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Keyan Fang, Xiaohua Gou, Fahu Chen, Edward Cook, Jinbao Li, Brendan Buckley, and Rosanne D’Arrigo
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Keyan Fang, Xiaohua Gou, Fahu Chen, Edward Cook, Jinbao Li, Brendan Buckley, and Rosanne D’Arrigo

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A preliminary study of a point-by-point spatial precipitation reconstruction for northwestern (NW) China is explored, based on a tree-ring network of 132 chronologies. Precipitation variations during the past ~200–400 yr (the common reconstruction period is from 1802 to 1990) are reconstructed for 26 stations in NW China from a nationwide 160-station dataset. The authors introduce a “search spatial correlation contour” method to locate candidate tree-ring predictors for the reconstruction data of a given climate station. Calibration and verification results indicate that most precipitation reconstruction models are acceptable, except for a few reconstructions (stations Hetian, Hami, Jiuquan, and Wuwei) with degraded quality. Additionally, the authors compare four spatial precipitation factors in the instrumental records and reconstructions derived from a rotated principal component analysis (RPCA). The northern and southern Xinjiang factors from the instrumental and reconstructed data agree well with each other. However, differences in spatial patterns between the instrumentation and reconstruction data are also found for the other two factors, which probably result from the relatively poor quality of a few stations. Major drought events documented in previous studies—for example, from the 1920s through the 1930s for the eastern part of NW China—are reconstructed in this study.

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R. Stockton Maxwell, Amy E. Hessl, Edward R. Cook, and Brendan M. Buckley

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This paper presents a multicentury reconstruction of May precipitation (1200–1997) for the mid-Atlantic region of the United States. The reconstruction is based on the first principal component (PC1) of two millennial-length Juniperus virginiana L. (eastern red cedar) tree-ring chronologies collected from rocky, limestone sites in the Ridge and Valley province of West Virginia. A split-calibration linear regression model accounted for 27% of the adjusted variance in the instrumental record and was stable through time. The model was verified by the reduction of error (RE = 0.21) and coefficient of efficiency (CE = 0.20) statistics. Multidecadal changes in precipitation were common throughout the reconstruction, and wetter than median conditions and drier than median conditions occurred during the medieval climate anomaly (1200–1300) and the Little Ice Age (1550–1650), respectively. The full reconstruction contained evidence of interannual and decadal variability; however, the twentieth century recorded the greatest number of decadal extreme wet and dry periods. A comparison of the May precipitation reconstruction to other regional reconstructions [Potomac River, Maryland, streamflow (Cook and Jacoby); Virginia/North Carolina July Palmer hydrologic drought index (PHDI; Stahle et al.); Missouri July PHDI (Cleaveland and Stahle); and White River, Arkansas, streamflow (Cleaveland)] showed that the eastern U.S. decadal drought and pluvial events extended into the mid-Atlantic region. A positive correlation between PC1 and the winter North Atlantic Oscillation (NAO) index and comparisons of smoothed May precipitation and the NAO (Luterbacher et al.) indicated that J. virginiana’s response to May precipitation was mediated by winter temperature.

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Neil Pederson, Gordon C. Jacoby, Rosanne D. D’Arrigo, Edward R. Cook, Brendan M. Buckley, Chultemiin Dugarjav, and R. Mijiddorj

Abstract

Reconstructions of annual (prior August–current July) precipitation and streamflow, 345 yr in length (1651–1995), are presented for northeastern Mongolia based on tree-ring width data. These precipitation and streamflow reconstructions account for 54% and 48% of the respective variance in instrumental data over the past 50 years. Variations in instrumental precipitation and streamflow are within the range of those reconstructed over the length of tree-ring records. However, there appear to be more frequent extended wet periods during the twentieth century. Multitaper spectral analysis revealed statistically significant peaks at 10.8 and 12.8 yr for the precipitation reconstruction, and at 12.8 and 20.3–23.8 yr for the streamflow reconstruction. Similarly, singular spectrum analysis identified spectral modes of variation at 12 and 21 yr for both series. These spectra resemble those found for tree-ring-based precipitation reconstructions in central China as well as the western United States, and may reflect solar influences on the climate of Mongolia.

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Kevin J. Anchukaitis, Rosanne D. D’Arrigo, Laia Andreu-Hayles, David Frank, Anne Verstege, Ashley Curtis, Brendan M. Buckley, Gordon C. Jacoby, and Edward R. Cook

Abstract

Northwestern North America has one of the highest rates of recent temperature increase in the world, but the putative “divergence problem” in dendroclimatology potentially limits the ability of tree-ring proxy data at high latitudes to provide long-term context for current anthropogenic change. Here, summer temperatures are reconstructed from a Picea glauca maximum latewood density (MXD) chronology that shows a stable relationship to regional temperatures and spans most of the last millennium at the Firth River in northeastern Alaska. The warmest epoch in the last nine centuries is estimated to have occurred during the late twentieth century, with average temperatures over the last 30 yr of the reconstruction developed for this study [1973–2002 in the Common Era (CE)] approximately 1.3° ± 0.4°C warmer than the long-term preindustrial mean (1100–1850 CE), a change associated with rapid increases in greenhouse gases. Prior to the late twentieth century, multidecadal temperature fluctuations covary broadly with changes in natural radiative forcing. The findings presented here emphasize that tree-ring proxies can provide reliable indicators of temperature variability even in a rapidly warming climate.

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