遥感分析天山北部植被覆盖对气候变化的多时间尺度响应

Response of climate changes on vegetation cover in north of Tianshan Mountains evaluated using multiple time scales

为分析植被-气候关系在时间上的多尺度特征,该研究首次以1981-2009年29 a归一化植被指数(normalized difference vegetation index,NDVI)和同期降水、温度数据为基础,采用小波互相关分析研究了中国新疆天山北部额尔齐斯河流域、天山北坡、准噶尔西部山地、博尔塔拉谷地和伊犁河谷区5个分区、29 a植被覆盖变化特征及其对区域降水、温度变化在不同时间尺度和时滞下的响应关系。结果表明:各分区降水和温度变化对NDVI变化存在明显的多时间尺度响应关系和时滞效应。对于降水,除准噶尔西部山地,其他各区域最能反映响应关系的时间尺度为15旬,时滞为5旬(准噶尔西部山地时滞为2旬);对于气温,各区域最能反映响应关系的时间尺度为15旬(准噶尔西部山地时间尺度为10旬),时滞为2旬。各区域NDVI变化与前期温度变化的相关性(0.587)高于与前期降水变化的相关性(0.456)。该研究对于监测植被覆盖变化、研究地气相互作用具有重要意义。

Climate is related with vegetation on regional and even global scales, and climate affects spatial distribution of vegetation. Studies on correlation between NDVI and changes in climate using different time scales and different regional condition are helpful to reveal the effects of climate changes on vegetation. This study investigated the characteristics of vegetation change and its response to precipitation and temperature change during the 29 years （1981-2009） in the north of Tianshan Mountains in Xinjiang Province by the method of wavelet cross-correlation technique combined with trend analysis. The explored study area included Irtysh River, Bortala Valley, Ili River Valley, the northern slope of the Tianshan Mountains and the western Junggar Basin. These regions are far from the sea and surrounded on three sides by the Tianshan Mountains, Tarbagatai Mountains, and Altai Mountains, creating a special climate system which was an ideal environment for the study of regional climate-vegetation interactions. The daily meteorological data from January 1, 1981 to December 31, 2009 were collected from NOAA/AVHRR NDVI digital images （1981-2001） and SPOT-4 VEGETATION NDVI digital images （1998-2010）. The results showed that in the northern Tianshan Mountains, temperature and precipitation change had similar tendencies except for the northern slopes of the Tianshan Mountains and in the Junggar Basin. The increase in the humid index decreased from the southwest to the northeast. Temperature increase may be primarily responsible for regional drying, while precipitation changes directly affected regional dryness and wetness. The annual mean NDVI distinctly differed among the six regions and it increased in the Bortala Valley, Ili River, Junggar Basin, and the mountains west of the Junggar Basin. The annual maximum NDVI decreased in all the regions except for the Junggar Basin. The correlation between early changes in climate and subsequent vegetation had multiple-time-scale characteristics, and all the regions showed similar overall correlations on different time scales. Time lag was another characteristic affecting the process above. The suitable time scale and time lag reflecting the response of vegetation to precipitation change was 15 ten-day periods and 5 ten-day periods except for the western Junggar Basin where time lag was 2 ten-day periods. The useful time scale and time lag reflecting the response of vegetation to temperature was 15 ten-day periods except the western Junggar Basin where the time scale was 10 ten-day periods and 2 ten-day periods, respectively. The correlation between NDVI change and early changes in temperature （0.587） was higher than that between NDVI and early changes in precipitation （0.456）. The response of vegetation to climate change suggested that the effects of climate change on vegetation could differ greatly with time lags. This study could provide theoretical support for vegetation coverage monitoring, and enrich the knowledge about the complex climate-vegetation relationships.