Evaluation of the surface energy budget equation with experimental data and the ECMWF model in the Ebro Valley

In numerical models of the climate system and in other applications, the surface energy budget is usually considered closed, allowing for estimation of missing terms as the residual of the others. Real measurements of this budget show significant uncertainties in the values of each flux and imbalances that range between 5% and more than 50%, as shown in recent literature. In this article, a derivation of the surface energy budget equation from the prognostic temperature equation is presented and the hypotheses are discussed. Minor terms, which are usually neglected, such as tendency or advection, are estimated. Then, the 2year statistics for a station in the Ebro Valley are analyzed, focusing on the imbalance, which is found to increase as the other terms in the equation increase, with values on the order of 30% of the net radiation. The same location seen by the model of the European Center for Medium-Range Weather Forecasts (ECMWF) is analyzed. Large differences between observations and model simulation results occur at a daily scale although the average terms are comparable, with a systematic overestimation of the ground and sensible heat fluxes by the model.