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 Niño–Southern Oscillation (ENSO) and sunspot activity.