The ISIMIP3a/3b protocol follows the known convention with the 3a-part addressing the historical period and designed for model evaluation and the 3b-part addressing historic and future impact projections. So far, the protocol addresses group 1 and group 2 simulations, while group 3 simulations will only be supported as soon as there is projected socioeconomic data available in the course of 2021.
Please make sure to use the same model version for running 3a and 3b simulations to ensure consistent interpretation of output data.
- ISIMIP3a (model evaluation + detection and attribution of observed impacts)
Historical simulations forced by observational climate and socio-economic information: In addition to the full forcing run (observed climate + observed socio-economic forcing) the protocol newly includes a counterfactual “no-climate change baseline” (detrended climate + observed socio-economic forcing, see fact sheet) to allow for the detection and attribution of observed impacts according to the WGII-AR5 Chapter 18 definition.
The new counterfactual climate data has been generated by a de-trending approach using global mean temperature instead of time as independent variable. The method will soon be described in a fact sheet. Currently we only provide the GSWP3 climate forcing and its counterfactual while the combined GSWP3-W5E5 datasets will soon be provided, too.
- ISIMIP3b (GCM-based quantification of impacts at different levels of climate change)
For ISIMIP3b we provide bias-corrected CMIP6 climate forcing for pre-industrial, historical, SSP1-RCP2.6, SSP3-RCP7.0 and SSP5-RCP8.5 conditions. The new bias-adjustment (see fact sheet) has been developed by Stefan Lange and corrects the simulated data towards corrected ERA5 observational data (W5E5). Basic analysis of global-mean-temperature levels in the ISIMIP3b climate data can be found here.
The ISIMIP3a/3b protocol basically reflects the decisions taken at the Strategy Group Meeting in Potsdam, September 2018.