A general model to estimate hourly and daily solar radiation for hydrological studies

As an important input for hydrological models and snowmelting models, surface solar radiation can be estimated from sunshine duration by the Angstrom-Prescott model. This model has sitedependent parameters and thus needs calibrations when applied to individual regions. The calibrations are particularly difficult in highland and mountainous areas because of unavailability of radiation measurements. In this study, a simple model that can explicitly account for radiative transfer processes in the atmosphere is developed to estimate hourly and daily solar radiation. Its inputs are surface meteorological data (sunshine duration, air temperature, and relative humidity), so it can be easily applied to hydrological modeling. The radiation model is compared with the Food and Agricultural Organization radiation model and globally and locally calibrated AngstromPrescott models at a number of sites in various climate and elevation regions, and it is suggested that the new model is more general and more accurate, especially for estimating hourly solar radiation. The source code of this model is available from the authors upon request.