NOAA Study on California Drought Focuses on Rain, Report Author Acknowledges More Research Needed on Temperatures

WASHINGTON (December 8, 2014)--The National Oceanic and Atmospheric Administration (NOAA) today released a new study that finds that reduced rainfall levels caused by “natural variability” are largely to blame for the ongoing California drought. However, according to the Union of Concerned Scientists (UCS), precipitation patterns do not tell the whole story of what is causing California’s record dry conditions.

Extreme high temperatures, caused by the burning of fossil fuels, are playing an important role in the California drought by reducing the moisture content of soils and streams as well as the depletion of reservoirs.  

“Warmer temperatures are widening the gap between water supply and demand by contributing to earlier spring snowmelt meaning less water is available when demands are the highest in mid-to-late summer,” said UCS climate scientist Juliet Christian-Smith. “As global warming continues, decreasing snowpack and earlier snowmelt — coupled with increasing demand for water — will likely exacerbate water shortages.”

The NOAA-sponsored study concluded that natural oceanic and atmospheric patterns are the primary drivers behind California's three-year drought. A persistent high pressure ridge over the North Pacific Ocean for the past three winters has blocked storms from sweeping into California with ocean surface temperature patterns making such a ridge much more likely, according to the study.

“The NOAA study points to natural variability, but it is important to note that these random variations are happening in the context of higher overall temperatures caused by climate change and warmer temperatures spell trouble for water in California,” said UCS senior climate scientist Brenda Ekwurzel.

UCS Fellow Robert Mera has analyzed California’s average summer temperatures, comparing the 2000s to the 1960s.

“We know that climate change is making California hotter. For example, the maximum temperature in last year’s heat wave in California was three times more likely to occur this century so far than in the 1960s,” Mera said. “The warmer temperatures are causing water in reservoirs and irrigation canals to evaporate much more quickly than in the past.  In addition, crops are taking in water from the soil and releasing that water into the atmosphere to a much greater extent. This sets up conditions for extreme heat waves and increases drought risk in California.”

To put Mera’s findings into context, the IPCC’s latest assessment found that between 1880 and 2012, the global average temperature increased 1.5 degrees Fahrenheit.  Mera found, in California, the average monthly temperature last winter (December through February 2013-2014) would have been 1.8 degrees Fahrenheit cooler without the extra carbon dioxide in the atmosphere.

Mera will release his latest findings on California drought at the American Geophysical Union meeting in San Francisco on December 18.  The NOAA report author acknowledged on today’s press call that more temperature research is needed to fully understand the drought.  UCS’s forthcoming analysis will help fill this void.