Rain-on-snow in the Southern Alps: hydrometeorology and imapcts

Abstract

Rain-on-snow (ROS) events are important hydrometeorological phenomenon in alpine catchments. Despite the frequent occurrence of ROS in the Southern Alps, the hydrometeorological characteristics of these events remain poorly understood. Of particular interest is understanding the characteristics of water vapour transport and its role in providing moisture and warm temperatures during the days leading to ROS events. Mid-latitude Southern Alps have been found to be largely influenced by frequent landfalling atmospheric rivers (ARs). The aim of study was to identify the role of ARs in producing winter- and spring -time ROS events by analysing integrated vapour transport (IVT). The climate variables from Mueller Hut automatic weather station located near the Main Divide of the Southern Alps were used to identify rain-on-snow events. In order to characterise the general patterns of moisture transport during major ROS events the 10 topmost ROS events with the highest daily accumulated rain were selected during the periods when snow was on the ground and a decrease in snow depth occurred. Our findings showed that all ten identified events were associated with strong fluxes of tropical water vapour travelling over Tasman Sea within a north-westerly airflow. Using an AR detection method, it was found that out of these 10 ROS events, nine were associated with ARs.