Multiscale comparison of LS factor calculation methods based on different flow direction algorithms in Susa Ancient landscape

摘要

Topography (LS factor) is one of the most important controlling factors of soil characteristics and geomorphic processes in the landscape. This study was performed in the Susa Ancient site and aimed to compare the estimation of three different LS factor calculation methods in which the catchment area was calculated based on seven types of flow direction algorithms using DEM with five spatial resolutions. For calculating the LS factor, the catchment area attribute was used to calculate the slope length based on the flow direction. Results showed that the catchment area is an entirely scale-dependent attribute and with decreasing the spatial resolution, the statistical values of catchment area increased. At high spatial resolution, the different flow direction algorithms despite the difference in the flow distribution to the neighboring cells, but the catchment area attributes calculated based on them, are statistically slightly different. By upscaling, the LS factor values calculated in Boehner and Selige and Moore et al. methods increase, whereas in Desmet and Govers method decrease and this change rate indicates that the LS factors calculated by these three methods have the lowest sensitivity to the slope length. At a same scale, the statistics of LS factors calculated based on different flow direction algorithms depicted no considerable different. The single flow direction algorithms of Rh and D8 cause to calculate the lowest mean values of LS factors at all spatial resolutions. The difference between frequency distributions of the LS factors calculated by these three methods increases with decreasing spatial resolution. The statistical analysis of this study confirms that estimating the LS factor scale and calculation method are more important than the type of flow direction algorithm.