Increasing radial growth in old-growth high-elevation conifers in Southern California, USA, during the exceptional “hot drought” of 2000–2020

Knapp, Paul A.; Soulé, Peter T.; Mitchell, Tyler J.; Catherwood, Avery A.; Lewis, Hunter S.

doi:10.1007/s00484-024-02619-3

Cited by 1 publication

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“…In California, which has the largest population [2], highest GDP [3], and highest value of crop sales [4] of all US states, the effects of warming have been extensive [5]. These warming impacts include increased drought risk [5], altered elevational distribution ranges of forest fires, greater burn frequency in the Sierra Nevada [6,7], increased extreme autumnal fires [8], lengthened fire season and area burned [9], reduced snowpack [10], earlier snowpack melt and runoff [11], and decreased (increased) growth of low-elevation (high-elevation) conifers [12,13]. Considerable spatial variability exists within California regarding the extent of 21st century warming effects, with the largest increases occurring in the southern third, and most populous region, of the state [14].…”

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confidence: 99%

Placing 21st Century Warming in Southern California, USA in a Multi-Century Historical Context

Knapp,

Catherwood,

Soulé

2024

Atmosphere

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Warming in southern California during the 21st century is unprecedented in the instrumental record. To place this warming in a multi-century historical context, we analyzed tree ring data sampled from Jeffrey pine (Pinus jeffreyi) and sugar pine (Pinus lambertiana) collected from minimally disturbed, old-growth high-elevation forests within Mt. San Jacinto State Park California, USA. Based on a calibration/verification period of 1960–2020 between earlywood radial growth and California Climate Division 6 climate data, we reconstructed annual (November–October) minimum temperature (Tmin) from 1658 to 2020. During the 61-year calibration/verification period, instrumental Tmin increased (r = 0.69, p < 0.01) and was positively associated with annual radial growth (r = 0.71, p < 0.01). Using regime shift analysis, we found that the 363-year reconstruction revealed Tmin stability until 1958 and then decreased until 1980, followed by the two warmest regimes (1981–2007, 2008–2020) on record. The last 13-year period was 0.77 °C warmer than the multi-century average with nine of the ten warmest years in the reconstruction recorded. These results suggest that 21st century warming in southern California is unique in the context of the past four centuries, indicating the rarity of exceptional warmth captured in the tree ring record.

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