BSF-NSF: Collaborative Research: Deciphering the role of extreme rainstorms and hydroclimatic regime on arid escarpment retreat and sub-cliff slope evolution

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Desert scenery often includes lines of cliffs draped with boulders and debris, presenting obstacles to hikers and highway engineers alike. Although it may not be obvious to the casual motorist, such desert cliffs, or escarpments, contain clues about the changing environment. For example, aprons of debris shed from cliffs during landslides and storms tell a story of past changes in rainfall and temperature, extending back thousands of years in the past. Until recently, it had only been possible to read that story in its broadest outlines. Today, new data and technologies are making it possible to decipher the story much more clearly. Using detailed terrain maps obtained from airborne laser surveys, together with rainfall records, new methods for dating sedimentary features, and computer simulations, this binational US-Israel project sets out to understand how rainfall shapes desert landforms over the long term, and to provide insight into how environmental changes might translate into hazards to people and adjacent infrastructure in the short term.A recent National Academy report highlighted an understanding of causes and consequences of topographic change as a top-priority research item. To this end, arid-region escarpments provide natural laboratories in which to study connections between precipitation and landforms, both because deserts minimize the confounding influence of vegetation and because their distinctive landforms are thought to reflect past changes in rainfall. This project tests the hypothesis that landforms associated with desert cliff retreat bear signatures of rainfall magnitude-frequency relationships. The project leverages three sites in the USA and Israel that span a gradient in hydroclimatic regime from hyperarid to arid, with systematically varying rainstorm properties. Analysis of high temporal resolution rainfall data (radar and gauges), lidar topography, geochronology, and field experiments in the Colorado Plateau (US) and the Negev Desert (Israel) will inform a suite of numerical experiments using a landscape evolution model. The impacts of heterogenous space-time rainstorm characteristics on escarpment retreat will be assessed, and new methods to upscale rainstorm variability to landscape evolution timescales will be developed. Numerical models and data tools for this project will be developed as new components in Landlab Toolkit, an open-source simulation software library, expanding their utility to the broader scientific community. Analyses and results from this project will also provide materials for two new learning modules for the Utah State University Native American STEM Mentorship Project, which provides gateway research experiences for freshman-level Native American students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.