| Metric | Description | Reference |
|---|---|---|
| HWN (Heat wave number) | The annual number of heat wave events | Fischer & Schär 2010 |
| HWF (Heat wave frequency) | The sum of participating heat wave days per year | Fischer & Schär 2010 |
| HWD (Heat wave duration) | The length (in days) of the longest yearly event | Fischer & Schär 2010 |
| HWDM (Heat wave duration mean) | The average length (in days) of heat wave events per year | Fischer & Schär 2010 |
| HWM (Heat wave magnitude) | The average daily magnitude across all heat wave events within a year, expressed as the anomaly against the mean Tmin or Tmax | Perkins & Alexander 2013 |
| HWMA (Heat wave magnitude absolute) | The average daily magnitude across all heat wave events within a year | |
| HWA (Heat wave amplitude) | The hottest day of the hottest yearly event, expressed as the anomaly against the mean Tmin or Tmax | Fischer & Schär 2010 |
| HWAA (Heat wave amplitude absolute) | The hottest day of the hottest yearly event |