Heavy Rainfall and Urban Flooding Hazards 2025

Map 02.24.1 Heavy Rainfall Information Map

The heavy rainfall information map provides an overview of areas at risk of urban flooding and regions in which heavy rainfall events have occurred in the past. It integrates results from various sources, including the BKG’s Advisory Map of Heavy Rainfall Hazards, the BWB’s topographic depression analysis, and city-wide heavy rainfall-related operations of the Berlin Fire Brigade. The map offers insights into water levels, the spatial extent of depressions as well as flow velocities and directions during extraordinary and extreme rainfall events. Fire service operations in connection with heavy rain are visualised as individual dots (from a scale of 1:25,000) and also aggregated per block segment or road area (based on ISU5 2021). Furthermore, the map indicates for which regions flood hazard maps have already been created based on a coupled 1D sewer network/2D surface runoff simulation. The Flood Hazard Map for Floods with Low Probability and Map of Bodies of Water are added to the map as individual layers.

Water levels, measured in centimetres above ground, are categorised into five shades of blue for the extraordinary event, consistent with the classification of the heavy rainfall hazard map (see below). The highest observed water level is displayed for each scenario. Flow velocity, measured in metres per second, is shown in five distinct shades of yellow and red, with arrows indicating the flow direction during extraordinary events. The water levels and flow velocity/ direction of extreme scenarios can be added as individual map layers.

The heavy rainfall information map comprises the following specialised layers:

1. Extraordinary event (extraordinary rainfall event [100-year, duration category of 60 min] with Euler Type II distribution):
   1. Water levels (cm)
   2. Flow velocities (m/s)
   3. Flow directions (clockwise/ 0° pointing north)
2. Extreme event (extreme rainfall events (100 mm in 60 min) with block rainfall distribution):
   1. Water levels (cm)
   2. Flow velocities (m/s)
   3. Flow directions (clockwise/ 0° pointing north)
3. Areas for which detailed heavy rainfall hazard maps are available
4. Fire service operations (visualised as dots; displayed from a scale of 1:25,000)
5. Building outlines
6. Bodies of water
7. Fire service operations (number of operations per block segment/ road area)
8. Topographic depression analysis
9. Flood Hazard Map for Floods with Low Probability

Fire service operations connected with heavy rain act as an indicator for the likelihood of a reoccurrence and, therefore, an elevated risk of flood damage due to heavy rain. The individual fire service operations are displayed as dots when the map is zoomed in to a scale of 1:25,000 or more. Figure 1 shows the annual number of fire service operations related to heavy rainfall. The year 2017 is particularly striking, with its heavy rainfall event from 29 June to 30 June 2017, and 1,004 recorded operations. On these two days, Berlin experienced unusually long and intense rainfall, which was mainly concentrated in the northwest of the city. Several regions experienced daily rainfall volumes equivalent to those of a 100-year event. Notably, Berlin-Tegel measured a daily rainfall total of 195.8 millimetres.

Figure 2 illustrates the distribution of fire service operations both by month and by year. Fire service operations related to heavy rain occur most frequently in the months between May and September, with concentrations peaking between June and August.

The depressions (turquoise) represent low points in the terrain where water might accumulate, potentially leading to the flooding of roads, squares, green spaces, and buildings. This topographic analysis is not based on any specific precipitation scenarios. Depressions are therefore depicted with their maximum potential volume, independently of rainfall events. Drainage through sewerage systems (sewers, etc.) or factors such as infiltration into the ground were not taken into account in the analysis. Uncertainty in the depression data mainly arises from obstacles that impede the flow, such as bridges, railway and road embankments, or large culverts. Although they are crucial in determining the actual extent of a depression, they were not always considered. Additionally, small-scale structures such as curbs etc., cannot be factored in due to limitations in precision and resolution of the terrain model used.

Additionally, the map highlights areas for which detailed heavy rainfall hazard maps, based on a coupled 1D/2D simulation, are available. The flood hazard map not only illustrates the spatial extent of river flooding but also provides information on water depths for low-probability flood scenarios. A comprehensive description of the flood hazard and flood risk maps may be found in the Environmental Atlas. For Berlin, maps were developed solely for risk areas and specifically for river flooding. They do not account for other types of flooding, such as those caused by overwhelmed sewerage systems, surfacing groundwater, failing water control structures or urban flooding from heavy rainfall.

In contrast, the heavy rainfall information map indicates areas potentially at risk of urban flooding and displays previously recorded heavy rainfall events. The map presented here combines a simplified risk assessment that considers potentially expected water levels and flow velocities for two different rainfall scenarios, along with a topographic depression analysis and data on fire service operations. It thus provides an initial indication of where urban flooding may occur as a result of heavy rainfall events and where damage from past flooding due to such events has taken place. It facilitates the early assessment and classification of areas at risk from heavy rainfall across Berlin, focusing on existing and new buildings, and infrastructure. Urban and land-use planning, for example, may then incorporate heavy rainfall preventive measures based on the heavy rainfall information map. With the map, regions that are potentially at risk may be identified and awareness for those involved may be raised early on. However, it does not account for the sewer network or soil infiltration. Additionally, some terrain details, such as culverts beneath roads, could not always be fully captured. As a result, the current heavy rainfall information map offers less precision and reliability compared to the more comprehensive heavy rainfall hazard maps. Please note, the heavy rainfall information map does not exempt individual projects from the responsibility to investigate and verify the hydraulic conditions on site. It is required to compare the model with the actual on-site conditions. All information is provided without a guarantee of accuracy. No liability will be assumed for damages resulting from the use of the retrieved information.

The heavy rainfall hazard map illustrates the spatial extent of floods, flood depths (water level above ground), and flow velocities during urban flooding for different scenarios (rare, extraordinary, and extreme events).

The heavy rainfall hazard map provides a detailed analysis of the spatial extent of urban flood events, flood depths, and flow velocities for a variety of heavy rainfall scenarios. These maps play a crucial role in wastewater planning and are the cornerstone of municipal heavy rainfall risk management. For the State of Berlin, these maps are particularly important for managing the heavy rainfall risks associated with rare (T = 30a, T = 50a according to KOSTRA-DWD as Euler Type II with a duration category of 180 minutes), extraordinary (T = 100a according to KOSTRA-DWD as Euler Type II with a duration category of 180 minutes), and extreme events (T extreme = 100mm in 60 minutes as block rainfall).

The water level, more precisely the water level above ground or inundation depth, is categorised into five classes. The highest observed water level is shown for each scenario. Levels below 10 centimetres are not displayed, as the accuracy of the method and the underlying data does not allow for reliable assessments at these depths. Damage may still occur in these cases, however. There is also an increased risk of accidents, e.g. due to aquaplaning. With inundation depths of 10 centimetres or more, the risk of water penetrating into buildings or lower-lying parts of structures, such as basement flats, garage entrances, or underpasses, especially through ground-level features such as windows or light shafts, is considerably greater. Apart from the immediate risk of drowning, particularly for infants and children, there is also the risk of electric shock. Moreover, at a water level of 10 to 30 centimetres, traffic is restricted. As inundation depths rise to between 30 and 50 cm, these risks amplify. Water is able to penetrate into buildings with slightly higher basement windows or raised entrances. Escape routes may be blocked due to the static pressure of the water. Furthermore, there is a risk of damage to parked vehicles, and roads become impassable for standard vehicles. Higher flood depths of 50 to 100 centimetres or more than 100 centimetres significantly increase the risk of drowning for both children and adults. The static load on building and structural components increases, potentially posing an additional threat to human health in the event of collapse. At this point, only specialised vehicles are able to navigate the roads.

The flow velocity and direction (colour-coded flow arrows), which are based on the depth-averaged maximum velocity, are displayed when the map is zoomed in to a scale of 1:2,500 or more. From this, the flow paths as well as the origin and catchment area of local floods may be derived. Even minor flow velocities of up to 0.5 m/s may pose a risk to older individuals, those with limited mobility, infants, and children, when traversing a flow path, especially at greater depths. Seals may break due to increased pressure. As flow velocities increase to between 0.5 and 1.0 m/s, the health risk of crossing a runoff path rises, posing a danger even to adults. Due to the combination of static and dynamic forces, the risk of failure of building and structural components rises. Higher flow velocities (greater than 1.0 m/s) may result in larger solid objects being carried by the flow (e.g., cars, tree trunks). These objects not only pose a direct threat to human safety but may also cause additional damage to building and structural components, amplifying the risk of failure. The water may be contaminated by foreign substances such as oil, faecal matter, or chemicals, leading to greater damage. For instance, damaged oil tanks not only jeopardise the building they are in, but also affect neighbouring structures as well as the environment. Undermining can damage the building structure, which may ultimately lead to the collapse of building and structural components. Time plays a crucial role during heavy rainfall events: prolonged exposure to water increases the risk of further structural damage.

The heavy rainfall hazard maps feature additional information. Apart from plots, they also display bodies of water, vegetation areas, roads, parking areas, sidewalks, tree pits, median strips and verges, railway tracks, and building functions. These details are displayed as background maps and reflect the current status, rather than that of the heavy rainfall hazard map.

Please note, the heavy rainfall hazard map does not exempt individual projects from the responsibility to investigate and verify the hydraulic conditions on site. It is required to compare the model with the actual on-site conditions. All information is provided without a guarantee of accuracy. No liability will be assumed for damages resulting from the use of the retrieved information.