Climate changes relevant to the action field

State: Heatwaves

Since 1951 there has been an increase in the number of hot days in terms of the surface area mean for Germany, from a mean of approximately three days per annum to a current mean of approximately ten hot days. Notwithstanding great variability of this index from year to year, this increase is backed up by statistics. Four of the five years indicating the greatest number of hot days occurred since 2015. Regarding Germany’s nationwide increase in hot days, it is to be noted that since the 1990s towns/cities have displayed a greater frequency of extreme heatwaves, indicating a day temperature mean in excess of 30 °C within a period of a fortnight (cf. figure 7).

Impacts of Climate Change

Impact: BAU-I-1 Heat stress in urban areas - case study

Owing to the heat island effect of large, contiguous built-up urban areas, the heat stress experienced by the population in cities is in most cases distinctly more severe than the nationwide average. In most years towns / cities have experienced more hot days; the differences being particularly significant in years with extraordinarily warm summers such as 2015, 2018 and 2019. For example, in 2018 the nationwide average was 20.4 hot days, whilst Frankfurt am Main experienced 42 hot days. One reason for this is that in cities, an increasing frequency of hot days can be observed even beyond the meteorological summer months of June, July and August.

Adaptations – activities and results

Response: BAU-R-2 Green roofs in cities

Vigorous verdure on roofs and building façades produces several positive effects thus making it an important adaptation measure for urban spaces. In view of increasing heat stress in towns and cities, the cooling effect of greening, on the building concerned and, in the case of verdure on façades, on the adjacent urban environment, is of particular importance. In respect of a verdure-covered building, this effect results from the reduced direct impact of irradiation by sunlight on the building’s envelope and the fact that plants – subject to adequate irrigation – evaporate water through their leaves. Moreover, a verdure-covered building reflects less heat into the environment, as the irradiated energy is in part absorbed by the greening.

Response: BAU-R-3 Investments in the energetic refurbishment of building envelopes

Measures taken for precautionary protection from summer heat are intended to pre-empt heating impacts on buildings. For example, the proportion of window surface areas and the orientation of a building need to be carefully designed; furthermore, blinds and roller blinds as well as anti-sun glass on the outside of windows are able to reduce irradiation. Likewise, good heat insulation and high energetic building standards can keep temperatures in buildings low. Since the mid-2010s, investments in energetic refurbishment have been on the increase. This applies both to residential and non-residential buildings, latterly owing to increasing prices in the building sector. Such investments include measures to insulate façades and roofs.