Climate scenarios for Switzerland: How to provide seamless information by bridging models and observations?

National climate scenarios reflecting the current scientific state of knowledge are an indispensable basis for public and private sectors to plan and design adaptation and mitigation measures. Regional or even local assessments of future climate change are therefore an important climate service. The next generation of climate scenarios for Switzerland is currently under development in the project Klima CH2025. Similar to previous climate scenario generations, the new project is a joint effort involving the Federal Office of Meteorology and Climatology MeteoSwiss, ETH Zurich, C2SM and further partners from academia and administration. The main goal of Klima CH2025 is to develop, update and provide the physical basis of climate change in Switzerland and related products. Two main scientific questions will be addressed: 1) How can we better merge observations and model-based climate scenarios in order to provide consistent and temporally seamless information to best serve user needs?; 2) What is the projected evolution of impact-relevant climate extremes in Switzerland and what are their underlying processes? Guided by these two questions, we will develop a range of new products, engage with stakeholders, and plan active communication and dissemination.

We build our scenarios upon the existing CMIP5-based EURO-CORDEX simulations but combine them with CMIP6 GCM information using a variant of a pattern scaling approach. Our approach bridges the gap between different CMIP and CORDEX generations and at the same time merges models and observations to provide consistent information on climate change for the past, the present and the future. In this presentation, the general approach of the Klima CH2025 framework will be presented together with the method applied to bridge models and observations and to integrate CMIP6 evidence into CMIP5-based EURO-CORDEX simulations. In addition, first results of the project and planned products will be presented.