Heat wave duration

Sector Heat stress and human discomfort
Description Heat waves are characterized as periods of sustained, extreme heat, although there is no universal definition of a heat wave. For this application, a heat wave is defined according to Meehl and Tebaldi (2004) based on daily maximum air temperature (Tmax) and two percentile thresholds (T1 and T2) from the distribution of daily Tmax during the reference scenario period. 
End User General public, health authorities, urban planners
Calculation method
  • A heat wave is defined as a period of consecutive days that satisfy the following conditions: i) Daily Tmax is above T1 for at least three days, ii) the average Tmax is above T1 over the entire period, and iii) the daily Tmax must be above T2 every day of the period (the total heat wave period must be greater than or equal to 3 days). Here, T1=97.5th percentile and T2=81st percentile, following Meehl and Tebaldi (2004). The T1 and T2 percentiles are calculated from Harmonie model output at the location of an official weather station, both for the historical period and for the present window of the  climate scenario. For the future window of the climate scenario, the same  T1 and T2 percentiles as calculated in the present window are used.
ID Title Period Statistical processing Unit Threshold Comment
heatwaveduration Hot period duration yearly Maximum number of consecutive days when: i) Daily Tmax is above T1 for at least three days, ii) the average Tmax is above T1 over the entire period, and iii) the daily Tmax must be above T2 every day of the period (the total heat wave period may be longer than three days). days T1 = 97.5th percentile T2 = 81st percentile 

 
Provenance Theese indicators are based on output from the Harmonie meteorological modell.
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:
Other caveats: O3, O4
Could be compared to:
Could be used with:
Motivation

Both duration and frequency of heat waves may increase in Europe (Perkins et al. 2011). The provided indicator can give planners a hint of changes to expect in their city. The selected method (Meehl and Tebaldi 2004) provides information about heat wave duration.
Experience user Many methods to define a heatwave (Souch and Grimmond 2004, Perkins 2015).
References

Meehl GA, C Tebaldi 2004: More intense, more frequent, and longer lasting heat waves in the 21st century. Science 305.5686, 994-997.

Perkins SE, Alexander LV, Nairn JR 2012: Increasing frequency, intensity and duration of observed global heatwaves and warm spells. Geophysical research letters. 39:20

Perkins SE 2015: A review on the scientific understanding of heatwaves—their measurement, driving mechanisms, and changes at the global scale. Atmospheric Research, 164, 242-267.

Souch C, CSB Grimmond 2004: Applied Climatology: Heat Waves. Progress in Physical Geography, 28, 599-606. doi: 10.1191/0309133304pp428pr