The Ridiculously Resilient Ridge

Welcome again to my blog,

as last week's post was talking about the anomalous cold weather in eastern US, I thought that talking about California's drought would make sense. As I said on my last post, US weather is more bipolar than ever!

California is the first US economy and half of the country's fruit is produced in it's central valley. This study by the University of California, Davis (Sacramento) assesses the massive economic impact of the drought (around 2.200 million dollars)

The official state of emergency was declared in January 2014, in order to address the problem and try to find ways to conserve and use water more efficiently. Serious problems related to water use had already begun: farms can not provide water for livestock, thousands of workers in agriculture are loosing their jobs and severe wildfires are taking place, just to name a few.

The gravity of California's drought is so great that it is already changing the geography of the state: one of it's most important rivers is not reaching the Pacific Ocean anymore.

Just look at a couple of pictures: 

Satellite images showing the snow cover over the Rocky Mountains in January 2013 vs January 2014

California's Governor Jerry Brown encourages individuals and companies to put to work strategies to try to save water and reduce consumption to 20% or more. While many of these initial measures are directed to residents, the agricultural sector accounts for up to 80% of total water consumption in California, according to MacDonald, 2010. The restrictions on water use are usually applied voluntarily, but in certain areas they have become mandatory.

In early February 2014, a heavy rainfall fell over Sonoma. 2013 was the driest year on record and because of this, soil was very poor in moisture.

When soils are lacking moisture so severely, they harden and crack, becoming less permeable to water and this results in heavy rainfall not being absorbed, causing flash floods.

As the drought deepens, flash floods may become more frequent, bringing new challenges to farmers in the area (including the cannabis industry).

As if it were not enough with these, Amos et al., 2014 link drought with higher earthquake probability.

This is the third consecutive year of drought in California. Now comes the one thousand dollar question... Can we attribute this to climate change?

Let's first check the science behind the event.

During the last three years, a vast anticyclone hast remained over the northeastern Pacific Ocean (the so called "Ridiculously Resilient Ridge" I love the nickname!) preventing the winter storms from reaching California and as a result, bringing extreme temperatures and massive drought to this area.

This is also a consequence of the Rossby waves we talked about in the last post.

In this report, the Stanford researchers Noah Diffenbaugh and David Swain (the video stars) analyze the impact of climate change in this particular event trough a combination of GCMs (Global Circulation Models) and statistical methods which have allowed them to determine whether the formation and resilience of such an anticyclone had been possible in the absence of the effects of Climate Change.

They concluded that the atmospheric conditions driving to this situation in California are very likely related to human-caused Climate Change. In other words, human-caused climate change has dramatically increased the likelihood of extremely high atmospheric pressure over the North Pacific Ocean which has lead to the drought in California.