川渝地区NDVI动态特征及其对气候变化的响应

四川、重庆位于我国西南、长江上游地区，地形条件复杂，区内生态环境对气候变化较为敏感，作为我国现代农业发展区和长江中上游重要生态屏障，探究区域植被覆盖与气候变化之间的关系对该地区生态文明建设与农业可持续发展具有重要意义。基于归一化差值植被指数（NDVI）和气象数据（气温、降水），采用Sen趋势分析、MK检验和偏相关分析法，以农业地貌分区视角分析1999-2018年川渝地区植被覆盖的时空变化特征，以及植被NDVI与气温和降水之间的时空响应。研究结果表明：（1）川渝地区及各农业地貌分区植被NDVI在近20年均呈显著上升趋势，增长速率为盆周山地区（0.0073/a）>四川盆地区（0.0063/a）>川西南山地区（0.0050/a）>川西高山高原区（0.0026/a），整体年际变化率为0.0047/a。（2）川渝地区91.51%的NDVI像元值变化为正，空间上呈现出东高西低的总体分布格局，其中盆周山地区NDVI值最高为0.60，川西高山高原区NDVI值最低为0.44。（3）川渝地区整体上NDVI与气温和降水呈正相关，且气温（r=0.707，P<0.01）强于降水（r=0.535，P<0.05），空间上植被NDVI与气温和降水呈显著正相关区域分别占39.31%、18.92%。（4）不同农业地貌区植被生长与气候变化的响应关系呈现出明显差异。在川西高山高原区NDVI与气温呈显著的正相关关系，但与降水的关系不明显，其中阿坝-若尔盖-红原等高平原地区及西北部石渠等丘状高原地区受气温的显著正效应驱动尤为明显；在四川盆地区和盆周山地区NDVI与气温和降水均呈正相关，特别是东北部平行岭谷及低山丘陵区受气温和降水的正效应影响显著。研究有助于进一步理解川渝地区植被与气候变化的响应机制，并为促进川渝地区生态建设及发展提供参考依据。

Variation characteristic of NDVI and its response to climate change in the Sichuan-Chongqing region

Sichuan-Chongqing region is located in the southwest of China and the upper reaches of the Yangtze River. The terrain conditions are complex, and the eco-environment in the region is relatively sensitive to climate change. As China''s modern agricultural development zone and importantly ecological barriers in the middle and upper reaches of the Yangtze River, the research about the relationship between regional vegetation coverage and climate change is of great significance to the ecological civilization construction and agricultural sustainable development of the region. Based on the normalized difference vegetation index (NDVI), and meteorological data (temperature and precipitation), we analyzed the characteristics of the spatio-temporal changes of vegetation cover and its response to climate factors in the Sichuan-Chongqing region from 1999 to 2018 from the perspective of agricultural geomorphology by using Sen trend analysis, Manna-Kendall test and partial correlation analysis. The results indicated that:(1) the NDVI in the Sichuan-Chongqing region and each agricultural geomorphic area exhibited a significant upward trend in the past 20 years, and the growth rate was as follows:Mountain area in Sichuan Basin (0.0073/a) > Sichuan Basin (0.0063/a) > Highland of Southwestern Sichuan (0.0050/a) > Western Sichuan Alpine and Plateau (0.0026/a). The overall inter-annual change rate was 0.0047/a. (2) About 91.51% of the NDVI pixel values in the Sichuan-Chongqing region were positive, showing a general distribution pattern of high in the east and low in the west. The highest value of NDVI was 0.60 in the Mountain area in Sichuan Basin, and the lowest value of NDVI was 0.44 in the Western Sichuan Alpine and Plateau. (3) The NDVI was positively correlated with temperature and precipitation in the Sichuan-Chongqing region, and the correlation between NDVI and temperature (r=0.707, P<0.01) was stronger than that of precipitation (r=0.535, P<0.05). In terms of space, the area with significantly positive correlation between NDVI and temperature and precipitation accounted for 39.31% and 18.92%. (4) In different agricultural geomorphic regions, climate change had obviously different effects on vegetation growth. In the Western Sichuan Alpine and Plateau, the NDVI was positively correlated with temperature, but not with precipitation. The NDVI was significantly affected by temperature and mainly distributed in the Aba-Zoige-Hongyuan flat plateau and Shiqu hilly plateau areas. In the Sichuan Basin and Mountain area of Sichuan Basin, the NDVI was positively correlated with temperature and precipitation, especially parallel ridge valley and low hilly area in the northeast, which was significantly affected by temperature and precipitation. The results help to further understand the relationship between vegetation and climate change in the Sichuan-Chongqing region, and provide scientific support for promoting ecological construction and development of the region.