Climate change may increase California’s rain

In a warmer world California’s rain may be more ample than today. But so far most climate scientists foresee more drought.

By Tim Radford

LONDON, 9 July, 2017 – If humans go on burning fossil fuels, then California might, after all, remain the Golden State. It will get warmer. But, against all predictions, it might also get wetter.

A new study suggests that by the century’s end, Californians could see 12% more rain than they experienced in the last 20 years of the 20^th century.

This is not the standard forecast. Almost all other climate models have warned that California – still recovering from a calamitous and sustained drought – could, like the whole of the US Southwest, become both hotter and drier and far more at risk of wildfire.

But that is not how two researchers see it. They report in the journal Nature Communications that although, under the notorious “business-as-usual” scenario, in which people go on filling cars with petrol and generating electricity by burning coal, the most southern tip of the state would indeed continue to parch, rain in northern California could increase by 14.1% and central California by 15.2%.

“The overall thought was California would become drier with continued climate change. We found the opposite, which is quite surprising”

The latest predictions are based – like all other previous analyses – on computer simulations of future climate, and, like all simulations, they depend on the data available to the modellers.

But overall, forecasts for California have repeatedly suggested that the state could be in for a run of very dry seasons, especially as falling winter precipitation would mean that the state could hardly rely on melting snow to deliver the irrigation for the orange groves, vineyards and market gardens.

But the latest researchers found that rain and snow in December, January and February – which has usually  been when the heavens opened for California – would actually increase: more than 39% in central California, 31.6% in the north, and 10.6% in the south, in comparison with averages from the years 1979 to 1999.

“Most previous research emphasised uncertainty with regards to future precipitation levels in California, but the overall thought was California would become drier with continued climate change,” said Robert Allen, of the University of California Riverside, one of the authors. “We found the opposite, which is quite surprising.”

Surprises

This is not the first contrary finding recently produced by climate modellers. Although, overall, climate scientists expect the already arid zones to become more arid, and the well-watered regions to get even more rain, climate change could deliver surprises.

One research team has just predicted the arrival of seasonal monsoons for the Sahel region of northern Africa, historically prone to drought. 

The Sahel forecasters and the Californian modellers linked their higher rainfall to shifts in ocean temperature. As the tropical eastern Pacific Ocean warms, there could be a shift in the jet stream to the southeast, which could bring more rain-producing cyclones over California.

“Essentially, this mechanism is similar to what we in California expect during an El Niño year,” Dr Allen said. “Ultimately, what I am arguing is El Niño-like years are going to become more the norm in California.” – Climate News Network