It has been a long time coming (sorry!), but it's time for the last post about drought in California. We've seen that the drought has been caused by persistent high pressure over the Pacific, and that agriculture in California is a key factor in water usage in California. In this post, it is time to ask the inevitable question asked about most events of extreme weather; is the drought due to climate change? Clearly, that isn't a yes/no question, but some evidence and scientific thought has been presented on the matter.
In 2014, a paper published in the Journal of Climate used climate models (computer simulations of climate) and palaeoclimatic data (historic records that provide clues as to past climates - e.g. ice cores, tree rings) in an attempt to assess the risk of persistent drought across the world. The paper identifies the U.S. Southwest (the region of the US in which California is located) as potentially being at the start of a multidecade 'megadrought' (an 80-90% chance), a conclusion that has also been echoed by other pieces of work. The likelihood of a drought of 35 years or longer is suggested to be between 20% and 50%, and the risk of an unprecedented 50 year drought is between 5-10%. Clearly, this high potential of a 'megadrought' is a concerning piece of analysis. The authors of the paper show that for as the global warming scenario in the climate model becomes more severe, the likelihood of 'megadroughts' increase. So, this analysis presents a picture that climate change is very much influencing drought in California.
Another paper of interest was published in Geophysical Research Letters in 2015. Here, it is made clear that the drought itself is primarily a product of natural climate variability - the drought itself was not caused by climate change, but by natural variability in precipitation levels. However, it is concluded that warming caused by human emissions intensified the drought 8–27% in 2012–2014 and 5–18% in 2014. The overall conclusions are summed up succinctly by the authors:
'Although
natural variability dominates, anthropogenic warming has substantially
increased the overall likelihood of extreme California droughts.'
So - while I have only presented two papers here, out of a myriad of similar scientific literature, we can say with some surety that climate change is likely intensifying the Californian drought.
One final item of climatic interest is the phenomenon known as 'El Nino'. Put simply, El Nino is a warming of the waters of the Pacific Ocean that has an effect on weather and climate around the world. El Nino occurs every so often often, and research has shown that climate change has been caused these events to become more intense. We are currently in the midst of an El Nino event (in fact, it has just peaked), and these events generally bring rainfall to the Pacific Coast of the USA. However, this increased moisture is unlikely to be enough to influence the Californian Drought - NASA suggest that El Nino can only caused increased rainfall in southern California, an area which is engineered with concrete channels (see a previous post on this blog discussing the subject) that cannot capture water. The surface reservoirs from which California is so reliant are located in the north, an area which is less likely to be affected by increased rainfall from El Nino.
There is no get out of jail free card. California is in real trouble.
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