Hyper-Arid Rain Ecogeomorphology (HARE): desert grass impacts on aeolian sand transport and protodune dynamics

In March 2025, the hyper-arid Namib Sand Sea experienced a highly unusual and significant rainfall event. At the Gobabeb Namib Research Institute, over 10 mm of rain was recorded in one day - the first such event since 2011 and the fifth-largest single-day of rainfall since records began in 1962. These events are extremely rare, with only nine comparable episodes recorded in the last 60 years. This unexpected rainfall provides an unprecedented scientific opportunity. From 2018 to 2023, our NERC-funded research at Gobabeb investigated the initiation of sand dunes, focusing on how local surface conditions, particularly gravel plains, influence aeolian sand transport. We demonstrated that gravel surfaces temporarily store sand and play a critical role in protodune formation. However, our observations were limited to the region's baseline hyper-arid state, with no vegetation present. This extraordinary rainfall will trigger a rapid but short-lived phase of vegetation growth, particularly grasses, across the very surfaces we previously studied. This introduces a previously unobserved and ephemeral control on the aeolian sediment budget: vegetation. The opportunity to study this ecogeomorphic feedback is both scientifically novel and time-sensitive. The interaction between emergent vegetation, wind, and sand transport remains poorly understood in hyper-arid systems. As climate change is predicted to increase the frequency of extreme rainfall events, understanding the potential role of vegetation in shaping and controlling sand transport pathways and dune system dynamics is both current and globally relevant. Immediate action is needed. Vegetation in this region responds rapidly to rainfall, and the seasonal onset of strong sand-moving winds in June will initiate active aeolian processes. To capture the system in its dynamic transition phase, field data collection must begin without delay. Gobabeb offers a uniquely controlled and previously instrumented site where both vegetative and sedimentary responses can be monitored in detail, making it the only viable location globally to conduct this kind of integrated study at this time. Objectives Objective 1: Over a six-month period, quantify how spatial and temporal changes in vegetation growth affect: a) surface roughness, b) rates of sand transport, and c) protodune development. Objective 2: During individual sand-transporting wind events (lasting <1 day), measure direct interactions between vegetated surfaces, airflow, and sand flux. Scientific Contribution This research will provide essential insight into the ecogeomorphic dynamics of hyper-arid dune systems. It will enhance our understanding of how vegetation, when briefly present, modifies wind-driven sand transport and bedform evolution. For the first time we will quantify the impact of this additional roughness element on the fundamentals of sand transport and dune initiation processes. These findings will capture environmental drivers that inform models of dune development in both hyper-arid and semi-arid environments, contributing to improved predictions under climate change scenarios. Furthermore, as vegetated dune systems may serve as transient carbon stores, this work may also have implications for global carbon budgets which are a critical and understudied contributor. Capturing these rapid, ephemeral processes requires immediate and targeted field investigation - precisely the purpose of this urgency grant.