Status: this preprint was under review for the journal HESS but the revision was not accepted.
How to simulate radiative inputs in complex topographic areas, an analysis on 115 Swiss Alps weather stations
Philippe Riboust,Nicolas Le Moine,Guillaume Thirel,and Pierre Ribstein
Abstract. In hydrology, solving the energy balance could be needed to estimate evapotranspiration or snowmelt. Shortwave (SW) and longwave (LW) incoming radiation fluxes are often derived from climate models or reanalyses. The resolution of these models is often too scarce to reproduce the variability of the energy fluxes in complex topography situations. For hydrological purposes, these radiations can also be simulated using empirical formulations with only maximum and minimum daily air temperature data as inputs. Many different formulations have been developed, mainly for specific areas. In this paper, we modify the existing Bristow atmospheric transmissivity equation so that it can be adapted to different areas and different elevation ranges. A calibration method for the transmissivity equation, coupled to the Sicart emissivity parameterization, has been determined. The new parameterization was developed and validated on a total of 115 meteorological stations from the MeteoSwiss network over the Swiss Alps. The results showed an increase in performances for simulating shortwave radiations in high-elevation areas, without decreasing the performance for lower elevations. However, the performance increase on transmissivity did not improve the longwave simulations as had been expected. The parameterization was also validated on reference surface temperature by solving a simplified energy balance. This makes it possible to evaluate the performance of the two parameterizations combined, considering a typical retro-action of the snow surface. This provided good results with a slight increase in performance compared to the original formulation. It also showed that the inaccuracy of SW radiations has a greater impact on the performance of the reference surface temperature than LW radiation errors. The drawback of this new formulation is that it converges to unexpected parameter values at the calibration process, which requires setting some parameters before calibration.
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In hydrological modelling complex forcing data are often needed to reproduce the energy balance, mainly for simulating snowmelt and evapotranspiration processes. Incoming radiation data are not widely measured and are often derived from reanalyses. We provide a method for simulating these radiations in mountainous areas using only daily temperature range data and a digital elevation model. The method has been validated on 105 weather stations and a simple snow surface temperature model.
In hydrological modelling complex forcing data are often needed to reproduce the energy balance,...
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