Interim solution for the conceptual errors of the soil-bound surface water GEM scenario

The Greenhouse Emission Model (GEM) versions 3.3.2 and 1.1.1 contain conceptual errors for the soilbound surface (SBSW) water scenario. These errors have lead to a restriction on the use of this scenario. The errors are caused by the model’s sensitivity for the application date. After consultation with the developing team (Alterra) of the GEM SBSW scenario, an interim solution was selected to by-pass the restrictions of the model due to the conceptual error.

As the result of a recently executed sensitivity analysis, it was concluded that the highest predicted concentrations (PEC) are expected when the application date of May 30th is selected. Therefore this date should be selected in the modelling. In case multiple applications within one season are modelled, the last date of application should be set to May 30th. Due to uncertainties related to this interim solution, the resulting PEC should be multiplied by a safety factor of 2. The resulting surface water concentrations can be used for risk assessment.

This interim solution is valid until a new version of GEM becomes available.