Multi-Model: Synthesis Cornerstone for scenarios of CH2018 Build on past experience, consistency with CH2011 or reasons why not Many parts build on it, data will continue to change for some time Which Emission Scenarios: RCP8.5/2.6 plus scaling recipe? Consistency across scenarios with different numbers of models/ensembles? Use CMIP5 to test? Transient or time windows? Blend near term with observations? How? Consistency near/longterm? How to construct a multi-model ensemble? Which Models? Model- dependence? Ensemble members? Bayesian Algorithm for model selection? For PDFs? Provide a present-day model evaluation (e.g. circulation, trend reproduction, etc.)? Do we need a bias-corrected dataset as basis for the whole CH2018 chain? E.g. from BCIP? Or select a “good” subset of models? Tasks: download&provide data, test pattern scaling, Bayes, CORDEX maps/timeseries, uncertainty/model dependence Reto

Which methods? Consistency with Block #1 and within SD block. Clear user guideline required (which product to use for which application)? Model selection (link to Block #1) Apply pattern scaling BEFORE downscaling? How to link to CH2011? Delta change still in? Can we recommend use of QM scenarios for extreme changes? (How to) Integrate convection-resolving runs? Which locations? Which parameters? Data requirements (SIM and OBS) Who will do what and by when? Include example application (-> Ole?)? Synthesis: STATISTICAL DOWNSCALING Block Sven

CH2018 | Planung, Andreas Fischer 3 Observation-Variability: Synthesis Past decades show, that variability and trends strongly depend on dynamics Do we have to explore dynamical biases and changes in GCM/RCMs in more depth? representativeness of reference period Link to dynamics, decadal variability, sparse sampling by 30years, how to obtain ‘improved’ PDF of current climate? Combination, comparison, discussion of observed trends and near-term projected trends? (-> hiatus) Signal of climate change projections < ‘noise’, current variability Extremes How to link changes in extreme precipitation to the precipitation extremes project of MeteoSwiss? Can non-stationarity assumption of Oliva/Jürg be applied to the analysis for Jan? Which climatological parameter and processes to cover? The same scope (variables) as for future climate or more? Extent defined by the needs of impact modelers? availability? Climatologies of other parameters like flashes, hail, cloudiness, sunshine duration, GCOS ECVs (Air temperature, Wind speed and direction, Water vapour, Pressure, Precipitation, Surface radiation budget) Agreement on common set of reference data sets Gridded over switzerland, E-Obs, Isotta et al, Stations: swiss, ECA&D,.. structure Observation & internal Variability as separate CH2018-topic or as direct reference to changes? extremes? Mark / Reto