Welcome to Acta Prataculturae Sinica ! Today is Share:

Acta Prataculturae Sinica ›› 2021, Vol. 30 ›› Issue (9): 1-14.DOI: 10.11686/cyxb2020398

   

Dynamic monitoring of grassland resources and their responses to environmental factors in Qinghai Province based on analyses of daily MODIS NDVI data from the past 20 years

Xin YANG1(), Wen-xia CAO1, Xiao-jun YU1, Hai-bin WANG2, Yuan-yuan HAO1()   

  1. 1.College of Pratacultural Science,Gansu Agricultural University,Key Laboratory of Grassland Ecosystem,Ministry of Education,Lanzhou 730070,China
    2.The Administration Committee of Yellow River Source National Park,Three-river-source National Park,Guoluo 813599,China
  • Received:2020-08-24 Revised:2020-12-14 Online:2021-08-30 Published:2021-08-30
  • Contact: Yuan-yuan HAO

Abstract:

Dynamic monitoring using remote sensing technologies is an important means to clarify the spatio-temporal dynamic changes in grassland vegetation, and an effective basis to explore the responses of grassland vegetation to environmental factors. Using MOD09GA data, we explored the spatio-temporal dynamic changes in grassland vegetation NDVI (normalized difference vegetation index) in Qinghai Province from 2000 to 2019 on various time-scales (e.g., daily, ten-day, monthly, annual) by conducting qualitative and quantitative analyses. The relationships between grassland vegetation and various environmental factors (elevation, slope, aspect, temperature and precipitation) were determined using the maximum value composite method, monadic regression trend analysis, and correlation analysis. The overall aim of this study was to provide a theoretical basis for ecological protection and the development of high-quality vegetation resources at the source of the Yellow River. The main results were as follows: 1) The daily change in the NDVI of grassland vegetation showed a stable trend. During the 20-year period, the 10-day fluctuation in NDVI increased, peaked in 2010, and then decreased, but the overall trend was an increase over time. In addition, the re-greening period became earlier and the peak date became concentrated and later, indicating that grassland grew better and its growth period was extended. The multi-year average NDVI gradually increased from northwest to southeast. 2) Grassland quality decreased from southeast to northwest. The area of high-quality grassland decreased at both sides of the study area, with the center at 4500-5000 m. The area of ordinary grassland decreased, then increased, then decreased with increasing elevation. The area of degraded grassland decreased with increasing elevation. The area of all types of grassland gradually decreased with increasing slope, and as the slope direction changed from shaded to sunny and to half-shaded and half-sunny. 3) From 2000 to 2015, both precipitation and temperature increased, with increases in temperature being more marked. Precipitation and temperature tended to decrease from southeast to northwest. Precipitation and temperature tended to be lower in the north and south and higher in the middle of the study area. The correlation between NDVI and precipitation was 6.76% higher than that between NDVI and temperature.

Key words: NDVI, MODIS, spatio-temporal dynamic changes, environmental factors, Qinghai Province