HEALTH ASSESSMENT OF THE WATER-LEVEL-FLUCTUATION ZONE (WLFZ) IN THE AREA BASED ON SPATIAL INFORMATION TECHNOLOGY

Rong Tian1, 2, Chunxiang Cao1, Huicong Jia1, Min Xu1, Haibing Xiang1, 2, Guangchun Lei3, Kun Tian4, Jingnong Weng5, Hanghe Cao6

1 State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing Applications of Chinese Academy of Sciences, 100101, P.R. China; 2 Graduate University of the Chinese Academy of Sciences, Beijing 100049, P.R. China; 3 College of Nature Conservation, Beijing Forestry University, Beijing 100083, P.R. China; 4 Department of Environmental Sciences and Engineering, Southwest Forestry University, Kunming 650224, P.R. China; 5 School of Computer Science and Engineering, Beihang University, Beijing 100191, P.R.China 6 Experimental Primary School of Beijing Normal Universtiy, Beijing 100875, P.R.China

ABSTRACT water ecosystem and terrestrial ecosystem, thus resulting in a series of environmental problems, such as environmental The WLFZ in the Three Gorges area is alternately controlled pollution cross water and land, biodiversity and ecosystem and influenced by both water ecosystem and terrestrial damages, environmental and geological disasters and ecosystem. Its ecological vulnerability and instability are epidemic diseases [1-2]. Ecological vulnerability and significant. Taking small watershed as a unit of assessment, instability of the WFLZ in the Three Gorges area are we select population density, urbanization intensity, significant [3-4]. Many scholars have researched on the temperature, precipitation, and humidity and vegetation ecological environment of the WLFZ in the Three Gorges coverage to construct the fluctuating zone wetland area [4-10]. ecosystem assessment index system. The comprehensive Remote sensing and Geographic information system health index is calculated after extracting the main provide an effective research tool for ecosystem studies. information of the six variables using principal component Remote sensing technology can obtain a lot of ground analysis. It is ranged into three levels: good, medium and information quickly, objectively and repeatedly in the poor. The results show that the health state of the entire watershed or regional landscape scale [1]. Based on the Three Gorges area is at medium and poor levels. Regions at spatial information technology, we assess and analyze the medium health state account for 58% of the entire area, and ecosystem health of the WLFZ in the Three Gorges area the remaining regions are at poor health. Taking Wanzhou taking the small watershed as the assessment unit. as the boundary, the health state of the southwest region is better than the northeast region. 2. STUDY AREA AND DATA

Index Terms— WLFZ, health assessment, small 2.1. Study area watershed, spatial information technology, the Three Gorges area The Three Gorges area covers 36 counties (districts) of and in China. Our study area ranging from 1. INTRODUCTION N29°30′ to 31°43′ latitude and from E107°30′ to 109°10′ longitude is located in the hinterland of the Three Gorges The Three Gorges reservoir is a large regulating reservoir. area with the total area is about 1.79×104 km2, including Kai According to the reservoir operation scheme of “Storage of County, , , , clean water and discharging of dirty material”, a WLFZ of Shizhu County and (Figure 1). This area has which the highest water level is 175m, the lowest water level a humid subtropical monsoon climate with warm winter and is 145m and the area is 440 km2 is formed [1]. hot summer as well as abundant rainfall and multiple clouds. WLFZ is one special kind of artificial wetland. For the The mean annual temperature of the study area is 17.9°C as special geography position of the Three Gorges area and the well as the mean annual rainfall is 1140~1200mm. With periodic change in water level, the WLFZ in the Three poor natural conditions and fragile ecological environment, Gorges area is alternately controlled and influenced by both it is a typical ecological fragile zone.

978-1-4673-1159-5/12/$31.00 ©2012 IEEE 7236 IGARSS 2012 A small watershed is a region unit with relatively full of natural ecological processes. Taking small watershed as a unit of comprehensive assessment and analysis is more conformable to the natural properties of the WLFZ. After determination of flow direction, calculation of accumulation area, extraction of river network and finding of outlets, the boundaries of the small watershed were set and the basin was divided by 151 small watersheds. When the threshold value of accumulation area is 20000, the division of the small watershed is most reasonable. Since the watershed and Figure 1 Location of the Three Gorges in China (a), administrative boundaries are almost overlapped, indicating Location of the study area (b) that division results are reliable.

2.2. Data and Processing 3.3. Calculation of each variable

The data used in this study include four parts. (1) HJ-1B Population density: Assuming uniform distribution of CCD1 image and HJ-1B CCD2 image population in the census area, we carried out spatial overlay (http://www.cresda.com/n16/n1115/n1432/index.html), of analysis for the census tract data and watershed boundaries, which the ground pixel resolution is 30m and the acquired thus population of watershed can be calculated as follows: time is August 31, 2010 and August 11, 2010 respectively. ETM images with the same resolution were downloaded Population of watershed = census area within watershed / from Global Land Cover Facility: Earth Science Data total census area × population of the census area (1) Interface (http://glcfapp.glcf.umd.edu:8080/esdi/index.jsp) Urbanization intensity: Based on the 2010 land use map to do geometric correction for the HJ images. (2) DEM data of study area produced by supervised classification of HJ were obtained from International Scientific Data Service image, we carried out spatial overlay analysis for the land Platform, Computer Network Information Center, Chinese use map and watershed boundaries, thus the Urbanization Academy of Sciences (http://datamirror.csdb.cn). After intensity of watershed can be calculated as follows: interpolating with the inverse distance weighted method by ArcGIS9.3, SRTM data with the resolution of 30m were Urbanization intensity of watershed = urban area within used in this study. (3) Climatic data of 2010 were obtained watershed / each watershed area (2) from China Meteorlogical Data Sharing Service System Temperature: We carried out spatial overlay analysis for (http://cdc.cma.gov.cn/). The monthly mean temperature, the interpolated temperature layer and the watershed precipitation and humidity values collected from 8 boundaries, and then the temperature is the average value of meteorological stations were interpolated with the inverse the temperature within each watershed. distance weighted method by ArcGIS9.3. (4) Population The calculation methods of precipitation and humidity data were obtained from Chongqing Statistical Yearbook are the same as that of temperature. 2011 Vegetation coverage: Vegetation coverage ( fcover ) (http://www.cqtj.gov.cn/tjnj/2011/yearbook/indexxlse.htm). has a good correlation with NDVI. Thus fcover can be 3. METHODOLOGY AND RESULTS calculated as follows: NDVI NDVI fcover  soil (3) 3.1. Construction of the WLFZ health assessment system NDVIveg NDVI soil

Where NDVI is NDVI of pixel covered by bare soil, DPSIR (Driving Forces-Pressure-State-Impact-Response) soil conceptual model was developed by the European NDVIveg is NDVI of pixel completely covered by vegetation. environmental organizations (EEA) for the comprehensive In this study, NDVI were retrieved by the red band and near- analysis, description of environmental issues and their infrared band of HJ-1B data by ENVI4.5. Based on the 2010 relationship with social development [11]. Based on this land use map, we extracted and calculated the histogram of model, taking scientificity and operability as basic principles, bare soil and vegetation, then the minimum value and urbanization intensity, temperature, precipitation, humidity maximum value were used to represent and and vegetation coverage were selected to construct the respectively. WLFZ health assessment system.

3.2. Automatic extraction of the small watershed 3.4. Data standardization boundaries

7237 In order to make each variable value be at the range of 0 to 4. DISCUSSION AND CONCLUSION 10, the range of standardized method was used to transform data in the following equations: Figure 2 shows that the entire health state of WLFZ wetland ecosystem in the Three Gorges area is worrying. There is  10 (XX  ) /( X  X ) (4) ij ij jmin j max j min none region at good level of IHI. Regions at medium health state account for 58% of the entire area, and the remaining Equation (4) is suitable for positive variables, including regions are at poor health. As can be observed in Figure 2(a), humidity, precipitation, and vegetation coverage. the entire health states of the study area has comparatively  10 (XXXX  ) /(  ) (5) obvious spatial distribution features. Taking Wanzhou ij jmax ij j max j min District as the boundary, the health state of the southwest region is better than the northeast region, showing that Equation (5) is suitable for negative variables, including within the River basin, the health state of the population density, urbanization intensity and temperature. upstream WLFZ is better than that of the downstream, and

the farther away from the Yangtze River's main river, the 3.5. Calculation of integrated Health Index (IHI) better the health status of watershed.

Of all the counties, Yunyang has the worst overall health state. As a national poverty county, Yunyang has a faced many problems such as rapid population growth, economic development lags and high level of urbanization. In recent years, intensive using of barren hills has leaded to the decreasing of the vegetation coverage. These are the probable reasons for poor overall health state in Yunyang. Chongqing Statistical Yearbook 2011 shows that the urbanization rate of total reservoir area is 44.54% and 38.65% in key area. High level of urbanization may be the cause of the poor health of the overall WLFZ ecosystem in the entire study area. Taking Wanzhou District for example, it has the largest ecology environmental change in the process of the Three Gorges Project. During the recent 20 years, the construction land, forest land and waters of Wanzhou District have being in increasing state, with the 0% most drastic change occurred in the period of 2000-2008[12]. b Changes of the land use status directly results in ecological changes of the environment, which may be the reason why poor 42% the overall health status of Wanzhou District is uneven. medium 58% good 5. ACKNOWLEDGEMENTS

This paper has been supported the Natural Science Foundation of China (Grant No. 41171330); State Key Laboratory of Remote Sensing Science Major Scientific Figure 2 Distribution map of WLFZ IHI (a), statistical Research Project (Grant No. Y1Y00245KZ); Thanks to all comparisons of IHI at different levels (b) people providing help on the paper. Principal component analysis was used to extract the main information contained in the 6 variables by SPSS16.0. The 6. REFERENCES results show that the first three principal components (PCA1, PCA2 and PCA3) contain more than 80% information of the [1] T. Chen, “Study on the existing problem and sustainable original data. According to the weights of the first three development of fluctuating belt in the Three Gorges Reservoir”, components, IHI can be calculated as follows: Journal of Anhui Agri. Sci., 37, pp. 9091-9092, 2009. [2] W.C. Su, “Main ecological and environmental problems of IHI0.35560 PCA 1 0.28191 PCA 2 0.18465 PCA 3 (6) water-level-fluctuation zone (WLFZ) in Three Gorges reservoir and their controlling measures”, Journal of Yangtze River Distribution of WLFZ IHI (Figure 2) was made after Scientific ResearchInstitute, 10, pp.32-34, 2004. ranging the IHI into three levels: good, medium and poor. [3] D.T. Xie, X.H. Fan, Evolution and regulation of the Water- Level-Fluctuation Zone ecosystem, Science Press, Beijing, 2010.

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