Water is running low in California. Reservoirs are receding, leaving lake beds cracking in the warm winter sun. Snowpack in the Sierra Nevada mountains, traditionally a third of the state鈥檚 water supply, has dropped to 12 per cent of its normal level. 2013 was the driest year in more than a century, and the resulting water shortages are providing a glimpse of California鈥檚 future in a warming world.
Alexander Gershunov of the Scripps Institution of Oceanography in San Diego points out that uneven warming of the planet 鈥� which is heating faster at the poles than at the equator 鈥� is changing the north-south temperature gradient, and weather patterns are changing accordingly. That has pushed some of the winter storms that usually soak the state further north. 鈥淢ost models agree that the frequency of winter storms will decrease, although the intensity of the largest storms will also increase, so annual average precipitation doesn鈥檛 change too much,鈥� Gershunov says.
A shorter, more intense storm season means that the chance of either a very dry or very wet winter goes up. Either way, that is a problem, because as temperatures warm, more precipitation will fall as rain than snow. Unlike snow, rain will come gushing down out of the mountains in one fell swoop 鈥� making it difficult for water managers to capture and store for later use.
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That means more precipitation flows into the Pacific Ocean, and less is available for farmers in California鈥檚 fertile Central Valley, which produces 8 per cent of the US鈥檚 food by value.
New sources
of the Pacific Institute in Oakland, California, says the state鈥檚 future water supply will need to be bolstered by new sources, and better conservation. Catching and treating storm water and pushing it into underground aquifers; cleaning and reusing domestic and industrial waste water; even sucking fresh water from a salty ocean will all be important sources of supply in future. All over the state, work to secure these new sources is already beginning.
In February a committee at the California Department of Public Health will meet to examine the possibility of permitting treated wastewater to be used as drinking water. New treatment plants are already running across California, although they are currently legally prevented from supplying the water for human use.
Behzad Ahmadi, who manages the groundwater programme for the Santa Clara Valley Water District, says that waste water treatment will play a key role in ensuring the state鈥檚 future water supply. Santa Clara county鈥檚 own treatment facility, the , will produce 36 million litres of water a day when it comes online later this year.
Filthy Walk of Fame
Water engineer is working on a way to gather storm water in the midst of the city鈥檚 concrete jungle, water that would otherwise run off into the Pacific Ocean 鈥� carrying with it pollutants that close LA鈥檚 beaches for days after big storms. In July, engineers will start punching holes in the city鈥檚 concrete skin to make 15-metre-deep wells that will be filter-lined to ensure that contaminants from the street don鈥檛 get washed into the groundwater below.
鈥淪ome people call it urban acupuncture,鈥� Hanna says. 鈥淲e鈥檝e figured out a way for a 30-acre neighbourhood to give 43 acre feet a year recharged on average.鈥� In metric terms, that鈥檚 over 50,000 cubic metres of water every year, collected by a neighbourhood covering 12 hectares.
Desalination is happening too, using electricity to pull salt out of seawater. in San Diego County is expected to be the largest desalination plant in the Western hemisphere when it starts pumping water in 2016. The project鈥檚 website advertises the future water supply as 鈥渄rought-proof鈥� 鈥� precisely what California is going to need.
