At the beginning of the winter, 2015, hopes were high for residents of California that a strong El Nino would be the answer to the severe drought conditions the state has faced for far too long. In some ways, El Nino delivered what was wanted; Northern California filled its reservoirs to the brim. However, Southern and Central California didn’t receive a great amount of the winter’s precipitation, and the statewide snowpack is 87 percent of normal.
Unfortunately, a drought-free California still appears to be far in the future. The state remains in drought, with weather extremes occurring frequently across the state. According to Daniel Swain, an atmospheric scientist at Stanford’s School of Earth, Energy, & Environmental Sciences and the lead author of a newly published paper in Science Advances, California is “seeing increasing temperatures and relatively little change in average precipitation, but an increase in the variability and the occurrence of both wet and dry extremes.”
This doesn’t bode well for the state. Atmospheric pressure patterns, specifically warm and dry patterns such as those that have characterized the past few years of drought, appear to be happening more often. However, when it comes to the wet periods, these patterns also show that there has been no corresponding decrease related to the increase in dry patterns. In fact, the wet periods have even shown an increase as well. Both of these weather extremes are cause for concern; the dry periods for drought impacts, and the wet for flood impacts.
A notable atmospheric pattern that has been affecting California (and the entire West Coast) is known as the Ridiculously Resilient Ridge (RRR). This high-pressure system was sitting right off the West Coast from the tip of Southern California to Alaska as California’s drought intensified beginning in 2013. The RRR deflected storms away from all of California and much of the coast during the past several winters, severely affecting the levels of precipitation. It is this type of deflective atmospheric pattern Swain says has been occurring more frequently in California.
El Nino was predicted to be strong this winter, and it turned out to be one of the strongest on record. However, it didn’t give California the precipitation it needed (especially in the south). The high-pressure ridge is to blame, although due to slightly different positioning it didn’t block storms from hitting the entire coast, which is why the north did okay precipitation-wise.
Another factor that related to California’s drought is climate change. Higher temperatures in the state lead to an increased drought risk and an increase in the severity of the drought. Global warming is also assumed to be causing extremely high pressures, like the RRR, to be more likely in the region.