Land-cover Change and Vulnerability to Flooding near Poyang Lake, Jiangxi Province, China

Inhabitants near Poyang Lake, in the Central Yangtze River Basin, China, are vulnerable to loss of life and livelihood because of the interactions of flooding and land-use policies and decisions. We analyzed implications of land-cover patterns for vulnerability to flooding in the Poyang Lake Region. Land-cover and change were mapped using multitemporal Landsat TM/ETM images at high and low water levels from 1987, 1993, 1999, and 2004. Vulnerability to flooding was analyzed based on the distribution of land covers relative to elevation and the levee quality. Results showed that patterns of Farmland, Urban, and Wetland covers varied by elevation, by the relative likelihood of flooding within polders, and over time; the general trend, with some notable exceptions, was toward less vulnerability of farmland and urban areas to flooding. Factors of markets, laws and regulations have likely influenced changes in landcover patterns and, therefore, in vulnerability. Introduction To support China’s population, which grew from 540 million in 1949 to 1.3 billion in 2006, agricultural self-sufficiency, especially in grain production, has been one of the central goals of the Chinese government. Because of a limited area of farmland per capita and inefficient farming methods, historically the primary means of increasing the total amount of agricultural yield has been to enlarge the farmland area. One consequence of this has been the conversion of large areas of natural wetlands in fertile areas, such as those in the Central Yangtze Basin, to farmland (wetland reclamation). During the past twentieth century, many levees were built to encircle new farmland in low elevation areas adjacent to lakes and rivers, forming polders that are protected against flooding (Zhao et al., 2003). In 1984, the Land-cover Change and Vulnerability to Flooding near Poyang Lake, Jiangxi Province, China Luguang Jiang, Kathleen M. Bergen, Daniel G. Brown, Tingting Zhao, Qing Tian, and Shuhua Qi Chinese government declared that agricultural grain selfsufficiency had been reached and certain land-use policies were reconsidered (Rozelle et al., 1997). Beginning in 1986, wetland reclamation was banned, and laws have promoted restoring some reclaimed farmland back to natural wetland (wetland restoration). In addition to the policies and laws regulating the conversion of wetlands and farmlands, grain markets have also had an impact on land-use. Beginning in the early 1990’s, China has transitioned from a planned economy, where grain prices were fixed by the government, to a market economy, where prices have been determined mainly by the grain market. Grain prices increased gradually in the period from 1980 to 1993, very rapidly from 1993 to 1997, and then decreased between 1997 and 2003 (Statistics Bureau of Jiangxi Province, 2004). In response to the recent decrease, the central government exempted farmers from agricultural taxes in 2004 to encourage farmers’ activity in grain production (Gale, 2005). In the transitioning economy, the trend has also been toward greater and more rapid economic growth and urbanization, including rural farming and wetland areas. Over time, intense land-use and human settlement in the floodplains of the Central Yangtze Basin have exposed millions of people to flooding hazards in that region. We used the distribution and changes of natural (e.g., wetlands and water) and human-managed land covers (e.g., urban and agriculture) over an approximate 20-year period to evaluate the vulnerability of a population and how it has changed as a result of these recent policy and economic changes. The Poyang Lake Region (PLR) in the Central Yangtze River Basin in Jiangxi Province is an important regional example of such interactions between government policies, human land-use, and natural flooding regimes. The goal of this study was to determine the changes in PLR land covers over time, especially between farmland, wetland, and urban, and then to analyze and interpret them across elevation zones and polder types to assess changes in the vulnerability of the population to flooding. The specific objectives were to: (a) compile spatial data, including digital elevation models (DEMs), polder maps, land-cover maps and landcover-change probabilities between 1987 and 2004, both of the last two being derived from multi-temporal Landsat PHOTOGRAMMETRIC ENGINEER ING & REMOTE SENS ING J u n e 2008 775 Luguang Jiang is with the Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China. Kathleen M. Bergen, Daniel G. Brown and Qing Tian are with the School of Natural Resources and Environment, University of Michigan, 440 Church St., Ann Arbor, MI 48109 ([email protected]). Tingting Zhao is with the Department of Geography, Florida State University, Tallahassee, FL. Shuhua Qi is with the Key Lab of Poyang Lake Ecological Environment and Resource Development, Jiangxi Normal University, Nanchang, Jiangxi, China. Photogrammetric Engineering & Remote Sensing Vol. 74, No. 6, June 2008, pp. 775–786. 0099-1112/08/7406–0775/$3.00/0 © 2008 American Society for Photogrammetry and Remote Sensing MM-8.qxd 5/15/08 1:35 AM Page 775