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The main task of C3S_34b_Lot2 is to produce Regional Climate Model (RCM) simulations for the standard EURO-CORDEX EUR-11 area at 12.5 km horizontal resolution. During its four years the project has contributed to a doubling of the number of simulations resulting in a matrix of GCM-RCM-RCP-combinations with more than 130 members. The large matrix constitutes a most valuable dataset from which future climate conditions in Europe may be assessed. As the future climate is uncertain both due to uncertainties in what the future forcing conditions will be and how the climate system responds to this, and how climate models may project these changes, there is a need for supporting information for anyone that may want to use the data for various purposes.
Regional climate modelers have a long tradition of working with such information and in facing questions from a wide range of users. Documentation of such interaction can be a valuable component for a climate service provider. In C3S_34b_Lot2 emphasis has been not only on production of climate change projections but also on detailed analysis of results, documentation of experimental protocols, climate models etc. As part of making this documentation accessible to a wide range of users this report includes a broad sample of typical frequently asked questions (FAQ) for a number of topics including suggested answers. A more comprehensive document is the user guidance provided by EURO-CORDEX to which the interested reader is recommended for more in-depth discussions: questions below are originally written with the perspective of providing user guidance related to EURO-CORDEX results, however many questions are broad and applies in a more general sense. This could mean that they can also be used by users of CORDEX information from other regions in the world and also in general every climate projection data user. Please note that there is a comprehensive user guide document provided by EURO-CORDEX and can be found at https://www.euro-cordex.net/imperia/md/content/csc/cordex/guidance_for_euro-cordex_climate_projections_data_use__2021-02_1.pdf.
We note that, even if this FAQ is written originally with the perspective of providing user guidance related to EURO-CORDEX results, many questions are broad and applies in a more general sense. This could for instance mean that they can also be used by users of CORDEX information from other regions in the world and also in general every climate projection data user._.pdf

The main topics are based on The FAQ are separated in different categories suggested by the climate modelers in C3S_34b_Lot2 modellers as "typical" categories for which questions often arise. As an additional input we have used questions sampled from questions asked by attendees at the C3S webinar series (M34b_Lot2.0.1.3 Final conference, https://climate.copernicus.eu/c3s-webinars-regional-climate-projections-europe) held in early March 2021. The webinar series consisted of four separate webinars with between 200 and 500 attendees from all over the world. These questions span a wide range of topics that often directly reflects a user perspective.
Despite its broad scope this FAQ is not to be seen as an exhaustive document covering all aspects of regional climate projections and how these can be used for climate service purposes. Also, it is noted that for many questions the answers involve suggestions for users how to handle the information. Most often this involves careful investigation of potential limitations in the data with respect to their specific questions. It is our experience that such investigation often benefits from a dialogue with climate modelers who have expertise in the performance of models and experience of guiding others using the climate model projections for different purposes.Please have a look also at the User Forum  C3S webinars on regional climate projections for Europe for relevant topics from that webinar.  

The main topics has primarily been chosen based on experience by the regional climate modelers in C3S_34b_Lot2 modellers in dialogue with the ECMWF. In the process of selecting these topics the questions from the webinar series has been considered. The main topics fall into eleven different categories as listed below. For each question (underlined) it is attempted to answer in two levels where the first level is a short more general answer (in italics), while the second layer goes slightly more into detail sometimes including references for further reading when appropriate. We remind again about the user guidance provided by EURO-CORDEX for more in-depth answers to many questions (https://www.euro-cordex.net/imperia/md/content/csc/cordex/guidance_for_euro-cordex_climate_projections_data_use_2021-02_1.pdf). Depending on the question, sometimes the answer includes a short recommendation (in bold face) on what a user may need to consider when using EURO-CORDEX climate projection data and some specific links (in red), when the information can be already found elsewhere.
Marked in red are parts where specific links to other pieces of documentation at the CDS or elsewhere could be included if these questions are used at the Copernicus Knowledge Base (CKB) or similarExtensive literature references can be found below (also at the specific questions).