Extraction and validation of abandoned farmland parcel in typical counties of Chongqing

Abstract: Farmland abandonment refers to the phenomenon of cultivated land remaining unused and idle for more than one year. Two-thirds of China's land area is hilly area and plateau area, and slope farmland area is larger. The quality of cultivated land in some provinces is not high as a whole, and there are a lot of phenomena of farmland abandonment. The farmland abandonment is distributed in many international and domestic regions, and in recent years there is a growing trend. But domestic research on farmland abandonment is more often conducted at the macro theoretical level, such as research on phenomenon, mechanisms, and countermeasures of farmland abandonment, however very few organizations or individuals have specified the scale of farmland abandonment or specific related data. Extraction of abandoned parcels is the foundation for further study on the status of farmland abandonment. This article describes the extraction process of abandoned farmland parcels in Chongqing's typical counties in detail, and selects the years of 2002-2011 as the study period; and for the regional level, through the general investigation of abandoned parcel, the article investigates the scale and distribution of abandonment. Farmland figure spots are extracted from the topographical map in 2002 and the current land use map in 2011. Then, the superposition of farmland layers in 2 periods provides a distribution map of abandoned farmlands in 2002-2011. The above step obtains information on abandoned farmlands, including abandoned farmlands that are returned to forest areas during the period of 2002-2011. The research object of this paper is abandoned farmland that was voluntarily abandoned by farmers, especially as this particular type of farmland must be removed. After eliminating the figure spots of returning farmland to forest (2002-2006) and forest projects (2008-2011), we get the distribution map of abandoned arable land. Through verifying abandoned farmland figure spots extracted from maps and Google Earth images, the correct rate of figure spot extraction of abandoned farmland reaches 85.3%. Based on the distribution map, farmland abandonment condition of Chongqing's typical counties is obtained. The study finds that farmland abandonment rates in Shizhu, Wushan and Youyang County were 14.0%, 19.9% and 19.2% respectively in 2011. The total area and farmland abandonment rate of the 3 counties were 56.3 thousand hm2 and 18.0%. Dryland was the main type of abandoned farmland, which was about 82.4% of the total abandoned farmland; dryland abandonment rate was 20.4%, and paddy field abandonment rate was 11.5%. In the 3 counties, farmland abandonment rates of Wushan and Youyang County were higher than that of Shizhu County. Moreover, in the aspect of abandoned paddy field, the abandonment rates of Wushan and Youyang County were 17.2% and 13.9% respectively, also higher than Shizhu County (6.3%). The phenomenon of farmland abandonment in the study area is more serious, and the main reason is that non-farm employment income increases, causing local farmers to give up farming and to be migrant workers; at the same time, the land is barren in hill and mountain area, and the agricultural production income is low, which causes the massive farmland abandonment. Thus in essence, because the farmers' income is low, they have to give up farming. To alleviate the farmland abandonment, the government needs to protect the income level of farmers.