Factors controlling snowmelt runoff in the semiarid Andes

Abstract:

Meltwater from the snowpack is a crucial component of catchment runoff in many dry mountain environments. In these regions, typical uncertainties in runoff generation associated with the spatial distribution of snow are exacerbated due to the dominant role of sublimation and latent turbulent fluxes in the mass and energy balance of the snowpack. Here, we assess the role of snow in runoff generation in the semiarid Andes between 26 and 32°S, a region characterized by low humidity, intense solar radiation, strong winds and a large inter-annual variability of precipitation. We use a combination of remote sensing products, field measurements and numerical modeling to identify persistent snow-covered sites and the snow processes that define the formation and evolution of the snowpack on those sites.

We run a physically-based snow evolution model (SnowModel) at different spatial scales ranging from local, highly-monitored sites to regional scales of hundreds of kms to simulate the dynamics of the seasonal snow cover in the study area over the last decades. We force the model using a network of local meteorological records and the ERA5-Land climate reanalysis, and compare its results against field measurements and two published products that reconstructed spatially-distributed snow water equivalent (SWE) across the Andes over the last two decades. Preliminary results indicate that most of the seasonal snow is stored between 4000 and 5000 m above sea level (a.s.l). Within this elevation range, areas with an easterly aspect accumulate more snow in winter, suggesting that snow is removed by the wind from west-facing slopes and deposited on east-facing slopes. We discuss the relevance of this result for the mass balance of glaciers in the region. Interestingly, an analysis of summer streamflow records at lower sites do not show a direct relationship with end-of-winter snow accumulation, which suggests that snow sublimation during spring and current groundwater levels are crucial for downstream runoff.