Frequency of tropical nights

Sector Heat stress and human comfort
Description Tropical nights are nights when minimum 2 m air temperature remains greater than 20° C (e.g. Fischer and Schär 2010).
End User General public
Calculation method
ID Title Period Statistical processing Unit Threshold Comment
tropicalnights Tropical Nights yearly Number of days with daily minimum temperature greater than 20°C. nights  20°C  
Provenance Computed by the HARMONIE model.
Validation The simulations made by HARMONIE-AROME in Urban SIS has been validated against observations in Urban SIS deliverable 5.1, where an overview is given in Table 4.  
Calculation caveats

Spatial representation: S1
Other caveats:
Could be compared to: 
Could be used with: 


This indicator has been shown, in combination with hot days (indicator id: hotdays), to explain temporal and spatial variance of excess mortality during recent European heatwaves (e.g. Fischer and Schär 2010). The temperature threshold used to identify a tropical night that is used follows EEA (2009).

The indicator “Tropical nights” is meant as an intuitive way to present high temperatures occurrences for the public.

Experience user  

EEA Report No 5/2009. Ensuring quality of life in Europe’s cities and towns – tackling the environmental challenges driven by European and global change. ISSN 1725-9177

Fischer EM, C Schär 2010: Consistent geographical patterns of changes in high-impact European heatwaves. Nature Geoscience 3.6: 398-403.