Ecogeomorphic expressions of an aspect-controlled semiarid basin: I. Topographic analyses with high-resolution data sets

Understanding vegetation effects on hydrogeomorphic processes requires detailed studies at the catchment scale using high-resolution topographic data. We perform topographic analyses in a semiarid basin in central New Mexico with opposing north and south facing slopes. Utilizing a set of terrain metrics, we explore the impact of topographic resolution and quality from three digital elevation models (DEMs): (1) Interferometric Synthetic Aperture Radar (10m); (2) differential Global Positioning System (4m); and (3) Light Detection And Ranging (LiDAR, 1m). The sequentially improved terrain data sets progressively reveal topographic and geomorphic differences in north and facing hillslopes associated with vegetation contrasts. For example, we found less frequent fluvial erosion in the more mesic, north facing slope with a juniper-grass ecosystem as compared with a more xeric, south facing slope with a desert shrubland. Furthermore, the high-resolution LiDAR data also revealed weakly steeper south facing slopes, contradicting previous work with coarser topographic products. A sensitivity analysis revealed that hillslope diffusion occurs in north facing ecosystems because of relatively higher slope, whereas fluvial erosion in the south facing ecosystem is a result of large contributing areas. The use of LiDAR data also discriminates statistically between different sediment transport regimes in the north and south facing slopes because of different dominant factors. Improvements in the definition of ecogeomorphic properties from LiDAR point to the need for high-resolution DEMs for assessing vegetation-hydrogeomorphic interactions at the catchment and hillslope scales.