The impact of extreme rainstorms on escarpment morphology in arid areas: insights from the central Negev Desert

The impact of climate on topography, which is a theme in landscape evolution studies, hasbeen demonstrated, mostly, at mountain range scales and across climate zones. However, in drylands, spatiotemporal discontinuities of rainfall and the crucial role of extreme rainstorms raise questions and challenges in identifying climate properties that govern surface processes. Here, we combine methods to examine hyperarid escarpment sensitivity to storm-scale forcing. Using a high-resolution DEM and field measurements, we analyzed the topography of a 40-km-long escarpment in the Negev desert (Israel). We also used rainfall intensity data from a convection-permitting numerical weather model for storm-scale statistical analysis. We conducted hydrological simulations of synthetic rainstorms, revealing the frequency of sediment mobilization along the sub-cliff slopes. Results show that cliff gradients along the hyperarid escarpment increase systematically from the wetter (90 mm yr-1) southwestern to the drier (45 mm yr-1) northeastern sides. Also, sub-cliff slopes at the southwestern study site are longer and associated with milder gradients and coarser sediments. Storm-scale statistical analysis reveals a trend of increasing extreme (>10 years return-period) intensities toward the northeast site, opposite to the trend in mean annual rainfall. Hydrological simulations based on these statistics indicate a higher frequency of sediment mobilization in the northeast, which can explain the pronounced topographic differences between the sites. The variations in landscape and rainstorm properties across a relatively short distance highlight the sensitivity of arid landforms to extreme events.