Large contribution from anthropogenic #warming to an emerging North American #megadrought — Science Magazine

A) Cross-validated reconstruction skill (R2) using tree-ring records that extend to 800 and 1700 CE (green contour: R2 ≥ 0.5; gray: reconstruction does not extend to 800 CE; yellow box: SWNA). (B) Time-resolved cross-validated R2 of the SWNA regional reconstruction. The inset shows observations versus cross-validated reconstructions during the 1901–1983 calibration interval using tree-ring records extending back to 800 and 1700 CE. (C) Time series of reconstructed (red) and observed (blue) 19-year running-mean standardized SWNA soil moisture (gray: 95% reconstruction confidence interval; blue horizontal line: 2000–2018 mean; pink and green shading: the five drought and pluvial periods with the most-negative and most-positive 19-year soil-moisture anomalies, respectively). (D) Maps of the local rank of the most negative 19-year anomaly to occur during each of the five drought events highlighted in (C). In the maps, the aqua color indicates no negative 19-year anomaly, and numbers in the top left corners indicate the rank of the most negative regionally averaged 19-year anomaly during each drought event.

Click here to access the paper (A. Park Williams, Edward R. Cook, Jason E. Smerdon, Benjamin I. Cook, John T. Abatzoglou, Kasey Bolles, Seung H. Baek, Andrew M. Badger, Ben Livneh):

Here’s the abstract:

Severe and persistent 21st-century drought in southwestern North America (SWNA) motivates comparisons to medieval megadroughts and questions about the role of anthropogenic climate change. We use hydrological modeling and new 1200-year tree-ring reconstructions of summer soil moisture to demonstrate that the 2000–2018 SWNA drought was the second driest 19-year period since 800 CE, exceeded only by a late-1500s megadrought. The megadrought-like trajectory of 2000–2018 soil moisture was driven by natural variability superimposed on drying due to anthropogenic warming. Anthropogenic trends in temperature, relative humidity, and precipitation estimated from 31 climate models account for 46% (model interquartiles of 34 to 103%) of the 2000–2018 drought severity, pushing an otherwise moderate drought onto a trajectory comparable to the worst SWNA megadroughts since 800 CE.

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