The Changes Of Watershed Terrain And Landuse And The Influence To Runoff Based On The Information Entropy Theory

This paper took the two small watershed of Qingshui and Caijiachuan in Loess Plateau Gully Region as the main study area, based on the theory of information entropy, using DEM and remote sensing images and applicating GIS as the technical support, established the comprehensive index which used to describe the information of topographic and landuse, and discussed the changes of topography and of landuse. Then combined with runoff data, the paper introducted the sensitivity index and analysed the sensitivity between runoff and landuse information entropy because the change of it is quite different while it is similar in terrain characterize through the research. The result shows that:(1) 0.80km2 is the critical support area of Qingshui River watershed for channel development while 0.14km2 for Caijiachuan watershed. (2) Qingshui River watershed and Caijiachuan and the nesting watershed have a certain similarity, and the terrain complexity is so closed because of they are at the same stage of development. So the two basins are on the same scale. At the same time, the terrain of Caijiachuan watershed is more broken than Qingshui River watershed's under the same scale. (3) In the same scale and in the study areas, the major factor of Terrain Information Parameter is the complexity of the terrain, not the area of the watershed. (4) The landuse structure of Qingshui River watershed in the mass is developing to balance,while The overall landuse structure of Caijiachuan watershed is developing to non-equilibrium state from 1990 to 2009. (5) Orderly landuse of Caijiachuan watershed is better than that of Qingshui River watershed. (6) Overall, the annual runoff has better sensitivity to the information entropy of landuse structure, and with the increase of entropy, the sensitivity increased. (7) Though the research on the sensitivity index of runoff to landuse structure on watershed of Qingshui and Caijiachuan, at the basin having the similar terrain complexity, sensitivity of runoff on the landuse structure information entropy is lower in the larger the watershed, that also means the chages of vegetation has smaller effect on runoff, indicating vegetation wound make a smaller contribution to runoff when study area is larger. Therefore, afforestation on a large basin wound decrease control to runoff.