04.10 Berlin Climate Modelling – Climate Analyse Maps 2022

Map Description

This section discusses the results of all individual model simulations collectively. To make the document easier to navigate, links are provided for each topic. Information is included on meteorological parameters, evaluation indices, and threshold days. Additionally, a climate analysis map summarising the findings is available. The urban climate analysis focuses on the impact of key parameters such as wind and temperature as well as derived variables like the Physiological Equivalent Temperature (PET), which are particularly relevant when evaluating the biometeorological impact on humans and air quality.

Each topic is further differentiated by spatial structure (grid or block-based), time point or elevation. These are represented by separate layers that can be toggled on or off via the layer control in the Geoportal Berlin (available in German only). Analysis maps 04.10.1 to 04.10.5 as well as maps 04.10.8 and 04.10.9, are available in both grid and block-based formats. In these maps, the values shown represent the unweighted statistical mean of either the block (segment) areas or the grid cells intersecting with road areas. The Climate Analysis Map (Map 04.10.7), however, is only available in block-based format, as it was not directly modelled but derived from grid-based climate modelling results.

Background

A key goal of model-based climate analysis is to capture the dynamics of near-ground air exchange processes. It also aims to connect these processes with a spatial classification of the study area into regions that are considered climatically and in terms of air quality either favourable or unfavourable. From a climatic perspective, these two categories serve to divide space into compensation areas, impact areas, and the ventilation corridors that link them. Together, they reflect an understanding of the area as an interconnected system of compensation and impact areas.

‘A compensation area is an undeveloped, vegetation-rich space that, by generating cooler and fresher air through effective air exchange, can reduce or alleviate air pollution or the bioclimatic stress in impact areas. An impact area is a burdened, built-up area, or one designated for development, that is connected to an adjacent compensation area either via air exchange processes or a ventilation corridor.’ (translated from Mosimann et al. 1999). This process marks a clear departure from the earlier more static concept based on urban climate zones (Stadtklimatope), which segmented the study area into spatial units where the essential microclimatic conditions and their effects were relatively uniform (cf. VDI 2015).

The approach taken here, using climate modelling in combination with the analysis of statistical baseline data from long-running climate stations (SenStadt 2025b), has the following important advantages:

• It ensures that results are comparable across the entire urban area.
• Beyond providing qualitative insights into individual urban climate phenomena, it enables quantitative assessments of climate and ecological conditions as well as air exchange processes.
• Areas that serve compensatory functions and processes related to climate and ecosystems are identified within the urban area and depicted as precisely as possible in terms of their spatial extent.
• Cold air dynamics, a key aspect of the potential of open spaces to provide compensatory functions for climate and ecosystems, can only be comprehensively assessed in this way.

This application of the climate model reaffirms the well-established connection between local climate conditions and the structure of buildings, open spaces, and vegetation in different parts of the city. However, climate at the local scale is shaped not only by the immediate urban structure, but also by a site’s position within the broader urban context. Different parts of the city can influence one another and interact with surrounding regions. Temperature contrasts between neighbouring areas are essential for climate-related air exchange. When these contrasts are diminished, due to increased building density or the homogenisation of urban structures, the overall urban climate deteriorates.

Meteorological Parameters

Map 04.10.1 Near-Ground Wind Field and Cold-Air Volume Flow Density (10 pm and 4 am)

The ‘near-ground wind field’ and the ‘cold-air volume flow density’ support effective ventilation in settlement areas, which can help reduce human-biometeorological stress (cf. Moriske and Turowski 2002). These stress levels are evaluated during the day using PET (Physiological Equivalent Temperature) (see Map 04.10.5), and at night based on air temperature (cf. Map 04.11, Planning Advice Urban Climate 2022).

At night, cooler air flowing in from surrounding areas can reduce urban temperatures and therefore ease heat stress for humans during the summer months. If this incoming air is free of pollutants (i.e., fresh air), ventilation also improves overall air quality.

The gridded map layers represent near-ground cold-air flow at a height of 2 metres and a spatial resolution of 10 m x 10 m, based on the modelled data for 10 pm and 4 am. The wind field is depicted using vectors, where arrow direction indicates flow direction and arrow length represents wind speed, for all model grid cells with a climate-relevant minimum speed of 0.1 m/s or more. This grid-based data is complemented by area-based values showing cold-air volume flow density, expressed in m³/s.

Key Content of the Map

Effectively assessing urban ventilation conditions requires the appropriate assignment of burdened and compensation areas, the latter providing unpolluted air, and an airflow system capable of transporting air masses.

Burdened Areas

Burdened areas refer to settlement and traffic areas that experience thermal stress during the day and/or night. These are typically densely built-up urban structure types, which are also often characterised by inadequate ventilation. At night, absolute air temperature is the relevant meteorological parameter; during the day, thermal stress is assessed using Physiological Equivalent Temperature (PET).

Compensation Areas

Any undeveloped area without impervious cover has the potential to provide compensatory functions that support climate and ecosystems, both within the city and also in its surrounding areas. Whether this potential can be realised depends on local conditions, including area size, vegetation structure, location within the urban area, and the built-up environment.

Compared to other metropoles, Berlin still has a relatively large number of inner-city open spaces, a real asset in a city with little topographical variation. Here, thermally driven air circulation is the primary means of balancing the urban climate in the city centre, which depends on the close spatial proximity of green spaces and built-up areas (cf. Map 04.11, Planning Advice Urban Climate 2022).

The map’s near-ground temperature field represents the gridded mean of air temperatures in the lowest part of the atmosphere (0 to 5 metres above ground). If a single grid cell includes multiple land uses of varying proportions, the displayed temperature reflects a proportional weighted mean. That means the modelled temperatures are only directly comparable to actual near-ground measurements in larger areas with either uniform or corresponding land use.

Temperature patterns are shaped by land-use-specific soil and surface properties, and their interaction with atmospheric processes in the surface boundary layer. Within the soil, heat and thermal conductivity are key: for example, the higher the soil’s heat conductivity, the more quickly and deeply heat can penetrate the material, and also be released again.

Surface properties of natural and artificial areas, such as albedo (reflectivity) and emissivity determine how much energy is available to heat or cool the environment in both the shortwave and longwave ranges of radiation. Additionally, turbulence conditions in the near-ground atmosphere significantly affect the sensible and latent fluxes between the ground surface and the air, in both directions. All of these processes are interrelated and part of the surface energy balance. They determine both the temperature of the surface and of the air layers above. As such, air temperature remains a key parameter in assessing urban overheating at night and the formation of air exchange processes.

Cold-Air Flow

Depending on the distribution of near-ground temperatures, horizontal differences in air pressure arise, which in turn trigger local thermally induced wind systems. This process begins with the temperature contrasts that develop overnight between settlement areas and open, vegetation-rich spaces. At night, the now cooler and therefore denser air begins to flow downslope toward the lowest points in the terrain. This results in nocturnal cold-air drainage flows (e.g., Mosimann et al. 1999) that form at these slopes. The speed of this small-scale phenomenon is primarily determined by the temperature difference relative to the surrounding air and the steepness of the slope.

In addition to orographically induced flows involving cold-air drainage, thermally induced inflow winds (Flurwinde) and winds shaped by urban structures (Strukturwinde) may also develop. These provide direct thermal compensation by flowing from areas of higher to lower air pressure. They occur when heavily built-up or impervious areas heat up more than surrounding open spaces, creating a thermal low over urban areas. The resulting pressure gradient can then be offset by the inflow of cooler air masses from the surrounding areas (e.g., Kiese et al. 1992). For these flows to fully develop, air must be able to accelerate over a certain distance without being slowed by obstacles such as buildings. Both types of airflow are generally weak and localised, and can be easily overridden by even light prevailing winds. Their speeds usually remain below 0.2 m/s (Mosimann et al. 1999).

These land-use-related temperature differences begin to emerge shortly after sunset and can persist throughout the night. Meadows and farmland are especially effective in producing cold air. Depending on surface characteristics and cooling rates, cold-air flows can develop rapidly. Initially, these flows are shallow, with a layer thickness of only 5 to 10 metres, and form between various surfaces that warm and cool at different rates.

Definition of Cold-Air Volume Flow Density

Cold-air volume flow density (hereafter referred to simply as cold-air volume flow) is defined as the product of the flow velocity of the cold air and the vertical (layer thickness) and horizontal dimensions of the cross-sectional area it passes through (flow width). In other words, it quantifies the volume of cold air (in m³) that flows per second across a one-metre-wide section (see Figure 4).

Fig. 4: Schematic diagram of cold air volume flow (Source: GEO-NET 2022)

Cold-air volume flow serves as a measure of cold-air inflow and determines the scale of its ventilation potential. As this parameter is integrated over the vertical extent, it is not represented specifically at roof level. The diagram shows all 10 m x 10 m grid cells with values exceeding 7 m³/s that are considered to potentially support climate and ecosystems.

Classification of the Cold-Air Volume Flow Density

The qualitative assessment of this meteorological parameter is presented in Table 2. The classification of grid-based cold-air volume flow density follows the z-transformation method described in VDI Guideline 3785 Part 1 (VDI 2008). This approach uses the local or regional value range within the study area and evaluates how far a given parameter deviates from the mean conditions in that region. Based on this, four classification levels are derived: low, medium, high, and very high.

Tab. 3: Classification of the grid-based cold-air volume flow density

In contrast to the previous 2014 analysis, which considered the total cold-air volume associated with flow velocities above 0.05 m/s, the current approach focuses on the volume integrated up to a height of 50 metres. The advantage of this method is that it targets the portion of the cold-air volume flow that is actually relevant for ventilating the settlement area.

Impact of Cold-Air Volume Flow Density

The depth to which cold air penetrates into settlement areas, and with it, the degree of its beneficial impact on the bioclimate during summer high-pressure weather conditions, depends on the structure of urban development and the strength of cold-air dynamics. In general, areas characterised by detached single-family homes or row houses are more easily ventilated than dense block or block-edge developments.

At 10 pm, shortly after sunset, the evening cooling phase begins. The strength of this cooling varies depending on urban structure and influences the development of local cold-air flow fields. In the vicinity of inner-city green and open spaces, these air exchange processes tend to be small-scale, with cold-air flow rates rarely exceeding 3 m³/s, classified as ‘low’.

Depending on the size of the cold-air-generating area and the type of surrounding development, this airflow can penetrate anywhere from 50 to 300 metres into built-up regions. This highlights the importance of a sufficient number of well-placed compensation areas for reducing environmental burdens in the inner city. At this hour, ‘high’ or ‘very high’ cold-air flow rates are typically observed on the outskirts of the city, in some cases associated with localised cold-air drainage. However, similarly high flow rates may also occur in larger green spaces within the inner city, such as the Tiergarten or Tempelhofer Feld.

By 4 am, the cooling of green and open spaces, and consequently, cold-air generation, has progressed significantly. The depth of cold-air penetration increases markedly, ranging from 100 metres to over 1,000 metres, depending on the surrounding urban morphology. In more vegetated types of development, cold air is also generated locally, contributing to particularly favourable bioclimatic conditions (SenStadt 2025a). In contrast, some parts of the block and block-edge developments, as well as borough centres, receive almost no cold-air inflow, even in the second half of the night. Their dense development structure and elevated surface temperatures tend to weaken cold-air movement, if they lie within the influence zone of nearby compensation areas at all.

Map 04.10.2 Air Temperature (2 pm and 4 am)

The main map also includes layers showing temperature patterns in the near-ground atmosphere. These are based on grid cells or block (segment) areas and road areas, and are provided for different time points. Air temperature is particularly relevant for assessing conditions at night.

Influence on Air Temperature

Temperature patterns are shaped by land-use-specific soil and surface properties, and their interaction with atmospheric processes in the surface boundary layer. Within the soil, heat and thermal conductivity are key: for example, the higher the soil’s heat conductivity, the more quickly and deeply heat can penetrate the material, and also be released again.

Surface properties of natural and artificial areas, such as albedo (reflectivity) and emissivity determine how much energy is available to heat or cool the environment in both the shortwave and longwave ranges of radiation. Additionally, turbulence conditions in the near-ground atmosphere significantly affect the sensible and latent fluxes between the ground surface and the air, in both directions (cf. Map 04.10.2).

All of these processes are interrelated and part of the surface energy balance. They determine both the temperature of the surface and of the air layers above.

Air Temperature Development Over Time

While nocturnal temperature patterns generally provide more insight into the climatic potential for either mitigating or exacerbating bioclimatic stress across different areas, the midday period (2 pm) also reveals distinct differences tied to land use.

During the day, both impervious areas and grassy open spaces heat up considerably. This is due to intense solar radiation, minimal shading, and strong warming of the near-ground air layer. In these areas, temperatures can reach between 30°C and 35°C, representing peak values in the modelled summer scenario.

Forest areas and large inner-city green spaces such as the Großer Tiergarten exhibit temperatures that are 5 to 10 K lower in their tree-covered sections compared to these maximum values.

Built-up areas generally display higher temperatures overall. However, the grid-based map layer reveals fine-scale variations in temperature that reflect local conditions. By contrast, the map layer based on block-level aggregation smooths out these differences due to the use of unweighted means.

Bodies of water display the lowest temperatures, due to their specific heat capacity. They maintain relatively stable temperatures, moderating surrounding climatic conditions during the day.

As night falls, the ground cools at different rates depending on surface properties and land use. Around 4 am, the temperature distribution usually reflects the point of maximum cooling.

While bodies of water cool only slightly at night due to their excellent heat storage capacity, open spaces such as farmland and meadows experience a much greater temperature drop. This is largely due to their unimpeded loss of longwave radiation. Dry soil can intensify this effect by further limiting the heat flux from deeper layers. The temperature distribution of forest areas stands out, as they remain relatively warm at night. Their tree canopy insulates the near-ground atmosphere and thus prevents significant heat loss.

In areas with some form of development, cooling is significantly limited due to the presence of heat-retaining materials such as concrete and stone. On the one hand, heat stored during the day noticeably reduces nocturnal cooling. On the other hand, low wind speeds suppress the turbulent and latent heat flux, both of which are critical for transporting heat away from surfaces. Consequently, urban areas retain considerably more warmth overall. By early morning, temperature differences between urban areas and the undeveloped outskirts or surrounding areas can exceed 8 K. However, this stark temperature contrast between the horizontal layers of air tends to be less pronounced near open spaces in the inner city. In some cases, built-up areas can even negatively affect nearby green spaces.

Map 04.10.8 Surface Temperature (2 pm and 4 am)

Surface temperature plays a vital role in shaping energy fluxes. Depending on physical properties, such as solar reflectivity and heat conductivity as well as local meteorological conditions, such as wind speed, air temperature, and the sun’s position, the FITNAH-3D model calculates the various heat fluxes for each type of land use. In the area close to the ground where people live, the surface temperature influences the temperature of the air layer directly above it. This is especially relevant at night, when cooling at the surface largely drives the formation of cold air.
Figure 5 illustrates how surface temperature, air temperature, and radiant temperature each vary over the course of the day. However, the modelled temperatures (in °C) should not be directly equated with the air temperatures of the grid or block in question, due to the complex nature of how these figures are derived.

Fig. 5: Diurnal variations of air temperature Ta, mean radiant temperature Tmrt (derived from radiation measurements Tmrt,meas. and calculated using RayMan Tmrt,calc.) and ground surface temperature Ts (derived from radiation measurements Ts,meas. and calculated using RayMan Ts,calc.), on a pleasant summer day above tree canopies (canopy cover: 0.88) in a green space in the northern city centre of Freiburg; reference height for Ta and Tmrt: 1.1 m above ground. (Matzarakis, A., Rutz, F., Mayer, H., 2000)

Effect Over the Course of the Day

The surface temperature at 2 pm illustrates that this parameter is largely influenced by solar radiation. At this hour, farmland and meadows, and impervious areas exhibit the highest temperatures with more than 35 °C. In forest areas, a lower surface temperature of around 26 °C is observed, which is due to the evaporative cooling effect provided by the tree canopy. Settlement areas are comprised of a fine-scale mosaic of high and low surface temperatures, resulting from the close interplay of buildings, impervious areas, and trees. The surface temperature of bodies of water reaches only 22 °C to 23 °C, aligning with the measured values used as input in the model. This is due to water’s high specific heat capacity and the turbulent mixing that takes place below the water surface.

At 4 am, the surface temperature is predominantly influenced by (longwave) thermal radiation emitted from different surface types. The highest values, around 20 °C to 24 °C, are found within the densely built-up settlement areas, which can be attributed to large building volumes and their heat emission at night. Bodies of water exhibit similar surface temperatures, as, at this hour, they release some of the heat stored during the day. The lowest surface temperatures are modelled above larger meadows and farmland. Temperatures drop to around 14 °C to 15 °C, as their surface areas experience the greatest nocturnal cooling. Although surface temperatures in forest areas are higher than those in open spaces (around 20 °C), they tend to be lower than those in settlement areas. The overall difference between the highest (dense block development) and lowest (open spaces) surface temperatures during the night is approximately 12 K.

Map 04.10.4 Nocturnal Cooling Rate between 10 pm and 4 am

Map 04.10.4 illustrates the rate of nocturnal surface cooling across various urban structures between 10 pm and 4 am, expressed in Kelvin (K) per hour, either per grid cell or as a mean across block (segment) areas and road areas.

This analysis reveals both areas prone to urban overheating and those offering thermal relief through intensive cooling. Together, these spatial patterns offer a comprehensive view of the city’s underlying thermal conditions. Nocturnal cooling is indirectly incorporated into the bioclimatic assessment of settlement areas via the temperature levels determined.

Effect Over the Course of the Night

The degree of cooling varies greatly depending on the physical properties of the soil and surfaces associated with different land uses. Urban structures exhibit distinct patterns in this regard. Due to their high thermal conductivity and heat capacity, both bodies of water and densely built-up settlement areas (urban heat island effect), show the lowest levels of nocturnal cooling. Moderate nighttime cooling is observed in much of the remaining built-up environment. In contrast, forest areas and heavily vegetated settlement types show significantly higher cooling rates, with the most pronounced cooling found in farmland and meadows.

Evaluation Indices

Meteorological parameters do not affect humans in isolation. Evaluation indices are used to assess their combined effects on the human body. These indices are particularly important for evaluating thermal stress, focusing on the heat exchange between humans and their surrounding environment. Key climatic variables that directly influence the human heat balance include air temperature, humidity, wind speed, and radiation, which directly affects the body’s thermal regulation.

To assess the combined thermal effects, two indices are commonly used: the Universal Thermal Climate Index (UTCI) and Physiological Equivalent Temperature (PET). These differ slightly in their evaluation methods.
For assessing bioclimatic conditions in Berlin at 2 pm, PET is used, since it has become the standard indicator for evaluating thermal comfort during the day (Höppe and Mayer 1987).

Map 04.10.5 Physiological Equivalent Temperature (PET) (2 pm)

PET was derived from the Munich Energy Balance Model for Individuals (MEMI) (Höppe 1984). Table 4 links PET values to levels of thermal perception and physiological stress under daytime conditions. Perception is derived from the thermal response of a ‘standard’ individual with average thermal sensitivity. Optimal thermal comfort is defined at 20 °C. Values above this threshold indicate increasing levels of heat stress, while values below it correspond to varying degrees of cold stress.

Tab. 4: Classification of threshold values for the PET evaluation index during daytime hours (Matzarakis 1996; VDI 2022)

At 2 pm, PET values highlight how strongly daytime heat stress depends on local shading conditions. On cloudless summer days with intense solar radiation, forested areas and green spaces with abundant trees and shrubs typically exhibit only moderate heat stress. In these areas, the shade provided by vegetation, along with the cooling effect of water evaporation contribute to relatively low potential heat stress. Urban green spaces play a key role, especially near densely built-up neighbourhoods, as they offer more comfortable environments. In contrast, areas with full sun exposure exhibit the highest levels of heat stress. Interestingly, lawns can reach temperatures similar to those of impervious areas.

Map 04.10.9 Evaluation Index Universal Thermal Climate Index (UTCI) (2 pm)

Alongside PET, the UTCI is also used in practice. This evaluation index is provided as an additional option. Like Physiological Equivalent Temperature (PET), the UTCI is based on a human heat balance model and takes into account the same key environmental factors such as solar radiation, air temperature, and humidity. Similar to PET, absolute values are linked to specific levels of physiological stress (cf. Table 5). While the UTCI was primarily designed to provide assessments under different climatic conditions, hence ‘Universal’, PET places more emphasis on the direct effects of temperature and humidity on human well-being.

Tab. 5: UTCI categories for different levels of thermal stress (Bröde et al. 2022; VDI 2022)

As is the case with PET, solar radiation has a strong impact on the UTCI. This means that at 2 pm, UTCI values are particularly high above surfaces exposed to intense solar radiation. Similarly, unshaded lawns can exhibit UTCI values comparable to those above impervious surfaces. In green urban structure types, the UTCI is therefore also tied to the presence of trees. Lower UTCI values, and thus higher thermal comfort for humans, occur in areas where vegetation provides shade.

Climate Analysis Map

The Climate Analysis Map presents the current state of the urban climate. It illustrates the extent of urban overheating, the compensatory effects of cold-air-generating green and open spaces, and the spatial relationships between compensation areas and impact areas. The map also accounts for the influence of surrounding open spaces on the city’s climate.

The aim of the map is to differentiate areas of the city according to their climatic function and to delineate their impact on other parts of the city. Initially, the study area is divided into settlement areas subjected to heat stress and/ or air pollution (impact area), and undeveloped, vegetation-rich areas that generate cold air (compensation areas). Provided these areas are not directly adjacent to each other and the air exchange processes are strong enough, linear and lightly developed open spaces (ventilation corridors) can connect the two. By distinguishing between favourable and unfavourable zones, along with the structures that connect them, a complex picture emerges of the air exchange processes within the interconnected system of compensation and impact areas.

Map Content

The depiction of the urban heat island effect across settlement and traffic areas illustrates thermal conditions within the city at night. It is based on how much the mean nocturnal air temperature in each area deviates from the overall mean of 17.5°C at 4 am. In the 2014 edition, the urban heat island effect was analysed using a statistical method called z-transformation, which grouped the results into four categories (‘not present’, ‘weak’, etc.). These categories were then directly incorporated into the Planning Advice Map. Since the Climate Analysis Map aims to objectively present urban climate processes at night, it does not include any evaluation at this stage. In the 2022 update, urban overheating is therefore shown simply as the absolute deviation from the mean temperature of settlement and traffic areas (17.5°C). Subsequently, an analysis is carried out as part of the Planning Advice Urban Climate Map.

Tab. 6: Classification of the nocturnal urban heat island effect in settlement and traffic areas during clear summer nights

Vegetation-rich open spaces such as forests, park facilities, and allotment gardens are considered cold-air generating zones and are classified as ‘green spaces’ according to their land use. To assess their capacity to balance the urban climate, the Climate Analysis Map uses cold-air volume flow density (hereafter referred to simply as cold-air volume flow). This metric quantifies the volume of cold air, in cubic metres (m³), that flows per second across a one-metre-wide section. To illustrate this, one can imagine a one-metre-wide net hanging perpendicular to the airflow, starting from a height of 50 metres and reaching down to the ground surface. The amount of air passing through this net every second defines the grid-based cold-air flow density (Map 04.10.1). Cold air is taken into account up to a height of 50 metres above the ground, as this is considered a relevant height range for the ventilation of urban areas.

Portions of green spaces with a cold-air volume flow exceeding 7 m³/s and considered significant for the urban climate are highlighted with hatching. This indicates which parts of a green space are particularly relevant for local climate regulation.

The Climate Analysis Map shows the extent of thermal relief as provided by cold-air generating zones to their respective influence zones. These reflect how cold-air volume flows originating from green and open spaces extend into settlement and traffic areas, where they support ventilation and help mitigate the urban heat island effect. Cold air can originate not only from nearby green spaces but also from air exchange processes within the urban structure itself, even in the absence of adjacent cold-air sources.

The map also identifies positive, climate-relevant residential developments, typically characterised by an average degree of impervious soil coverage of less than 30%. Thanks to their favourable microclimatic characteristics, these areas can generate cold air internally to varying extents, and contribute to its movement into more distant settlement areas during the night.

Near-ground air exchange is further supported by both linear and planar connections of varying strengths, referred to as cold-air ventilation corridors in this context. These corridors link cold-air generating zones (compensation areas) with heat-stressed regions (impact areas), making them a vital element of air exchange processes. The Climate Analysis Map distinguishes between four different types of air exchange, based on the processes involved:

• cold-air ventilation corridor, primarily thermally driven,
• cold-air ventilation corridor, primarily shaped by orography (e.g. small river floodplains),
• planar cold-air drainage on sloped terrain (with inclines > 1°), and
• large-scale ventilation corridors (in floodplains along large rivers).

The mapping of these cold-air ventilation corridors is based on the locally originating or ‘autochthonous’ flow fields simulated by the FITNAH-3D model. Except for river floodplains, the designated corridors generally consist of vegetation-rich areas that extend linearly toward their areas of impact.

To identify sloped areas (with inclines of more than 1°) where cold air flows over a wide surface, a relief analysis was carried out using the terrain elevation model in FITNAH-3D.

To illustrate traffic-related air pollution, data from Environmental Atlas Map 03.11.2 ‘Traffic-Related Air Pollution Along Streets 2020 and 2025’ was included for reference (SenStadt 2018). This map combines the two primary traffic-related pollutants, particulate matter (PM₁₀) and nitrogen dioxide (NO₂), into a single emissions index.

The ‘wind field changes’ symbol marks settlement areas with the potential for increased gustiness and sudden changes in wind direction. These effects are particularly associated with core areas and large housing estates, where building structures can affect the wind field.

Noise barriers are also shown on the Climate Analysis Map, carried over for reference from the noise mapping (SenStadt 2022). With heights of up to several metres, noise barriers can affect climatic functions and potentially disrupt nocturnal cold-air flows. Knowing their location provides important additional information for assessing air exchange processes, as noise barriers were not explicitly included in the simulation model.

The approach, data and methodology of the process used to update the climate data aim to maximise the level of detail and coverage of the resulting findings. In view of the dynamic development in the city, however, the initial conditions used for the assessment can change more quickly in individual cases than the update cycle of the Environmental Atlas can record. It is therefore recommended to display the layer with current aerial images in the Geoportal (available in German only) in order to check the area and compare it with the factual data of the analysis maps. This allows conclusions to be drawn about the usability of the results.

Differentiation of Spatial Units

The differentiation of the spatial units ‘settlement areas’ and ‘green and open spaces’ is based on a classification system derived from the area types of the Urban and Environmental Information System (ISU) (SenStadt 2020). Further details on how these spatial units are defined can be found in the description accompanying the Planning Advice Urban Climate Map (SenStadt 2025a, available in German only). Figure 6 shows their spatial distribution across the city.

Fig. 6: Citywide distribution of the spatial units within the climate model, based on the area types from the Urban and Environmental Information System (ISU) (SenStadt 2020)

Green and Open Spaces

Vegetated open spaces with substantial cold-air generation serve as important compensation areas for urban climate regulation and pollution mitigation. During nights with low air exchange and high-pressure conditions, longwave radiation leads to significant cooling of the near-ground air layer. The volume of cold air generated depends on the dominant vegetation type, soil properties, and the associated nocturnal cooling rate.

Across the city, green spaces with the potential to generate cold air cover around 347 km² or roughly 39% of Berlin’s total area, a considerable share. However, the capacity for cold-air generation varies within these spaces. In many inner-city green spaces, central sections tend to exhibit a lower cold-air flow than those located next to buildings. This is because the cold air, driven by the temperature contrast between open spaces and built-up areas, must first accelerate; flow rates therefore increase as the cold air moves towards built-up areas. The sharpest temperature gradients, and thus the most effective air exchange, occur where green spaces meet urban development. On the map, areas with cold-air volume flows of more than 7 m³/s are labelled as areas with high or very high air exchange (cf. Table 3). Some of these areas also extend into built-up regions and are classified as ‘cold-air influence zones within settlement and traffic areas’.

Large, linear open spaces with relatively low surface roughness serve as cold-air ventilation corridors. Notable examples include sections of the Havel and Spree river valleys, for example, the stretch of the Havel between Pichelssee and Ruhlebener Straße, which channels cold air northward into the borough of Spandau over a distance of about 3 km. Also worth mentioning in this regard is a section of Dahme river along Grünauer Straße and Regattastraße. These findings are consistent with a report by Germany’s National Meteorological Service (DWD 1996). The Wuhletal valley also stands out as a cold-air ventilation corridor.

However, due to Berlin’s relatively flat orography, such terrain-driven ventilation corridors are rare. There is no evidence that river floodplains contribute significantly to the transport of cold air from the surrounding countryside into the city; instead, only certain sections within the urban area function effectively as ventilation corridors.

Settlement and Traffic Areas

As discussed in the Methodology chapter, the nocturnal urban heat island effect was assessed by comparing the mean nocturnal air temperature of block (segment) and road areas, at 2 metres above ground, to the mean temperature across all settlement and traffic areas. This deviation allows for a spatial differentiation of these areas based on whether the heat island effect is above or below average. The distribution of nocturnal air temperatures also served as a basis for identifying zones of bioclimatic stress in the Planning Advice Map (SenStadt 2022).

Areas with mean temperatures below 17.5 °C typically exhibit little to no heat island effect. These regions are generally positively influenced by a cold-air influence zone and tend to be well-ventilated. The extent to which this airflow penetrates built-up areas depends both on the productivity of cold air generation, including from the built-up areas themselves, and on how much the prevailing development types obstruct air movement. In densely developed neighbourhoods, even blocks located within the influence of cold-air generating zones can still exhibit moderate to strong urban heat island effects at night. These local phenomena suggest that in some cases, the cooling effect of incoming cold air may be insufficient to significantly lower air temperatures.

By contrast, settlement areas with high levels of vegetation typically experience little or no nocturnal urban overheating. Built-up areas with climate-relevant characteristics often feature an open urban structure, a total impervious coverage below 30%, and show little to no urban overheating. These areas can therefore potentially contribute to local cold-air generation. The actual cooling effect, however, is still strongly dependent on local conditions, particularly the presence and type of vegetation. Typical examples of area types conducive to the climate include single-family homes, row houses and duplexes, or more broadly residential areas featuring gardens and green spaces. These areas often border cold-air-generating green spaces and help ventilate more distant neighbourhoods affected by nocturnal overheating.

Air Exchange

Structures that facilitate air exchange and channel cold air into urban areas serve as essential links between compensation areas and impact areas under bioclimatic stress. Ideally, ventilation corridors should have low surface roughness. Suitable structure types therefore include sparsely vegetated valleys and floodplains, expansive green spaces, particularly open spaces with low-growing vegetation, and railway areas. While wide roads can contribute to balancing the urban climate, their high pollutant levels make them unsuitable for channelling clean air into urban areas. In the Climate Analysis Map, these ventilation corridors are categorised based on the nature of the airflow processes involved. In the ideal case, a cold-air generating zone is also part of a ventilation corridor.

Most of the ventilation corridors are primarily thermally induced, meaning they rely on air movement caused solely by land-use-related temperature gradients. A good example of such a flow system in the inner city is the allotment garden facility near Priesterweg. These gardens not only generate cold air locally but also channel cooler air from the Bergstraße cemetery in Steglitz and from the Insulaner hill northward.

Thermally induced ventilation corridors that have been identified are mainly concentrated in the following areas:

• north of the Tegel-Lichtenberg line,
• west of Schlosspark Charlottenburg extending to the city boundary at Staaken, with some inflow of cold air from the northern Gatower Feld and the surrounding areas, and
• in the south, east of the city boundary near Groß-Ziethen, particularly in the neighbourhoods of Rudow and Bohnsdorf.

Regions directly adjacent to both green spaces and built-up areas were not included in ventilation corridors.

Ventilation corridors that are primarily orographically induced are concentrated in the eastern part of the city. These include valley areas such as those of the Wuhle and Mühlenfließ, which take on the role of ventilation corridors due to their orientation, width, and surface characteristics. In the western part of the city, a similar function is performed by a series of connected lowlands extending from Grunewald through Hundekehlsee, Dianasee, Koenigssee, and Halensee.

Larger river floodplains, such as those of Spree and Havel go beyond this role and act as primary ventilation corridors. They support air exchange in surrounding built-up areas even under more dominant, large-scale weather conditions.

Planar cold-air drainage is generally limited to areas with inclines above 1°, and is relatively rare in Berlin due to the city’s rather negligible differences in terrain elevation. As a result, cold-air drainage is mostly confined to a few areas with significant inclines, such as Grunewald and Köpenicker Bürgerheide. Additionally, localised cold-air drainage can be assumed in specific areas such as north of Tegeler See, in Kaulsdorf, and in Forst Düppel. Cold-air generation and outflow are above average in these sloped forested areas, as radiative cooling takes place mainly in the upper canopy, rather than near the ground. Owing to the large radiating surface of the tree stands, cold air drains within and above the canopy, rather than descending directly into the trunk space (Groß 1989).

Additional Notes

Air quality along Berlin’s primary road network is assessed using the Air Pollution Index, which is based on concentrations of nitrogen dioxide (NO₂) and particulate matter (PM₁₀) (SenStadt 2018). The spatial distribution of pollution levels is closely linked to traffic volumes and the urban development along road sections. The latter plays a key role in the dilution and dispersion of polluted air masses. As a result, elevated pollution levels are typically found in densely built-up areas with high traffic volumes.

Changes in wind fields, such as increased turbulence as well as updrafts and downdrafts, can occur near large buildings. This is the case for urban structure types ‘heterogeneous inner-city mixed development’, ‘large estate with tower high-rise buildings’, and ‘core area’ uses. These changes can have both positive and negative consequences: on the one hand, they may enhance the dispersion of polluted air; on the other, they can often lead to reduced wind comfort. On hot days, Berlin’s bodies of water provide a cooling effect to nearby areas in the city. In addition, they function as ventilation corridors, even under weather conditions with stronger air exchange.

Noise barriers are installed along sections of road and rail infrastructure that produce high noise levels near sensitive land uses. They are mainly found along railway lines in the southern and western parts of the city. These barriers are shown as additional information on the map, as their potential impact on air mass dispersion could not be explicitly accounted for in the modelling process.

According to VDI Standard 3787, Part 1, the Climate Analysis Map ‘depicts the spatial climatic characteristics of a reference area based on land use and topography. It presents thermal conditions, wind dynamics, and air quality. Note: The Climate Analysis Map includes and replaces the previous Synthetic Climate Function Map.’ (translated from VDI 2015)

Guide to Reading the Map Using an Example Area

In this section, the modelled climate parameters and the resulting Climate Analysis Map (04.10.7) are discussed using an example area. This region, measuring approximately 5 by 3 kilometres, is located in the borough of Charlottenburg-Wilmersdorf (cf. SenStadt 2022). It complements the information provided in the Map Description chapter.

The selected example area encompasses a broad spectrum of urban land use types found in Berlin, making it particularly well suited for a detailed analysis of urban climate relationships. It extends from Grunewaldsee in the southwest to Hohenzollernplatz in the northeast and is marked by the diagonal A100 motorway (cf. Figure 7). Grid cells representing buildings are shown in black.

Fig. 7: Spatial extent and land use structure in the transitional area between Forst Grunewald and City West (Charlottenburg-Wilmersdorf)

Preliminary Note

The climate simulation results are displayed in two layers. The grid data represents modelled parameters based on input data, highlighting the climatic effects of different land uses (e.g. impervious soil cover, lawn, or trees). For example, during the day, areas shaded by trees show lower equivalent temperatures than their surroundings.

However, individual grid cells are of limited use when analysing bioclimatic relevance or assessing specific areas. For this kind of analysis, the study area must be divided into zones comprising structurally similar units. These zones should be recognisable and definable on site, for example on the basis of administrative boundaries or land use patterns. This zoning is achieved by calculating the mean values of the individual parameters based on the areas defined in the Urban and Environmental Information System (ISU5), which serve as the base geometries. In other words, all grid cell values within a unit were averaged to produce a single total value. A high proportion of green spaces thus leads to a lower mean temperature, while a high degree of impervious soil coverage results in a higher mean temperature. The area mean reflects the combined climatic effect of all relevant structures within the unit.

Map 04.10.1 Near-Ground Wind Field and Cold-Air Volume Flow Density

The high spatial resolution of 10 m x 10 m makes it difficult to effectively visualise the small-scale wind field in the example area. Therefore, the grid-based cold-air volume flow is used to represent the cold-air flow field (cf. Figure 8).

The cold-air volume flow remains consistently high to very high over a large area, extending deep into the surrounding built-up regions to the east. This is mainly due to the strong cold-air generation in the Grunewald area, which is further supported by cold-air drainage on slopes steeper than 1° in the eastern part of the forest.

Fig. 8: Cold-air volume flow in the transitional area between Forst Grunewald and City West (Charlottenburg-Wilmersdorf) at 4 am on a clear summer night

Heavily vegetated settlement areas adjacent to Grunewald benefit significantly from a very high cold-air volume flow. Owing to their minimal structural barriers to the cold-air flow and their own capacity to generate cold air, these regions can already be considered climatically beneficial in their own right. Moving eastward, cold-air volume flow values remain high up to the A100 motorway, but then gradually decline to moderate levels. This reduction is attributed to steadily increasing urban density and rising temperatures, both of which impede cold-air volume flow. East of Brandenburgische Straße, the flow drops locally to a low level.

The map also highlights surface structures that enable cold air to penetrate deep into built-up areas. These are predominantly vegetation-dominated regions with few buildings. In the northern part of the map section above, the green corridor formed by Dianasee, Koenigssee, and Halensee, together with the adjacent railway tracks, stands out as a major cold-air ventilation corridor with a very high cold-air volume flow. To the south, the cluster of green spaces comprising Sommerbad Wilmersdorf, Wilmersdorf-Friedhof, and the Wilmersdorf/ Fennsee area are clearly identifiable as a cold-air ventilation corridor. The high to very high volume flow continues beyond Uhlandstraße into Volkspark Wilmersdorf, emphasising the ventilation corridor potential of such green infrastructure.

Map 04.10.2 Near-Ground Air Temperature

At 4 am, the simulated temperature field reveals a range of about 8 Kelvin (K), with minimum values of 14.2°C and maximum values of 21.8°C (cf. Figure 9). As expected, the temperature gradually rises moving from the Grunewald area toward the more built-up City West. The lowest air temperature, at 14.2°C, is recorded just north of Grunewaldsee, above lawns of the Hundekehlefenn. Within the built-up area, the allotment gardens south of Forckenbeckstraße stand out as a cold-air zone, also due to their remarkable size. In comparison, Friedhof Wilmersdorf shows slightly milder cooling effects, with temperatures ranging from 14.9°C to 16.6°C. Above smaller green spaces, nocturnal cooling is generally less pronounced depending on the size of the area.

Fig. 9: Near-ground air temperature in the transitional area between Forst Grunewald and City West (Charlottenburg-Wilmersdorf) at 4 am on a clear summer night

Within the built-up areas, air temperature varies depending on the mix of buildings and green spaces. Larger green inner courtyards can reach relatively low temperatures between 16.5°C and 18°C. In contrast, similarly sized courtyards that are fully impervious (sealed) as well as wide road areas, can be up to 1.5 Kelvin (K) warmer. Vegetated settlement areas generally range between 15°C and 18°C. The highest air temperatures, reaching 21.8°C, are recorded above larger bodies of water.

Map 04.10.8 Surface Temperature

Surface temperatures are shaped mainly by surface colour and land use structure. Lighter surfaces reflect more solar radiation, while darker surfaces convert solar radiation into heat. Depending on the material, this heat is stored during the day and released back into the near-ground air layer at night. Impervious surfaces or concrete, for example, retain more heat than dry sandy soil. As a result, air temperatures directly above the ground are particularly affected both during the day and at night.

Fig. 10: Surface temperature in the transitional area between Forst Grunewald and City West (Charlottenburg-Wilmersdorf) at 2 pm on a clear summer day

The map section shown in Figure 10 reveals that temperatures below 30 °C occur in tree-dominated land uses at the simulated midday hour of 2 pm on a clear summer day. These comparatively low temperatures are widespread throughout the Grunewald area, while in settlement areas, they depend on the presence of tree stands. As a result, more vegetated neighbourhoods bordering Grunewald tend to display noticeably cooler temperatures than the more densely built-up, less green areas east of the A100 motorway. In these latter regions and in wide road areas, unshaded surfaces can reach temperatures exceeding 35 °C. The presence of street trees can locally mitigate this effect by providing shade. This can be observed along major thoroughfares such as Kurfürstendamm, visible at the upper edge of the figure, and Hohenzollerndamm, which cuts diagonally through the area. Interestingly, even grassy areas within parks and green spaces can exhibit high surface temperatures if unshaded, with temperatures only slightly below those of impervious areas.

Map 04.10.4: Nocturnal Cooling

Figure 11 illustrates how temperatures drop across different grid cells between 10 pm and 4 am on a clear summer night. The extent of nocturnal cooling is closely tied to the thermal properties of various surfaces without building structures, particularly their heat flux. This determines how much energy is absorbed by the surface during the day and stored in the material, and how much is released back into the atmospheric layer near the ground at night.

Fig. 11: Nocturnal cooling rate in the transitional area between Forst Grunewald and City West (Charlottenburg-Wilmersdorf) between 10 pm and 4 am on a clear summer night

Due to their strong nocturnal cooling, large grassy sections generally show the most significant temperature drop overnight, with rates of around -0.6 to -0.8 K per hour. Within the ‘Forst Grunewald-City West’ section, this is particularly evident in the Hundekehlefenn, the fallow area near the railway tracks along the A115, and the southern part of the Friedrichshall allotment gardens (light blue on the map). Grassy areas show moderate cooling rates, typically between -0.4 and -0.6 K per hour. In contrast, road areas, impervious surfaces, and areas shaded by tree canopies cool less, with rates between -0.2 to -0.4 K per hour (orange). In forested and tree-covered areas, the canopy reduces the amount of heat radiated from the ground, while on impervious surfaces, a high upward heat flux from the ground slows the cooling. Owing to the heat storage capacity of water, bodies of water exhibit the weakest nocturnal cooling, with rates below -0.2 K per hour (light red).

Map 04.10.5: Physiological Equivalent Temperature (PET)

The Planning Advice Urban Climate Map (Map 04.11.1) uses Physiological Equivalent Temperature (PET) to assess daytime heat stress. PET is based on the human body’s heat exchange with its environment (Höppe 1984). Radiative energy fluxes play a central role in this metric, making its spatial distribution closely tied to surface radiation temperatures.

Under the shaded canopy of Forst Grunewald, PET values generally remain below 29 °C; conditions corresponding to a ‘slightly warm’ thermal perception and ‘slight heat stress’ (cf. Figure 12). Similar PET values are observed above larger bodies of water. Above shorelines, however, increased near-ground wind speeds lead to a drop in PET with minimums as low as 20.1 °C (turquoise). In the human heat exchange model underlying PET, stronger winds enhance evaporative cooling via the skin, thereby reducing perceived temperature. Slightly higher PET values extend also into adjacent vegetated settlement areas, depending on tree cover. Here, the environment is generally perceived as ‘warm’, predominantly within the range of ‘moderate heat stress’. Under summer conditions with potential heat stress, these types of urban settlement thus offer favourable bioclimatic conditions, not only at night, but also during the day.

Fig. 12: PET (Physiological Equivalent Temperature) Evaluation Index in the transitional area between Forst Grunewald and City West (Charlottenburg-Wilmersdorf) at 2 pm on a clear summer day

PET values exceeding 35 °C are observed in the remaining urban structure types and can reach up to 42 °C in large areas with intense solar radiation. Notable hotspots include the A100 motorway, large flat impervious (sealed) surfaces, and sports fields, all of which are directly exposed to the sun. In contrast, tree-lined road areas can exhibit PET values up to 10 K lower, significantly enhancing thermal comfort for both pedestrians and cyclists. Interestingly, lawns in green and open spaces show similarly high PET values to large parts of the road network. Overall, the PET range within the mapped area spans around 21 K. For context on how PET relates to thermal comfort and physiological stress, please refer to Table 4.

Map 04.10.9 Universal Thermal Climate Index (UTCI)

Both the UTCI and PET are based on a human heat balance model, incorporating key factors like solar radiation, air temperature, and humidity. Both indices link absolute values to levels of physiological stress. While PET places more emphasis on the direct effects of temperature and humidity on human comfort, the UTCI was developed to provide insights under different climatic conditions.

Figure 13 shows UTCI values for the City West area. The UTCI generally ranges between 35 °C and 38 °C in unshaded road areas and can climb to 40 °C in inner courtyards exposed to intense solar radiation. In these areas, reduced wind speeds due to surrounding buildings can increase UTCI values and intensify heat stress. In contrast, areas with extensive tree cover exhibit significantly lower UTCI values, between 25 °C and 26 °C, reflecting a pattern similar to that observed with PET.

Fig. 13: UTCI (Universal Thermal Climate Index) in the transitional area between Forst Grunewald and City West (Charlottenburg-Wilmersdorf) at 14:00 on a clear summer day

Map 04.10.7 Climate Analysis Map

The Climate Analysis Map is the main outcome of the analysis and is based on the meteorological parameters described earlier. By differentiating between cold-air generating zones, impact areas, and the structures that connect them, the map paints a complex picture of air exchange processes within the interconnected system of built-up areas and green spaces.

In the Climate Analysis Map, green and open spaces are represented as climate compensation areas. In the example area shown below, most of these spaces also support cold-air flows that benefit the local climate and ecosystem, driven by strong air exchange. The smaller green spaces east of Brandenburgische Straße form an exception. They do not qualify as compensation areas, primarily due to their limited size and, consequently, below-average cold-air generation (cf. Figure 14).

Fig. 14: Insights from the Climate Analysis Overview Map for the Transitional Area Between Forst Grunewald and City West (Charlottenburg-Wilmersdorf)

A large portion of the settlement area lies within the influence zones of regions that generate cold air, which extend beyond the A100 motorway up to around Brandenburgische Straße. In addition, vegetated settlement areas are identified as built-up regions with important functions for the urban climate. The nocturnal urban heat island effect in this area is relatively weak, with temperature differences of below 1 K. At 4 am, the mean air temperature within some of these block areas falls below the overall mean of 17.5 °C recorded across all settlement areas in the city. Toward the borough of Mitte, the heat island effect intensifies, with moderate overheating prevailing east of the A100. Along Kurfürstendamm, individual building blocks and road areas exhibit significant overheating, reaching up to 3 K above the mean.

Air exchange on the eastern edge of Grunewald is primarily shaped by cold-air drainage, which can develop on slopes steeper than 1°. Additionally, the area north of Halensee, between Grunewald and Charlottenburg S-Bahn stations, functions as a cold-air ventilation corridor. Air quality is marked by the presence of several major, high-traffic thoroughfares. Kurfürstendamm and Hohenzollerndamm, in particular, show elevated pollution levels. In contrast, traffic-related pollutants such as particulate matter (PM₁₀) and nitrogen dioxide (NO₂) generally remain in the low to moderate range west of the A100 motorway (for detailed information, cf. Environmental Atlas Map 03.11, 2018 Edition).

Individual block areas indicate potential for wind field changes. These includes, for example, large housing estates such as the Schlangenbader Straße motorway superstructure as well as ‘core-use’ areas around Kurfürstendamm.

A planning-oriented interpretation of the functions depicted in the Climate Analysis Map (areas requiring protection/ thermally favourable or unfavourable conditions) is provided in the Urban Climate Planning Advice Map. This map provides a planning-oriented synthesis of the modelled data and the resulting Climate Analysis Map, serving as a key reference for urban climate-related considerations and decision-making processes. Figure 15 shows the relevant section for the example area.

Fig. 15: Insights from the Main Map for the Transitional Area Between Grunewald Forest and City West (Charlottenburg-Wilmersdorf)

The assessment of thermal conditions in settlement areas is based on a combination of nocturnal air temperature and daytime Physiological Equivalent Temperature (PET). Accordingly, the vegetated settlement areas west of the A100 motorway exhibit very favourable to favourable conditions. Moving eastward, increasing building density and impervious soil coverage lead to rising heat stress. Bioclimatically unfavourable conditions are concentrated around Kurfürstendamm, Hohenzollerndamm, and Brandenburgische Straße.

Thermal conditions in road areas are assessed based on PET. On clear summer days, they are primarily negatively affected by the intensity of solar radiation and positively influenced by shade from buildings or trees. Sections of Kurfürstendamm and Hohenzollerndamm therefore offer pleasant to very pleasant conditions. Conversely, road areas exposed to intense direct sunlight during the day are classified as less pleasant or even unpleasant.

The compensatory function of green and open spaces within built-up areas is rated from high to very high across much of the example area. This is largely due to their proximity to heat-stressed settlement areas and their strong nocturnal cooling effect on adjacent developed regions. Additionally, the cold-air ventilation corridor near Halensee is designated as part of a broader ventilation corridor area.