For three years strong, the atmosphere steering flow has hit a road block along the West Coast (dubbed the “ridiculously resilient ridge”), but connecting that to climate change has proven difficult.
But even as climate change probably isn’t driving the weather pattern behind the drought, it is directing the background temperatures: up. Atmospheric levels of the heat-trapping gas carbon dioxide, due to the burning of fossil fuels, have risen about 25 percent since 1958.
Carbon dioxide and other heat-trapping gases act like a performance-enhancing steroid when it comes to warm weather extremes. They substantially increase the likelihood new records for hot weather are set. Like steroids are suspected for inflating homerun totals in Major League Baseball in the 1990s, the atmosphere’s version of steroids is a prime suspect for exploding hot weather records in California.
The number of heat records set in California in the last two years is staggering. Here are just a few:
* The state had its hottest year on record in 2014
* The state had its hottest winter on record in 2014-2015, shattering the previous record – set just the year before (2013-2014) – by 1.5 degrees.
* In March, Los Angeles doubled its record for 90-degree days in that month, logging 6 such days compared to the previous record of 3 (from 1977).
* In March, Redding, Sacramento, Fresno, Los Angeles, and San Diego set records for average maximum temperatures in the month.
The added heat from climate warming acts to intensify the drought in important ways:
* When it’s warmer, the evaporation of water speeds up, allowing the ground to heat up faster, which then evaporates more water in a vicious cycle which continues until meaningful rain stops it.
* When it’s warmer, the snow season shortens. In other words, snow starts falling later in the fall and stops falling earlier in the spring, and snowpack declines.
* When it’s warmer, snow levels rise. In other words, the elevations at which rain changes to snow in the mountains goes up, and snowpack declines.
It’s interesting to note that in 1976-1977, California experienced a similar weather pattern to this year and was also mired in drought. But the drought was not as severe. Consider California’s April snowpack in 1977 was 25 percent of normal compared to 5 percent in 2015. The fact background temperatures in 1977 were not as hot very likely had something to do with the far less dire snowpack situation.
Indeed, research by Stanford professor Noah Diffenbaugh and colleagues has shown that drought potential has ramped up over time due to the effect of rising temperatures.
“Of course low precipitation is a prerequisite for drought, but less rain and snowfall alone don’t ensure a drought will happen. It really matters if the lack of precipitation happens during a warm or cool year,” Diffenbaugh said. “We’ve seen the effects of record heat on snow and soil moisture this year in California, and we know from this new research that climate change is increasing the probability of those warm and dry conditions occurring together.”
Future projections suggest warming temperatures will continue to tip the scales towards stronger and more frequent drought.
“We found that essentially all years are likely to be warm – or extremely warm – in California by the middle of the 21st century,” said Daniel Swain, a graduate student of Diffenbaugh’s. “This means that both drought frequency – and the potential intensity of those droughts which do occur – will likely increase as temperatures continue to rise.”