Spatial patterns of wet season precipitation vertical gradients on the Tibetan Plateau and the surroundings

Lan Cuo,Yongxin Zhang

doi:10.1038/s41598-017-05345-6

Abstract

The Tibetan Plateau and the surrounding (TPS) with its vast land mass and high elevation affects regional climate and weather. The TPS is also the headwater of 9 major Asian rivers that provide fresh water for 1.65 billion people and many ecosystems, with wet season (May–September) precipitation being the critical component of the fresh water. Using station observations, ERA-Interim and MERRA2 reanalysis, we find that wet season precipitation displays vertical gradients (i.e., changes with elevation) that vary within the region on the TPS. The decrease of precipitation with elevation occurs in the interior TPS with elevation larger than 4000 m, little or no change over the southeastern TPS, and increase elsewhere. The increase of precipitation with elevation is caused by increasing convective available potential energy (CAPE) and decreasing lifting condensation level (LCL) with elevation overwhelming the effects of decreasing total column water vapor (TCWV) with elevation. The decreasing precipitation with elevation is due to the combined effects of increasing LCL and decreasing TCWV. LCL and CAPE play a more important role than TCWV in determining the spatial patterns. These findings are important for hydrology study in observation scarce mountainous areas, water resources and ecosystem managements in the region.

Highlights

The TPS, located in 25°N–42°N and 77°E–105°E, is the largest and highest plateau on Earth
On the TPS, wet season precipitation accounts for more than 70% of annual total precipitation at most stations
Precipitation decreases from the southeast to the northwest as a result of the prevailing atmospheric circulations combined with the effects of local elevation and terrain

Summary

Introduction

The TPS, located in 25°N–42°N and 77°E–105°E, is the largest and highest plateau on Earth. The TPS, often referred to as the “Water Tower of Asia”, contains the headwaters of 9 major rivers in Asia that provide vital fresh water resources for 1.65 billion people[6] or about 22% of the world’s population as well as numerous ecosystems The headwaters of these 9 major rivers, the Yellow, Yangtze, Mekong, Salween, Irrawaddy, Brahmaputra, Indus, Tarim and Ganges Rivers (see Fig. 2 for their locations) are mostly fed and sustained by precipitation and frozen water[7]. The observed mean annual precipitation during 1979–2015 at the stations of the TPS (Fig. 2a) ranges widely from ~20 mm in the northwest to ~1900 mm in the southeast (Fig. 2b) This southeast-northwest precipitation horizontal gradient is related to the combined effects of the East and South Asia monsoons, of the westerlies, and of the interactions between the local topography and the large-scale weather systems[10,11,12,13,14,15,16]. This study aims to fill the gap by making use of the recently available precipitation observations in the region and the global reanalyses as described in the Data and Method section

Objectives

Results

Conclusion