Damage to buildings due to heavy rain and river floods
Besides storms, heavy rain and river floods cause the greatest damage to buildings. While the danger from river floods only exists in the immediate vicinity of a river, heavy rain can occur anywhere. For river floods, early warning is usually possible several days in advance, whereas heavy rainfall can often only be predicted a few hours in advance.
How vulnerable a building is to heavy rain or flooding depends on the settlement structure and the characteristics of the building. In areas with high soil sealing and on slopes, the risk from urban flash floods is particularly high. The areas that could be flooded can be shown in flood risk maps and municipal heavy rain hazard maps.
The most vulnerable part of a building is the basement. The extent of damage depends on the type of use. In addition, the type of materials used influences the extent of damage in the event of an emergency. For example, it plays a role which heat-insulating composite materials were installed. This can determine whether renovation is possible or whether demolition is necessary. Contamination with dirty water or water-polluting substances such as chemicals or oils (e.g. from an oil heating system) also plays a major role. These can lead to a considerable increase in the extent of damage or the costs of remediation.
With regard to heavy rain, insufficient driving rain protection of basement windows or the extension of attics, roof terraces and balconies can lead to higher damage. Low building base heights, insufficiently dimensioned drainage systems and unfavourable roof construction methods can also increase the extent of damage. Heavy rain can damage the facade if there is no roof overhang. The consequences can be felt when water enters the building components and leads to moisture penetration damage. Other factors include the construction method of the exterior wall, the year of construction as well as maintenance, servicing and modernisation of roof and drainage systems.
Indicators from the monitoring on the DAS: Heavy rain in residential areas, Insurance density natural hazard insurance residential buildings
Vegetation in settlements
Public green spaces, urban trees, private gardens as well as green roofs and facades have an important urban climatic function: they cool the city and reduce the heat load for the inhabitants. In contrast to buildings and sealed surfaces, vegetation stores hardly any heat and lawns in particular cool down more quickly at night. In addition, there is cooling through evapotranspiration. During the day, the shade cast by trees is also very important.
Vegetation in settlements not only makes valuable contributions to climate protection and climate adaptation, it is also directly affected by climate change. In particular, multiple stresses due to drought, heat, pests, diseases as well as storms are likely to put further pressure on settlement vegetation.
About 70 per cent of the street trees in Germany are of just six species. These are already exposed to multiple stresses such as abiotic stress factors, diseases and pests, so that their resistance is limited. Drought and heat stress in particular are putting frequently used tree species such as lime and maple under increasing pressure and making them even more susceptible to pests and diseases. Some of the classic urban trees will therefore no longer be able to cope with future demands. Poor site conditions are also further stress factors for street trees, such as a small root space due to soil compaction and sealing, low soil and air quality, and pollutant inputs such as road salt.
Urban climate and heat islands
The urban heat island is a typical feature of the urban climate and describes the effect that it is warmer within an urban area than in the surrounding rural areas. The larger and more densely built-up the city, the greater the heat island effect tends to be. A high degree of surface sealing, few cooling green spaces, low air circulation, dark surfaces, high-rise buildings and heat emissions, for example from traffic and building air conditioning, all contribute to this. As buildings store heat and cool down only slowly, the urban heat island effect is strongest at night.
Urban heat islands can lead to a significantly increased heat load. In addition, the urban heat island effect can amplify the negative effects of air pollutants, especially ground-level ozone. Increasing urbanisation leads to an expansion of urban heat islands in terms of area, which can be expected to increase heat stress for people in urban agglomerations.
In the case of long-lasting high temperatures, indoor spaces can also heat up strongly. This can lead to health risks, especially for older people. High indoor temperatures are particularly relevant for facilities such as retirement and nursing homes, facilities for people with physical and mental disabilities, hospitals, emergency and rescue services, rehabilitation facilities, schools, day-care centres and certain workplaces.
Indicators from the monitoring on the DAS: Heat stress in urban environments and summer heat island effect, Cooling degree days
Further climate impacts
Indoor climate: The increasing number and duration of hot spells will increasingly lead to high indoor temperatures without structural adaptation measures. In addition to increasing heat stress, this can also have a negative impact on air quality and indoor hygiene by encouraging the release of hazardous substances and mould growth.
Times for construction activity: Strong winds, heavy rain, heat and exposure to ultraviolet radiation can increase the risk of accidents and health hazards on construction sites and thus lead to construction interruptions for occupational safety reasons.