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The Analysis for Characters of Vegetation Cover Change in Yangtze River Basin Based on SPOT VEGETATION Data

Author: XuHui
Tutor: ZhouZhiXiang
School: Huazhong Agricultural University
Course: Ornamental Plants and Horticulture
Keywords: Yangtze River basin SPOT VGT NDVI Changes in vegetation cover slope analysis Hurst exponent
CLC: S127
Type: Master's thesis
Year: 2011
Downloads: 145
Quote: 3
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Abstract

Vegetation dynamics and land resources and environmental change research. This article is based on remote sensing technology, based on 1999-2009 SPOT VEGETATION time series image data, the integrated application of a variety of mathematical methods to analyze the spatial distribution of the vegetation cover of the Yangtze River Basin and dynamic characteristics. Mean method to get the multi-year average NDVI image of the spatial distribution of vegetation cover on the Yangtze River basin average condition, slope analysis, Mann-kendall trend analysis, change vector analysis (CVA) and Hurst exponent R / S analysis different scales (year, quarter, month) NDVI time series of mathematical operations, analysis of the vegetation cover variation in the Yangtze River basin, as well as different watershed segmentation water system partition at different altitudes and different vegetation type NDVI spatial distribution and temporal variations characteristics. The results show: (1) the Yangtze River basin overall condition of the vegetation cover better ,1999-2009 annual average NDVI value lt; 0.1 vegetation area is the total area accounted for only 1.8% in high NDVI between 0.5-0.65 vegetation coverage area and NDVI gt; 0.65 high vegetation coverage area, respectively, accounted for 47.4% and 31.7% of the total area of ??the Yangtze River basin. Seasonal level, the spring and autumn mainly in high vegetation coverage mainly to high vegetation cover in summer, in winter mainly in vegetation cover; monthly level in mid-July, the area of ??high vegetation cover than accounted for the total basin 88% of the area, the worst of vegetation growth status in February annual average NDVI gt; area of ??the smallest proportion of more than 0.5, less than 9%. The spatial distribution of the whole more than do less in line with South East Dorsey few trends. Annual NDVI values ??less area is mainly distributed in Qinghai Yangtze River source and the middle and lower reaches of large lakes and surrounding medium-sized cities. (2) years of change, the Yangtze River basin NDVI year changes showed a single peak, the value of the lowest in February, began to decline in July after reaching the maximum. Largest increase in April, the largest decrease in October. Year NDVI in different River Basin water system area curves differ downstream of the river basin segment changes in NDVI during the year showed a bimodal type, especially the downstream farmland curve peak in April and August, June the small troughs value; midstream, downstream and lt; 200m low plains in August maximum. The eastern part of the growing season than the end of the north-west to be late. (3) in the interannual variability, the vegetation of the Yangtze River Basin for nearly 11 years, covering a whole showed a significant upward trend, the average annual increase the slope 0.0059,11 annual increase to 0.0649, an increase of 14.25% in 1999 on the basis of . Which contribute to the improvement of the summer and autumn of vegetation cover of the Yangtze River basin largest quarter the NDVI increase 0.070,0.067, an increase of 11.92%, 13.75%. Different vegetation types, forest, shrub and grass and farmland NDVI showed a significant increase in the trend farmland increase of 0.079, an increase of 17.17%. The different altitudes 500-1000 altitude belt NDVI largest increase was 0.092, an increase of 17.94%. From the the water system partition point of view, only Taihu Lake water system was degraded vegetation cover and decreasing trend. (4) the spatial distribution of the trends on nearly 11a, 92.3% of the Yangtze River Basin of NDVI pixel upward trend, and reduce the number of pixels in only 7.7%. Indicating that the last ten years of the Yangtze River Basin \Performance decreasing trend in the region is mainly distributed in the source of the Yangtze River, the upper reaches of the Jinsha River Basin, northern Min Tuojiang River, local Jiangnan foothills, and part of the large and medium-sized cities. According to the F-test, the trend is not significant regional area ratio of 39.4%, generally significantly increase the area in the basin was fragmented distribution, accounted for 18.5% of the area was a significant increase in most parts of the change, the area accounted for 42.1%. Spring, summer, autumn and winter seasons showed a significant increase in area accounted for 54.1%, 42.1%, 35.5%, and 9.8% of the watershed area. 12 months were April significantly increase the area of ??the largest, accounting for 43.5% of the watershed area, a significant increase in the area of ??the smallest, with 4.5 per cent in December. (5) change vector (CVA) analysis period 1999-2009, 1999-2003, 2004 and 2004-2009 3 change vector mode (‖ △ p ‖), found that more than half of the image element six years or 11 years, the NDVI ‖ of △ p ‖ the value in the low change region of 0.2-0.4. Transition matrix changes in intensity between 2004-2009 than 1999-2004. 1999-2009 ‖ △ p ‖ space differentiation: Downstream gt; midstream gt; upstream; the Wujiang River gt; the Upriver area gt; Taihu Lake water system (3), the Jinsha River ‖ △ p \large-1000m low altitude mountain ‖ △ p ‖, elevation gt; 4000m high altitude area ‖ △ p ‖ smaller; four main vegetation types, farmland gt; shrub gt; forest gt; grass. ‖ △ P ‖ size and vegetation afforestation projects, agroforestry production and the process of urbanization is closely related to human activities. (6) The Mann-kendall's analysis of the results and slope analysis results very close between interannual NDVI change significantly with more consistent judgments and not significant with on but distinguish increased trend extremely significant with and a significant level, there are 10 % difference. According to the size distribution of the Z value can be more flexible choice of significant level is an advantage of this method. Mann-kendall analysis of NDVI sequence Z value of the spatial variation: (1.64) Downstream the NDVI increase the trend was not significant at the 0.1 level; water system region Jinsha, Min the Tuojiang increased trend was not significant, Tai Lake Basin to reduce the trend was not significant; gt; 4000m high altitudes increasing trend is not significant; the grass increasing trend of vegetation types was not significant, significant trend of the rest basin section / elevation / vegetation type. (7) Hurst index analysis showed that the Yangtze River basin of NDVI is not purely random walk but biased random walk sequence, self-similarity and time-dependent. Whole basin Hurst (?) Aims average number of 0.8344, each basin section / elevation gradient / vegetation types like Hurst exponent yuan on average above 0.75, indicating that sustainable trends. Where downstream Hurst (?) The purport number than the upstream and midstream higher; water system region Hanjiang river systems of the stream area and downstream mainstream area Hurst (?) Aims higher number; elevation gradient the Hurst index value difference to The low altitude of 500-1000m mountain highest gt; 4000 high altitudes lowest; vegetation type on farmland gt; shrub gt; forest gt; grass. NDVI sequence data on these areas / vegetation types of self-similarity higher sustained relatively strong, may be related to the production activities of human regularity. The above conclusions will Yangtze River basin ecological environment protection and construction, and land resource management and decision-making, as well as regional economic, environmental and social sustainable development, to provide a reference.

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