Using high-resolution aerial images to study gully development at the regional scale in southern China

There are 239,100 gullies in southern China,which cause the degradation of ecological system.However,studies on gully development at the regional scale is relatively lack.The purpose of this study is to analyze the regional gully dynamics and explore how land use and topographic factors affect gully development.Input data consists of land use maps derived from high-resolution images from 2004 to 2014,and topography maps from a digital elevation model with a pixel size of 8 m×8 m in two 25-km2 study sites of Anxi(AX)and Xingning county(XN).The following results were obtained:(1)AX gullies decreased from 2006 to 2014 while XN first increased from 2004 to 2009,and then decreased from 2009 to 2014.Both AX and XN gully area in percentage of the total area ranged from 1%to 3%,which was higher than the average 0.25%of the whole southern China by the artificial survey in 2005.(2)Most of AX and XN gullies occurred along the ridgeline and had the close relationships with the upstream contributing area and slope gradient.(3)New gullies developed on the exposed land and forestland.The lost gullies were converted into forestland and grassland.In fact,most of these gullies were only covered by vegetation,not real disappearance.These results proved that gully decreased,but construction of roads and buildings intensified gully development.Consequently,these findings reveal that vegetation protection and ecological restoration should be adopted in southern China.