The total number of rainy days each year is contributing to an early arrival of spring for plants in northern climates. Scientists know that warmer temperatures have led to the first leaves coming out at earlier dates in recent decades.
A new study found out that fewer rainy days plays the second largest role in this early leaf-out.
Scientists investigated how temperature affects when leaves first appear. The study has been published in the journal Nature Climate Change. They calculated the decline in rainfall frequency will lead to the arrival of spring to an additional one to two days earlier each decade.
Scientists are expecting an even earlier spring in the future compared to what current models tell.
Scientists analysed data sets from the United States, Europe and China. The data included the dates each year when Scientists noticed the first evidence of leaves. Scientists also used satellite images from 1982 to 2018. It was recorded when vegetation started to green.
Scientists compared that with data on how many rainy days there were each month at the sites.
Results showed that as rainy days declined over the years, spring arrived earlier for most of the areas in the Northern Hemisphere. But the only exception was grasslands located in semi-arid regions. There fewer rainy days delayed spring slightly.
Rainy days are cloudy days. Fewer rainy days in late winter and early spring means that trees and other plants are receiving more solar radiation earlier in the year. This stimulates leaf growth.
Fewer days with clouds mean daytime temperatures will be higher with more sunlight heating the ground and atmosphere. Night time temperatures will cool more rapidly as there will be no clouds to trap the heat.
Scientists used their findings to create a model estimating how much sooner spring would arrive now through 2100. Models suggested that spring for plants will arrive about five to 10 days earlier for most of these northern climates by the end of the century.
But scientists have taken the decline in rainy days into account. The new model suggested spring will arrive another day to two earlier than expected each decade.