Indicator: Hot days

A graph shows the number of hot days in the areal mean for 1951 to 2016. Although the trend varies greatly, the increase is clearly visible. A trend line has also been plotted on the graph which shows a significant rise.Click to enlarge
Number of days when maximum air temperature exceeds 30 degrees Celsius (areal mean)
Source: Deutscher Wetterdienst Figure as PDF

Table of Contents

 

At a glance

  • The highest number of hot days averaged across Germany were recorded in 2003 and 2015.
  • 2016 also had above-average numbers of hot days.
  • Despite considerable fluctuations between individual years, the overall trend is rising significantly.
  • More hot days are expected during summer months in the coming decades due to climate change.
 

Environmental importance

Rising temperatures can adversely affect human health. The Deutscher Wetterdienst defines the ‘hot day’ as any day on which the maximum temperature exceeds 30 degrees Celsius (°C).

High air temperatures have a direct impact on the human body, as the heat can cause circulatory problems. Indirectly, hot weather can raise pollutant levels in the air we breathe, leading to an increase in respiratory and circulatory diseases. High air temperatures combined with intense sunlight encourage the formation of ground-level ozone. Ozone irritates the eyes and airways and can exacerbate existing respiratory diseases. It can also trigger allergic reactions.

 

Assessing the development

In 2016 Germany recorded 9 ‘hot days’, when temperatures exceeded 30 °C. Thus 2016 was a year with an above-average number of ‘hot days’.

The strain on heat in 2003 and 2015 was particularly high: in these years there were 19 respectively 18 ‘hot days’. Seven of the ten hottest years based on the number of hot days were recorded between 1994 and 2016. Although the annual figures for this indicator vary greatly, the overall trend has increased significantly since records began.

Climate models show that in future Germany can expect an increase in the number of hot days in summer and more prolonged heat waves.

 

Methodology

The indicator is based on temperature measurements taken at Deutscher Wetterdienst (DWD) monitoring stations. Temperature readings and indicator values must be calculated for those areas not covered by monitoring stations. The results can be presented in a grid (1×1 km) which shows the distribution. An annual total of hot days is calculated for each grid point. The indicator is the mean of the annual values for all grid points (areal mean). More information about the calculation method can be found at Müller-Westermeier (1995, in German only).

More detailed information: 'Trends der Lufttemperatur' (in German only).