A practical approach to assessing climate change impacts on snow cover and streamflow in southeast Australia

Abstract

: Globally, the impact of climate change on snow melt has become a growing concern. Snowfall is often a critical component of streamflow as it plays a crucial role in regulating seasonality and persistence. However, in Australia, snow cover is both intermittent and limited in space, with a lack of publicly available snow data records. As a result, snowfall is often neglected within streamflow analysis. This study presents a practical method to explicitly consider interactions with snow cover when examining risk to water supply and hydrology due to the impact of climate change. Although snow coverage in Australia is relatively small, the catchments affected are important for water supply. Previous studies have been limited in scope (e.g., focused on commercial outcomes such as changes to the ski season), and publicly available studies considering implications for water supply and hydrology are rare. The method presented here aims to be readily applicable in areas with limited data on snow fall and coverage, and within the context of broader regional water resource assessments. We integrate a snow module into a monthly rainfall-runoff modelling framework using the southern Murray-Darling Basin as a case study. Challenges include that existing snow models can be complicated, requiring data inputs such as atmospheric fluxes that are not readily available for this region. To address this, we incorporate a simple temperature-dependent threshold to determine snow cover based on an existing widely used monthly-timestep snow module (Xu et al, 1996). Calibrated to a snow extent dataset based on remote sensing imagery over 2000-2014 (Thompson, 2015), we found the method can replicate snow dynamics across several climatically-distinct snow-covered areas in south-east Australia, increasing confidence in applicability under climate change. The snow module was then added to an existing monthly rainfall runoff model (WAPABA, Wang et al, 2011). This process was applied to the Snowy Mountains (Australia’s largest alpine region) to allow a “stress test” of climate change impacts on streamflow and snow cover. As expected, results suggest that both snow coverage and duration will likely significantly reduce in the future. Results suggest