Our directory of things of interest

University Directory

California lacking a whole year of rain

Dried out irrigation channels in California, USA Dried out irrigation channels in California, USA Tom Grundy
12 Aug
2015
The full scale of the state’s ongoing drought crisis is being described as ‘completely without precedent’

The long-running drought currently affecting California shows no signs of easing up. Declaring a state of emergency, as Governor Jerry Brown did in January 2014, would, to most people, have been the most extreme this situation could have reached. However, that was later followed by talk of a ‘megadrought’, predicting conditions ‘far worse than anything those regions have seen in the past several thousand years at least’.

Meanwhile, water resources dwindle, agriculture continues to suffer, and a new NASA study has concluded that the state has now missed a total of a whole year’s worth of rainfall within just the past three years.

The findings show that Californians can expect, within normal conditions, to experience as much as 30 per cent higher or lower annual rainfall, compared to the historical average, which is about 20 inches (53 cm) per year. These alternating conditions should balance out the state’s overall rainfall.

Between 2012 and 2014, however, California accumulated a deficit of almost 13 inches (33 cm). When added to the record-breaking drought in 2014, which saw another seven inches missing from the rainfall pattern, it makes the total deficit from 2012 to 2015 a full 20 inches, which Californians would normally expect to have falling on them within a single year.

15-162-masterCalifornia’s precipitation deficit from 2012 to 2014, as a per cent change from the 17-year average (Image: NASA/Goddard Scientific Visualization Studio)

The record dry conditions are a result of interference with ‘atmospheric rivers’, powerful flows of water vapour, which normally carry moisture in the atmosphere from the Pacific Ocean over the North American landmass. ‘When they say that an atmospheric river makes landfall, it’s almost like a hurricane, without the winds,’ says Andrey Savtchenko, lead author of the NASA study. ‘They cause extreme precipitation.’

Since 2011, however, high pressure systems over the Pacific have prevented these rivers from forming, and without the rivers, a huge source of Californian water is lost. That in itself isn’t an unusual situation, however the length of the drought, coupled with significant population growth in California, makes the impact more severe.

One possible outlet for the drought may come in the form of an El Niño event, one of which is currently building over the Pacific. ‘If this El Niño holds through winter, California’s chances to recoup some of the precipitation increase,’ says Savtchenko. ‘Most likely the effects would be felt in late 2015 to 2016.’ However, the evidence analysed in the study suggests that El Niño events have driven ‘at best only six per cent of precipitation variability in California in the past three decades’.

If that wasn’t a clear enough explanation of the dire situation facing California, a separate study from Indiana University observes that the 2012 to 2014 drought can be classified as ‘nearly a 10,000-year event’, while the ongoing lack of rainfall over the past year means that the overall 2012 to 2015 drought ‘has an almost incalculable return period and is completely without precedent’.

Related items

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...

Wildlife

Since 2006, tiger habitats have shrunk by more than 40…

Climate

Advances in space-based lightning mapping have allowed scientists to measure…

Energy

The amount of energy used by the wealthy minority dwarfs…

Wildlife

Left denuded and depleted of wildlife following a decades-long civil…

Climate

Katie Burton explores the practicalities and ethics of geoengineering, the…

Energy

Though the pandemic has gripped the world's attention, lying just…

Climate

The IPCC embraced the notion of carbon offset schemes in…

Geophoto

The shortlist for the 2020 Wellcome Photography Prize has been…

Climate

Millions have been displaced due to severe floods in central…

Wildlife

A portable DNA assay could revolutionise the way border officials…

Climate

A handy gathering of facts about carbon emissions with graphs…

Oceans

Researchers have revealed just how many polluting microfibres are released…

Wildlife

Increasing reports of seized jaguar fangs and skin suggest that…

Geophoto

Forced isolation has given many of us the chance to…

Oceans

A fifth of the ocean floor has now been mapped,…

Wildlife

Four ex-circus lions discovered in France are due to be…

Oceans

A roundup of some of the top discussions from the…

Energy

The agave plant, used to make Tequila, has proven itself…