Abstract
Abstract. Vegetation phenology in Qinghai-Tibetan Plateau (QTP) has been proved to be more sensitive to climate change. The previous researches have reported divergent phonological responses of alpine vegetation in QTP from the analyses of remote sensing data, thus the demand for further analysis based on long-term observed vegetation data becomes more urgent. In the lack of long-term remote sensing monitoring data and ground observation data, phenology model simulation can be used as an effective remedy. In this study, we used a phenology model (unified model, UM) to simulate the green-up date for Kobresia pygmaea alpine meadow, and model evaluation shows that the unified model is able to make reasonable estimation for green-up date derived from satellite observations. Based on the phenology model and its parameters, spatial and temporal changes in green-up dates for Kobresia pygmaea alpine meadow in QTP from 1961 to 2016 were simulated, the results indicated that, the variation in green-up date presented an overall insignificant temporal trend with obvious spatial differences; furthermore, complex stage characteristics about the variation in green-up date were also clearly revealed, the period from 1991 to 2005 could be considered as a turning point, before which the trend was mainly in advan1ce and after which the trend was mainly in delay.
Highlights
Phenology is an excellent means by which the impact of climate change on vegetation can be detected and measured
Alpine vegetation in Qinghai-Tibetan Plateau (QTP) is characterized by a high elevation, low temperature and harsh conditions of the alpine environment, the plateau's alpine ecosystems is inherently fragile and instable, and numerous studies have shown that alpine vegetation phenology in this region is highly sensitive to climate change (Shen et al, 2011; Dong et al, 2012; Zhang et al, 2013; Ide et al, 2013; Che et al, 2014; Whenk et al, 2014; Wang et al, 2017; Zhu et al, 2018)
Cheng et al highlights the phenological property with an advancing green-up date for meadow in the eastern Tibetan Plateau from 1982 to 2014 (Cheng et al, 2018).Wang et al found that the green-up date of grassland in QTP primarily advanced with values of 0-2 days from 1985 to 2010 (Wang et al, 2018)
Summary
Phenology is an excellent means by which the impact of climate change on vegetation can be detected and measured. As an important indicator of climate change, phenology shifts of alpine vegetation in QTP have been a research focus during the past decade (Shen et al, 2015), previous work based on remote sensing investigations and field observations provided phenological data at different scales (Yu et al, 2010; Zhang et al, 2013; Zhou et al, 2014; Zhu et al, 2017), but up to now, the understanding about its temporal trend and spatial pattern is still insufficient. Ding et al reported that from 1999 to 2009, green-up dates of the alpine grassland advanced significantly (six days per decade) in the eastern Plateau (Ding et al, 2013). Zhao et al found that the trend of green-up date was postponed in QTP from 2001 to 2014, which was different from most regions of China (Luo et al, 2017). Ganjurjav et al (2016) proposed that the phenology has advanced in some years and at some locations in QTP since 2000, whereas it has been delayed in others (Ganjurjav et al, 2016). Zhang et al (2018) and Wang et al (2019) revealed that turning point of the greenup date metrics was near the year 1998, before which the greenup date advanced and after which the green-up date delayed, and temperature was found to be the dominant meteorological variable impacting phenology (Zhang et al, 2018; Wang et al, 2019). Piao et al (2011) reported that the vegetation green-up significantly advanced by 0.88 days year−1 from 1982 to 1999, but a marginal delaying trend is evidenced from 1999 to 2006 , there has no statistically significant trend of the vegetation green-up date from 1982 to 2006 at the regional scale (Piao et al, 2011). Yu et al (2010) indicated that during 1982-2006 for meadow and steppe vegetation in QTP, spring phenology
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