Forecasting drought in the Colorado River, one of the most important rivers in the arid western US, could come down to ocean temperatures thousands of kilometers away.
The Colorado River runs for around 2300 kilometres, providing water to vast farmlands and 30 million people in seven US states and Mexico. A team of researchers found that distant sea surface temperatures today could help predict the river’s water supply up to two years into the future.
“If we can predict the shortage of Colorado River water supply one year before, the water resource managers can develop a mitigation plan against the upcoming water shortage,” says Yoshimitsu Chikamoto at Utah State University.
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Most models that forecast water in the Colorado River rely on recent atmospheric and weather data, but when preparing for a drought requires more time, policy-makers and scientists need longer-term forecasting models.
Chikamoto and his colleagues’ model uses data on global sea surface temperatures between 1960 and 2015, and relies on “ocean memory”, or the ocean’s ability to retain heat and release it slowly. While atmospheric heat is released and transferred relatively quickly, the ocean can store large amounts of heat and release it over the span of years.
According to the researchers’ results, Colorado River water shortages were preceded by cooling in the tropical Pacific Ocean one to two years prior, warming in the north Pacific Ocean two to three years prior and warming in the southern tropical Atlantic Ocean three to four years prior. They found that more distant oceans affected the river more strongly.
The researchers say this could be due in part to the Pacific North American pattern, an annual climate fluctuation that affects the East Asian jet stream and temperatures over western North America.
The approach doesn’t explain all the variability in water supply, but rather seeks to predict general water availability on an annual scale, says Chikamoto.
“Scientifically, the results are intriguing and seem well founded,” says Connie Woodhouse at the University of Arizona, who researches water in the western US. She says the study has the potential to be very useful for water managers, but it doesn’t fully explain how faraway oceans like the southern tropical Atlantic Ocean can affect the river.
Considering the data constraints before 1960, researchers may need to wait and test the prediction against the coming years, says Woodhouse.
Communications Earth and Environment
