Unravelling the responses of different apple varieties to water constraints by continuous field thermal monitoring

•The tree response to water constraints was continuously assessed by thermal sensors.•Variations in apple canopy temperature were used as a proxy of stomatal closure.•Stressful conditions both resulted from evaporative demand and soil drought.•Diurnal stomatal regulation occurred earlier in trees under soil water deficit.•Thermal phenotyping contributed to the assessment of varietal adaptation capacities.