Aim: WP3 will integrate developments from WP1 and WP2 and evaluate their impact on model performance and forecast quality at seasonal and multi-annual time scales, assessing the benefits of the improved land cover and vegetation, tropospheric aerosols and volcanic emissions.

Approach and methodology: The impact of improved land surface conditions will be assessed with extensive sets of seasonal reforecast experiments comparing fixed, specified and interactive treatments, with large ensembles being used to enable small changes to be detected. Impact of volcanic aerosols forcing on seasonal forecasts of the surface and troposphere will be similarly studied with a comparison of specified and predicted aerosol, again with large ensembles to enable signal detection. Multi-year and annual-range forecasts will also be assessed for the impact of volcanic and tropospheric aerosols and enhanced land surface, since some of the impacts of the changes are anticipated to be most evident at longer forecast lead times.

Suitability of the research approach: WP3 reforecast evaluation is based on operational verification metrics and use of the ERA5 climate reanalysis. The model resolution and ensemble size for each experiment is designed to give results relevant for operational usage, but at a reduced cost where scientifically feasible. The research will inform as to the benefits that can be achieved now as well as to potential predictability limits of relevance for future developments. Comparisons will be made against existing operational practice, so as to motivate operational providers to consider uptake of the research results. The assessment will be done using two of the C3S models to ensure a scalable and yet robust evaluation. Combining expertise in operational systems, modelling and evaluation ensures the transferability of research into operational use, as well as its sustainability. 

Measures for Success of the Work Package/ KPIs:

• New evaluation of impact of improved volcanic aerosols forcings on seasonal and near-term predictions.
• New evaluation of impact of variable land cover and vegetation on seasonal and near-term predictions