Jones et al. (2026) Tree Rings Indicate Potential for Severe Soil Moisture Drought in California Is Much Greater Than Observations Suggest

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Geophysical Research Letters
• Year: 2026
• Date: 2026-11-06
• Authors: Jacob Jones, Park Williams
• DOI: 10.1029/2026gl125616

Research Groups

Not specified in abstract.

Short Summary

This study reconstructs California's summer soil moisture anomalies from CE 1100–2025 using tree rings, revealing that 1579–1580 was the driest two-year period and demonstrating that tree-ring data significantly alters the expected frequency of extreme droughts compared to instrumental records alone.

Objective

• To produce a gridded tree-ring reconstruction of summer soil-moisture anomalies for California from CE 1100–2025.
• To perform a peaks-over-threshold extreme value analysis on statewide mean drought severity.
• To assess how including tree-ring reconstructions changes the expected frequency of extreme droughts on realistic planning horizons.

Study Configuration

• Spatial Scale: Statewide California, gridded.
• Temporal Scale: CE 1100–2025 (tree-ring reconstruction), 1901–2025 (instrumental record).

Methodology and Data

• Models used: Peaks-over-threshold extreme value analysis.
• Data sources: Tree-ring reconstructions, instrumental record (observations).

Main Results

• The period 1579–1580 was by far the driest pair of years across California since at least CE 1100.
• Marginal annual exceedance probabilities (AEP) were approximately 0.24% for 1579 and approximately 0.04% for 1580.
• The two-year block exceedance probability for 1579–1580 was approximately 0.05%.
• Considering only the instrumental record (1901–2025), AEPs for the reconstructed drought severities of 1579 and 1580 cannot be robustly estimated, with 1580 appearing essentially impossible.
• Including tree-ring reconstructions meaningfully changes the expected frequency of droughts on realistic planning horizons, such as a 1% AEP (100-year) event.

Contributions

• Provides the longest and most detailed gridded tree-ring reconstruction of summer soil moisture anomalies for California (CE 1100–2025).
• Demonstrates that modern drought risk assessments based solely on instrumental observations likely underestimate the true probability of extreme drought events.
• Highlights the critical importance of paleoclimate data (tree rings) for robustly estimating the frequency of extreme drought events, even without accounting for anthropogenic climate change.

Funding

Not specified in abstract.

Citation

@article{Jones2026Tree,
  author = {Jones, Jacob and Williams, Park},
  title = {Tree Rings Indicate Potential for Severe Soil Moisture Drought in California Is Much Greater Than Observations Suggest},
  journal = {Geophysical Research Letters},
  year = {2026},
  doi = {10.1029/2026gl125616},
  url = {https://doi.org/10.1029/2026gl125616}
}