气候变化和工程活动对青藏铁路沿线植被指数时空变化的影响

基于1982—2015年的GIMMS NDVI3g+及同期气候数据,利用最大值合成法获得青藏铁路沿线直接影响区和生态背景区的年内NDVI最大值、年际NDVI平均值,对其进行了趋势分析、变异分析、气候相关分析和残差分析,部分结果用MODIS NDVI（2001—2018年）进行了验证。研究表明：① 青藏铁路年际NDVI高度响应气候变化和工程活动,即施工前主要响应气候变化,年际NDVI呈缓慢上升趋势;施工中主要响应工程活动,年际NDVI呈显著下降趋势;运营中响应气候变化和工程活动的综合影响,年际NDVI呈缓慢上升趋势。② 青藏铁路的工程活动对沿线植被有显著影响。即施工前直接影响区和生态背景区年际NDVI增长率相近;施工中直接影响区年际NDVI增长率低于生态背景区;运营中直接影响区年际NDVI增长率高于生态背景区。③ 研究利用时空不变量,剔除了植被覆盖的空间异质性分量、周期性绿度分量,甄别出了气候变化与工程活动的贡献量。

Impact of climate change and engineering activities on spatio-temporal changes of vegetation index along Qinghai-Tibet Railway

The fragile ecological zone of the Tibetan Plateau is extremely sensitive to human activities and global changes. To reveal the response characteristics of the normalized difference vegetation index (NDVI) to engineering activities and climate changes in the direct impact area and ecological check area (CK) of the Qinghai-Tibet Railway construction, GIMMS AVHRR NDVI3g plus data (1982-2015), MODIS NDVI data (2001-2018), and meteorological data from the same period were selected in this study. Using the maximum value compositing (MVC) method, the annual maximum NDVI and interannual average NDVI of the direct impact area (8-km buffer zone) and CK (16-km buffer zone) along the Qinghai-Tibet Railway were obtained, and trend, variation, correlation, and residual analyses were performed. The results show the following aspects. (1) Using spatio-temporal pseudo-invariant features, the spatial heterogeneity component and periodic greenness component from vegetation coverage were eliminated, and the contribution of climate change and engineering activities were identified. (2) The annual NDVI along the Qinghai-Tibet Railway was highly responsive to climate change and engineering activities. In the early stage of construction, the annual NDVI mainly responded to climate change, and the annual NDVI showed a slowly rising trend. In the middle stage of construction, it mainly responded to engineering activities, and the annual NDVI showed a significant downward trend. In the operation of the railway, it responded to a combination of climate change and engineering activities, and the annual NDVI slowly increased. (3) The engineering activities of the Qinghai-Tibet Railway had a significant impact on the vegetation along the railway. In the early stage of construction, the annual NDVI growth rates in the direct impact area and CK were similar. In the mid-construction period, the annual NDVI growth rate in the direct impact area was lower than that in the CK. In the operation of the railway, the annual NDVI growth rate in the direct impact area was higher than that in the CK. (4) From 1982 to 2015, climate change along the Qinghai-Tibet Railway responded significantly to global change. In the Xining-Golmud section, the temperature increase rate was 0.57°C/10a, and the precipitation growth rate was 4.67 mm/10a; in the Golmud-Lhasa section, the temperature increase rate was 0.20°C/10a, and the precipitation growth rate was 1.78 mm/10a. Both temperature and precipitation increased.