Weatherwatch: autumn colours linger as growing seasons get longer

Autumn colours have been a treat this year. Looking out of my window I am mesmerised by the fiery leaves and deep red berries on a nearby rowan tree and the golden hues of a silver birch. But it is nearly November. How come autumn is lingering so late? New research shows that the trend towards longer growing seasons and rain falling less frequently but in more extreme bursts has shifted autumn back by about two weeks over the past 40 years. Yangjing Nie, from the University of Beijing, China, and colleagues used satellite images and weather data to assess how changes in rainfall had impacted the timing of mid to high latitude northern hemisphere trees putting on their autumn display between 1982 and 2020. They found that the increased overall levels of rainfall during the growing season and the decreased frequency of rainstorms both contributed to autumn being delayed. Writing in Geophysical Research Letters they describe how the extra rainfall helped to keep soils moist for longer and promoted soil mineralisation, providing plants with more moisture and nitrogen and allowing them to hold on for longer before dropping their leaves. The findings will help us better understand the impact of climate change on growing season length and better estimate how much carbon plants are able to absorb.