A comprehensive study of more than 600 years of tree-ring data from the San Joaquin Valley shows the region faces more extreme climate variability than has been recorded in recent history. The study highlights the combined impact of natural variability and human-induced climate change in shaping these climate extremes, suggesting that future impacts of climate hazards may be underestimated when assessed based on current records.
The San Joaquin Valley in California has experienced dramatic variability in climate extremes, with droughts and floods exceeding modern records in severity and duration, according to new research on 600-year tree rings in California's San Joaquin Valley.
This new method of combining paleontological information with synthetic weather generation could help policymakers and scientists better understand and predict flood and drought risks in California and how climate change will exacerbate those risks. The research team's paper was recently published in Earth's Future, a journal of the American Geophysical Union.
The San Joaquin Valley, located in the southern part of California's Central Valley, is an important agricultural center from which much of the country obtains its agricultural products. Cornell University engineering professor Patrick Reed is the co-first author of the paper.
The models show how flood and drought extremes evolve in the San Joaquin Valley and help illuminate how natural variability and climate change are exacerbating each other's effects.
"People often want to separate internal variability from climate change to understand changes in signals from anthropogenic warming," Reed said. "But when we plan in complex water systems, both are happening. We need to understand what happens when the two work together. The result is that we get extremes that we have never seen before. This opens the door to a viable future in a broader sense."
These findings include:
Much of the variability in flood and drought extremes in the San Joaquin Valley can be attributed to natural variability in the short term, but human-driven climate change has an influence on flood and drought extremes that last longer than 30 years.
Over the past 600 years, there have been continuous periods of flooding and drought lasting for decades.
Estimates of drought incidence and severity over the past 30 years rival the worst megadrought period in 600-year reconstructions, but estimates of modern drought duration are slightly shorter than the paleoclimate record.
Therefore, relying solely on modern instrumental records may not adequately reflect hydroclimate hazards. The combination of natural variability and climate change will result in extreme floods and droughts that are more frequent, severe, and prolonged than in the past 600 years.