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Ocean patterns help scientists forecast drought, water flow in the Colorado river

Oct. 9 (UPI) — By analyzing what researchers call “long-term ocean memory,” scientists have been able to identify connections between flow rates in the Colorado River and sea surface temperatures in parts of the Pacific and Atlantic oceans.

The breakthrough analysis — described Friday in the journal Communications Earth and Environment — allowed scientists to develop a forecasting model capable of predicting the Colorado River water supply on multi-year timescales.

The Colorado River, the most important water resource in the West, is essential to energy production, food and drinking water security, forestry and tourism in California, Arizona, New Mexico, Colorado and Utah.

Access to more accurate long-term forecasting models could aid water resource management decisions.

“Using our tool we can develop an operational forecast of the Colorado River’s water supply,” lead study author Yoshimitsu Chikamoto, assistant professor of earth systems modeling at Utah State University, said in a news release.

Current forecasting models for predicting droughts and Colorado River flow are over-reliant on short-term weather patterns. The models are easily skewed by short-term weather phenomena — a big storm or an especially dry couple of months, for example.

“This new approach is robust and means that water managers, for the first time, have a tool to better estimate water supply in the Colorado River for the future,” said study co-author Robert Gillies, director of the Utah Climate Center and professor at Utah State University. “The model can be run iteratively so every year a new forecast for the next three years can be created.”

A two to three year lead on water flow and drought forecasts can allow farmers to make important decisions on crop rotations.

To build their model, scientists used their ocean memory analysis to draw connections between sea surface temperature and subsequent atmospheric effects. Next, researchers accounted for the influence of land systems on precipitation patterns — including soils, groundwater, vegetation and snowpack.

Because the upper basin of the Colorado River isn’t located in the Southwest, forecasters have previously failed to account for the influence of climate pattern El Niño and La Niña on Colorado River flow.

The new predictive model accounts for a complex array of natural phenomena: currents, water mixing and heat exchange in the ocean; clouds and aerosols in the atmosphere; and surface characteristics across the West’s semi-arid landscape.

In addition to aiding the decision making of farmers and water resource managers, the new model could used to inform preparations for future wild fire seasons.

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Climate patterns linked in Amazon, North and South America, study shows

amazon rainforest
Credit: CC0 Public Domain

University of Arkansas researchers have established a link between climate patterns in the Amazon and large parts of North and South America using their newly developed tree-ring chronology from the Amazon River basin.

The discovery helps researchers better understand large-scale climate extremes and the impact of the El Niño phenomenon.

Tree growth is a well-established climate proxy. By comparing growth rings in Cedrela odorata trees found in the Rio Paru watershed of the eastern Amazon River with hundreds of similar chronologies in North and South America, scientists have shown an inverse relationship in tree growth, and therefore precipitation patterns, between the areas. Drought in the Amazon is correlated with wetness in the southwestern United States, Mexico and Patagonia, and vice versa.

The process is driven by the El Niño phenomenon, which influences surface-level winds along the equator, researchers said. El Niño is the name given to a large-scale irregularly occurring climate pattern associated with unusually warm water in the Pacific Ocean.

“The new Cedrela chronologies from the Amazon, when compared with the hundreds of tree-ring chronologies in temperate North and South America, document this Pan American resonance of climate and ecosystem extremes in the centuries before widespread deforestation or human-caused climate change,” said Dave Stahle, Distinguished Professor of geosciences and first author of a study documenting the findings in the journal Environmental Research Letters.

Credit: University of Arkansas

The connection was not documented until researchers at the University of Arkansas Tree Ring Laboratory, along with colleagues from Brazil and Argentina, developed rainfall reconstructions from growth rings in Cedrela trees. Most rainfall records in the Amazon only date back about 70 years, but Cedrelas live for 200 to 300 years, providing valuable rainfall proxies that pre-date human-influenced climate change. Their work in the Amazon is documented in a short video, and also on a dedicated web site.

In the past 40 years, drought and flood extremes have increased in the Amazon basin, the researchers noted, raising the question of whether human-induced climate change and deforestation are affecting Amazon climate. While that remains an open question, the longer Cedrela-based precipitation record indicates that periods of rainfall extremes occurred in the past and the current extremes might be partly due to natural climate rhythms.

The study will help researchers better understand an area of unequaled biodiversity. The Amazon is home to an estimated 16,000 species of trees and one-tenth of all known species found on the planet, Stahle noted. “The long climate history written in the growth rings of old Cedrela trees in Amazonia will surely be important to the sustainability of the biome.”

Study quantifies Saharan dust reaching Amazon

More information:
D W Stahle et al. Pan American interactions of Amazon precipitation, streamflow, and tree growth extremes, Environmental Research Letters (2020). DOI: 10.1088/1748-9326/ababc6
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University of Arkansas

Climate patterns linked in Amazon, North and South America, study shows (2020, October 9)
retrieved 9 October 2020

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