Abstract
Abstract. Enhanced temperature-index distributed models for snowpack simulation, incorporating air temperature and a term for clear sky potential solar radiation, are increasingly used to simulate the spatial variability of the snow water equivalent. This paper presents a new snowpack model (termed TOPMELT) which integrates an enhanced temperature-index model into the ICHYMOD semi-distributed basin-scale hydrological model by exploiting a statistical representation of the distribution of clear sky potential solar radiation. This is obtained by discretizing the full spatial distribution of clear sky potential solar radiation into a number of radiation classes. The computation required to generate a spatially distributed water equivalent reduces to a single calculation for each radiation class. This turns into a potentially significant advantage when parameter sensitivity and uncertainty estimation procedures are carried out. The radiation index may be also averaged in time over given time periods. Thus, the model resembles a classical temperature-index model when only one radiation class for each elevation band and a temporal aggregation of 1 year is used, whereas it approximates a fully distributed model by increasing the number of the radiation classes and decreasing the temporal aggregation. TOPMELT is integrated within the semi-distributed ICHYMOD model and is applied at an hourly time step over the Aurino Basin (also known as the Ahr River) at San Giorgio (San Giorgio Aurino), a 614 km2 catchment in the Upper Adige River basin (eastern Alps, Italy) to examine the sensitivity of the snowpack and runoff model results to the spatial and temporal aggregation of the radiation fluxes. It is shown that the spatial simulation of the snow water equivalent is strongly affected by the aggregation scales. However, limited degradation of the snow simulations is achieved when using 10 radiation classes and 4 weeks as spatial and temporal aggregation scales respectively. Results highlight that the effects of space–time aggregation of the solar radiation patterns on the runoff response are scale dependent. They are minimal at the scale of the whole Aurino Basin, while considerable impact is seen at a basin scale of 5 km2.
Highlights
Seasonal snow cover is important as storage and source of meltwater for human use, irrigation and hydropower production in many regions of the world
For the application of TOPMELT presented in this work, clear sky shortwave solar radiation (W m−2) is computed at each element of the digital terrain model (DTM) by taking into account shadow and complex topography, calculating the apparent sun motion (Swift, 1976; Lee, 1978; Oke, 1992) and the intersection of radiation with topography (Dubayah et al, 1990; Ranzi and Rosso, 1991)
This paper presents TOPMELT, a parsimonious snowpack simulation model which integrates an enhanced temperatureindex model into a semi-distributed basin-scale hydrological model
Summary
Seasonal snow cover is important as storage and source of meltwater for human use, irrigation and hydropower production in many regions of the world. ETI models have been found to provide a better representation of the spatial and temporal variability of melt controlled by solar radiation, when compared with simple temperature-index models, as reported by a number of authors (Cazorzi and Dalla Fontana, 1996; Hock, 1999; Pellicciotti et al, 2005; Carenzo et al, 2009, among others) Some of these approaches better cope with the physical character of the melt process and provide a promising approach to modelling the snowpack at the catchment scale with fewer input data than energy-balance models, but allow for better model parameter transferability than standard temperatureindex models (Carenzo et al, 2009). The sensitivity analysis is performed on modelled snowpack in terms of snow water equivalent and on the ensuing simulated runoff, comparing the output from simulations performed at different aggregation intervals with a reference represented by the finest aggregation levels
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