Berlin Environmental Atlas

04.11 Climate Model Berlin - Planning Advices Urban Climate (Edition 2016)

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Excursus: "Urban climate and health"

Urban climate and health – a challenge for the design of urban living spaces

uman health is the basis of our life. The urban living and environmental conditions significantly influence the well-being, the health and the life expectation for urban populations. The environmental impacts on human health in the context of the urban climate can be derived from the bioclimatic properties of the city, especially as determined by urban heat islands and air pollutants.

Already today, but especially in the future, the specific features of the urban climate in conjunction with the impacts of climate change, the ageing of society, urban lifestyles and an unequal social distribution of environmental loads pose great challenges for the design of urban living spaces.

Since metropolises such as Berlin exhibit an inner-city mosaic of different urban, population and social structures as well as environmental conditions, health impacts are likewise spatially differentiated. Thus, not only the environmental conditions in an urban area are crucial, but also the proportion of the groups of persons who exhibit a particular vulnerability towards these loads. Especially elderly, chronically ill or socially deprived people and those living on their own are often affected by environmental loads to a greater extent (Böhme et al. 2013).

In order to preserve or create an urban environment healthy for humans, it is on the one hand crucial to understand the impacts of the urban climate on health. On the other hand, spatially differentiated considerations concerning human-environment relations in urban areas form an important basis. Urban planning has a significant task in this regard, particularly with respect to the impact of climate change. The Berlin Senate Department for Urban Development and the Environment published the Urban Development Plan Climate (SenStadtUm 2011) in 2011 and developed the partial climate protection concept "Adaptation to the Impacts of Climate Change" ("Anpassung an die Folgen des Klimawandels" SenStadtUm 2016) in the framework of the climate adaptation strategy of the State of Berlin.

Planning advices maps support the aim of preserving or creating a healthy urban climate. In assessing situations of urban climate load and relief functions and in designating areas with particular urban climate deficits and vulnerability towards the urban climate, demographic structures are taken into account in addition to land use and the supply with green spaces. The identification of increased health risks through thermal load and air pollution on the basis of health-related data in spatial resolution can be understood as an important supplement for the planning and implementation of mitigation and adaptation measures for health protection.

What is the connection between urban climate and human health?

Urban structures modify the bioclimatically relevant parameters air temperature, humidity and airflows, and the exchange of radiation and energy. The urban climate can impact on humans directly and indirectly, since urban heat islands and air pollutants in the urban atmosphere not only have a direct influence on humans, but also on water, soil, flora and fauna in the city. And through these partial spheres (hydrosphere, pedosphere, biosphere), indirect effect pathways to humans can also be traced. In the following, the focus of the considerations will be on the direct impacts of the urban thermal load on human health.

Urban heat islands

The urban heat island has both a beneficial and a detrimental bioclimatic impact on human health. A shortening of the winter frost season and a reduction of the number of heating days, through which air pollutant immissions decrease (Kuttler 1998) and the risk of cold-related illnesses and deaths is reduced, is to be assessed positively. However, shortened frost seasons and milder winters also entail an extension of the vegetation period and thus the pollen season, which can increase and exacerbate allergies and change the allergen spectrum (Eis et al. 2010). Increased risks of infection are also to be expected, as the conditions for alternate animal hosts and carriers (vectors) of pathogenic organisms to live and proliferate are more favourable (Eis et al. 2010). The urban overheating has negative effects especially in the summer months, when the intensity is greatest at night. As these particularly heavy loads coincide with the nocturnal recovery phase of humans, they constitute an additional strain for the human organism on continuously hot days (Koppe et al. 2004). However, high air temperatures, low wind intensities and spatially diverse radiation conditions can lead to heat stress also during daytime in the summer. The degree of thermal load is mainly determined by the insolation.

Heat waves, i.e. several consecutive days with thermal load, are a special problem in cities, as buildings and impervious areas heat up over days, store this heat and release it with a delay. If there is no adequate night-time ventilation in these cases, residents in these urban areas experience a continuous thermal stress across the day and night hours, whereas residents in favourable urban areas experience heat relief overnight through the cooling influence of adjacent open spaces. Berlin distinguishes itself with its outstanding mixture of developed and green areas through a mosaic of different micro-scale climates and thus large differences in the thermal conditions in a small space. Assessing their climatic impact is a priority task of the three-part Planning Advices Urban Climate Map.

Thermal load

Thermal load is understood as a health-relevant assessment of the thermal environment. The thermal load is determined either by means of simple methods, e.g. threshold values of the air temperature (climatological threshold days), or by means of complex methods, e.g. via the Predicted Mean Vote (PMV), the perceived temperature, the Physiological Equivalent Temperature (PET) or the Universal Thermal Climate Index (UTCI), an update of the Klima-Michel model applied by the German Meteorological Service and of the perceived temperature (Koppe 2005, Jendritzky et al. 2009). The thermal load is divided into heat load and cold stimulus. A severe thermal load is also referred to as a heat load or heat stress, but the terms are often used synonymously and there are no standardised definitions.

If the mortality (mortality or mortality rate related to the total population) and e.g. the air temperatures are considered across the calendar year, one usually finds a U-shaped curve (cf. Figure 21).

Figure 21
Fig. 21: Schematic representation of the air-temperature-mortality relationship according to Eis et al. (2010), Koppe et al. (2004), Laschewski (2008), Schneider et al. (2009) and Breitner et al. (2013).
Continuous line:: Temperature-mortality relationship across the calendar year.
Dotted line: Temperature-mortality relationship during phases of great thermal load or during summer months (Scherber 2014)

The curve progression can vary depending on the regional climate, the season under consideration and the cause of death (Koppe et al. 2004, Michelozzi et al. 2009, Schneider et al. 2009). In the middle latitudes, the total mortality (all causes of death) exhibits a maximum in winter and a minimum in summer. However, in particularly hot summers, as was the case in Berlin in 1994, 2006 and 2010, the total mortality can exceed the winter maximum (cf. Figure 22).

Figure 22
Fig. 22: Daily deaths (all causes) and daily maxima of the Universal Thermal Climate Index (UTCI) in Berlin in 2010 compared to mean values based on 2000-2010 (Scherber 2014)

Heat-related diseases

The human organism tolerates deviations of the body's core temperature only to a small extent. By contrast, the body shell (arms, legs and skin) can tolerate varying temperatures to a much greater extent. If the body’s core temperature increases, if the upper limit of the so-called thermal comfort is exceeded or the human thermal regulation is disturbed, the organism increasingly suffers from heat stress. Even healthy persons can experience significant increases of the pump performance of the heart, even under conditions of physical rest, and may therefore suffer from reduced physiological functional reserves and limited intellectual cognitive performance (BMU 2011). The body reacts with discomfort, reduced physical performance and lack of concentration. Symptoms of heat stress are a feeling of impairment and strain. Increased medication may be necessary for people who are already ill. A continuous exposure to high temperatures can result in heat-related emergency situations (e.g. heat cramps, heat stroke), diseases and even death. Heat-related diseases mainly affect the cardiac, vascular and respiratory system, which is strained due to additional effects of air pollutants and pollen (BMU 2011, Michelozzi et al. 2009, Schneider et al. 2011). In addition, high temperatures and low humidity can dehydrate the mucous membranes, which is relevant both in summer and indoors in winter. Pathogenic organisms which cause diseases of the respiratory system or worsen existing symptoms can easily settle on dry mucous membranes.

Persons at risk and risk factors with respect to thermal load

The water loss via the skin when sweat evaporates significantly increases when the surrounding temperature is higher and is further reinforced under conditions of physical work or an existing disease which is itself water-consuming (e.g. diabetes mellitus, diarrhoea). High water loss is particularly problematic for elderly and sick people, infants and toddlers, as their thermal regulation system is restricted, their perception of thirst is reduced, and the hormonal regulation of the water and electrolyte balance is modified. If the water and electrolyte regulation is not balanced accordingly, the water loss leads to a lack of volume in the circulatory system, and the circulatory function and renal activity are impaired, which may result in the collapse of the organism. In the short term, young adults can compensate even severe water loss solely by drinking. Elderly people often need several days for this (Wichert, von 2004).

People at heat risk further include persons with existing severe health impairments e.g. by diseases of the cardiovascular and respiratory systems and persons who are bedridden or have neurological or psychiatric diseases. They may not be able to provide for themselves independently and usually take medication which impacts on the electrolyte and thermal regulation, e.g. diuretics (flushing out water), neuroleptics (antipsychotic), beta blockers (reducing blood pressure) and barbiturates (enhancing sleep). In addition to age and pre-existing diseases, further risk factors for heat-related diseases are alcohol and drug abuse, exhausting physical activities during extreme weather conditions, lack of acclimatisation, low levels of fitness, overweight, physical fatigue, physical and social isolation, low socio-economic status, living in conurbations and lack of or insufficient air conditioning (Eis et al. 2010, Koppe et al. 2004).


Acclimatisation is an essential aspect regarding the impacts of thermal load. Acclimatisation is to be understood as the physiological adaptation of the human organism to changed climatic conditions. The thermal load impacting on the body is reduced through increased efficiency in the thermal regulation system and hormonal changes. A short-term heat acclimatisation is usually reached after 3-12 days, whereas a long-term heat acclimatisation can take several years. The effects of short-term heat acclimatisation include increased sweat production, even at a lower body temperature, and a reduced concentration of salt in sweat and urine. However, this form of acclimatisation is only reached if the heat exposure occurs for several hours daily, and it reverts within several weeks after the heat exposure (Koppe et al. 2004). The speed and extent of the acclimatisation depend on different individual factors such as age, gender, genetic predisposition, state of health, physical performance and fitness. External factors, e.g. the use of air conditioning, and national, geographical and seasonal differences are also crucial for the acclimatisation and individual heat tolerance (Koppe 2005).

Due to the relevance of the physiological adaptation in assessing the thermal environment, the HeRATE method (Heat Related Assessment of the Thermal Environment) was introduced (Koppe 2005). This method is taken into account in calculating the threshold values of the thermal index "perceived temperature" for heat alerts of the German Meteorological Service. For this reason, the threshold values of the perceived temperature for heat alerts are slightly lower for early summer heat waves and at higher latitudes, and slightly higher in midsummer and at lower latitudes.

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