Changes in the snow-rain transition altitude along the South American Andes

Abstract:

In most regions of the world, the freezing and melting level heights have increased significantly in the past decades and will continue increasing in the future in the context of global climate change. The less-known melting level is defined as the altitude at which ice crystals and snowflakes begin to melt as they descend below the freezing level through the atmosphere. The melting level height is typically located a few hundred meters below the freezing level, and it is a key variable for the snow cover formation, the energy budget of snow cover and glaciers due to the albedo feedback, and the water volume available for runoff during storms in high-elevation catchments. Despite its crucial role in mountain regions, few is known about its past and future changes and possible impacts on the cryosphere and natural hazards of the Andes. Here we examine time series of precipitation and freezing level height extrapolated from surface observations on the slopes of the Andes, and radiosonde and satellite-based (Cloudsat and GPM) vertical profile observations, complemented with model output products (ERA5 and a regional climate model). We identified regional and seasonal patterns of changes in freezing and melting level heights and put it into the context of large-scale climate oscillations (such as ENSO, PDO). Our results indicate that the melting level is not changing with the same rate as the freezing level, particularly in arid regions where precipitation events are not frequent. Especially societies in large catchments along the foothills of the Andes with elevations around the present-day melting level may be impacted by increasing melting level and related hazards.