Stronger rains in warmer climate could lessen heat damage to crops, says
study
But overall yields could still decline sharply

Date:
August 10, 2020
Source:
Earth Institute at Columbia University
Summary:
Intensified rainstorms predicted for many parts of the United States
as a result of warming climate may have a modest silver lining:
they could more efficiently water some major crops, and this would
at least partially offset the far larger projected yield declines
caused by the rising heat itself.



FULL STORY ========================================================================== Intensified rainstorms predicted for many parts of the United States
as a result of warming climate may have a modest silver lining: they
could more efficiently water some major crops, and this would at least partially offset the far larger projected yield declines caused by the
rising heat itself. The conclusion, which goes against some accepted
wisdom, is contained in a new study published this week in the journal
Nature Climate Change.


========================================================================== Numerous studies have projected that rising growing-season temperatures
will drastically decrease yields of some major U.S.crops, absent adaptive measures.

The damage will come from both steadily heightened evaporation of soil
moisture due to higher background temperatures, and sudden desiccation
of crops during heat waves. Some studies say that corn, which currently
yields about 13 billion bushels a year and plays a major role in the
U.S. economy, could nosedive 10 to 30 percent by the mid- to late
century. Soy-the United States is the world's leading producer-could
decline as much as 15 percent.

Since warmer air can hold more moisture, it is also projected that
rainfall will in the future come more often in big bursts, rather
than gentle downpours- a phenomenon that is already being observed in
many areas. Many scientists have assumed that more extreme rains might
further batter crops, but the new study found that this will probably
not be the case. The reason: most of the projected heavier downpours
will fall within a range that benefits crops, rather than passing the
threshold at which they hurt them.

"People have been talking about how more extreme rain will damage crops,"
said lead author Corey Lesk, a PhD. student at Columbia University's Lamont-Doherty Earth Obsevatory. "The striking thing we found was, the
overall effect of heavier rains is not negative. It turns out to be good
for crops." That said, the effects will probably be modest, according
to the study. It estimates that corn yields could be driven back up 1
or 2 percent by the heavier rains, and soy by 1.3 to 2.5 percent. These increases are dwarfed by the potential losses due to heat, but even a few percent adds up when dealing with such huge quantities of crops. And,
the researchers say, "Our findings may help identify new opportunities
for climate-adaptive crop management and improved modeling." The team
reached their conclusions by studying hour-by-hour rainfall patterns
recorded by hundreds of weather stations in the agricultural regions
of the U.S. West, South and Northeast each year from 2002 to 2017. They
then compared the rainfall patterns to crop yields. They found that years
with rains of up to about 20 millimeters an hour-roughly the heaviest
downpour of the year on average-resulted in higher yields. It was only
when rains reached an extreme 50 millimeters an hour or more that crops suffered damage. (20 millimeters an hour is about three-quarters of an
inch; 50 is about 2 inches.) Moreover, years in which rain came mainly
as mere drizzle actually damaged yields.

The researchers outlined several possible reasons for the differences. For
one, drizzle may be too inefficient to do much good. In hot weather,
it can mostly evaporate back into the air before reaching subsurface
root zones where it is needed; in cooler weather, it might remain on
leaves long enough to encourage the growth of damaging fungi. "There
are only a fixed number of hours of rain you can get in a season," said
Lesk. "If too much of them are taken up by useless drizzle, it's wasted." Heavier storms on the other hand, are better-at least up to a point. These allow water to soak thoroughly into the soil, carrying in both moisture
and artificial fertilizer spread on the surface. It is only the most
extreme events that hurt crops, say the researchers: these can batter
plants directly, wash fertilizer off fields, and saturate soils so
thoroughly that roots cannot get enough oxygen.

To study the effects of future potential rainfall patterns, the
researchers used basic physical models to estimate how much heavier
rains might become under different levels of warming. They found that in
most cases, more rain would, as expected, come in bigger downpours-but
these heavier rains would fall within the fairly wide range where they
are beneficial. The most extreme, damaging rains would also increase-but
would still be rare enough that the greater number of beneficial rainfalls would outweigh their effects.

Because the study averaged out statistics over vast areas, and many other factors can affect crop yields, it would be hard to say exactly what the effects of future rainfall will be in any one area, said Lesk. "No single farmer would use a study like this to make decisions on what to plant or
how," he said. But, as the paper concludes, the results "suggest that
beyond extreme events, the crop yield response to more common rainfall intensities merits further attention." The study was coauthored by Ethan Coffel of Dartmouth College and Radley Horton of Lamont-Doherty. Funding
came from the U.S. National Science Foundation, U.S.

Department of Interior, and U.S. Geological Survey.


========================================================================== Story Source: Materials provided by
Earth_Institute_at_Columbia_University. Original written by Kevin
Krajick. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Corey Lesk, Ethan Coffel, Radley Horton. Net benefits to US soy
and maize
yields from intensifying hourly rainfall. Nature Climate Change,
2020; DOI: 10.1038/s41558-020-0830-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200810141004.htm

--- up 3 weeks, 5 days, 1 hour, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)