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ABSTRACT:We have reconstructed the Palmer Drought Severity Index (PDSI) from 1618 to 2005 for the Guiqing Mountain area, north central China, using tree rings of Pinus tabulaeformis. The reconstruction explains 49% of the actual PDSI variance during the common period . The PDSI reconstruction is representative of moisture conditions over a large area to the south and east of the sampling site, the core area for the 1997 severe drought. It shows slightly different variations when compared to other available PDSI reconstructions north and west of the sampling sites. The drought epoch since 1994 is most severe for our study region, with least intensity for the Helan Mountain area. The drought in 1997 was centered in the Guiqing Mountain area, and appears to be the most extreme drought event over the length of reconstruction. Significant spectral peaks are identified at 2.1, 2.3, 2.5, 3.2, 3.6, 42.7 and 53.8 years. Our reconstructed droughts are significantly correlated with sea surface temperature in the northern Indian Ocean, western equatorial Pacific Ocean, eastern equatorial Pacific Ocean, Eastern China Sea and Sea of Japan. The linkages to the Indian and Pacific Oceans suggest the connection of regional moisture variations to the Asian monsoon circulations.

Unprecedented heatwave-drought concurrences in the past two decades have been reported over inner East Asia. Tree-ring–based reconstructions of heatwaves and soil moisture for the past 260 years reveal an abrupt shift to hotter and drier climate over this region. Enhanced land-atmosphere coupling, associated with persistent soil moisture deficit, appears to intensify surface warming and anticyclonic circulation anomalies, fueling heatwaves that exacerbate soil drying. Our analysis demonstrates that the magnitude of the warm and dry anomalies compounding in the recent two decades is unprecedented over the quarter of a millennium, and this trend clearly exceeds the natural variability range. The “hockey stick”–like change warns that the warming and drying concurrence is potentially irreversible beyond a tipping point in the East Asian climate system.

Drought reconstruction from 1794 to 2003 in the eastern part of NW China was developed by calibrating tree rings of Picea wilsonii on Xinglong Mountain with the Palmer drought severity index (PDSI). The reconstruction explains 40% of the actual PDSI variance during the period from 1951 to 2003. The most significant drought period over the reconstructed time span occurred during the 1920s to 1930s. The drought reconstructions show a climate transition in 1921 on a decadal scale and significant cyclic patterns that were identified in intervals of 10.5, 7.9-8.3, ~3.5, 3.0-3.2, 2.7-2.8 and ~2 yr. This reconstruction is representative of regional drought patterns in eastern NW China and demonstrates that they are different from patterns in western NW China.

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