Climate dictates magnitude of asymmetry in soil depth and hillslope gradient

Hillslope asymmetry is often attributed to differential eco-hydro-geomorphic processes resulting from aspect-related differences in insolation. At midlatitudes, polar facing hillslopes are steeper, wetter, have denser vegetation, and deeper soils than their equatorial facing counterparts. We propose that at regional scales, the magnitude in insolation-driven hillslope asymmetry is sensitive to variations in climate, and investigate the fire-prone landscapes in southeastern Australia to evaluate this hypothesis. Patterns of asymmetry in soil depth and landform were quantified using soil depth measurements and topographic analysis across a contemporary rainfall gradient. Results show that polar facing hillslopes are steeper, and have greater soil depth, than equatorial facing slopes. Furthermore, we show that the magnitude of this asymmetry varies systematically with aridity index, with a maximum at the transition between water and energy limitation, suggesting a possible long-term role of climate in hillslope development.