Fewer rainy days leading to earlier spring in northern climes
New model shows leaves arriving 1-2 days earlier each decade
Date:
February 17, 2022
Source:
Ohio State University
Summary:
A drop in the total number of rainy days each year is contributing
to an earlier arrival of spring for plants in northern climates,
a new study finds.
FULL STORY ==========================================================================
A drop in the total number of rainy days each year is contributing to
an earlier arrival of spring for plants in northern climates, a new
study finds.
========================================================================== Scientists have known that warmer temperatures due to climate change have
led to the first leaves coming out at earlier dates in recent decades.
But this study shows that fewer rainy days plays the second largest
role in this early leaf-out, said Desheng Liu, co-author of the study
and professor of geography at The Ohio State University.
"Scientists have looked mainly at how temperature affects when leaves
first appear and, if they considered precipitation at all, it was just
the total amount," Liu said.
"But it isn't the total amount of precipitation that matters the most --
it is how often it rains." In the new study, published recently in the
journal Nature Climate Change, the researchers calculated that the decline
in rainfall frequency will lead to spring arriving an additional one to
two days earlier each decade through 2100 compared to what scientists previously thought.
==========================================================================
"We should expect an even earlier spring in the future compared to what
current models tell us," said study co-author Jian Wang, a doctoral
student in geography at Ohio State.
The researchers analyzed data sets from the United States, Europe and
China (all north of 30 degrees latitude, which includes most of the
United States).
The data included the dates each year when observers noted the first
evidence of leaves. They also used satellite images from 1982 to 2018,
which recorded when vegetation started to green.
They compared that with data on how many rainy days there were each
month at the sites studied.
Results showed that as rainy days declined over the years, spring
arrived earlier for most of the areas in the Northern Hemisphere. The
one exception was grasslands mostly located in semi-arid regions, where
fewer rainy days delayed spring slightly.
Why do fewer rainy days lead to earlier arrival of spring? There are
two main reasons, according to the study.
==========================================================================
One is that rainy days are also 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, which stimulates leaf growth.
Fewer days with clouds also means daytime temperatures will be higher with
more sunlight heating the ground and atmosphere. Nighttime temperatures
will cool more rapidly without clouds to trap the heat.
"This contrasting effect earlier in the year makes the plants think it
is spring and start leaf onset earlier and earlier," Wang said.
The researchers used their findings to create a model estimating how
much sooner spring would arrive now through 2100. Current models already suggest that spring for plants will arrive about five to 10 days earlier
for most of these northern climates by the end of the century, Liu said.
But by taking the decline in rainy days into account, the researchers'
new model suggests spring will arrive another day to two earlier than
expected each decade.
"We need to plan for a future where spring arrives earlier than we
expected.
Our model gives us information to prepare," Liu said.
The study was funded by the National Science Foundation.
Other co-authors were Philippe Ciais of Laboratoire des Sciences du Climat
et de l'Environnement in France, and Josep Pen~uelas of the Centre for
Research on Ecology and Forestry Applications in Spain.
========================================================================== Story Source: Materials provided by Ohio_State_University. Original
written by Jeff Grabmeier. Note: Content may be edited for style and
length.
========================================================================== Journal Reference:
1. Jian Wang, Desheng Liu, Philippe Ciais, Josep Pen~uelas. Decreasing
rainfall frequency contributes to earlier leaf onset in
northern ecosystems. Nature Climate Change, 2022; DOI:
10.1038/s41558-022-01285-w ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/02/220217155232.htm
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