Stability of the Almond Blooming Date in a Changing Climate

Although global warming is increasing the medium air temperature over time, this negative temperature trend cannot be yet appreciated in some areas. Analysis of air temperatures in the Ebro Central Valley (Zaragoza, Spain) during the last 24 years shows drastic changes in temperature during winter and spring and high variability among years. Under these conditions, there is an excess of chill and most almond cultivars satisfy their chilling requirements very early, during the first two weeks of December, when endodormancy finishes. As a consequence, bloom dates are ruled mainly by the heat requirements. Early-blooming almond cultivars showed a higher variation in dates of full bloom because they are more dependent on warm temperatures during January and February, where heat accumulation is slower. Late-blooming cultivars showed more stable blooming dates because their greater heat requirements are quickly satisfied by the higher March temperatures. Cultivars with high cold and heat requirements are desirable for stable late blooming. This characteristic and its relationship with local climatic conditions is essential in choosing cultivars to be planted in a given region, especially to avoid frost risks.