Spatial-temporal characteristics of vegetation coverage and its relationship with environmental factors in the Three-river headwaters region

In order to explore the temporal and spatial characteristics of vegetation coverage and its relationship with environmental factors in the Three-River headwaters region, this study adopted MODIS MYD13Q1 land vegetation data product with a spatial resolution of 250 m and a time interval of 16 days. The vegetation coverage was retrieved based on the improved pixel binary model, and the relationship between the elevation, temperature and precipitation data was analyzed. The results show: 1) From the spatial feature, the vegetation coverage gradually increases from northwest to southeast in the three-river headwaters region, and the boundary is more obvious. The overall vegetation coverage distribution in the three-river source region is as follows: the source region of the Yellow River > the source region of the Yangtze River > the source region of the Lancang River. 2) From the temporal characteristics, In 2019, the monthly normalized vegetation index showed obvious seasonal changes. From January to July, the normalized vegetation index increased from 0.06 to 0.29, and then decreased to 0.09 from August to December. From 2000 to 2019, the average annual vegetation coverage showed a slow upward trend on the whole, with the vegetation coverage between 0.40 and 0.45. In 2015, there was a process of first declining and then rising. 3) Environmental factors: On the whole, the vegetation coverage decreased with the increase of elevation, and the value of normalized vegetation index reached the maximum at 3900-4000 m. Locally, there is a fluctuation at 4500 m; The correlation coefficients between accumulated annual precipitation and accumulated annual mean temperature and NORMALIZED vegetation index are 0.26 and 0.72, respectively, indicating that temperature has a great influence on vegetation coverage.