The Spatiotemporal Changes and Influencing Factors of Vegetation NDVI in the Hehuang Valley of Qinghai Province from 2000 to 2020

Abstract

[Objective] This study is aimed to understand the spatiotemporal changes in vegetation in the Qinghai Hehuang Valley and clarify the effects of climate change, land development and utilization and human activities on vegetation change. [Methods] The MODIS NDVI dataset from 2000 to 2020 was used to characterize vegetation changes. Based on Theil-Sen Median trend test, partial correlation analysis, geographical detectors and other methods, this paper explored the spatiotemporal changes of NDVI in Qinghai Hehuang Valley and its relationship with temperature, precipitation, slope, soil type, human activities and other influencing factors. [Results] (1) In the past 20 years, the vegetation NDVI in the Hehuang Valley region had shown a fluctuating growth trend, with a significant increase in the area of 2.21×104 km2 (p<0.05), accounting for 53.39% of the total area of the Hehuang Valley. The area with a significant decrease in vegetation NDVI was 7.04×102 km2 (p<0.05), mainly distributed in the central part of the Huangshui Valley, accounting for 1.69% of the total area. (2) In terms of natural factors, the areas, in which NDVI was positively correlated with temperature and precipitation, accounting for 50.32% and 80.14% of the total area, respectively. The areas with significant vegetation increase were mainly distributed in areas with an altitude of 2 800~3 100 m, slope of 15°～20°, and a north facing slope. Within the range of elevation less than 3 200 m, vegetation NDVI changes showed an upward trend with the increasing of elevation, with a significant increase in the area accounting for 54.37% of the total area. In terms of human activity factors, the areas, in which NDVI was positively correlated with population density and nighttime lighting, accounting for 50.52% and 38.53% of the total area, respectively. Vegetation NDVI showed a significant upward trend in forests, shrubs, grasslands and construction land. (3) Based on the partial correlation analysis and the attribution analysis of vegetation NDVI changes by geographic detectors, it could be concluded that that there were obvious differences in vegetation changes among different soil types. Annual rainfall and human activities were the main influencing factors for vegetation NDVI changes in Hehuang Valley. The interaction between various influencing factors presented mutually reinforcing and non-linear enhancing relationships. [Conclusion] The spatiotemporal changes of vegetation NDVI in the Hehuang Valley were revealed, and the driving mechanisms of natural and human factors on vegetation NDVI changes were clarified, which could provide theoretical support for the future ecological protection, construction planning and the implementation of ecological engineering in Hehuang Valley of Qinghai Province.

Keywords

• hehuang valley
• ndvi
• spatiotemporal variations
• climate change
• human activity
• geographic detector