VEGETATION COVER ANNUAL CHANGES BASED ON MODIS/TERRA NDVI IN THE
THREE GORGES RESERVOIR AREA
Sun Xiaoxia 3 ' b ’*, Zhang Jixian 3 , Liu Zhengjun 3
3 Key Laboratory of Mapping from Space of State Bureau of Surveying and Mapping, Chinese Academy of Surveying
and Mapping, Beijing, P.R.China -sunxx@casm.ac.cn
b China University of Mining and Technology, Xuzhou, P.R.China
Commission VII, ICWG VII/IV
KEY WORDS: Vegetation, Change, Analysis, Remote Sensing, Multi-temporal, Accuracy
ABSTRACT:
Vegetation coverage change is a very important indication of the ecological enviroment change. In this paper, we detected the
vegetation cover change by retrieving the fraction of the vegetation coverage, using the Normalized Difference Vegetation Index
(NDVI) data from MODIS/Terra imagery in recent years from 2000 to 2006, the period before and after the Three Gorges Dam
construction. In addition, the accuracy of vegetation fraction retrieval was assessed by the classification data from SPOT5 images.
Based on these results, we analyzed the annual vegetation change quantitatively, and it was shown that the vegetation cover took on a
little increase in the Three Gorges Reservoir Area in recent seven years, and the vegetation cover grades was transforming from low
coverage to high coverage.
1. INTRODUCTION
Along with the construction of the Three Gorges’ dam and
hydropower station, the eco-environment in the Three Gorges
Reservoir Area has been given full attention by local
government and scientific community. The main potential
environmental problem such as Land use and land cover
changes (LUCC), water pollution, geological disasters, soil
erosion, and the subsequent impact on the microclimate and
biodiversity, have been recognized. In which, LUCC has been
considered as one of the dominant causes of ecological
environment changes, and that vegetation cover changes are one
of the important components of LUCC (Zhang, 2008). In the
Three Gorges Reservoir Area, the vegetation cover is changing
year by year. The project constructed, emigration moving and
factories built made the vegetation cover reducing, and moreover,
some retrieval policies such as enclosing the hills for natural
afforestation, and conversion from cropland to forest, brought
an increase in vegetation cover. Therefore, the researches on
change detection and change assessment of vegetation, as well
as subsequent impact on environment are necessary for future
regional planning and governmental policy-making. Here we
used NDVI data from MODIS/Terra sensor to retrieve the
fraction of vegetation coverage, obtaining and analyzing the
recent vegetation cover changes in the Three Gorges Reservoir
Area from 2000 to 2006.
2. STUDY AREA
Reservoir Area (TGRA) locates at latitude
28°56'N-31°44'N and longitude 106°16'E -111°28'E, central
China (Fig.l), lower section of the upper reaches of the Yangtze
River at the boundary of Sichuan and Hubei with the area of 58
000 square kilometers and with the population of almost 20
million (Meng, 2005). The TGRA consists of submerged
The Three
portions at 175 meters water level and resettlement area
involved in 21 counties and cities of Chongqing city and Hubei
province, which stretches along the Yangtze River fom Jiangjin
City to Yichang City (Zhang, 2008). The reservoir area is very
narrow and where the geography is complex. The mountainous
areas represent 74% of the region only with 4.3% plain area in
the river valley and 21.7% hilly area. Sloping lands of the
gradients greater than 5 degree are accounting for 90 percent in
the whole fields, and the average slope value is more than 25
degree. The climate of the Three Gorges Reservoir Area is the
subtropical monsoon climate. The vegetation are abundant and
various, but self-sown plants are reducing instead of manual
plants in farming area, because of a long reclaiming history.
Compared to farming area, the self-sown vegetation are more in
woodland area, however, the area and types are reducing
quickly because of the over-felling, as a result, water and soil
erosion in some area are serious. Moreover, the increasing
population is destroying the natural plants continuously, and the
slope croplands are reclaimed severely.
Figure 1 . Location of study area
Corresponding author.