• Fewer rainy days leading to earlier spri

    From ScienceDaily@1:317/3 to All on Thu Feb 17 21:30:44 2022
    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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