Californication

There are approximately 196 countries in the world (political differences mean that not everyone recognises the same amount). California, just one state of 50 in the United States of America, has a population greater than all but the 34 most populated countries in the world - a population greater that 132 countries in the world.  Such a population requires a lot of water, particularly a resource hungry 'western' population, with huge urban areas like Los Angeles and San Francisco that have big water requirements. Unfortunately, that water simply hasn't been there - for the last four years, California has been gripped by drought. In April 2014, 100% of California was classed as being in drought, for the first time in at least 15 years:

It is notable that central southern USA were also in drought at the time. However, as the most recent picture shows, this area of the USA has recovered well.  However, for the Pacific Coast, there has been no recovery. In California, things have gone from bad to worse, with the majority of the state classed as being in exceptional or extreme drought:

Clearly, this is a difficult situation. The severity of the drought has necessitated implementation of the first mandatory water restrictions in the history of the state in April 2015, cities and towns being told to reduce consumption by 25%. Encouragingly, it was reported that Californian cities cut their water usage by 31.3% in July 2015, exceeding the mandatory water restrictions, rising steadily per month since the implementation in April 2015.

This is all very well and good - but why has California been in drought? Unsurprisingly, it is the simple matter that there has been a lack of rainfall. This has been caused by a persistent high pressure area over the Northeast Pacific Ocean, which has deflected winter storms and prevented them from depositing precipitation on California.

As a result of this lack of rainfall, California's reservoirs are nearly empty - in March 2015 it was estimated that there was one year of surface reservoir water left. This has lead to the use of an alternative source of water, particularly by agriculture: groundwater. Groundwater is a useful resource to have in dry times, but it takes a long time to be replenished once used. Nearly 75% of freshwater is now coming from groundwater in California, as there simply isn't enough surface water. This is a problem - if too much groundwater is used, and it runs out, it will take a very long time to replenish again. California needs to avoid using too much groundwater, but that is not easy when there is little rainfall - both surface water and groundwater stores are not being replenished.