Increasing control of climate warming on the greening of alpine pastures in central Asia

High-altitude environments are among the most sensitive to climate change, where impacts are amplified. To clarify alpine pasture dynamics in three typical mountains (i.e., Altay, Tianshan, and Kunlun) in central Asia, the change trends in the long-term summer peak Normalized Difference Vegetation Index (NDVI) were examined by applying three satellite sources: Landsat ETM+/OLI (1999-2020), Global Inventory Modeling and Mapping Studies (1981-2013), and Moderate Resolution Imaging Spectroradiometer (2000-2020). Satellite-derived NDVIs are reliable because similar variations can be observed during overlapping periods. The results show that the alpine pastures experienced overall greening. The most significant greening was observed in Kunlun Mountains and the high-altitude areas of Tianshan and Altay Mountains, where the annual average temperature is lower. Relationships between NDVI and potential driving factors, such as average precipitation (AP), surface soil water content (SSWC), total water storage (TWS), snow cover frequency, growing degree days (GDD), and average temperature (AT), were further analyzed. Over the last two decades, the optimal habitat of alpine pastures became warmer and wetter, as the AT, GDD, SSWC, TWS all showed increased trends. However, AP decreased at a rate of -0.625 mm/year, indicating that melting ice materials under current warming helped preserve moisture and soil water availability for pasture growth. Additionally, the primary factor regulating greenness patterns shifted from AP during 2002-2011 to GDD during 2012, 2014, and 2016-2020, indicating that the alpine pastures in central Asia have been increasingly dependent on climate warming. Our study highlights that the response of alpine pastures to climatic factors might change under ongoing climate change.

Automated summary

The study found a greening trend in alpine pastures in Altay, Tianshan, and Kunlun Mountains, with Kunlun Mountains and high-altitude areas of Tianshan and Altay Mountains showing the most significant greening. The optimal habitat of alpine pastures became warmer and wetter, with trends in average temperature, growing degree days, surface soil water content, and total water storage all increasing. This shift indicates increasing dependency of alpine pastures in central Asia on climate warming.