Chinese cropland losses due to urban expansion in the past four decades.

Since 1970s, China has experienced the large-scale losses of croplands during urban expansion process, which has drawn great attentions to Chinese government. Although in-depth studies about cropland losses have been executed widely, relatively little attention has been paid to describe long term and high frequency influences of urban expansion on it and reveal its differences systematically. Based on remote sensing and GIS technology, we quantified, analyzed, and mapped cropland losses in China due to urban expansion from the national, administrative-level, population-size, and city scales. Results indicated that (1) Since the 1970s, croplands were the primary contributor to urban expansion in China, and their losses due to urban expansion underwent five obvious stages. The consciousness of cropland protection is being strengthened continuously and has developed from the initial to the deep execution stages. (2) Cropland losses were unbalanced in China, with the loss magnitude, rate, and influences on urban expansion positively related to the administrative-level and large population-size. That is, obvious losses always emerged in cities with high administrative-level and large population-size. (3) Seven basic trends of cropland losses were quantitatively recognized, which was conducive to the formulation of different policies or strategies for cropland protection for different cities.