A Simple New Model for Incoming Solar Radiation Dependent Only on Screen-level Relative Humidity

Global incoming shortwave radiation (Rg) is the energy source for the majority of biogeochemical processes on Earth, as well as for photo-voltaic power production. Existing simple site-specific models to estimate Rg commonly use the daily range of air temperature as input variable. Here, we present a simple model for incoming short-wave radiation, requiring only screen-level relative humidity data (and site specific astronomical information). The model was developed and parameterized using high quality global radiation data covering a broad range of climate conditions. It was evaluated at independent sites which were not involved in the process of model development and parameterization. Despite its simplicity, the new model clearly outperforms conventional approaches, and it comes close to more labor- and data-intensive alternative models.