Recent vegetation browning and its drivers on Tianshan Mountain, Central Asia

The strong signal of vegetation increases since the 1980s is considered as reliable evidence of anthropogenic climate change. However, some studies have alerted us to the recent stalling or even reversal of vegetation greening. To determine whether vegetation browning exists on Tianshan Mountain, we investigated the changes in the Normalized Difference Vegetation Index (NDVI) based on long-term satellite-derived NDVI data series from 1982 to 2015. Although the trend of growing season NDVI was statistically significant throughout the study period (0.0006a-1, p < 0.01), two different periods with opposite trends were evident around 1998. The NDVI showed a significant increase before 1998 but a reversal after 1998, when vegetation browning began to appear. The strong correlation between the interannual variability of vegetation and growing season temperature only existed in wet years, indicating that vegetation on Tianshan Mountain is extremely vulnerable and sensitive to water deficits. Our results also suggest that relative to high vapor pressure deficit, soil moisture deficit played a greater role in the recent browning of vegetation on Tianshan Mountain. This study is of scientific value in understanding the response of vegetation growth and carbon cycling to environmental changes and predicting future developments.

Automated summary

The study reveals that there has been noticeable vegetation browning in the Tianshan Mountain region over the past few decades, particularly evident post-1998, indicating a high vulnerability and sensitivity to water deficits.