Climate–Vegetation Coverage Interactions in the Hengduan Mountains Area, Southeastern Tibetan Plateau, and Their Downstream Effects

Abstract

Little is known about the mechanism of climate–vegetation coverage coupled changes in the Tibetan Plateau (TP) region, which is the most climatically sensitive and ecologically fragile region with the highest terrain in the world. This study, using multisource datasets (including satellite data and meteorological observations and reanalysis data) revealed the mutual feedback mechanisms between changes in climate (temperature and precipitation) and vegetation coverage in recent decades in the Hengduan Mountains Area (HMA) of the southeastern TP and their influences on climate in the downstream region, the Sichuan Basin (SCB). There is mutual facilitation between rising air temperature and increasing vegetation coverage in the HMA, which is most significant during winter, and then during spring, but insignificant during summer and autumn. Rising temperature significantly enhances local vegetation coverage, and vegetation greening in turn heats the atmosphere via enhancing net heat flux from the surface to the atmosphere. The atmospheric heating anomaly over the HMA thickens the atmospheric column and increases upper air pressure. The high pressure anomaly disperses downstream via the westerly flow, expands across the SCB, and eventually increases the SCB temperature. This effect lasts from winter to the following spring, which may cause the maximum increasing trend of the SCB temperature and vegetation coverage in spring. These results are helpful for estimating future trends in climate and eco-environmental variations in the HMA and SCB under warming scenarios, as well as seasonal forecasting based on the connection between the HMA eco-environment and SCB climate.

摘要

青藏高原东南部的横断山区地形复杂、 气候敏感、 生态脆弱, 其气候和植被覆盖间的耦合变化机制尚不清楚. 本研究利用卫星资料及气象观测和再分析资料等多源数据, 揭示了青藏高原东南横断山区近几十年来温度与植被覆盖度变化的相互反馈机制及其对下游四川盆地气候的影响. 气温上升与横断山区植被覆盖度增加之间存在显著的相互促进作用, 该效应在冬季最显著, 春季次之, 夏季和秋季不显著. 从机制上来讲, 气温上升增加了当地植被覆盖, 植被绿化反过来又通过增加地表到大气的净热通量来加热大气. 横断山区上空的大气加热异常使大气柱变厚、 高空气压升高, 高压异常通过西风向下游扩散至四川盆地上空, 最终导致四川盆地温度升高. 这种效应可从冬季持续到次年春季, 进而导致春季四川盆地温度和植被盖度出现极大增加趋势. 本研究结果有助于全球变暖背景下横断山区和四川盆地气候和生态环境的未来趋势预测以及基于横断山区气候环境变化的下游效应对四川盆地气候环境开展季节预测.