Analysis of cultivated land change by remote sensing data in the Huangshui River watershed, northwestern China

The Huangshui River basin is located in a transitional zone between the Loess Plateau and Qinghai-Tibetan Plateau in northwest China. Rapid urbanization has resulted in loss of a large amount of cultivated land in valley region; at the same time, a lot of steep slope cultivated land which located in hilly-gully region and mountain region was returned back into forest land and grassland for ecological land use conservation. The objective of this study is to monitor and analyze the spatial and temporal patterns change of cultivated land in the Huangshui river watershed by the combination method of Landsat TM image and Geographical information System technologies. Our study results indicated that in 2007, the total cultivated land was 540792.1ha whereas in 2007 it dropped to 484159.15 ha, with a net loss of 56633.01ha. Specially, during 1996-2007, the irrigated land in valley region decreased from 110446.25 ha to 104141.07 ha with a net loss of 6305.18ha, mainly being converted to built-up land. In hilly and gully region and mountain region, dry farmland rapidly decreased from 430345.88ha in 1996 to 380018.08ha in 2007, with a net decease of 50327.8ha, respectively. The decrease in cultivated land in hilly-gully region and mountain region was mainly converted to forest land and grassland.