Analysis of spatiotemporal changes and influencing factors of NDVI in the permafrost area of the Tuotuo River source area on the Qinghai-Xizang Plateau
As a sensitive region to global climate change,the climate of the Tibetan Plateau has gradually changed to a warm and humid state in recent decades,and this change and the resulting permafrost changes have directly affected the hydrothermal conditions for vegetation growth. The normalized difference vegetation index (NDVI) is an important variable to characterize the growth of vegetation,and its time-series variation can well reflect the response of vegetation to natural factors. In order to more accurately characterize the impact of cli-mate change on vegetation growth in the permafrost areas of the Qinghai-Tibet Plateau,this study selected the source of the Tuotuo River,where permafrost is relatively continuous,as the study area. Based on Landsat NDVI data,trend analysis,partial correlation analysis,and geographic detectors were used to analyze the response characteristics of NDVI in the vegetation growing season (May-September) in the study area from 2000—2021 to climate change and different terrains and vegetation types. The results show that:(1) NDVI in the growing season in the source area of the Tuotuo River showed an overall fluctuating growth trend during 2000—2021,with a growth rate of 0.013 (10a)-1,of which the NDVI growth rate was faster during the period of 2000—2010[0.019 (10a)-1],and then slowed down to half of the growth rate of NDVI during the period of 2011—2021[0.011 (10a)-1]. The interannual changes of NDVI in different vegetation types were analyzed,and it was found that the better the vegetation development,the faster the growth rate of NDVI,among which the fastest growth rate was found in alpine swamp meadow[0.018 (10a)-1]and alpine meadow[0.017 (10a)-1],followed by alpine grassland[0.015 (10a)-1],and the slowest growth rate of NDVI was found in alpine desert grassland[0.009 (10a)-1]. The analysis of the inter-annual changes of NDVI in different terrain areas showed that the growth rate of NDVI increased and then decreased with the elevation,and the growth rate was faster between 4700～5300 m[>0.02 (10a)-1];The growth rate of NDVI showed a trend of increasing first and then decreasing with the change of slope,and the fastest growth rate[0.023 (10a)-1]was found in the gentle slope area with a slope of 2°～6°;the growth rate of NDVI decreased with the increase of the thickness of the active layer of perma-frost,and the fastest growth rate[0.029 (10a)-1]was found when the thickness of the active layer was less than 150 centimeters. (2) On the spatial scale,the areas with an increasing trend of NDVI in the growing season in the source area of the Tuotuo River during the period of 2000—2021 accounted for a total of 82.1％ of the total area of the study area,and the area with a highly significant increasing trend accounted for 27.0％,which was mainly distributed on both sides of the river at lower elevations and in the areas near the glacier;and the areas with decreasing trend of NDVI accounted for 16.0％,which was mainly distributed in the northern part of the study area in the alpine desert grassland areas in the northern part of the study area. (3) From 2000—2021,the source area of the Tuotuo River showed an overall trend of warming and humidification,and precipitation,air temperature,solar radiation and soil water content all showed fluctuating upward trends in the growing season. 2000—2021 NDVI changes in the source area of the Tuotuo River in the growing season were most significantly affected by soil water content,and warmer temperatures would prompt the melting of the cryosphere and in-crease soil water content,which would improve the growth status of the vegetation;NDVI changes in the grow-ing season showed the same trend as precipitation;NDVI changes in the growing season showed the same trend as precipitation. NDVI changes in the growing season were positively correlated with precipitation;the correla-tion between NDVI changes in the growing season and air temperature varied widely in space,with 55.4％ of the regions showing a positive correlation and 43.8％ showing a negative correlation;and NDVI changes in the growing season were negatively correlated with the solar radiation as a whole. Increased precipitation in the growing season in the source area of the Tuotuo River promoted vegetation growth in the meadow area more than in the grassland area;changes in air temperature promoted vegetation growth in the meadow area more than in the grassland area,and inhibited vegetation growth in the grassland area more than in the grassland area. (4) The spatial differentiation of NDVI in the study area is mainly influenced by soil water content,climate factors and slope,and the influence is greatest when soil water content and slope interact. This paper quantifies the ef-fects of climatic factors and their interactions on vegetation changes using various methods through the study of NDVI changes in the source area of the Yangtze River,which further reveals the influence mechanism of region-al climatic and environmental factors on NDVI changes,and provides a new basis for the study of vegetation changes and ecological environmental protection in the Tibetan Plateau region.
Qinghai-Xizang PlateauLandsat NDVIspatial and temporal variabilitydriving factors
万方数据
维普
