Spatio-temporal variability of snow water equivalent in the extra-tropical Andes Cordillera from distributed energy balance modeling and remotely sensed snow cover

E Cornwell,J Mcphee,N P Molotch

doi:10.5194/hess-20-411-2016

Abstract

Abstract. Seasonal snow cover is the primary water source for human use and ecosystems along the extratropical Andes Cordillera. Despite its importance, relatively little research has been devoted to understanding the properties, distribution and variability of this natural resource. This research provides high-resolution (500 m), daily distributed estimates of end-of-winter and spring snow water equivalent over a 152 000 km2 domain that includes the mountainous reaches of central Chile and Argentina. Remotely sensed fractional snow-covered area and other relevant forcings are combined with extrapolated data from meteorological stations and a simplified physically based energy balance model in order to obtain melt-season melt fluxes that are then aggregated to estimate the end-of-winter (or peak) snow water equivalent (SWE). Peak SWE estimates show an overall coefficient of determination R2 of 0.68 and RMSE of 274 mm compared to observations at 12 automatic snow water equivalent sensors distributed across the model domain, with R2 values between 0.32 and 0.88. Regional estimates of peak SWE accumulation show differential patterns strongly modulated by elevation, latitude and position relative to the continental divide. The spatial distribution of peak SWE shows that the 4000–5000 m a.s.l. elevation band is significant for snow accumulation, despite having a smaller surface area than the 3000–4000 m a.s.l. band. On average, maximum snow accumulation is observed in early September in the western Andes, and in early October on the eastern side of the continental divide. The results presented here have the potential of informing applications such as seasonal forecast model assessment and improvement, regional climate model validation, as well as evaluation of observational networks and water resource infrastructure development.

Highlights

Predicting the spatial and temporal distribution of snow water equivalent (SWE) in mountain environments remains a significant challenge for the scientific community and water resource practitioners around the world
To explore the implications of the simplified energy balance with respect to model errors, we focus on the representation of turbulent energy fluxes, represented here through a linear temperature-dependent term
This paper presents the first high-resolution distributed assessment of this critical resource, combining instrumental records with remotely sensed snow-covered area and a physically based snow energy balance model

Summary

Introduction

Predicting the spatial and temporal distribution of snow water equivalent (SWE) in mountain environments remains a significant challenge for the scientific community and water resource practitioners around the world. The extratropical stretch of the Andes, extending south from approximately latitude 27◦ S, is a snow-dominated hydrological environment that provides key water resources for a majority of the population in Chile and Argentina. E. Cornwell et al.: Spatio-temporal variability of snow water equivalent in the extra-tropical Andes Cordillera sources. This research presents the first spatially and temporally explicit high-resolution SWE reconstruction over the snow-dominated extratropical Andes of central Chile and Argentina based on a physical representation of the snowpack energy balance (Kustas et al, 1994) and remotely sensed snow extent (Dietz et al, 2012) between years 2001 and 2014. Estimates of maximum SWE accumulation and depletion curves are obtained at 500 m resolution, coincident with the MODIS MOD10A1 Fractional Snow Cover product (Hall et al, 2002)

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