In experiments at 5 sites, each with different grape cultivars, temperatures and phenological development were monitored. Various models relating temperature sums to flowering were tested, and the best ones for each site identified. The following conclusions were drawn : (1) it is better to take account of maximum rather than mean temperatures ; (2) some models are better adjusted to a fixed date, rather than to the time of budburst ; and (3) variability in thermal requirements can usually be explained as a climatic adaptation, although climatic conditions at the time of flowering can perturb this effect. / L'objectif de cette étude est de proposer une méthodologie de modélisation du déclenchement de la floraison qui a été ensuite appliquée dans 5 vignobles. La mise au point d'un outil informatique permet de transférer facilement ce travail à d'autres vignobles. Ces résultats confirment l'intérêt de l'approche "besoin thermique" et conduisent à plusieurs remarques