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

doi:10.11686/cyxb2020398

Abstract

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

Xin YANG, Wen-xia CAO, Xiao-jun YU, Hai-bin WANG, Yuan-yuan HAO. 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[J]. Acta Prataculturae Sinica, 2021, 30(9): 1-14.

Figures/Tables 13

Fig.1 Location and digital elevation model （DEM） of the study area

Table 1 Growth status of grassland vegetation in Qinghai Province

类别Class	类型Type	NDVI值NDVI value
Ⅰ	冰雪覆盖 Cryoconite cover	-1.0~0
Ⅱ	无植被区No vegetation area	0~0.1
Ⅲ	退化草地Depleted grassland	0.1~0.4
Ⅳ	普通草地Ordinary grassland	0.4~0.7
Ⅴ	优质草地High quality grassland	0.7~1.0

Fig.2 Daily average dynamic changes of grassland vegetation NDVI in various regions of Qinghai Province from 2000 to 2019

Fig.3 Dynamic changes of ten-days NDVI in various regions of Qinghai Province from 2000 to 2019

Fig.4 Dynamic changes of the start of growning season time of ten-days grassland vegetation in various regions of Qinghai Province from 2000 to 2019

Fig.5 Dynamic changes of the ten-days maximum of grassland vegetation in various regions of Qinghai Province from 2000 to 2019

Fig.6 Monthly proportions of fine grassland in various regions of Qinghai Province from 2000 to 2019

Fig.7 Vegetation distributions and NDVI variation trends in Qinghai Province from 2000 to 2019

Table 2 Grassland change trends in various regions of Qinghai Province from 2000 to 2019 （%）

区名 District name	退化 Deterioration	轻度退化 Mild deterioration	稳定 Stablilzation	轻度改善 Mild improvement	改善 Improvement
青海省Qinghai Province	15.79	28.54	12.97	29.94	12.75
环湖及祁连山区Around the lake and Qilian Mountains	9.91	29.19	13.31	34.49	13.10
柴达木盆地Qaidam Basin	27.84	24.17	5.92	22.68	19.39
青南高原Southern Qinghai Plateau	11.09	30.88	15.66	32.80	9.57
东部农业区The eastern agricultural region	3.28	29.93	27.88	35.02	3.89

Fig.8 Fluctuation ranges of NDVI in Qinghai Province from 2000 to 2019

Fig.9 Distributions and grassland areas of different altitudes， slopes and aspects in Qinghai Province from 2000 to 2019

Fig.10 Distribution and fluctuations of precipitation and temperature in Qinghai Province from 2000 to 2015

Fig.11 Correlation and partial correlation coefficients between grassland vegetation NDVI and precipitation or temperature in Qinghai Province from 2000 to 2015

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