The Long-term Variability of Floods and Droughts in California

In an abstract presented at the 26th PACLIM Conference that was published in a recent issue of Quaternary International, Verosub (2015) writes about the challenges of maintaining and utilizing water supplies in California. However, the geologist from the University of California notes that what is often missing from discussions of water security is a consideration of the effects of natural climate variability beyond the historical record. As an example of such variability, Verosub cites the fact that river flow and lake measurements during the 20th century “document the occurrence of several multi-year droughts in the past 100 years while tree ring records show that 20-year and 70-year droughts occurred during the last 300 years.”

On an even longer time scale, the scientist reports that “at least once and probably several times in the last few thousand years, there have been droughts severe enough to drop the level of Lake Tahoe by several tens of meters, which allowed Douglas fir trees to grow to maturity on exposed lake beds.” Furthermore, other data indicate episodes of extreme flooding, such as the water year of 1861-1862 that brought extensive rainfall from Oregon down through southern California.

In consequence of these realities, Verosub concludes that “the paleoclimate history of California suggests that even in the absence of climate change due to anthropogenic greenhouse gases, decadal, multi-decadal, or even century-long droughts are a real possibility in the future for California as is flooding on a greater scale than was seen in the twentieth century.” According to Verosub, if such natural events were to occur today, they would easily “wreck havoc with California’s delicately balanced water delivery system” in the case of drought, and “overwhelm the levee system and destroy California’s ability to transfer water from north to south” in the case of flooding. No doubt, such events would quickly be labeled by climate alarmists and advantage-seeking politicians as “human-caused.” Yet, given the historic periodicity of these events, there would be no way to prove that they weren’t natural. In fact, their mere occurrence would simply confirm that they are natural, recurring over and over again throughout history, human influence notwithstanding. As such, the title of the author’s work provides some good advice for Californians: Don’t worry about climate change; California’s natural climate variability will probably “get us” first.

 

Reference

Verosub, K. 2015. Don’t worry about climate change; California’s natural climate variability will probably “get us” first. Quaternary International 387: 148.