How does weather affect autumn colour?
The amount and brilliance of the colours that develop in any particular autumn season are related to weather conditions that occur before and during the time the chlorophyll in the leaves is dwindling. Temperature and moisture are the main influences. A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular colour displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions-lots of sugar and lots of light-spur production of the brilliant anthocyanin pigments, which tint reds, purples, and crimson. Because carotenoids are always present in leaves, the yellow and gold colours remain fairly constant from year to year. The amount of moisture in the soil also affects autumn colours. Like the weather, soil moisture varies greatly from year to year. The countless combinations of these two highly variab
