ISIMIP3a/3b protocol published

Posted by Martin Park on Feb. 27, 2020

Dear ISIMIP Community,

we are very happy to share the new ISIMIP3a/3b simulation protocol with you: High time to start the new simulation round with at least a small chance to still provide input for the IPCC AR6! The new protocol basically reflects the decisions taken at the Strategy Group meeting in Potsdam, September 2018.

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) 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. Matthias Mengel, Simon Treu und Stefan Lange have developed the method that 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, 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).

So far, the 3b protocol only addresses group 1 (historical period accounting for observed changes in socio-economic forcing) and group 2 simulations (future projections assuming fixed year-2015 socio-economic forcing), while group 3 simulations (accounting for future changes in socio-economic forcing) will only be added and started in summer 2021, since the socio-economic forcing data still has to be developed.

We encourage you to start with both protocols and run 3a- and 3b-simulations in parallel as we consider both to be equally important for AR6, and please make sure to use the same model versions for 3a- and 3b-simulations. Most of the input data is already in place on the DKRZ server, and we are going to fill in the rest over the coming days.

You will see that the protocol has a new layout. It’s based on controlled vocabularies that help us keep variables and other definitions harmonized across sectors, and was developed by Jochen Klar. We hope you will enjoy it. Please take a look at the protocol as soon as you can, and let us know if anything seems confusing; the sooner we can fix things, the better.

We'd like to express our heartfelt thanks to all the sectoral coordinators and the data developers who contributed to preparing this new simulation round, and we look forward to filling it with life together!

Best regards from Potsdam,

the ISIMIP team