Featured Research

from universities, journals, and other organizations

Study predicts lag in summer rains over parts of US and Mexico

Date:
March 11, 2013
Source:
The Earth Institute at Columbia University
Summary:
A delay in the summer monsoon rains that fall over the southwestern United States and northwestern Mexico is expected in the coming decades according to a new study. The North American monsoon delivers as much as 70 percent of the region's annual rainfall, watering crops and rangelands for an estimated 20 million people.

A delayed monsoon could affect vegetation across the Sonoran desert, including saguaro cactuses.
Credit: Jeremy Weiss

A delay in the summer monsoon rains that fall over the southwestern United States and northwestern Mexico is expected in the coming decades according to a new study in the Journal of Geophysical Research. The North American monsoon delivers as much as 70 percent of the region's annual rainfall, watering crops and rangelands for an estimated 20 million people.

"We hope this information can be used with other studies to build realistic expectations for water resource availability in the future," said study lead author, Benjamin Cook, a climate scientist with joint appointments at Columbia University's Lamont-Doherty Earth Observatory and the NASA Goddard Institute for Space Studies.

Much of the arid U.S. Southwest is expected to get even drier as winter precipitation declines under climate change, but the present modeling study predicts that summer rain levels will stay constant over southern Arizona and New Mexico, and northwestern Mexico. What will shift is the arrival of the heaviest rains, from July and August or so, to September and October, the study says. "There still will be a healthy monsoon which is good news for agriculture in the southern U.S. and northwestern Mexico-the timing is the problem here," said study co-author Richard Seager, a climate scientist at Lamont-Doherty.

A delayed monsoon could potentially lower crop yields as rains come later in the growing season, when the days are getting shorter. By prolonging hot and dry conditions during spring, a late monsoon could also trigger more wildfires and force cities to stretch diminished water supplies. The study makes use of the latest climate change models (those used by the Intergovernmental Panel on Climate Change in its Fifth Assessment Report due out next fall), to estimate monthly changes in precipitation by the end of the century, 2080-2099. The researchers hypothesize that future warming will make it more difficult to form clouds and rainfall early in the monsoon when soils are dry, followed reduced winter rain and snowfall, thus delaying the onset of the monsoon rains until enough moisture can be moved in from the oceans.

There is some evidence that the monsoon may already be arriving later. A 2007 study in the Journal of Climate led by researcher Katrina Grantz, then at the University of Colorado found a decline in July rainfall since the late 1940s, and a corresponding increase in August to September rainfall. Other scientists are cautious about drawing conclusions from a relatively short instrumental record, given the monsoon's natural year-to-year variability. The second-latest monsoon onset was recorded in 2005, but for three years after, the monsoon came earlier than average or on schedule, said Chris Castro, a monsoon researcher at the University of Arizona who was not involved in the study.

The Sonoran Desert and Sky Islands ecoregion lies at the northern edge of the North American monsoon, where vegetation ranges from saguaro-studded subtropical desert in the lowlands to high-altitude boreal forests. It is unclear how plants finely attuned to the monsoon's arrival will cope with the longer wait. "Will their growth slowdown or will some species grow dormant?" said Jeremy Weiss, a geosciences researcher at the University of Arizona who was not involved in the study.

A delay is bound to have economic impact, whether in northwestern Mexico or Arizona where agriculture and rangelands respectively are mostly rain-fed. The late monsoon in 2005 hindered summer grass development to the point that U.S. ranchers had to buy supplemental feed for their cattle, Andrea Ray, a researcher at the National Oceanic and Atmospheric Administration, noted in a 2007 study in the Journal of Climate.

Though total monsoon rainfall is projected to stay the same, warmer summer temperatures under climate change will cause more evaporation, leaving less water for crops, reservoirs and ecosystems. "It is important to look at the big picture before getting too sanguine about monsoon rainfall staying steady," said Jonathan Overpeck, a climate scientist at the University of Arizona who was not involved in the study. "Farmers who rely on summer rain will have a trickier time as the rainfall timing and amounts changes-they like predictability. Ultimately, the jury is still out, but this is a fine study that gives us more information to plan with."


Story Source:

The above story is based on materials provided by The Earth Institute at Columbia University. Note: Materials may be edited for content and length.


Journal Reference:

  1. B. I. Cook, R. Seager. The response of the North American Monsoon to increased greenhouse gas forcing. Journal of Geophysical Research: Atmospheres, 27 FEB 2013 DOI: 10.1002/jgrd.50111

Cite This Page:

The Earth Institute at Columbia University. "Study predicts lag in summer rains over parts of US and Mexico." ScienceDaily. ScienceDaily, 11 March 2013. <www.sciencedaily.com/releases/2013/03/130311173909.htm>.
The Earth Institute at Columbia University. (2013, March 11). Study predicts lag in summer rains over parts of US and Mexico. ScienceDaily. Retrieved August 27, 2014 from www.sciencedaily.com/releases/2013/03/130311173909.htm
The Earth Institute at Columbia University. "Study predicts lag in summer rains over parts of US and Mexico." ScienceDaily. www.sciencedaily.com/releases/2013/03/130311173909.htm (accessed August 27, 2014).

Share This




More Earth & Climate News

Wednesday, August 27, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Calif. Quake Underscores Need for Early Warning

Calif. Quake Underscores Need for Early Warning

AP (Aug. 26, 2014) Researchers at UC Berkeley are testing a prototype of an earthquake early warning system that California is pursuing years after places like Mexico and Japan already have them up and running. (August 26) Video provided by AP
Powered by NewsLook.com
Hurricane Marie Brings Big Waves to California Coast

Hurricane Marie Brings Big Waves to California Coast

Reuters - US Online Video (Aug. 26, 2014) Huge waves generated by Hurricane Marie hit the Southern California coast. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Brazil Tries Genetically Modified Mosquitoes to Fight Dengue

Brazil Tries Genetically Modified Mosquitoes to Fight Dengue

AFP (Aug. 25, 2014) A factory in the industrial state of Sao Paulo produces genetically modified mosquitoes to fight dengue, a deadly tropical disease more prevalent in Brazil than anywhere else in the world. Duration: 00:57 Video provided by AFP
Powered by NewsLook.com
Raw: Prime Minister at Japan Landslide Site

Raw: Prime Minister at Japan Landslide Site

AP (Aug. 25, 2014) Japanese Prime Minister Shinzo Abe visited Hiroshima on Monday as rescuers expanded their search for dozens still missing from landslides around the western Japanese city that killed at least 50 people. (Aug. 25) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

    Environment News

    Technology News



    Save/Print:
    Share:

    Free Subscriptions


    Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

    Get Social & Mobile


    Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

    Have Feedback?


    Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
    Mobile: iPhone Android Web
    Follow: Facebook Twitter Google+
    Subscribe: RSS Feeds Email Newsletters
    Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins