Définition
The climate severity index is the ratio between an observed climate indicator and a reference climate indicator (thirty-year period). This indicator is made up of unified day degrees (daily difference between the observed temperature and 17°C). By convention, the unified day degree is equal to zero if the observed temperature is greater than or equal to the reference temperature.
Remarque
Source : Service de l'observation et des statistiques (SOeS) au Ministère de l'Écologie, de l'Énergie, du Développement durable et de la Mer (site : www.statistiques.developpement-durable.gouv.fr/, rubrique " sources et méthodes ".