Abstract: Lakes in alpine regions remain sensitive to regional climate change,mapping and monitoring of these lakes would facilitate our understanding of regional climate change. However,few observational data is available due to its low accessibility. Remote sensing provides an efficient tool to map and monitor these lakes with long spatial-temporal data. As the largest alpine lake in the western Tianshan Mountains of Xinjiang,Sayram Lake had become eutrophic during last decades. In order to analyze its spatio-temporal changes during the last 30 years, 155 multi-source remote sensing images from 1989 to 2014 were used to map lake area changes. The hydro-metrological data were also used to discuss the factors for lake changes under the climate change conditions. The results show resource environment satellite images of 30 m resolution can map the minor lake changes effectively; and the time-series analysis performs well in describing the temporal procedures of lake area changes. The annual areal curve of the Sayram Lake shows an overall increasing trend in recently years. In detail,the expanding rates accelerated during the periods 1993-1998 and 2001-2005,while ascended gently after 2005. The seasonal characteristics of lake area curve shows the lake was totally ice-covered from January to March. The lake area was increasing from June to August,while decreasing during the periods of April-May and September-October. The spatial distribution characteristics show the directions of the expanding lake boundary were in west and north-west, where the land was low and flat,mainly covered by grassland,it is because that the prevailing wind direction is east to west,which makes the lake extent eroded easily in wind direction. Meteorological records for the last 30 years show that lake areal change had good correlation with precipitation,and lake shrink-expand was the indicator of climate change from dry-cold to wet-warm. However,the negative impact by climate change on Sayram Lake was obvious,lake shorelines were eroded severely by the rising lake surface,and risks of the road collapse near the shorelines were also increasing. The progressively development of tourism industry and overgrazing of the livestock's,together led to the rangeland degradation and eutrophication aggravation. Therefore,controlling reasonably the grassland development and reduction of grazing capacity,strengthening the local ecological restoration and controlling comprehensively the pollution source of the lake are very important tasks for protecting Sayram Lake ecology.

Key words: Sayram Lake, lake area, spatio-temporal characteristics, climate change, remote sensing