Possible widths of Indian summer monsoon trajectories in Tibetan Plateau revealed by the direction of maximum summer precipitation decreases in recent decades.

The Tibetan Plateau (TP) affects its surrounding regions through thermal and dynamic processes. Hydrological cycles in TP are experiencing dramatic changes under the warming climate. As one of the most important circulations, the Indian summer monsoon (ISM) affects precipitation changes and therefore has a major effect on TP water resources. In this paper, the widths of ISM are defined as extents perpendicular to the moisture trajectories. They were calculated using ground-based measurements and verified with reanalysis datasets. The directions of maximum summer precipitation decreases (Dir_min) were selected using the cluster proxy of directions of daily maximum winds (W_d) and the slope aspects derived from digital elevation models (DEMs) at various resolutions. The major findings were that (1) similar southwestern Dir_min were found based on the W_d and the slope aspects derived from DEMs with resolutions of 100 and 200 km; (2) Reanalysis data from China Meteorological Forcing Dataset verified that a high percentage (~ 90%) of cells showing precipitation decreases also had slope aspects (derived from 100- and 200-km resolution DEMs) in the range of 112.5°–247.5°; (3) The possible widths of ISM trajectories in TP were approximately 100–200 km. [ABSTRACT FROM AUTHOR]