Tree-ring-based drought variability in the eastern region of the Silk Road and its linkages to the Pacific Ocean

Drought variability from 1568 to 2014 was presented for the eastern region of the Silk Road by using five tree-ring chronologies and an optimal information extraction method (i.e., one of the composite-plus-scale methods). The inspection results of the split calibration-verification procedure for the transfer functions showed that the reconstructed Palmer drought severity index (PDSI) was credible throughout the entire time interval. During the past 447 years, there were seven dry periods (1616-1622, 1629-1645, 1682-1730, 1760-1778, 1805-1884, 1919-1933 and 1990-2009) and seven wet periods (1573-1615, 1623-1628, 1646-1681, 1731-1759, 1779-1804, 1885-1918 and 1934-1989). The dry periods were well-documented historical drought events. Significant interannual periods of 2.1-3.8 years and interdecadal cycles of 17.1, 18.3, 23.8, 42.7, 51.3 and 73.0 years were identified via the multitaper method for spectral analysis. Similar patterns of drought fluctuations were found in the records of the drought/flood index and other drought reconstructions. By comparing the reconstructed PDSI with the El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) at the multidecadal scale, it was discovered that when ENSO and PDO were in phase (i.e., high-PDO/warm-ENSO phase or low-PDO/cold-ENSO phase), the study region was dry or wet more often, respectively, especially before 1850. The influence of ENSO and PDO on the decadal variability of drought has been affected by global warming.