Weatherdem's Weblog

Bridging climate science, citizens, and policy

California’s Ongoing Drought & Related Climate News

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California’s drought is severe and lengthy.  2013 was a record dry year for areas in the state with extensive data records: Los Angeles’s 3.60″ (14.93″ normal) and San Francisco’s 5.59″ (23.65″ normal) among others.  Recent research characterized California as drier than at any time in the past 500 years (an important point that I’ll return to below).  California experienced three consecutive very dry years (2011-2013), and 2014 provided little difference so far.  This dryness and the ensuing drought conditions are part of a longer term decadal-plus drought affecting the southwest US since 2000.

Additional metrics include:

Seventeen rural communities in California are in danger of running out of water within 60 to 120 days, according to a list compiled by state officials. As the drought goes on, more communities are likely to be added to the list.

With only about seven inches of rain in California in 2013 — far below the average of 22 inches — wells are running dry and many reservoirs are about 30 percent full (including Folsom Lake, shown above).

The Sierra snowpack, where California gets about a third of its water, was 88 percent below average as of Jan. 30.

Soon, people will face a lack of fresh water to their homes.  With reservoirs at record low levels, farmers will not be able to plant the crops they want which will reduce our food availability and increase food prices later this year.  This means the impacts will be local and national.  Moving forward, legal fights over very limited water will likely occur.  Folks are about to find out they water they’ve taken for granted is legally obligated to other users.  No one knows what the results will be, but many people have feared this very set of circumstances for a long time.

It would take between 8″ and 16″ of liquid water across most of California to break the drought.  That is unlikely to happen any time soon.  California’s drought is directly related to the snowy winter the eastern half of the nation experienced due to the persistent high-amplitude anomalous jet stream.  High pressure pushed the jet stream to the north over the western US while low pressure allowed the jet stream to dive south over the eastern US.  Usually such a pattern breaks down after a short time.  This winter’s jet stream has been essentially stuck for months now.

In related news, Arctic albedo decreased more than previously thought due to melting Arctic sea ice.  This phenomenon warms the Arctic, including the Arctic Ocean, which affects other parts of the globe, including the US.

And now back to the interesting point I wrote about above: CA is drier than at any point in the past 500 years.  Not forever, 500 years.  That means CA has been this dry in the past (the relatively recent past, in geologic time scales).  Moreover, we should all recall that CO2 concentrations were much lower 500 years ago than they are today.  That means that CA’s dryness is to some extent caused by natural variability.  The scientific question then becomes: “How much?”  Climate attribution studies remain at the forefront of climate research, which is another way of saying we don’t know how much natural variability plays a role in today’s dryness.

A NY Times article captured this recently:

While a trend of increasing drought that may be linked to global warming has been documented in some regions, including parts of the Mediterranean and in the Southwestern United States, there is no scientific consensus yet that it is a worldwide phenomenon. Nor is there definitive evidence that it is causing California’s problems.

The article notes that there are significant similarities between this drought and a similar drought in 1976-77.  What we do know is that temperatures are higher during this drought than they were in 1976-77, which exacerbates the drought’s effects.  What precipitation fell in 2013 evaporated more quickly than before because of warmer temperatures.  So we can say that a similar drought is occurring in a warmer environment, which is something relatively new and noteworthy.

An important point is that this drought is occurring in a world with higher CO2 concentrations than in 1976 or in the 1500s.  But this drought is similar to previous droughts.  Today’s higher CO2 concentrations aren’t the dominant cause of this drought.  Droughts later this century will likely have a more noticeable human fingerprint, but this drought could have (and did) occur in contemporary history.  There is nothing about today’s state of the climate (or 1970’s or 1930’s state of the climate) that precludes this drought.  Quite the opposite is true: this drought belongs to the state of the climate today, not tomorrow.

It is true that the southwest has been in some level of drought condition for 15 years or so.  Those conditions also exist in today’s climate.  They might also exist in the end of the century’s climate, but they will exhibit characteristics that we can’t foresee with any accuracy today.  That said, there are people today in the southwest US that this drought impacts.  That is the reality regardless of the anthropogenic or natural influence on the climate system.  The demand on annual available water now exceeds the supply.  That reality will increasingly shape the southwest in the near future, not the distant future.  Increasingly restrictive water usage policies are more likely than not.


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