Combating Extreme Hot Temperatures Through the Creation of Urban Nature

As cities become hotter, the need for green spaces increases

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After an already hot June, July 2023 arriwed with extreme heat to the US, Mexico, southern Europe and China, breaking many local temperature records. The climate crisis is intensifying heat waves, making them longer and more frequent. On July 6, global temperatures surpassed the 2016 record [1], marking the hottest day on record. ERA5 data from Copernicus C3S shows that the first three weeks of July were the warmest on record, making this probably the warmest month on record.

These high temperatures are linked to heat waves in North America, Asia and Europe, exacerbated by fires in Canada and Greece.

Hottest Three Weeks on Record: Global Average Surface Air Temperature, July 1-23
Hottest Three Weeks on Record: Global Average Surface Air Temperature, July 1-23

The average global temperature has temporarily exceeded the 1.5°C threshold [1] above pre-industrial levels in the first and third weeks of the month. Since May, the global sea surface temperature has been well above previously observed values for this time of year, contributing to an exceptionally warm July.

During a meeting of the UN (United Nations – Organization of the United Nations) [2], Secretary General António GUTERRES stressed the need for action about global measures, regarding greenhouse gas emissions, adaptation to climate change and a climate finance. He warned that “the era of global warming is over” and that “the era of global boiling has arrived”. Although climate change is evident, “we can still stop the worst”, he said. “But to do that, we need to turn a year of heat into a year of burning ambition”.

"The extreme weather that affected many millions of people in July is unfortunately the harsh reality of climate change and a preview of what's to come."

“The need to reduce greenhouse gas emissions is more urgent than ever. Climate action is not a luxury but a necessity.” [3]

Unless fossil fuel consumption is reduced quickly, heat waves will intensify, occurring every 2-5 years in a 2°C warmer world [4].

Lethal heat is less recognized; in Spain, however, 4,600 deaths were recorded in 2022 alone, due to temperatures exceeding 40°C. Without reducing emissions, 90,000 Europeans could die annually from the heat [5]. Heat-related deaths increased in the US, Mexico, Spain, Italy, Greece, Cyprus, Algeria and China; so are hospitalizations. More than 100 million people in the southern US and in Italy and Spain are facing heat alerts, which is impacting electricity demand and crops such as olives and cotton. Urban areas, home to 75% of Europeans, face urgent threats as heat-absorbing infrastructure and limited green space create ‘heat islands’. Temperatures on the urban surface can be 10-15°C higher compared to those in the neighboring rural areas [5].

Global mean daily surface air temperature from 1 January 1940 to 23 July 2023, plotted as time series for each year. 2023 and 2016 are marked with thick lines colored light red and dark red. There are other years represented by thin shaded lines by decade, from blue (1940s) to brick red (2020s). The dotted line and the gray shell represents the 1.5°C threshold above pre-industrial levels (1850-1900) and its impreciseness. Data: ERA5. Credit: C3S/ ECMWF. Source: climate.copernicus.eu
Global mean daily surface air temperature from 1 January 1940 to 23 July 2023, plotted as time series for each year. 2023 and 2016 are marked with thick lines colored light red and dark red. There are other years represented by thin shaded lines by decade, from blue (1940s) to brick red (2020s). The dotted line and the gray shell represents the 1.5°C threshold above pre-industrial levels (1850-1900) and its impreciseness. Data: ERA5. Credit: C3S/ ECMWF. Source: climate.copernicus.eu

Europe’s rapid warming is intensifying health-risk heat waves, which will worsen in all regions, especially in the south. Between 2017 and 2021, Europe warmed by 2°C above 19th century norms (C3S, 2022a). Since 2000, much of the continent has experienced recurrent intense heat waves (AEM, 2022c). Growing risks include warmer days, high night-time temperatures and increasing wet heat waves (AEM, 2021a). Urban heat islands (>2°C) affect almost half of hospitals and schools in cities, exposing vulnerable people [6].

Heat waves rank first among the deadliest weather phenomena in Europe. Vulnerability to extreme heat will increase morbidity and mortality if left untreated. The number of heat-related deaths is increasing, especially in southern Europe. Rising temperatures led to an annual loss of 16 hours of
work per year for each worker in high-exposure jobs between 2016 and 2019, compared to 1965-1994, with the south of the continent most affected. Urgent climate change mitigation and adaptation is imperative for human health [4].Current and future threats to health in Europe [4]. Current and future threats to health in Europe require increased climate action.

The study reports provide local authorities with practical strategies to combat urban heat islands. By creating wind corridors for ventilation, by designing green roofs and facades for buildings, by using lighter colors in construction, by creating many green spaces and by making better use of water, it is possible to reduce urban temperatures [7] nd to improve the living conditions of city dwellers. 

Heat action plans are being put in place more often and there is evidence that they lead to reduced heat-related mortality.

In addition, cities that have urban planning for extreme heat tend to be cooler and reduce the urban heat island effect. There is an urgent need to accelerate the implementation of heat action plans, given the increased vulnerability driven by the intersecting trends of climate change, population aging and urbanisation.

A heat wave - in terms of health - is a period of at least two consecutive days in which the maximum apparent temperature (Tappmax) exceeds the 90th percentile of Tappmax and the minimum temperature (Tmin) exceeds the 90th percentile of Tmin. temperatures apparent is a measure of the relative discomfort due to the combined high heat and humidity. Health-related heat waves are calculated for the months of June, July and August. Source: Climate-ADAPT (2022a) www.eea.europa.eu
A heat wave - in terms of health - is a period of at least two consecutive days in which the maximum apparent temperature (Tappmax) exceeds the 90th percentile of Tappmax and the minimum temperature (Tmin) exceeds the 90th percentile of Tmin. temperatures apparent is a measure of the relative discomfort due to the combined high heat and humidity. Health-related heat waves are calculated for the months of June, July and August. Source: Climate-ADAPT (2022a) www.eea.europa.eu

European policies promote the use of nature-based solutions and urban greening [6]. EU Biodiversity Strategy 2030 encourages bringing nature back into cities by creating biodiverse and accessible green infrastruc-ture. The strategy also emphasizes the importance of developing urban greening plans in cities and large towns (EC, 2020c). The role of nature-based solutions in climate resilience is recognized by the EU strategy on adaptation to climate change (EC, 2021a).

Vegetation in cities helps reduce temperatures through evapotranspiration, shading and lower heat absorption and thus may contribute to lower heat-related mortality (PASCAL et al., 2021). Parks, trees and green roofs appear as effective measures to reduce ambient air temperature and improve thermal comfort both outdoors and indoors (AEM, 2020a). UBA (2022) identifies retention of existing trees and planting of new trees, complemented by green roofs and facades, among the heat adaptation options suitable for climate moderation.

Plants help cool the environment, making vegetation a simple and effective way to reduce heat islands. Source: Festus KIPLAGAT, Linkedin
Plants help cool the environment, making vegetation a simple and effective way to reduce heat islands. Source: Festus KIPLAGAT, Linkedin

The greening of tram lines is an effective solution for mitigating the urban heat island effect, as sedum plants or even simple lawns have a considerable cooling effect and positively influence the local climate.

In urban environments, the implementation of vegetation between tram tracks can reduce the temperature by up to 50%, reducing the risk of rail deformation and eliminating the need for frequent inspections.

Thanks to green tram lines, cities can benefit from natural cooling, with multiple advantages, such as: improving air quality, creating more pleasant microclimates and promoting community spaces, bringing nature closer to the urban environment and increasing the mental wellbeing of the inhabitants.

In order to combat the increase in temperatures, it is essential to resort to solutions based on the creation of an urban nature. Like for example increasing tree cover in urban areas to 30% [5] – a measure that could prevent almost 40% of heat-related deaths (The Lancet).

The temperature difference between built-up urban areas and areas with green vegetation can be significant, especially in conditions of extremely hot weather – thermoscan camera testing tram lines area - Arad, 23.08.2023
The temperature difference between built-up urban areas and areas with green vegetation can be significant, especially in conditions of extremely hot weather – thermoscan camera testing tram lines area - Arad, 23.08.2023
The temperature difference between built-up urban areas and areas with green vegetation can be significant, especially in conditions of extremely hot weather – thermoscan camera testing tram lines area - Arad, 23.08.2023

Urban greening offers a number of benefits: temperature reduction, water retention to limit flooding, air filtration, noise reduction and increased mental well-being (AEM, 2019a). Its impact on health is substantial, potentially preventing premature deaths in European cities and promoting sustainability (Pereira Barboza et al., 2021)

WHO recommends 0.5-1 ha of green space within 300 m around urban dwellings (WHO Europe, 2017b) [6].

It is essential to take immediate action to prepare for heat waves and mitigate their impact. The EU offers support in this endeavor, with different solutions:

  • Initiatives such as the LIFE@Urban Roofs project in Rotterdam [5] plant green roofs, adding 20,000 square meters of green infrastructure by 2024.
  • LIFE Archiclima project from Poland adapt large structures such as airports and shopping malls with green roofs and walls to reduce temperatures.
  • Vienna supports homeowners with subsidies for green facades and roofs, encouraging the integration of vegetation.
Green tram lines with sedum carpets – Arad, 2023, Ecostratos
Green tram lines with sedum carpets – Arad, 2023, Ecostratos
  • Antwerp [6] enforces green roof regulations, while Stuttgart prioritizes urban green spaces for temperature reduction. Adaptation measures implemented in Stuttgart include green roofs, shading of facades with street trees, greening of tram lines or the installation of fountains and other water features.
  • Financing Adaptation to climate change in social institutionsof the German federal ministry protects vulnerable populations by promoting green roofs and other structural modifications.
  • Waste treatment facilities in Oslo [6] integrates green roofs with solar panels for heat regulation,
    rainwater absorption and dust capture.

These actions exemplify the EU’s commitment to tackling heat challenges with nature-based solutions and green infrastructure. The severity of current and projected climate impacts on health in Europe calls for increased action on both climate change mitigation and adaptation.

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