Abstract:

Lake ice phenology is considered to be an accurate indicator of regional climate change. This work studies the changes in the ice characteristics of the large lakes in Xinjiang, China. The lakes chosen in this study are equally distributed in the oasis and mountain areas. With their different geographical locations, the evolution and ice conditions of the lakes are influenced by human activities to different extents; thus, these lakes are ideal research items for research on arid-semiarid areas. This study conducts an analysis predominantly based on long term MODIS and Landsat data, which is used to reveal the phenological characteristics of lake ice on the large lakes in Xinjiang during the period 2000—2019 via multiband threshold analysis, trend analysis, and other methods. The results of this work can be summarized as follows: (1) Lakes in Xinjiang begin to freeze in the period from October to December every year, and their ice cover periods end in the period from March to June; during the study period the lakes that exhibited a freeze-up start (FUS) increasingly late in the year were Bosten Lake, Sayram Lake, Ebinur Lake, Jingyu Lake, Ulunggur Lake, and Surigh Yilganing Kol Lake; the rate of change of the FUS was between 0.51-1.53 d·a^-1. The break-up start occurred later in the year for Ayakkum Lake, Aksayqin Lake, and Aqikkol Lake; the change rate of this trend was found to be -1.04 d·a^-1, -0.41 d·a^-1, -0.31 d·a^-1, respectively. (2) The complete freeze duration (CFD) is one of the most important parameters in ice phenology, which can be used to directly represent the process of climate change. Most lakes showed a decrease in CFD between the years 2000 and 2019, among them Ebinur Lake, Jili Lake, and Bosten Lake had significant reduction in CFD, with a rate of change of -1.76 d·a^-1, -2.13 d·a^-1, -0.81 d·a^-1, respectively, whereas Ayakkum Lake has the highest increase in CFD among all lakes in Xinjiang (3.51 d·a^-1). (3) The variations in phenology and evolution of the ice cover of the Xinjiang large lake are the result of local and climate-related factors. The temperature, lake morphology factors, lake area, and shape of the shore line are found to be the principal factors that affect the phenology of lake ice. However, the effect of lake salinity and geological structure of lake ice evolution cannot be neglected. As the climatic conditions of Xinjiang has evolved toward being warmer and wetter, most lakes show a reduction in CFD. This study on the phenological characteristics of lake ice on the many lakes in Xinjiang provides data related to arid/semiarid areas that until now have lacked data and provides more accurate parameter indicators and a scientific basis for studying climate change.

Key words: large lakes, lake ice phenology, variation characteristics, multi-band threshold, MODIS