Recent warming evidence inferred from a tree-ring-basedwinter-half year minimum temperature reconstructionin northwestern Yichang, South Central China, and its relationto the large-scale circulation anomalies

High-resolution winter temperature reconstructions in China are rare, yet vital for the comprehensive understanding of past climate change. In the present work, the first winter-half year minimum mean temperature from previous November to current April in northwestern Yichang, South Central China, was reconstructed back to 1875 based on tree-ring material. The reconstruction can explain 55 % of the variance over the calibration period during 1955&ndash;2011. The temperature maintained at comparatively low level before 1958, and an abnormal warming was seen since 1959. However, the warming trend stagnated after 2000 AD. 2001&ndash;2010 was the warmest decade not only during the instrumental period but also during the whole reconstructed period. The reconstruction indicates good spatial resemblance to other temperatures series in adjacent areas and Northern Hemisphere, yet the recent warming in this study is earlier and more prominent than that of Southeast China. This work also manifests that the winter-half year minimum temperature in study area has good agreement with summer (June&ndash; September) maximum temperature variation in Southeast China at decadal scale, except that the winter-half year warming in recent decades is more evident than summer. This reconstruction is not only useful in improving our knowledge of long-term temperature variation but also useful in predicting the tree growth dynamics in the future in the study area.</p

April-September mean maximum temperature inferred from Hailar pine (Pinus sylvestris var. mongolica) tree rings in the Hulunbuir region, Inner Mongolia, back to 1868 AD

Two robust tree-ring width chronologies were developed for the Hulunbuir region, Inner Mongolia, northeast China. Both chronologies were significantly correlated with each other and were arithmetically averaged to build a regional chronology (NBSTD). NBSTD showed significant and negative correlations with the growing season maximum temperature from April to September. Based on this relationship, the mean maximum temperature of April to September was reconstructed for the period from 1868 to 2008. The percentage of variance in the data explained by the reconstruction was 40.3% during the calibration period of 1953-2008. Five severe warm events of two years or more were found in 1905-1909, 1996-1997, 2000-2001, 2003-2005 and 2007-2008. Five cold events occurred during the periods 1880-1881, 1897-1900, 1948-1949, 1955-1960 and 1962-1964. On a decadal scale, several warm intervals (above the 1868-2008 mean) were 1904-1913, 1920-1933, 1968-1975 and 1990-2003. Cold intervals (below the mean) were 1893-1901, 1950-1963 and 1976-1989. Warmer events and intervals corresponded to dry periods. Colder events and intervals coincided with wet or moist conditions in and near the study region. Spatial correlation patterns revealed that our reconstruction represents a regional temperature and drought signal for the central and eastern Mongolian Plateau. Comparison with other tree ring-based temperature reconstructions from surrounding areas provides a high degree of confidence in our reconstruction. Power spectrum and wavelet analyses suggest that the reconstructed mean maximum temperature variation may be related to large-scale atmospheric-oceanic variability such as the Pacific Decadal Oscillation (PDO), El Nino-Southern Oscillation (ENSO) and sunspot activity.</p

Hydroclimate variability in the North China Plain and its link with El Nino-Southern Oscillation since 1784 AD: Insights from tree-ring cellulose delta(18)O

We present here a chronology of tree-ring cellulose delta(18)O from 1784 to 2003 that is based on the individual measurements of five Larix principis-rupprechtii trees growing in the semiarid North China Plain (NCP; 34 degrees-41 degrees N, 107 degrees-120 degrees E). This chronology has a significant, negative correlation with summer precipitation, relative humidity, and the Palmer Drought Severity Index. It is representative of regional summer hydroclimate variability in the NCP by analyzing its spatial correlation patterns with CRU TS3 precipitation grid data sets. Historically, extreme climate events (drought and flood) could be detected by the high-frequency (annual) signals in the chronology. The low-frequency (11 year moving average) signals are consistent with the time series of the drought frequency and the regional dryness-wetness index derived from historical documents in the NCP. Significant spatial correlation patterns of measured precipitation and the tree-ring cellulose delta(18)O chronology from the NCP with observed sea surface temperature in the eastern equatorial Pacific during the 1954-2003 and 1854-2003 periods suggest that the summer hydroclimate of the NCP has a close link with El Nino-Southern Oscillation. Mostly extreme dry or wet years identified by the chronology follow historical El Nino or La Nina events over the past 220 years, respectively.</p

Tree-ring-based annual precipitation reconstruction in Kalaqin, Inner Mongolia for the last 238 years

A tree-ring-width chronology of Pinus tabulaeformis from Kalaqin, Inner Mongolia was developed using modern dendrochronological techniques. Based on the results of correlation function analysis, the total precipitation from the previous August to current July was reconstructed for 1771-2008 AD with an explained variance of 49.3%. The reconstruction correlated well with the dryness/wetness series derived from historical documents, as well as the precipitation reconstruction of the Chifeng-Weichang region. There were eight intervals with greater precipitation than the average (associated with the strong East Asian summer monsoon) and seven intervals lower than the average (weak monsoon). A power spectrum analysis showed that there were 120 a, 80 a, 8 a and 2 a periodicities.</p