Quantifying the phenological variations of Populus euphratica (P. euphratica) resulting from climate change is vital for desert ecosystems in extremely arid regions. P. euphratica phenology and its response to climate change are lacking in extremely arid area. In this study, a modified method was proposed to explore P. euphratica phenology and its response to climate change using 15-year Global LAnd Surface Satellite (GLASS) leaf area index (LAI) time-series data (2002–2016) in the upper Tarim

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... iver basin. The start of the growing season (SOS), length of the growing season (LOS), and end of the growing season (EOS) were obtained with the dynamic threshold method from the reconstructed growth time series curve by using the Savitzky-Golay filtering method. The grey relational analysis (GRA) method was utilized to analyze the correlation between the phenological features of P. euphratica and climatic factors. Importantly, we also revealed the positive and negative effects between interannual climate factors and P. euphratica phenology using the canonical correlation analysis (CCA) method, and the interaction between the SOS in spring and EOS in autumn. The results revealed that the SOS of P. euphratica was delayed by about 5.3 days/10a, while EOS was advanced by about 3.1 days/10a. The phenology of P. euphratica was extensively changed, with high spatial heterogeneity. Spring sunshine duration (SD) and average air temperature (AT) controlled the SOS and EOS, although the impacts of average relative humidity (RH) and precipitation (PR) on phenology cannot be overlooked. The SOS was positively correlated with the EOS, implying a later SOS may generally be accompanied by a later EOS. Global warming may lead to SOS advance and EOS delay, and the increase of SD may lead to later SOS and earlier EOS. Groundwater was found to be a key factor for controlling P. euphratica phenology than runoff in this region.