Grassland coverage dynamics and its relationship to climatic factors at different spatial and temporal scales in the Three Rivers Source Region (TRSR) from 1982 to 2012 were analyzed based on MODIS-NDVI and GIMMS-NDVI data and climate data.The responses of the grassland coverage to climatic variations at annual and monthly time scales were analyzed.The results showed that grassland coverage distribution had increased from northwest to southeast across the TRSR during the study period.During 1982-2012,the mean grassland coverage of the TRSR was 48.73％ and exhibited spatial heterogeneity,being the highest (65.45％) in the source region of Yellow River and the lowest (4.25％) in the source region of Yangtze River.The mean grassland coverages of meadow,alpine and sub-alpine meadow,plain grassland,alpine and sub-alpine grassland,and desert grassland were 59.86％,57.39％,39.50％,33.70％,and 14.13％,respectively.The grassland coverage of the study area increased with a linear tendency of 0.23％ per year,of which the source region of Yellow River presented the fastest increasing trend (0.27％ per year).The grassland coverages in meadow,alpine and sub-alpine meadow,and plain grassland were mainly affected by temperature,whereas grassland coverages in desert grassland and alpine and sub-alpine grassland were affected more by precipitation.At the monthly timescale,grassland coverage had a one-month time-lag effect compared to temperature.However,there was less than one month or no time-lag effect for precipitation.After the Three Rivers Nature Reserve was founded,the growth of grassland coverage accelerated to some extent.Meanwhile,the sensitivity effect of temperature on grassland coverage increased throughout the entire district.In addition,the influence of precipitation on grassland coverage decreased in the source region of Yellow River.The ecological engineering and grassland protection measures have gained some achievements in the TRSR,whereas a falling trend of grassland coverage was exacerbated in some areas,especially desert grassland;therefore,greater attention should be paid to this region.%采用1982-2012年的多源遥感数据,结合像元二分模型,分析了三江源保护区不同时期代表性河流源区不同类型草地的植被覆盖度及其动态,并研究了草地植被覆盖度对气候因子的响应.结果表明,三江源草地覆盖度整体上呈现出西北低东南高的特征,全区草地平均植被覆盖度为48.73％,黄河源草地覆盖度最高(65.45％),长江源最低(4.25％),草甸、高山亚高山草甸、平原草原、高山亚高山草原和荒漠草原的平均植被覆盖度分别为59.86％、57.390％、39.50％、33.70％和14.13％;31年间全区草地覆盖度整体上呈现上升趋势,增长速度为每年0.230％,黄河源区的增长速度最快(每年0.27％);整体而言,低温比干旱对三江源草地覆盖度增长的限制作用更强,草甸、高山亚高山草甸和平原草原受气温影响较大,高山亚高山草原和荒漠草原受降水影响较大,在月尺度上草地覆盖度对气温表现出明显的滞后效应,而对降水不存在明显的滞后效应;三江源保护区成立(2001年)后,草地覆盖度的增长速度和增长面积都有所提升,全区草地覆盖度对气温的敏感度有所升高,黄河源草地覆盖度对降水的敏感度有明显下降.生态工程和草地保护措施整体上已经取得了一定的成效,但局部草地覆盖度下降趋势有所加剧,以荒漠草原最为突出,应在今后的保护工作中加以重视.
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