Changing landscape in the Three Gorges Reservoir Area of Yangtze River from 1977 to 2005: Land use/land cover, vegetation cover changes estimated using multi-source satellite data

Abstract

The eco-environment in the Three Gorges Reservoir Area (TGRA) in China has received much attention due to the construction of the Three Gorges Hydropower Station. Land use/land cover changes (LUCC) are a major cause of ecological environmental changes. In this paper, the spatial landscape dynamics from 1978 to 2005 in this area are monitored and recent changes are analyzed, using the Landsat TM (MSS) images of 1978, 1988, 1995, 2000 and 2005. Vegetation cover fractions for a vegetation cover analysis are retrieved from MODIS/Terra imagery from 2000 to 2006, being the period before and after the rising water level of the reservoir. Several analytical indices have been used to analyze spatial and temporal changes. Results indicate that cropland, woodland, and grassland areas reduced continuously over the past 30 years, while river and built-up area increased by 2.79% and 4.45% from 2000 to 2005, respectively. The built-up area increased at the cost of decreased cropland, woodland and grassland. The vegetation cover fraction increased slightly. We conclude that significant changes in land use/land cover have occurred in the Three Gorges Reservoir Area. The main cause is a continuous economic and urban/rural development, followed by environmental management policies after construction of the Three Gorges Dam.

Introduction

In recent years, to satisfy the hydrological energy and water resources consumption demand from the rapid development of economy and society, many large-scale water conservation projects have been undertaken at the global level. These major projects have brought certain economic benefits, but have also had adverse effects on the ecological environment. For example, the influence of Egypt's Aswan High Dam, on water and soil quality, human health 20 years after its completion (White, 1988, Moussa et al., 2001); the influence of the Itaipu Project located along the border river between Brazil and Paraguay, on vegetation, animals, water quality and soil pollution (Murphy, 1976, Strand et al., 2007). Therefore, for many years using new technologies to monitor the impacts of these activities on the ecological environment has been a focus of attention around the world (Ivits et al., 2009, Liao, 2004, Liu et al., 2002, Veldkamp and Lambin, 2001).

As the largest water conservation project in the world, China's Three Gorges Project has attracted worldwide attention. This attention has not been only for its comprehensive social and economic benefits such as flood prevention, hydropower generation, and shipping capacity, but also for the potential security impacts on the natural environment, potential geological disasters, as well as on the biological diversity imposed on the surrounding reservoir area. Specifically, the major impacts include land cover changes caused by population migration, potential water pollution and soil erosion following the construction of the Three Gorges Dam and the immigration towns, etc. The Chinese Government and the environmental management professionals have long been aware of these problems, and have gradually formulated and implemented a series of relevant policies (Luo and Shen, 1994, Tullos, 2009).

Among these impacts, land use/land cover change (LUCC), as well as the vegetation cover change, have been well recognized as some of the most important indicators for global and regional environmental changes (Meyer and Turner, 1994, Lindquist et al., 2008). Therefore, quantifying the LUCC and vegetation cover change is crucial for assessing the effect of land management policies and environment protection decisions (Opoku, 2007).

Many studies have been carried out about land use mapping, change detection, as well as vegetation monitoring using multi-temporal satellite data for regional ecological and environmental change research (Veldkamp and Lambin, 2001, Peng et al., 2006, Pouliot et al., 2009, Berberoglu and Akin, 2009). Various techniques have been successfully used in the land use/land cover classification and change detection, e.g., pixel based classification (Foody, 1996, Duda et al., 2001), object oriented classification (Geneletti and Gorte, 2003, Elmqvist et al., 2008), artificial neural network classification (Kanellopoulos et al., 1992, Liu et al., 2004), post-classification comparison change detection (Serra et al., 2003), and visual interpretation (Liu et al., 2005). For vegetation monitoring, some biophysical parameters, e.g., vegetation leaf area index (LAI), fraction of photosynthetically active radiation (fPAR), and vegetation cover fraction, have been recommended for monitoring its long-term changes (Ganguly et al., 2008, North, 2002, Sun et al., 2008, Mostovoy et al., 2008). For vegetation changes estimation over large areas, the retrieval of the fraction of vegetation cover (FVC) from remotely sensed data has been an effective method (Carlson and Ripley, 1997, Zhang et al., 2006).

In this paper, the multi-temporal satellite dataset in the Three Gorges Reservoir Area has been analyzed to understand LUCC as a consequence of driving factors. Our study focused on the following two aspects: (1) to estimate LUCC from 1977 to 2005 in the TGRA, and to obtain vegetation cover changes from 2000 to 2006, being the time before and after the water line rising of the reservoir, and (2) to incorporate and analyze landscape changes in the TGRA using these estimated results.

The remaining sections of this paper are organized as follows. Section 2 introduces the background of the study area. Section 3 describes the data and method used in this article. In Section 4, the LUCC and vegetation change results are presented, followed by a discussion of the results in Section 5. The conclusions of this research are given in Section 6.