Aridity change in the Northern Hemisphere (NH) is a vital topic in exploring climate change. The Tibetan Plateau (TP) is essential for its role in climate variability over the NH. We applied the ensemble empirical mode decomposition (EEMD) to the aridity index (AI) from 20°-60°N in this study. The EEMD method extracts a set of intrinsic mode functions (IMFs) with various timescales. Results from our analysis reveal that the multi-decadal oscillation of AI makes 35% contribution to the variability of the AI. And the multi-decadal oscillation of the TP thermal forcing makes 18.15% contribution to the multi-decadal variability of the AI, which is often ignored in previous studies. The dynamic and thermal effects of the TP also affect the AI change, which illustrates a mode of meridional difference around 40°N, with wetting in the north and drying in the south. Meanwhile, the dynamic effects of the TP lead to latitudinal difference north of 40°N in Asia, with drying Northeast Asia. Such meridional and latitudinal differences over South Asia, Southeast Asia and southern China are controlled by a high-pressure system from 850 hPa up to 500 hPa, which results in an increase of sinking motion from 20°-40°N with obvious continuous drying effect.

Tibetan Plateau,aridity index,multi-decadal variability,dynamic effect,thermal effect