为了了解川西高原植被EVI的时空变化特征,以MODIS-EVI数据、DEM数据和气象格点数据为基础,基于相关性分析、趋势分析和最大值合成等方法,探讨了川西高原2001-2020年植被EVI时空变化特征及不同海拔高程下植被EVI分布和变化规律.在此基础上,对研究区植被EVI时空变化的气候因子驱动力进行了分析研究.结果表明:(1)川西高原20年间植被EVI均值介于0～0.88,空间分布具有明显的地域分异.(2)近20 a来,川西高原植被EVI整体增长趋势,速率为1.0％/10 a,植被EVI的相对年际变化率介于-4.26％～13.58％.有13.09％的地区植被EVI变化通过显著性检验,其中约10.18％的区域植被EVI呈增加趋势.(3)川西高原近20 a不同海拔高程下植被EVI都呈波动增加趋势,变化速率以及增加趋势的显著性都有明显的差异.在＜2 500 m,2 500～3 000 m,4 500～5 000 m 3个海拔高程区间内,植被EVI增加趋势显著.(4)川西高原植被EVI与气温和降水呈正向相关的区域面积占比分别为56.42％,64.09％.在0.05显著性水平下,川西高原植被EVI变化受气候因子驱动的地区约占研究区总面积的21.87％.整体而言,近20 a来川西高原植被EVI呈增加趋势,且具有明显空间差异,EVI与气温和降水整体呈正向相关.川西高原大部分地区的植被EVI变化受非气候因子驱动.

[Objective] The vegetation change and important climate factors influencing fractional vegetation coverage (FVC) in Sichuan Province were analyzed in order to provide theoretical support for the sustainable development of natural resources in this area. [Methods] Based on the MODIS-NDVI dataset for Sichuan Province from 2000 to 2020, FVC for the study area from 2000 to 2020 was statistically analyzed, and its spatiotemporal variation characteristics and relationships with climate factors were analyzed. [Results] ① The FVC of Sichuan Province tended to be stable, and the average FVC value was about 0.50. ② FVC exhibited obvious spatial heterogeneity. FVC in the east was higher than in the west, and presented an increasing spatial distribution pattern from northwest to southeast. ③ The areas with high FVC in Sichuan Province accounted for about 70% of the total area, and the overall vegetation status was good. There were signs of slow growth in FVC over time. ④ FVC changes in the study area were positively and negatively correlated with air temperature and precipitation, and the area proportions were close to each other. ⑤ The driving forces of FVC change in Sichuan Province were mainly non-climate factors, and the area driven by climate factors accounted for 21.17% of the total area. [Conclusion] Sichuan Province has complex topography. The good climatic conditions, vigorous vegetation growth, and stable FVC experienced over a period of many years has maintained the ecological environment of the middle and upper reaches of the Yangtze River. In the future, Planners and officials should give more attention to the impacts of human activities FVC, and actively build an ecological barrier in the middle and upper reaches of the Yangtze River.

植被物候是植被生长发育、枯萎凋落的周期性变化现象,揭示植被物候变化及其对水热因子的响应机制具有重要的生态意义.采用两种动态阈值分别提取川西高原近20 a森林植被、草地的生长季开始期(Start of Growing Season,SOS)和生长季结束期(End of Growing Season,EOS),利用Theil-Sen Median(Sen)趋势分析、偏相关系数分析植被物候的变化特征及其对季节性气温、降水的响应.结果表明,(1)川西高原植被平均SOS以70—130 d为主,平均EOS以260—290 d为主;植被SOS整体呈提前趋势、EOS整体呈推迟趋势,SOS的平均变化速率大于EOS;植被SOS平均提前速率为2.4 d·(10 a)?1(α=0.05),EOS平均推迟速率为1.4 d·(10 a)?1(α=0.05);草地和森林植被SOS平均提前速率大致相同,分别为2.4 d·(10 a)?1、2.3 d·(10 a)?1;草地EOS平均推迟速率1.4 d·(10 a)?1,小于森林植被2.2 d·(10 a)?1.(2)温度是影响植被SOS、EOS变化的主要因素.春季温度上升导致大部分植被SOS提前,这种现象在草地和森林植被间都很常见;冬季温度上升并不能使植被SOS出现普遍提前,且由于冬季温度升高可能会影响植被的春化作用,部分植被SOS甚至与冬季温度呈正相关;秋季温度上升是植被EOS推迟的主要因素,对草地的影响尤其显著;部分植被EOS与夏季温度呈负相关,这可能与夏季温度上升产生的水分胁迫以及植被生长周期的提前结束有关.(3)冬春季降水对植被SOS的影响不明显;夏季降水减少虽然对EOS有提前效应,但秋季降水增加以及升温对植被EOS的推迟作用强于夏季降水减少所带来的影响.

基于MOD10A2数据对2001-2020年川西高原积雪的时空变化特征及其影响因素进行分析.结果表明:1)川西高原积雪覆盖率(SCP)年内分布呈双峰型周期变化趋势.2)2001-2020年来川西高原SCP整体呈缓慢减少的趋势.3)川西高原积雪覆盖频率(SCF)的空间分布差异明显,SCF随海拔的增高而增长,且迎风坡和阴坡的SCF高于背风坡和阳坡.4)整体上,川西高原SCF与气温总体相关性为负、与降水总体相关性为正.气温对积雪覆盖频率变化的影响更显著.

The climate-induced spatio-temporal evolutionary characteristics of glaciers have a strong response in understanding the surface earth system processes, including hydrology, ecology, and topography. With use of multispectral remote sensing, this study explores the longtime glacier shrinkage evolution and their geographical features of Gongga Mountain glaciers (i.e. Gongga Mountain glacier group), in eastern Qinghai-Tibetan Plateau, China. We used a band ratio and decision-tree classification mixed method to automatically delineate Gongga Mountain glaciers shrinking nature. Based on the multispectral Landsat images over nearly 30 years, the long-time spatiotemporal shrinkage evolution of Gongga Mountain glaciers was extracted, in which the glacier shrinkage area changes are consistent with the results from previous works. This study analyzed the nature of shrinking glaciers with topographic derivatives (i.e., different glacier scale, altitude, slope gradient, and slope direction). We noticed that the characteristic of shirking glaciers is associated with the topographic variables. The maximum shrinkage was concentrated at altitudes of 5000-5500 m, and a slope angle of 30 degrees in the south direction. Findings shed light that glaciers in our study area are correlated with temperature changes and precipitation with a correlation coefficient of-0.97 and 0.35, respectively, suggesting that the decreasing glaciers are highly correlated with the temperature increase. This study implies the usefulness of remote sensing in understanding the long-time ecological environment change and helping manage the potential glacial disasters in eastern Qinghai-Tibet Plateau. (C) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.

冰川时空演化不仅对河川径流、生物生存环境、地表形态产生巨大的影响,而且冰川本身对气候变化有着强烈的响应. 在全球气候变暖背景下,对冰川长时间演化过程进行监测具有重要意义. 文章利用TM影像、OLI影像,通过非监督分类法、监督分类法、比值阈值法、雪盖指数法(NDSI)、基于多尺度分割的面向对象法、基于神经网络的冰川识别方法对梅里雪山地区的冰川信息进行提取. 结果表明,基于神经网络的冰川识别方法对于裸冰区及冰碛覆盖区的冰川信息提取效果相对较好,提取精度最高. 在此基础上,基于ENVI深度学习模块,利用神经网络分类法解译1989、1998、2009年和2019年梅里雪山地区的冰川信息,并结合Google Earth和DEM数据,对其进行目视修正,最终得到了1989—2019年梅里雪山地区冰川边界变化图,结果显示1989—2019年梅里雪山地区的冰川退缩了23.77 km2,年均退缩0.79 km2,面积相对退缩率为17.03%,年均相对退缩率为0.57%.