WG4: Extremes

Short description: Extremes. Review, validate and improve methods to downscale extremes.

In the first phase, an inventory of extreme definitions, downscaling methods and validation measures will be carried out.
The inventory of extreme definitions will build on inventories of earlier projects (e.g. STARDEX, EMULATE), modified and extended to meet the needs of VALUE.
The inventory of downscaling methods will encompass the range of state-of-the-art RCMs, empirical statistical downscaling methods, and MOS methods. Additionally, the inventory will search for new methods based on stochastic models and downscaling of PDFs. The inventory will group the methods according to the downscaling approach as well as to its applicability (e.g., number of downscaled variables, local vs. spatially distributed, time scales provided). The inventory will be based on a literature review of methods to downscale extremes.
A range of validation measures will be compiled with a focus on extreme events. For this purpose existing validation studies will be analysed and limitations will be identified. Guidelines will be compiled for the validation of extremes.

In a second phase, the actual validation will be carried out.
To enable a smooth and objective validation, the chosen measures will be coded as a software package (R, FORTRAN).
The validation of extremes will be carried out against the observational benchmark data set. To isolate GCM errors and to enable a comparison of observed and modelled weather sequences, perfect boundary conditions will be used. Empirical statistical downscaling methods will use predictors from ERA40 reanalysis, and RCMs – both for the validation of MOS SDS methods and for the validation of the RCMs themselves - will be forced by ERA40 reanalysis data. The validation of variability on long time scales will be carried out in a pseudo reality. Passing the pseudo reality validation is a minimum requirement for a downscaling method to be sensibly applied for climate change studies.

Development of methods
Based on the initial inventory, WG4 will identify key problems related to extremes. Possible approaches for improvements and possible new directions of research will be discussed. In a later stage, the results of the validation exercise will be integrated into the development. Possible directions of research are the development of downscaling methods for spatially extended extremes and MOS methods specifically for extremes.
A suite of software packages for a range of well performing state-of-the-art downscaling methods will be developed and made available for the public.
Guidelines on the strengths and limitations of state-of-the-art downscaling methods directed towards researchers applying downscaling methods will be compiled.

Years 1-4

Coordinators: Elke Hertig
Members: Webmaster, Douglas Maraun, Elke Hertig, Rasmus E. Benestad, Joanna Wibig, José M. Gutiérrez, Neyko M. Neykov, Mathieu Vrac, Gabriella Szepszo, jun-ichi yano, Lino Sant, Constantin Mares, Christoph Matulla, Adam Jaczewski, Henrik Madsen, Judit Bartholy, Rita Pongracz, Bojan Srdjevic, Bartosz Czernecki, Geraldine Wong, Jonathan Eden, Malaak Kallache, Maria Antonia Sunyer Pinya, Yves Tramblay, Ida Scheel, Hayley Fowler, Julie Carreau, Christoph Beck, Ana Monteiro, Noel Aquilina, Alrun Jasper-Tönnies, Pedro M.M. Soares, Thordis Thorarinsdottir, Jan Rajczak, satyanarayana.Tani, Eleni Katragkou, Peter Szabo, Jana Sillmann, Patrick Willems, Robertas Alzbutas, Meron Teferi Taye, JESUS ASIN, JESUS ABAURREA, Ana C. Cebrian