Progress on a comprehensive earth system model evaluation framework

Thorough evaluation of model fidelity is critical to have faith in a model’s capability to simulate surprise; i.e. in the model’s capability to accurately simulate hydrologic behavior under changing conditions. We define three elements that should support such thorough model evaluation. First, test cases with known solution should be used to isolate the implementation of specific processes in a model and to make sure that the model code can reproduce these known solutions. Second, model simulations of individual processes should be compared to observations of these processes to determine the accuracy and appropriateness of the equations used to represent these processes in the model. Third, benchmarks need to be defined that both provide a lower limit to the accuracy we require the model to have and an upper limit to system’s predictability based on the information contained in the input and output observations.  We present progress on all three themes covering (1) the development of test cases with known solutions called “laugh tests”; (2) progress in setting up a continental-scale model for process-based model evaluation; (3) critical notes about the still common use of aggregated efficiency criteria for model evaluation; (4) a summary of existing work on the need of lower and upper benchmarks which will inform further benchmarking work. A guiding principle in our work is to make our code available as open-source, so that the community can reproduce and use our work if desired. As such, we explicitly invite the community to share their own thoughts about these topics with us.