College of Urban and Environment, Northwest University, Xi'an, 710127, China.
Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, The Chinese Academy of Sciences, Beijing, 100101, China.
Sci Rep. 2020 Nov 25;10(1):20591. doi: 10.1038/s41598-020-75845-5.
The Qin Mountains region is one of the most important climatic boundaries that divide the North and South of China. This study investigates vegetation covers changes across the Qin Mountains region over the past three decades based on the Landsat-derived Normalized Difference Vegetation Index (NDVI), which were extracted from the Google Earth Engine (GEE). Our results show that the NDVI across the Qin Mountains have increased from 0.624 to 0.776 with annual change rates of 0.0053/a over the past 32 years. Besides, its abrupt point occurred in 2006 and the change rates after this point increased by 0.0094/a (R = 0.8159, p < 0.01) (2006-2018), which is higher than that in 1987-1999 and 1999-2006. The mean NDVI have changed in different elevation ranges. The NDVI in the areas below 3300 m increased, such increased is especially most obviously in the cropland. Most of the forest and grassland locate above 3300 m with higher increased rate. Before 2006, the temperature and reference evapotranspiration (PET) were the important driven factors of NDVI change below 3300 m. After afforestation, human activities become important factors that influenced NDVI changes in the low elevation area, but hydro-climatic factors still play an important role in NDVI increase in the higher elevations area.
秦岭地区是中国南北气候的重要分界线之一。本研究利用 Google Earth Engine（GEE）提取的 Landsat 归一化植被指数（NDVI），研究了过去三十年秦岭地区植被覆盖的变化。结果表明，过去 32 年来，秦岭地区的 NDVI 从 0.624 增加到 0.776，年变化率为 0.0053/a。此外，其转折点发生在 2006 年，此后的变化率增加了 0.0094/a（R = 0.8159，p < 0.01）（2006-2018），高于 1987-1999 年和 1999-2006 年。平均 NDVI 在不同海拔范围内发生变化。海拔低于 3300 米的地区的 NDVI 增加，特别是在耕地中增加最为明显。大部分森林和草原位于海拔 3300 米以上，增加率较高。2006 年之前，温度和参考蒸散量（PET）是海拔低于 3300 米地区 NDVI 变化的重要驱动因素。造林后，人类活动成为影响低海拔地区 NDVI 变化的重要因素，但气候因素在高海拔地区 NDVI 增加中仍发挥着重要作用。
