Abstract:

Greenness can reflect the quality of surface ecological environment. Studying the temporal and spatial variation characteristics of surface greenness and the law of topographic differentiation in Qaidam Basin under the background of climate change will help understand the law of vegetation change in Qaidam Basin in recent years, and provide a theoretical basis for Qaidam basin to deal with climate change and ecological environment construction. The temporal and spatial evolution trends, topographic differentiation characteristics and the influence of climate factors of surface greenness over Qaidam Basin from 2000 to 2021 were analyzed by using Sen+M-K trend analysis method and correlation analysis method based on MODIS NDVI remote sensing data, DEM, meteorological data and snow area data. The results showed that (1) from 2000 to 2021, NDVI in Qaidam Basin showed the characteristics of centripetal ring distribution with high edge and low hinterland changing regularly with the altitude. High value areas were mainly concentrated in the foothills and internal oases around the basin, with an average value of more than 0.3, while most areas in the hinterland of the basin were less than 0.1, and 65.62% of the regional NDVI showed a fluctuating increasing trend, accounting for 53.04% of the areas that showed significant increases, with an average increasing rate of 1.8×10^-3 a^-1. (2) There was an obvious variation trend of NDVI and NDVI in Qaidam Basin from 2021 to 2021. As a whole, it changed in a parabola with the rise of altitude. Among them, the NDVI of 4.25-4.75 km was the highest with more than 0.30 value; The annual increase rate of NDVI between 3.5-4.5 km was fast, all exceeding 2.75×10^-3 a^-1;The north slope of NDVI was greater than the south slope; the west slope was greater than the east slope; the northwest slope was the largest, which was 0.19; and the NDVI increase rate of the northwest slope was the fastest, which was more than 1.93×10^-3 a^-1. (3) The obvious “warm and humid” climate change characteristics of Qaidam Basin in the growing season from 2000 to 2021 were the main reasons for the improvement of surface greenness. The increase of precipitation, the increase of snow days and the acceleration of glacier melting rate were important driving factors. The water and heat matching at different altitudes and the climate differences of precipitation, snow melting water and solar radiation in different slope directions led to the differences in the distribution and change of NDVI.

Key words: Qaidam Basin, NDVI, surface greenness, climate change, altitude, slope direction

摘要：

绿度可以反映地表生态环境质量,研究气候变化背景下柴达木盆地地表绿度时空变化特征和地形分异规律,有助于了解近年来柴达木盆地植被变化规律,为柴达木盆地应对气候变化和生态环境建设提供理论依据。基于MODIS NDVI（Normalized Difference Vegetation Index）遥感资料、DEM、气象数据和积雪面积数据,综合利用Sen+M-K趋势分析法、相关性分析法,分析了2000—2021年柴达木盆地地表被绿度的时空演变趋势、地形分异特征、气候因子的影响。结果表明,（1）2000—2021年柴达木盆地NDVI呈边缘高、腹地低的向心环状分布特征,随海拔变化规律性明显。高值区主要集中在盆地外围的山麓及内部绿洲地区,均值普遍大于0.3,而盆地腹地大部地区小于0.1,65.62%的区域NDVI呈波动增加趋势,显著增加区域占比53.04%,平均增加速率为1.8×10^-3 a^-1。（2）2000—2021年柴达木盆地NDVI及其变化趋势存在明显的海拔和坡向分异。整体随海拔上升呈抛物线型变化,其中,4.25—4.75 km的NDVI较高,超过0.30;3.5—4.5 km的NDVI年际增加速率较快,均超过2.75×10^-3 a^-1;NDVI北坡大于南坡、西坡大于东坡,西北坡最大,为0.19,且西北坡的NDVI增加速率最快,超过1.93×10^-3 a^-1。（3）2000—2021年生长季柴达木盆地明显的“暖湿化”气候变化特征是地表绿度改善的主要原因,降水量增多、积雪日数增多、冰川消融速率加快是重要的驱动因素,不同海拔的水热匹配和不同坡向的降水及冰雪融水、太阳辐射的气候差异造成了NDVI分布和变化的差异。

关键词: 柴达木盆地, NDVI, 地表绿度, 气候变化, 海拔, 坡向