"Monsoon rains are critical for the southwest US and northwest Mexico, yet the fate of the North American monsoon is quite uncertain," said Salvatore Pascale of Princeton University, US. "The future of the monsoon will have direct impacts on agriculture, on livelihoods."

General circulation models had suggested that the rains were decreasing in July but increasing in September and October. The new approach, with higher-resolution data and corrections for sea surface temperature bias, indicates that precipitation could reduce strongly along the northern edge of the monsoon as warming progresses.

Since it can take many years to plan and build water infrastructure, the findings have significant implications for regional policymakers, according to Pascale’s colleague Sarah Kapnick, who is now at NOAA's Geophysical Fluid Dynamics Laboratory.

"The North American monsoon is also related to extreme precipitation events that can cause flash floods and loss of life," Kapnick said. "Knowing when the monsoon will start and predicting when major events will happen can be used for early warnings and planning to avoid loss of life and property damage. This paper represents the first major step towards building better systems for predicting the monsoon rains."

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