Project aims

The goal of work package 3 (WP3), “Ensemble Generation” of objective C3 “Optimising regional ensembles” is to produce a comprehensive set of dynamically downscaled regional decadal hindcast simulations from which recommendations for the optimum operational ensemble can be derived. For this purpose, the already existing ensemble from the first phase of MiKlip (baseline1 CCLM4.8, 0.44° resolution) was completed covering all annual starting years and all members. Additional MiKlip II hindcast generations (preop, dcppA) were generated with an improved model version and a higher resolution (0.22°). Furthermore, simulations with a different land surface scheme and an perturbed physics approach (Breil and Schädler, 2017) were tested. The simulations were performed with the regional climate model (RCM) COSMO-CLM (CCLM). They focus on the EURO CORDEX region (see Figure 1) and cover up to now the staring-years 1960 – 2018. The full MiKlip hindcast period from 1960 was considered in order to account for inter-decadal variability and to assess the robustness of the analyses. The skill and added value of the regional hindcasts have been assessed in Mieruch et al. (2014), Reyers et al. (2017) and Feldmann et al. (2018).

Project structure

The IMK-TRO/KIT and the German Weather Service ( DWD) share the work.

Tasks of the project

Task C3-3.1: Generation of the basic regional hindcast ensemble

Extend the existing decadal ensembles a) by downscaling the MPI-ESM decadal hindcasts for an extended ensemble at a horizontal grid spacing of 0.22° (initial conditions perturbation) to analyse the impact of inter-decadal variability on the ensemble metrics, and b) by using advanced perturbed physics methods based on those developed in MiKlip I, in order to achieve a balanced spread.

Task C3-3.2: Provide ensemble members at high resolution
For selected decades and realisations high-resolution simulations at 0.0625° will be performed, followed by an analysis of the added value of the higher resolution and the impact on the ensemble metrics, especially for high/low quantiles.

Task C3-3.3: Provide ensemble members using a different SVAT and/or coupled ocean
In cooperation with the work package C1-WP2, “Soil vegetation processes”, simulations using the soil-vegetation-atmosphere transfer scheme (SVAT) Veg3d instead of the standard scheme TERRA will be performed for selected decades and realisations. Furthermore, coupled ocean simulations provided by C1-WP1, “Regional ocean coupling”, will be integrated in the ensemble. The impact of the additional members on the ensemble metrics, especially for high/low quantiles, will be analysed.

Task C3-3.4: Very high-resolution simulations

Depending on the overall progress of this work package and the available computing power, very high-resolution simulations (0.0025°) will be carried out for a selected subregion of Central Europe, and their added value will be assessed.

Task C3-3.5: Overall ensemble assessment, analysis and optimisation

This is the synthesis task of work package C3-WP3. The various ensemble compositions are analysed over several decades to assess the inter-decadal and intra-ensemble variability in terms of ensemble size and quality criteria and. The aim is to derive recommendations for an optimum ensemble size and composition taking into account also technical and computing efficiency issues. This work will be done in cooperation with work packages C3-WP1, “Post-processing”, and C3-WP2, “Optimized ensemble characteristics”.
 

Deliverables

• comprehensive decadal ensemble matrix at a spatial resolution of 0.22°
• provision of ensemble members for selected decades at high (0.0625°) and very high (0.0025°) spatial resolutions
• provision of ensemble members for selected decades based on alternative SAVT and/or coupled ocean models
• synthesis of tasks 3.1 to 3.4 in order to derive recommendations for an optimum ensemble size and composition