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13.08.2021 - Ausgabe: 4/2021

Heat Waves and Heavy Rainfall – What are the Impacts of Climate Change and Which Adaptation Measures are Appropriate?

By Dr. Helmke Hepach, Dr. Sebastian Sonntag, Dr. Claas Teichmann and Prof. Dr. Daniela Jacob (Climate Service Center Germany (GERICS) an institution of Helmholtz-Zentrums Hereon)

© Günter Albers / stock.adobe.com

The impacts of global climate change are already being felt. Carbon dioxide (CO2, a greenhouse gas that is a major cause of global warming) levels in the atmosphere are currently over a third higher than 60 years ago. Overall, one of the best-known time series, the Keeling Curve, which can prove by way of measurements the steady increase in atmospheric CO2 levels since 1958, shows that the amount of CO2 in the atmosphere now is about as much as it was more than 4 million years ago. The average global mean temperature has risen by 1.2 degrees Celsius since record-keeping began (Global Warming Index, 2021). In general, the temperature increase is higher over the continents than over the oceans. For Europe, for example, it is a mean temperature increase of 1.7 - 1.9 degrees Celsius compared to the global mean of 1.2 degrees Celsius (European Environment Agency, 2021). 

The greenhouse gas CO2 is released into the atmosphere through various industrial processes or from transport and is a major contributor to this rise in temperature. Emissions of other greenhouse gases such as methane, of which food production is a major source, also continue to increase. Other anthropogenic activities increase greenhouse gas emissions and at the same time deplete natural carbon sinks, such as large-scale deforestation in the Amazon region. 

It is already clear today that the impacts of climate change will be felt even more acutely if anthropogenic activities that control the levels of greenhouse gases in the atmosphere are not reduced and, at the same time, natural buffer mechanisms, such as the uptake of CO2 by vegetation or by the oceans, are not preserved. 


Regional impacts of climate change 

The effects of global warming vary from region to region. However, temperatures are rising everywhere. Recently, for example, an extreme heat wave gripped North America, with an all-time record temperature of 49.6 °C measured in Lytton, western Canada, which was 4.6 °C higher than the maximum temperature last recorded there in 1937 (World Meteorological Organization, 2021). And extreme weather events are also becoming more frequent in Germany. A record temperature of 41.2 °C was last recorded in Duisburg during the 2019 heat wave, after 2018 had already been characterized by extreme heat and drought, making it the warmest year on record. Recent studies indicate that heat waves, and with them the days when it gets hotter than 30 degrees Celsius, are likely to become even more frequent. Projections based on a high CO2 emissions scenario show how the climate will change in the years to come compared to the reference period from 1971 to 2000 if few climate protection measures are taken (GERICS Climate Outlooks Federal States https://www.gerics.de/products_and_publications/fact_sheets/klimaausblicke/index.php.de ). In the following, the median of all climate model simulations examined within this scenario involving little climate protection is given in each case (i.e. the value of the simulation that lies in the middle when the simulated values are arranged in sorted order). The number of hot days across Germany may increase by 3 days per year by 2065 - and even up to 9 days per year by the end of the century - if further warming cannot be contained, i.e. the climate scenario involving little climate protection would occur (see GERICS- Climate Outlooks Federal States). As is already the case, regions in Germany would be affected differently. The southwest of Germany could be hit hardest: in both Baden-Württemberg and Saarland, the number of hot days (over 30 degrees Celsius) per year can be expected to increase by 5 by the middle of the century. The effects could be more moderate in northern Germany (Schleswig-Holstein: 1 additional hot day). However, heat waves with daytime temperatures of over 25 degrees Celsius could also become significantly longer. In general, metropolitan areas are more affected than rural areas, which is due to the heat island effect, as it is termed. Urban areas, especially with high-density building development and few green spaces, experience significantly higher temperatures than outlying areas. Depending on city size, characteristics of the building fabric, solar radiation properties of surfaces or building symmetry, this difference can be up to 10 °C (German Meteorological Service), which can lead to significantly increased heat stress in city centres.

In addition to temperature, precipitation in Germany may also change regionally in terms of both quantity and intensity. In this projection, summers are getting ever drier (by about 40% by mid-century), while the autumn and winter seasons tend to be characterized by higher precipitation rates (an increase of about 30%). 

Due to less precipitation in summer, we are already experiencing more frequent dry periods and droughts, such as in 2018 and 2019 in combination with very high temperatures. As a result, groundwater levels are declining. While the topsoil (up to a depth of about 25 cm) has recovered in the meantime, total soil (up to 1.8 m) moisture levels in some areas of Germany will continue to be very low in 2021, partly as a result of this particularly dry and hot year (see UFZ Drought Monitor of the Helmholtz Centre for Environmental Research, https://www.ufz.de/index.php?de=37937 a partner of the Helmholtz Climate Initiative https://www.helmholtz-klima.de/). North-East and South-East Germany, as well as the Rhine-Main region are particularly affected. At the same time, there is an increase in extreme precipitation events in summer, known as heavy precipitation days, on which at least a total of 20 mm of rain falls per hour. As a result, flooding is becoming more frequent, partly exacerbated by the combination with drought, which makes the soils less absorbent. For example, the current low Bernd (mid-July 2021) with storms and heavy rainfall has wreaked havoc in numerous regions of Germany. ‪In the climate scenario mentioned above involving little climate protection, the median number of heavy precipitation days in Germany could increase by one per year by the middle of the century. Again, the southwest and west of Germany will be particularly affected, where the increase could be more than one day per year. 

Scientists can now also attribute the more frequent occurrence and increased intensity of extreme weather events - such as severe thunderstorms with squalls and heavy rain or severe storms - to climate warming, but with a lower degree of statistical certainty than is the case with rising temperatures or droughts. All known climate projections show that storms could also become up to 20% more severe and intense in Western Europe by mid-century. Even more severe and intense thunderstorms could form due to increased seasonal warming of continental landmasses, resulting in a higher degree of atmospheric instability (German Meteorological Service, NASA Global Climate Change). In addition, the periods in which severe thunderstorms form could become longer due to warmer temperatures in spring and autumn. 

The Helmholtz Climate Initiative has compiled further information on the general facts and impacts of climate change: www.helmholtz-klima.de/aktuelles/aktuelle-fakten-zum-klimawandel 


Climate change adaptation measures 

There are several aspects that have to be taken into account when considering the appropriateness of climate change adaptation measures. 

For instance, the aforementioned urban heat island effect should be considered when siting outdoor facilities. Due to the more intense heat in city centres, outlying locations are more suitable for poorly shaded outdoor facilities such as playgrounds or sports fields. However, the heat island effect does not manifest itself in the same way in all parts of the city centre. It is closely related to soil sealing, because the more extensive the sealing, the higher the temperature in the inner-city area. The proportion and type of building development also have an effect, e.g. high-density development with taller buildings has a warming effect due to poorer ventilation. High proportions of water bodies and green spaces, on the other hand, have a cooling effect (Bottyán and Unger, 2003). Downtown areas with water bodies and green spaces are therefore less prone to the urban heat island effect and are therefore more suitable for the construction of outdoor facilities such as playgrounds; in addition, the creation of green spaces and water bodies during the construction of outdoor facilities can also mitigate the heat island effect. However, the nature of the built-up areas is not only crucial because of the heat island effect. The runoff behaviour of built-up areas must also be taken into account in planning through appropriate drainage concepts, as this plays a role during droughts and heavy rainfall events.

When it comes to the suitability of building materials, not only the texture but also the colour of the material plays a role. For instance, the use of lighter and reflective materials can have a cooling effect. The use of low thermal conductivity materials should also be considered. Furthermore, when building outdoor facilities, care should be taken to ensure that the materials can withstand storm damage and are correspondingly wind- and break-resistant. 

In addition, shading is a key component. Green infrastructure not only reduces the heat island effect described above, but the planting can also be used to shade outdoor facilities. However, natural shading requires long-term planning. Some criteria to consider are growth rates, frost hardiness as well as heat and shade tolerance of the corresponding plants. Existing buildings in the vicinity can also be used to provide shade for outdoor facilities. Another way of providing shade is, for example, using fabric sunshades or awnings on buildings, which also provide protection against UV radiation.  


Sustainable solutions

In addition to adapting to the impacts of climate change, certain climate protection measures can also actively contribute to mitigating climate change. The construction or use of buildings, for example, accounts for about 30% of CO2 emissions in Germany. Half of these emissions are generated during construction alone (German Environment Agency, 2020). The choice of sustainable materials can therefore make a decisive contribution to further reducing CO2 emissions and curbing global warming. Locally sourced raw materials also help to reduce CO2 emissions as they don’t need to be transported over long distances. Building materials that have a similar lifespan and are easy to replace reduce refurbishment effort and costs. Examples of such materials are wood, clay, brick, loam or natural stone. Wood in particular is also suitable because the material does not heat up much. Sustainability could also be taken into account when choosing paints and glazes as protection against adverse weather conditions. If less sustainable materials are used, the carbon footprint can be reduced through more sustainable production, such as using renewable energy in the production of steel parts or components made of other metals. 

Overall, it is apparent that by taking into account available information about current and future climatic conditions, it is possible to design and build sustainable, long-lasting and climate-friendly outdoor facilities and playgrounds where young and old people alike enjoy spending time.


Further information

The Climate Service Center Germany (GERICS) is an institution of the Helmholtz-Zentrum Hereon and was established by the German Federal Government in 2009 as part of the "High-Tech Strategy for Climate Protection". 

The impacts of climate change present us with new challenges to which we must adapt. Climate-adapted urban development or adapting corporate planning processes are some of the issues that decision-makers have to deal with. GERICS, headed by Prof. Dr. Daniela Jacob, works in close cooperation with scientists and partners from politics, business, industry and administration to support them in climate change adaptation strategies. To this end, the parties involved are networked with each other and scientifically sound prototype products and services for adaptation to climate change are developed at GERICS. Examples of such projects are the GERICS adaptation toolkit for cities (https://www.climate-service-center.de/products_and_publications/toolkits/stadtbaukasten/index.php.de) to support sustainable and resource-saving urban planning or the GERICS Climate Fact Sheets, which provide clear and concise information on essential climate characteristics of individual countries or regions and focus in particular on the characteristics and development of various climate indices in the future. These Climate Fact Sheets are available for various countries worldwide and for individual regions, e.g. in Germany at federal state level and recently even at district level (https://gerics.de/products_and_publications/fact_sheets/landkreise/index.php.de). 



Botyán, Z. und Unger, J.: A multiple linear statistical model for estimating the mean maximum urban heat island, Theoretical and Applied Climatology, 75, https://doi.org/10.1007/s00704-003-0735-7, 2003.

European Environment Agency, article on warming in Europe: https://www.eea.europa.eu/data-and-maps/indicators/global-and-european-temperature-10/assessment, accessed : 09th July 2021

Global Warming Index: https://www.globalwarmingindex.org/, accessed : 13th July 2021

Keeling-curve: https://keelingcurve.ucsd.edu/, accessed : 14th July 2021

NASA Global Climate Change, article on stormshttps://climate.nasa.gov/blog/2956/how-climate-change-may-be-impacting-storms-over-earths-tropical-oceans/, accessed : 09th July 2021

Umweltbundesamt (German Environment Agency), article on sustainable building https://www.umweltbundesamt.de/publikationen/13-thesen-treibhausgasneutrale-gebaeude, accessed : 09th July 2021

World Meteorological Organization, article on heat wave: https://public.wmo.int/en/media/news/june-ends-exceptional-heat, accessed : 09thJuly 2021

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