Recent and projected changes in rain-on-snow event characteristics across Svalbard

Abstract

Rain-on-snow (ROS) events in Svalbard are occurring more frequently during the winter season due to rapid and ongoing climate warming across the Arctic. ROS events have gained increasing attention in recent decades due to their cascading impacts on the physical environment, and terrestrial and marine ecosystems that are impacted by snowmelt. While the frequency of ROS events in Svalbard has been well studied and documented, other characteristics of ROS, specifically their duration, intensity and seasonal timing have received less attention. Such characteristics are equally important to quantify due to their potential consequences for the winter snowpack and snow-dependent ecosystems. This study addresses this knowledge gap using the Copernicus Arctic Regional Reanalysis (CARRA) for the present-day analysis and km-scale climate projections from the HARMONIE Climate (HCLIM) regional model obtained by downscaling the Max Planck Institute for Meteorology Earth System Model Version 1.2 at Low Resolution. The HCLIM projections cover the near future period of 2030-2070 under the high emissions scenario SSP5-8.5. For the present climate, the results show significant and positive trends in the mean duration, intensity and total precipitation of ROS events but these are confined mainly to low-lying areas of Nordaustlandet and some areas in the east of the archipelago, while no statistically significant trend was found in the southern and western areas which typically exhibit the largest values in these characteristics. On the other hand, there are significant and positive trends in ROS frequency across most parts of the archipelago except for the highest lying glaciated areas in northern Spitsbergen and Nordaustlandet. Analysis of the HCLIM future projections showed that the largest changes relative to present day conditions in all ROS characteristics are projected to occur over the mountainous and glaciated areas in the north and northeast of the archipelago, while some low lying western coastal areas are projected to experience a decrease. Moreover, while ROS has increased most in October and May in the present climate, the future climate simulations project a substantial increase in ROS events in April, which currently experiences very few, if any, ROS events. This may lead to considerable changes in snow hydrology. The frequency of ROS is projected to increase most over high elevation and glaciated areas in October, November, April and May by 2070, but with considerable reductions in low lying areas close to the western and southern coast as well as across many valleys in central Svalbard in October and May. While km-scale models, such as the model used here, reduces some of the uncertainty in projected changes in ROS through improved representation of important physical processes, their computational costs prohibit the use of model ensembles to address uncertainty in projected changes. We partially addressed the uncertainty associated with model parameterisation and internal climate variability by analysing two coarser-resolution, 11 km-scale climate projections under the moderate emissions SSP3-7.0 scenario. Our analysis indicated that there are areas of Svalbard where the change in all ROS characteristics carries greater uncertainty, as demonstrated by the opposite direction of change exhibited in the two additional global climate models. On the other hand, all three model projections showed agreement over the increase in ROS frequency over large parts of the archipelago in the 2050-2070 period. Further work should include analysing a larger ensemble of climate projections downscaled by several RCMs for Svalbard to produce a broader range of ROS scenarios, as well as carrying out a more in-depth analysis of the changes in relative contributions of local vs. remote moisture sources to changing patterns of precipitation, and analysing the hydrological impacts associated with the changes in ROS characteristics identified in this study.