Antecedent rainfall as a critical factor for the triggering of debris flows in arid regions

Abstract

In arid regions, debris flows (DFs) are occasionally observed when heavy rainfall hits steep slopes with unconsolidated materials. Despite the related hazards, not much is yet known about the critical rainfall conditions for DF initiation in dryland areas mainly due to a lack of observations and data. In this study, we use high-resolution digital surface models and orthophotos to detect DFs on the arid slopes of the Dead Sea's northwestern margins, as well as weather radar rainfall estimates for the characterization of the triggering and non-triggering storms. We identify deposits from over 40 relatively small DFs that occurred between 2013 and 2019. We divide them into four groups based on their spatial distribution and triggering period, and we identify the most likely triggering storms based on weather radar data and additional information. We show that the DFs were likely triggered by an intense convective cell (lasting less than 45 min) which was preceded by non-negligible rainfall amounts (about 10 mm) delivered during the storm. Comparing triggering and non-triggering storms, we observed that rain intensity alone is insufficient to explain the phenomena and discuss the possibility that antecedent rainfall could represent a critical factor for the triggering of DFs on steep slopes of arid environments.