Phenological Changes in Alpine Grasslands and Their Influencing Factors in Seasonally Frozen Ground Regions Across the Three Parallel Rivers Region, Qinghai-Tibet Plateau

• Published in: Frontiers in Earth Science
• Main Authors: Chun-Ya Wang, Jin-Niu Wang, Xu-Feng Wang, Dong-Liang Luo, Yan-Qiang Wei, Xia Cui, Ning Wu, Priyamvada Bagaria
• Format: Article in Journal/Newspaper
• Language: English
• Published: Frontiers Media S.A. 2022
• Subjects: vegetation phenology; river basin; spatio-temporal changes; climate factors; freezing/thawing index; TIMESAT; Science; Q; permafrost
• Online Access: https://doi.org/10.3389/feart.2021.797928; https://doaj.org/article/bc9a9bf7d3e34f0580e27ae24b1fba8f

Alpine ecosystems are sensitive and vulnerable to climate change. In this study, we extracted three phonological parameters, viz. the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LOS) from the moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) dataset during 2000–2019 for alpine grasslands across the three parallel rivers region (TPRR), and also examined the spatiotemporal heterogeneity of the three phenological parameters in seasonally frozen ground regions (hereafter referred to as SFGR) in response to climate change. The results showed that the multiyear mean SOS gradually delayed from 100 to 160 days along higher elevation, EOS advanced as a whole (from 320 to 280 days), and LOS shortened (from 210 to 130 days). The multiyear mean spatial distribution of all the three parameters showed significant north-to-south differences in the TPRR. In general, the variation trends in all the phenological parameters were not significant (p > 0.05) in the past 20 years, where SOS was advanced by 0.16 days year−l, EOS delayed by 0.08 days year−l, and consequently LOS extended at a rate of 0.07 days year−l, likely due to the warming and drying climate during the study period. In addition, annual mean temperature (AMT) was negatively correlated with SOS (50.26%) and positively correlated with EOS and LOS (72.25 and 60%, respectively). As for the annual mean total precipitation (AMP), it was positively correlated with SOS and EOS (50.77 and 52.97%, respectively) and negatively correlated with LOS (52.07%). Furthermore, a higher freezing index led to a delayed SOS and an advanced EOS and a shortened LOS at the regional scale. Similar to AMT, a higher thawing index advanced the SOS, delayed the EOS, and extended the LOS. Our results confirmed the importance of climate and permafrost status on vegetation phenological processes and also contributed toward understanding the response of cold region ecosystems to ...