Climate: Study looks at changing monsoon patterns

Natural climate variables so far outweigh global warming impacts

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The North American monsoon is an important climate factor in the Rocky Mountains.

By Summit Voice

SUMMIT COUNTY — The timing and amount of monsoon rains in the northern hemisphere have important economic and environmental ramifications, for example for farmers in Asia and the wildfire season in the southwestern U.S.

As a result, climate researchers have been trying to determine how the Earth’s steady warming will affect those seasonal rainfall patterns, and so far, the jury is still out. Some recent research has suggested that the timing of the North American monsoon might be delayed, while other studies have indicated that there could be an overall increase in monsoon precipitation.

In one of the latest studies, scientists with the International Pacific Research Center, University of Hawaii at Manoa, say that monsoon rainfall patterns appear to more influenced by natural long-term swings in ocean surface temperatures. The Interdecadal Pacific Oscillation or mega-El Niño-Southern Oscillation, which has lately been in a mega-La Niña or cool phase is one key factor, and shifts in the Atlantic Multidecadal Oscillation, also contributes to the intensification of monsoon rainfall. Continue reading

Climate: Study suggests that irrigation in California’s Central Valley pumps up western Monsoon rainfall

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This NASA satellite image shows California’s Central Valley filled with fog and gives a sense of the size of the valley.

Climate models illustrate a little-known part of the hydrological cycle in the Colorado River Basin

By Bob Berwyn

SUMMIT COUNTY — Research by scientists at the University of California, Irvine suggests a previously unexplored connection between irrigated agriculture in California and summer monsoon rains in the greater Colorado River Basin.

The new study by climate hydrologist Jay Famiglietti shows that huge amounts of the water used for irrigation in California’s Central Valley ends up back in the atmosphere, helping to fuel and intensify summer thunderstorm activity in the interior West.

The moisture, which reaches the atmosphere via evapotranspiration, may add up to as much as 100 billion gallons in additional runoff, about enough water for 3 million people for a year, Famiglietti said. Continue reading

Global warming to shift timing of North American monsoon

Greenhouse gas-induced heating inhibits early monsoon precipitation

Colorado weather lightning

The North American monsoon usually starts in mid-July in Colorado.

graph showing monsoon changes

The North American monsoon will dry up in June and July and become wetter in September and October. Graphic courtesy NASA and the Coumbia University Earth Observatory.

By Bob Berwyn

SUMMIT COUNTY —Global warming result in a significant shift of the North American monsoon, with less rain during the early part of the season, in June and July, and more rain later in the summer and early autumn. The trend toward a later start to summer precipitation has already started, but will become more pronounced — and easier to distinguish from the background “noise” of natural variability — during the next few decades, according to researchers with NASA and Columbia University’s Lamont-Doherty Earth Observatory.

“We expect that increased greenhouse gases will make the atmosphere more stable and more difficult for precipitation to occur … When the warming is strong enough, it effectively delays the start of the monsoon,” said NASA researcher Benjamin Cook. “One way to overcome that is when the air near the surface is really moist. That’s what happens at the end of the monsoon season. At that point, it leads to an increase in rainfall,” Cook said, explaining that the study points to big change in the total amount of monsoon precipitation, but that the change in timing is still likely to have significant ecological societal impacts. Continue reading

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