Vegetation Expansion on the Tibetan Plateau and Its Relationship with Climate Change

Jianshuang Wu,Ben Niu,Jiaxing Zu,Meng Li,Xianzhou Zhang,Yongtao He,Zhipeng Wang

doi:10.3390/rs12244150

Abstract

The natural shift in land cover from non-vegetated to vegetated land is termed as vegetation expansion, which has substantial impacts on regional climate conditions and land surface energy balance. Barrens dominate the northwestern Tibetan Plateau, where vegetation is predicted to expand northwestward with the ongoing climate warming. However, rare studies have confirmed such a forecast with large-scale vegetation monitoring. In this study, we used a landcover dataset, classified according to the International Geosphere–Biosphere Program criteria, to examine previous model-based predictions and the role of climate on the expansion rate across the plateau. Our results showed that shrublands, open forests, grasslands, and water bodies expanded while evergreen and deciduous broadleaf forests, croplands and barrens shrank during the period 2001–2018. Vegetation expanded by 33,566 km2 accounting for about 1.3% of the total area of this plateau and the land cover shifting from barrens to grasslands was the primary way of vegetation expansion. Spatially, the vegetation expanded northwestward to lands with colder, drier, and more radiation in the climate. Increasing precipitation positively correlated with the vegetation expansion rate for the arid and semi-arid northwest Tibetan Plateau and warming contributed to the vegetation expanding in the semi-humid southeast Tibetan Plateau. Our results verified the predictions of models and highlighted the “greening” on barrens in recent years.

Highlights

The warming rate at high latitudes and elevations is higher than the averages of the northern hemisphere and those of the world in recent decades [1,2], and the amplification is mainly attributed to the cryospheric snow-ice feedback [1,3,4]
Compared with the classification in 2001, the vegetated coverage classified in 2018, including forests, shrublands, open forests, grasslands and croplands, increased by 134,264 pixels, which is approximately equal to 33,566 km2 and 1.3% of the total area of the Tibetan Plateau (TP)
We examined the response of the vegetation expansion rate to climate variables (GST, growing season (May–October) precipitation (GSP) and growing season radiation (GSR)) with linear and non-linear models (Figure 9 and Table A2)

Summary

Introduction

The warming rate at high latitudes and elevations is higher than the averages of the northern hemisphere and those of the world in recent decades [1,2], and the amplification is mainly attributed to the cryospheric snow-ice feedback [1,3,4]. Greening has been observed at high latitudes via satellite records, which is interpreted as warming induced shrub expansion, tree line advance and tundra growth, which has contributed to global warming [5]. The vegetation growth and dominant species transition-induced “greening” has positive feedback for warming by reducing the land surface albedo and increasing the radiation absorption [10,11]. It is crucial to monitor the land cover change and explore its responses to climate change, in the high latitudes and elevations, where the land is undergoing a higher warming rate and the vegetation might play a role of forerunner and feedbacks [5,16]

Methods

Results

Discussion

Conclusion