban heat island effect is literally a burning problem in many European cities, leading to higher temperatures and related coupled problems. However, Europe is leading the way in implementing innovative solutions to combat MWC. Through green infrastructure, sustainable urban planning and educational initiatives, cities are working to create a more livable, resilient urban environment. Continued efforts will be crucial in addressing the challenges ahead in a few years. New building codes are promotingenergy efficiency and the use of reflective materials. These measures help reduce heat absorption and lower overall temperatures in urban areas.
Magdalena Milert
[1] European Union agency providing knowledge and data to support European environmental and climate goals
[2] Masselot, P., Mistry, M., Vanoli, J., Schneider, R., Iungman, T., Garcia-Leon, D., ... & Aunan, K. (2023). Excess mortality attributed to heat and cold: a health impact assessment study in 854 cities in Europe. The Lancet Planetary Health, 7(4), e271-e281.
[3] Cities Facing the Climate Crisis, DEVELOPMENT AND ENVIRONMENT.
[4] Ciapa, S., & Sliwka, M. (2023). Greenery in the city and its impact on air quality and the urban heat island effect on the example of the city of Cracow.
