Urban expansion in China and its effect on cultivated land before and after initiating "Reform and Open Policy"

Urbanization in China has expanded at an unprecedented speed since the declaration of "Reform and Open Policy" and presented many challenges. Unbalanced regional development, appearance of super megacities and concomitant problems, and conflicts between urbanization and cultivated land protection are three critical problems that Chinese urbanization has to face. To develop new plans for foreseeable future urbanization in China, it is critical to understand the evolving history of cities across China. This study maps urban expansion of 60 typical Chinese cities based on large amount of remote sensing data and the labor-intensive image interpretation method, in order to understand the history of urban expansion from the 1970s to 2013. Results showed that area of cities expanded 5.23 times compared to their area in the 1970s. Urban expansion in China accelerated three times (1988–1996, 1999–2006, and 2009–2011) and decelerated three times (1997–1998, 2007–2008, and 2012–2013) over the 40 years. The urban area of South China expanded most significantly 9.42 times, while the urban area in Northeast China expanded only 2.37 times. The disparity among different administrative ranks of cities was even greater than (3.81 times) the differences among different regions. Super megacities have been continuously expanding at a fast rate (8.60-fold), and have not shown obvious signs of slowing down. The proportion of cultivated land among the land sources for urban expansion decreased to a small extent in the 1990s, but cultivated land continues to be the major land source for urban expansion. Effective future urbanization needs controlling the expansion scale of large cities and reasonably developing medium and small cities, as well as balancing regional development.