Tree-Ring Reconstruction of the Atmospheric Ridging Feature That Causes Flash Drought in the Central United States Since 1500

Rapid drought intensification, or flash droughts, is often driven by anomalous atmospheric ridging and can cause severe and complex impacts on water availability and agriculture, but the full range of variability of such events in terms of intensity and frequency is unknown. New tree-ring reconstructions of May-July mid-tropospheric ridging and soil moisture anomalies back to 1500 CE in the central United States-a hotspot for flash drought-suggest that over the last five centuries, anomalies in these two variables combined to indicate flash-drought conditions in similar to 17% of years and exceptionally severe flash drought in similar to 4% of years, similar to frequencies in recent decades. However, over one-third of all inferred exceptional flash droughts occurred since 1900, suggesting the 20th century was highly flash-drought prone. These results may guide future work to diagnose the roles of external, oceanic, and land-surface forcing of warm-season atmospheric circulation and hydroclimate over North America.