Rainfall intensity-duration thresholds for debris flows in hyperarid zones with sparse meteorological monitoring.

Northern Chile is characterized by hyperarid conditions, with annual precipitation averaging < 100 mm/year, however, during the austral summer, few short-duration, high-intensity local convective rainfall, typically originated by cut-off lows, accounts for > 90% of annual precipitation. Large scale events, dominated by synoptic activity, such as those occurring in March 2015 and May 2017 in the southernmost Atacama desert, triggered debris flows in more than 100 creeks, causing significant damage to infrastructure, the local economy, and loss of human lives. However, numerous debris flow events associated with mesoscale convective systems in the Andes have also been documented despite not being recorded by low-elevation meteorological stations. Based on a debris flow inventory compiled by the National Geology and Mining Service, the characteristics of storms within a 10 km radius of each event were analyzed. Rainfall intensity-duration (ID) thresholds were identified, revealing that storms with an intensity exceeding ~7 mm/h have a high probability of triggering debris flows. The identified ID curve generally  represents lower thresholds compared to global studies, attributed to the convective nature of the storms and the low density of meteorological stations. Although low, the proposed threshold is conservative and suitable given the low meteorological monitoring density in the area. The use of a  convection-permitting storm simulation through the Weather Research and Forecasting model (WRF) is being explore to reproduce local scale precipitation triggering debris flows in the area.