Ensemble Empirical Mode Decomposition of the variability of precipitation over the Tianshan Mountains, Central Asia

Considerable knowledge gaps remain in understanding the spatial and temporal patterns of precipitation in the Tianshan, a large system of mountain ranges located in Central Asia. Based on the Global Precipitation Climatology Centre (GPCC) data set and NCEP/NACR reanalysis data, this study investigates the precipitation variations over the Tianshan Mountains on different time scales using the Ensemble Empirical Mode Decomposition (EEMD), and a subsequent attribution analysis with respect to large-scale climate modes.

During 1950-2016, the annual precipitation in most of the Tianshan regions showed an increasing trend with the exception of its wettest sub-regions, the Western Tianshan. In addition to the overall trend, the annual precipitation in Tianshan shows high-frequency variations of 3-year and 6-year quasi-periods and low-frequency variations of 12-year and 27-year quasi-periods. Winter precipitation in the Tianshan Mountains exhibits multi-decadal oscillations with periods of 26.8 and 44.7 years, with similar multi-decadal variability as the East Atlantic-Western Russia (EATL/WRUS) teleconnection pattern. The enhanced meridional characteristics of the EATL/WRUS trigger more water vapor fluxes from low-latitude oceanic regions, resulting in a wet period of Tianshan in winter after 1988. Similarly, summer precipitation in the Tianshan Mountains entered a wet period after 1986. The Scandinavian (SCAND) teleconnection pattern is significantly negatively correlated with Tianshan summer precipitation. During the negative phase of SCAND in summer, strong high pressure over the Ural Mountains and low pressure over Central Asia combine to induce enhanced conveying of water vapour to the Tianshan from the Arctic Ocean. Furthermore, the Silk Road pattern (SRP) and East Asia-Pacific teleconnection (EAP) have affected Tianshan summer precipitation for the periods 1964-1984 and 1985-2004.