Interannual variability of average minimum temperatures derived from tree rings in the mid-Qinling Mountains, China, for the past 138 years.

In this study, spruce tree rings from the southern slope of mid-Qinling Mountains were adopted to investigate the characteristics of average minimum temperatures during the past 138 years. Analysis showed that the interannual variability in radial growth of trees was positively correlated with the interannual variability of average minimum temperatures from previous December to current September (VTM ) in the study area during 1955-2010 AD. Based on the correlation analysis, the VTM were reconstructed for 1876-2013 AD with an explained variance of 42.5 % for the calibration period. Among the 22 dramatic changing years, extreme changes occurred more times when it was cooling, while the warming was comparatively gentle. Both the 10-year filtering of VTM series and the frequency of occurrences for those dramatic changing years showed a relatively stationary variation after the early 1950s. Over the last five decades, the accumulated VTM series showed an obvious warming trend, and the increase of the minimum temperature had contributed to the regional warming. The comparison of VTM and the dryness/wetness indices generally reflected cold-wet and warm-dry climate conditions in the study area. Significant positive correlations between the reconstructed VTM and the gridded minimum temperature indicated a regional representative of the temperature reconstruction, and positive correlations between VTM and sea surface temperature (SST) of the Indian Ocean and western Pacific regions suggested a possible linkage between the VTM variations and the Asian summer monsoon. Synchronous fluctuations in three tree-ring study series and connections of VTM with Arctic oscillation (AO) and El Niño-Southern Oscillation (ENSO) activities suggested that the minimum temperature variations in the TTH area responded sensitively to large-scale climate fluctuations and were the results of atmosphere-ocean interactions.