California suffering extreme drought following driest year on record
Last Friday, the California Governor Jerry Brown declared a drought emergency across the state, following its driest year on record.
As a result, 62.7 per cent of the state is now in extreme drought and 89.9 percent in severe drought, according to the US Drought Monitor.
During 2013, California had just 32.8 per cent of the rainfall that it would normally expect to see, leaving fresh water reservoirs with a fraction of their normal reserves.
Also the normally full American River has slowed so dramatically that brush and dry riverbed are showing through in areas normally teeming with fish.
Such a dry year has also left the state prone to wildfires, as high temperatures and lightning strikes result in wildfires that are then fanned by dry, gusty Santa Ana winds that the state is renowned for.
Why has it been so dry?
California relies on rain and mountain snow moving in off the Pacific Ocean, driven by the jet stream – the fast-moving ribbon of air five miles up in the sky that forms and steers areas of low pressure.
However, during the last year – especially during autumn and early winter – the jet stream has been persistently stuck much further north than usual, resulting in a blocking area of high pressure forming over the state.
This has kept the weather largely dry, as the usual train of low pressure systems travelled further northwards into western Canada, taking the rain and snow there.
Lack of snowfall
Late-autumn and winter are when California would expect to receive the greatest portion of its annual rainfall.
Snowfall across the mountains also plays a huge role in California’s water resources because it builds up in the winter, then provides a steady supply of water for the reservoirs as it melts during the spring.
The persistent dry weather has meant that there has been little snowfall across the mountainous parts of the state so far this winter.
The NOAA satellite image below comparing 13 January 2013 to the same day this year shows a huge difference in snow cover.
Snow cover for the state as of the 16 January 2014 was just 17 per cent of the average. This means that unless there’s a rapid change to wetter conditions, there will be little snowmelt to top up the reservoirs in spring.
Reservoirs worryingly low
Major reservoirs across California are already significantly below normal, with the largest reservoir in the state, Lake Shasta, 36 per cent full, compared to the average of 55 per cent.
Further south, Folsom Lake is just 17 per cent full, when it would normally be 34 per cent full at this time of year.
Any sign of rain?
The latest forecast for the next 7-10 days doesn’t offer much hope for much needed rainfall in the parched state.
With the jet stream still likely to be stuck further north, the blocking area of high pressure will persist, offering very little, if any rainfall at all.
Appeals are already being made for Californians to conserve water by aiming to reduce consumption by 20 per cent, with warnings that mandatory restrictions may lie ahead.
Whilst the immediate future looks bleak, as we know from the drought concerns that we had in the UK early in 2012, the weather pattern can suddenly flip, so that when it does eventually rain, it can pour.
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