One of main objectives of the ESCAPE-2 project is to provide a Validation, Verification and Uncertainty Quantification (VVUQ) package based on the URANIE platform (an open-source VVUQ toolbox) for weather and climate simulations. In this context, the deliverable D4.1 has been published that presents the first essential step which is the definition of VVUQ framework between the two communities: 

• weather and climate modeling on one side, and 
• URANIE community on the other side, which historically covers energy, defense and security. 

After introducing some URANIE concepts (for example the fact that it uses a non-intrusive approach and sees numerical simulation as a black box), the notions of Verification and Validation are discussed to converge towards the same definition between both communities: 

• The verification is the step of controlling the capability of the numerical model to solve the mathematical equations of the model. It solely focuses on numerical aspects. 
• The validation represents the comparison between reality (represented by experiments), and the numerical model. 

Both URANIE and weather/climate communities deal with uncertainties in numerical simulations. While, the whole set of error sources is represented within the Ensemble Prediction System for Numerical Weather Prediction, URANIE is only considering random perturbations in model parameters, also called physical parameters, for applying non-intrusive Uncertainty Quantification (UQ) technics. Both communities agree that making a distinction between the various sources of uncertainties (model parameters, initial conditions, etc.) is a key point for the following of the project.