The 30m-NDVI-based Alpine Grassland Changes and Climate Impacts in the Three-River Headwaters Region on the Qinghai-Tibet Plateau from 1990 to 2018

doi:10.5814/j.issn.1674-764x.2022.02.002

Abstract

Abstract:

The response of long-term vegetation changes and climate change has been a hot topic in recent research. Previously, a Landsat-based fusion model was developed and used to produce a dataset of normalized vegetation index (NDVI) for the Three-River Headwater region on the Qinghai-Tibet Plateau with a spatial resolution of 30 m and the time spanning the nearly 30 years from 1990 to 2018. In this study, the NDVI was applied to an analysis of the spatial and temporal changes in the alpine grassland and the impacts from climate change using the Theil-Sen Median method and linear regression. The results showed that: (1) The regional mean NDVI was 0.39 and showed a spatial pattern of decreasing from the southeast to the northwest in the recent three decades. Among the three parks, the Lancang River Park had the highest NDVI (0.43), followed by the Yellow River Park (0.38) and Yangtze River Park (0.23). (2) An upward trending was found in the NDVI time series at a rate of 0.0031 yr^-1 (R² =0.62, P < 0.01) over the whole period of 1990-2018. The increasing rate (0.00649 yr^-1, R²=0.71, P < 0.01) in the latter period of 2005-2018 was nearly 2.3 times of that (0.00284 yr^-1, R² =0.31, P < 0.01) in the previous period of 1990-2005. In the latest periods, the three parks experienced rates that were 2.3 to 63 times the corresponding values in the early period. (3) The NDVI is correlated more positively with temperature than precipitation. The impacts of climate change decreased along with the coverage fraction from the higher, median and then lower levels. The climate change can explain 34% of the variability in the NDVI time series of the areas with a higher fraction of grassland coverage, while it was 31% for the median fraction and 20% for the lower fraction. This study is the first to use the 30 m NDVI dataset spanning nearly 30 years to analyze the spatial and temporal variability and climate impacts in the alpine grasslands of the Three-River Headwater region of the Qinghai-Tibet Plateau. The results provide a basis for assessments on the ecological management effects and ecological quality based on long-term baseline data with a higher spatial resolution.

Key words: Normalized Difference Vegetation Index (NDVI), the Three-River Headwater region, alpine grassland, climate change

SUN Ziyu, WANG Junbang. The 30m-NDVI-based Alpine Grassland Changes and Climate Impacts in the Three-River Headwaters Region on the Qinghai-Tibet Plateau from 1990 to 2018[J]. Journal of Resources and Ecology, 2022, 13(2): 186-195.

Figures/Tables 11

Fig. 1 Land-use and land-cover changes of the Three-River Headwaters region

Fig. 2 The spatial distribution of average NDVI for whole period from 1990 to 2018 in the Three-River Headwaters region

Fig. 3 Interannual trends of NDVI from 1990 to 2018 in the Three-River Headwaters region

Table 1 The frequency of the mean NDVI from 1990 to 2018 in the Three-River Headwaters region

NDVI	Area (km²)	Percentage (%)
< 0.1	1410.9	15.7
0.1-0.4	3155.8	46.3
0.4-0.6	2249.3	33.0
> 0.6	340.8	5.0
Total	6816.07	100

Fig. 4 Interannual changes of NDVI and its linear regression for the whole period (a) and the two stages (b) before and after 2005 in the period from 1990 to 2018 in the Three-River Headwaters region on Qinghai-Tibet Plateau

Fig. 5 Interannual changes of NDVI for the grassland with higher, median and lower coverage fractions of the wetland in the period from 1990 to 2018 in the Three-River Headwaters region Note: The abbreviations HFC, MFC and LFC are for higher, median and lower fractions of grassland coverage, respectively.

Fig. 6 The spatial pattern of the inter-annual trend of NDVI during the nearly three decade time-span in the Three-River Headwaters region

Fig. 7 Inter-annual changes in annual total precipitation and annual mean air temperature in the period from 1990 to 2018 in the Three-River Headwater region

Fig. 8 Interannual changes of precipitation and air temperature for the grassland with higher, median and lower coverage fractions and the wetland in the period from 1990 to 2018 in the Three-River Headwaters region. Note: The HFC, MFC and LFC indicate higher, median and lower fractions of grassland coverage, respectively.

Fig. 9 Multiple correlation coefficients from the linear regression for the NDVI with the climatic factors time series from 1990 to 2018 for each of the major vegetation types in the Three-River Headwaters region.

Table 2 Correlation between NDVI and climatic factors in the Three-Rivers Headwater region

Region	LUCC	y=a₁x₁+b₁ (Temperature)			y=a₂x₂+b₂ (Precipitation)			y=a₃x₃+a₄x₄+b₃ (Temperature + Precipitation）
Region	LUCC	a₁	R²	P	a₂	R²	P	a₃	P	a₄	P	R²
Lancang River Park	HFC	0.135	0.018	0.486	-0.305	0.093	0.104	0.307	0.164	-0.343	0.122	0.106
	MFC	0.306	0.094	0.106	0.134	0.018	0.189	0.269	0.225	-0.259	0.243	0.072
	LFC	0.077	0.006	0.691	-0.158	0.061	0.158	0.211	0.342	-0.272	0.223	0.062
	Wetland	0.117	0.014	0.545	-0.269	0.073	0.157	0.265	0.224	-0.311	0.155	0.089
	Whole	0.115	0.013	0.552	-0.285	0.070	0.134	0.269	0.222	-0.313	0.158	0.087
Yangtze River Park	HFC	0.341	0.116	0.071	0.069	0.005	0.721	0.404	0.051	-0.162	0.418	0.139
	MFC	0.392	0.154	0.036	0.280	0.078	0.141	0.391	0.050	0.003	0.988	0.154
	LFC	0.363	0.138	0.043	0.201	0.041	0.295	0.398	0.042	-0.100	0.631	0.140
	Wetland	0.374	0.140	0.046	0.146	0.021	0.451	0.436	0.033	-0.165	0.403	0.163
	Whole	0.341	0.116	0.041	0.136	0.019	0.481	0.323	0.054	-0.005	0.760	0.098
Yellow River Park	HFC	0.387	0.150	0.038	0.009	0.008	0.644	0.390	0.046	-0.007	0.969	0.150
	MFC	0.424	0.180	0.022	0.266	0.071	0.163	0.347	0.839	0.180	0.360	0.207
	LFC	0.405	0.164	0.029	0.236	0.056	0.219	0.333	0.100	0.171	0.388	0.188
	Wetland	0.355	0.420	0.046	-0.104	0.011	0.589	0.452	0.032	-0.219	0.283	0.165
	Whole	0.404	0.163	0.030	0.122	0.015	0.529	0.395	0.048	0.021	0.916	0.164
Three-River Headwater region	HFC	0.406	0.165	0.029	-0.114	0.013	0.555	0.540	0.009	-0.295	0.137	0.234
	MFC	0.456	0.207	0.013	0.084	0.007	0.665	0.505	0.014	-0.117	0.544	0.219
	LFC	0.363	0.202	0.043	-0.015	0.002	0.739	0.441	0.035	-0.186	0.357	0.160
	Wetland	0.304	0.223	0.023	-0.168	0.028	0.384	0.457	0.026	-0.362	0.073	0.200
	Whole	0.403	0.162	0.030	-0.076	0.017	0.397	0.518	0.013	-0.263	0.185	0.218

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