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Keywords:

  • moisture variability;
  • NAO;
  • ENSO;
  • PDO;
  • Tibetan Plateau

ABSTRACT

Spatial and temporal variations in moisture across the Tibetan Plateau (TP) during the years 1300–2005 were investigated using 50 gridded Palmer drought severity index (PDSI) series extracted from the newly developed Monsoon Asia Drought Atlas (MADA). The first four spatial patterns of moisture variations were identified by empirical orthogonal function analysis. They represent coherent moisture variations on the northern, southern, northwestern and southeastern TP, respectively. Similar spatial patterns were seen for the reconstructed and observational PDSI series. Comparisons between the first four principal components (PCs) of 50 MADA-PDSI and Dai-PDSI series confirmed that the PCs based on the MADA-PDSI are reasonable proxies for regional moisture variations over the TP during the past 700 years. During the last century, wetness has generally increased on the northern and southern TP, which is in accord with the simulation of the global monsoon rainfall and paleoclimate records from Monsoonal Asia. The results of spatial correlation analysis indicated that the North Atlantic Oscillation is a primary cause of the contrasting moisture conditions between the northern and southern TP on a decadal time scale. Decadal moisture variations are also closely associated with the Pacific decadal oscillation which contributes to the difference in moisture conditions between the eastern and western TP. Moreover, interannual moisture variations over the TP were found to be closely linked to the El Niño southern oscillation. Large-scale dryness and wetness are possibly caused by the joint effects of each of these three atmospheric oscillation modes. © 2013 Royal Meteorological Society