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For the first time, the Limited-Area Mode of the new ICON (Icosahedral Nonhydrostatic) weather and climate model has been used for a continuous long-term regional climate simulation over Europe. Built upon the Limited-Area Mode of ICON (ICON-LAM), ICON-CLM (ICON in Climate Limited-area Mode, hereafter ICON-CLM, available in ICON release version 2.6.1) is an adaptation for climate applications. A first version of ICON-CLM is now available and has already been integrated into a starter package (ICON-CLM_SP_beta1). The starter package provides users with a technical infrastructure that facilitates long-term simulations as well as model evaluation and test routines. ICON-CLM and ICON-CLM_SP were successfully installed and tested on two different computing systems. Tests with different domain decompositions showed bit-identical results, and no systematic outstanding differences were found in the results with different model time steps. ICON-CLM was also able to reproduce the large-scale atmospheric information from the global driving model. Comparison was done between ICON-CLM and the COnsortium for Small-scale MOdeling (COSMO)-CLM (the recommended model configuration by the CLM-Community) performance. For that, an evaluation run of ICON-CLM with ERA-Interim boundary conditions was carried out with the setup similar to the COSMO-CLM recommended optimal setup. ICON-CLM results showed biases in the same range as those of COSMO-CLM for all evaluated surface variables. While this COSMO-CLM simulation was carried out with the latest model version which has been developed and was carefully tuned for climate simulations on the European domain, ICON-CLM was not tuned yet. Nevertheless, ICON-CLM showed a better performance for air temperature and its daily extremes, and slightly better performance for total cloud cover. For precipitation and mean sea level pressure, COSMO-CLM was closer to observations than ICON-CLM. However, as ICON-CLM is still in the early stage of development, there is still much room for improvement.

Seasonal prediction is one important element in a seamless prediction chain between weather forecasts and climate projections. After several years of development in collaboration with Universität Hamburg and Max Planck Institute for Meteorology, the Deutscher Wetterdienst performs operational seasonal forecasts since 2016 with the German Climate Forecast System, now in Version 2 (GCFS2.0). Here, the configuration of the previous system GCFS1.0 and the current GCFS2.0 are described and the performance of the two systems is compared over the common hindcast period of 1990–2014. In GCFS2.0, the forecast skill is improved compared to GCFS1.0 during boreal winter, especially for the Northern Hemisphere where the Pearson correlation has increased for the North Atlantic Oscillation index. Overall, a similar performance of GCFS2.0 in comparison to GCFS1.0 is assessed during the boreal summer. Future developments for climate forecasts need a stronger focus on the performance of interannual variability in a model system. Plain Language Summary Information about the expected departure from the “normal” climatic conditions of an upcoming season would be tremendously valuable for many sectors of society. In Germany, three institutes join their expertise to build a climate forecast system using the Earth system model of the Max Planck Institute for Meteorology. This model describes the atmosphere, land and rivers as well as the ocean and sea ice. The model describes their interactions and is well designed for climate studies on a much longer timescale than a season. Max Planck Institute for Meteorology, Universität Hamburg and the German Meteorological Service Deutscher Wetterdienst have developed the methods those are necessary for such a forecast system and operationally perform the seasonal predictions. This paper compares two versions of our forecast system. The forecast quality during different seasons is particularly investigated. The expectation that the second model system is much better than the first system is not entirely fulfilled. We discuss possible reasons and suggest a stronger focus on the model quality for interannual variability for future model development. Key Points A climate forecast system is developed on the basis of a coupled climate model The comparison of the first to the second version shows improvements in North Atlantic Oscillation forecasts. Forecast skill in tropical regions is not improved

Feeding monogastric livestock in organic agriculture is challenging due to several tradeoffs between animal welfare aspects, resource efficiency, as well as ecological and social sustainability. Organic standards may even increase such conflicts, as is currently the case with upcoming new regulations regarding restrictions of feed sources for organic pigs in Europe. In order to contribute data for balancing reasons to minimize tradeoffs, we compared four different piglet diets, each targeted to reach a high protein quality by either a high proportion of soybean cake (SOY), inclusion of milk powder (MILK), fermentatively produced lysine (LYS) or conventional potato protein (POT). All diets were designed to meet the nutritional requirements of piglets in the best possible way, however they all represented different conflicts with either organic regulations or sustainability goals. In each of five consecutive runs, respectively three litters were assigned to every dietary treatment, resulting in 15 litters per treatment in total. In each litter, seven focus animals were defined. The piglets were studied from birth until 58 days of age. They were weaned at day 46 and sold from the farm at day 58. Piglets were individually weighed at an average age of 3, 21, 43, 50 and 58 days with simultaneous assessment of body condition score (BCS) and prevalence of diarrhea. Feed intake (FI) was recorded litter wise weekly, starting from week three. Feed conversion ratio (FCR) was calculated for the period after weaning. Statistical analysis was executed using linear mixed effect models. Regarding FI, FCR and daily weight gains, no treatment effect was found. Only at day 21, BCS was lower for piglets receiving POT. Prevalence of diarrhea increased after weaning for all treatments. All four tested diets led to similar weight gains and feed conversion in the piglets. Animals fed diet POT recovered better from diarrhea compared to the other treatments. A high soybean cake content or lysine supplementation in the diet was disadvantageous with regard to the occurrence of diarrhea. LYS diet led to signs of threonine deficit, indicating that lysine addition alone may not solve the issue. The addition of milk powder provided no extra benefit. In recognition of the health benefits, the use of 5% potato protein, even if it is sourced from conventional production, must still be considered as a sustainable option for feeding organic piglets. The sustainability implications are discussed in the paper.

The ultimate objective of organic pig production is to use ingredients of 100% organic origin in the animals’ diets. However, this approach is challenging, especially when needing to ensure adequate quantities of essential amino acids (EAAs) and protein in grower-finisher diets. The current standard is 95% organic feed ingredients, but this percentage can be increased by reducing the EAA supply or by accepting an unbalanced EAA profile. A further incentive also exists to include forages in organic diets as a way to raise dietary crude fibre content. The current study therefore investigates three organic diets (T95: 5% of non-organic origin; T100: 0% of non-organic origin and T100-CF: T100 plus an increased crude fibre level), which were offered ad libitum to 48 pigs (16 per diet) weighing 22 to 110 kg. Comparison of the three diets revealed that increasing the crude fibre content (T100-CF) reduced growth, increased total feed intake and impaired feed and protein deposition efficiency, but the unbalanced EAA profile (T100) had no effect on growth traits and protein deposition efficiency. The T100 and T100-CF pigs differed from the T95 pigs in terms of feeding behaviour traits, as they displayed more frequent but shorter feeder visits, shorter between-meal intervals and smaller meals. Increasing the fibre content with press cake ingredients raised the degree of unsaturation of the backfat and might cause problems in meat processing. In conclusion, the results revealed that pigs could cope with a mild EAA imbalance.

Within the Clim2Power project, two case studies focus on seasonal variations of the hydropower production in the river basins of the Danube (Germany/Austria) and the Douro (Portugal). To deliver spatially highly resolved climate data as an input for the hydrological models, the forecasts of the German Climate Forecast System (GCFS2.0) need to be downscaled. The statistical-empirical method EPISODES is used in this approach. It is adapted to the seasonal data, which consists of ensemble hindcasts and forecasts. Beside this, the two case study regions need specific configurations of the statistical model, providing appropriate predictors for the meteorological variables. This paper describes the technical details of the adaptation of the EPISODES method for the needs of Clim2Power. We analyse the hindcast skill of the downscaled hindcasts of all four seasons for the two variables near-surface (2 m) temperature and precipitation, and conclude that on the average the skill is conserved compared to the global model. This means that the seasonal information is available at a higher spatial resolution without losing skill. Furthermore, the output of the statistical downscaling is nearly bias-free, which is, beside the higher spatial resolution, an added value for the climate service.

A pragmatic approach to estimate the impact of climate change on the urban environment, here called the cuboid method, is presented. This method allows one to simulate the urban heat load and the frequency of air temperature threshold exceedances using only eight microscale urban climate simulations for each relevant wind direction and time series of daily meteorological parameters either from observations or regional climate projections. Eight representative simulations are designed to encompass all major potential urban heat-stress conditions. From these representative simulations, the urban-heat-load conditions in any weather situation are derived by interpolation. The presented approach is applied to study possible future heat load in Frankfurt, Germany, using the high-resolution Microscale Urban Climate Model in three dimensions (MUKLIMO_3). To estimate future changes in heat-load-related climate indices in Frankfurt, climate projections from the regional climate models Max Planck Institute Regional Model (REMO), Climate Limited-Area Model (CLM), Wetterlagen-basierte Regionalisierungsmethode (WETTREG), and Statistical Regional Model (STAR) are used. These regional climate models are driven by the \"ECHAM5\" general circulation model and Intergovernmental Panel on Climate Change emission scenario A1B. For the mean annual number of days with a maximum daily temperature exceeding 25°C, a comparison between the cuboid method results from observed and projected regional climate time series of the period 1971–2000 shows good agreement, except for CLM for which a clear underestimation is found. On the basis of the 90% significance level of all four regional climate models, the mean annual number of days with a maximum daily temperature exceeding 25°C in Frankfurt is expected to increase by 5–32 days for 2021–50 as compared with 1971–2000.

In recent years, several decadal prediction systems have been developed to provide multi-year predictions of the climate for the next 5-10 years. On the global scale, high decadal predictability has been identified for the North Atlantic sector, often extending over Europe. The first full regional hindcast ensemble, derived from dynamical downscaling, was produced within the German MiKlip project ('decadal predictions'). The ensemble features annual starting dates from 1960 to 2017, with 10 decadal hindcasts per starting year. The global component of the prediction system uses the MPI-ESM-LR and the downscaling is performed with the regional climate model COSMO-CLM (CCLM). The present study focusses on a range of aspects dealing with the skill and added value of regional decadal temperature predictions over Europe. The results substantiate the added value of the regional hindcasts compared to the forcing global model as well as to un-initialized simulations. The results show that the hindcasts are skilful both for annual and seasonal means, and that the scores are comparable for different observational reference data sets. The predictive skill increases from earlier to more recent start-years. A recalibration of the simulation data generally improves the skill further, which can also be transferred to more user-relevant variables and extreme values like daily maximum temperatures and heating degree-days. These results provide evidence of the potential for the regional climate predictions to provide valuable climate information on the decadal time-scale to users.

The decadal time scale (~1–10 years) bridges the gap between seasonal predictions and longer-term climate projections. It is a key planning time scale for users in many sectors as they seek to adapt to our rapidly changing climate. While significant advances in using initialized climate models to make skillful decadal predictions have been made in the last decades, including coordinated international experiments and multimodel forecast exchanges, few user-focused decadal climate services have been developed. Here we highlight the potential of decadal climate services using four case studies from a project led by four institutions that produce real-time decadal climate predictions. Working in co-development with users in agriculture, energy, infrastructure, and insurance sectors, four prototype climate service products were developed. This study describes the challenge of trying to match user needs with the current scientific capability. For example, the use of large ensembles (achieved via a multisystem approach) and skillfully predicted large-scale environmental conditions, are found to improve regional predictions, particularly in midlatitudes. For each climate service, a two-page “product sheet” template was developed that provides users with both a concise probabilistic forecast and information on retrospective performance. We describe the development cycle, where valuable feedback was obtained from a “showcase event” where a wider group of sector users were engaged. We conclude that for society to take full and rapid advantage of useful decadal climate services, easier and more timely access to decadal climate prediction data are required, along with building wider community expertise in their use.

A comprehensive performance assessment of the empirical–statistical downscaling (ESD) technique named EPISODES is presented. Pertaining evaluation analyses consist of multifarious validation experiments as well as various comparisons of EPISODES’ projections with those of three RCMs and two ESD methods based on the same GCM scenarios driven by two distinct representative concentration pathways (RCPs). EPISODES combines the downscaling of GCM simulations with a follow-up production of synthetic local time series. EPISODES is a comparably simple, computationally rather inexpensive technique, providing multi-variable and multi-site data that are suitable for being merged in an ensemble of RCM projections. This allows (e.g. for different RCPs) the compilation of large multi member ensembles derived from various GCM simulations via both main downscaling strategies (ESD and RCMs). Evaluation experiments reveal satisfying degrees of compliance between various results generated by EPISODES and observations. The grid cell bias for yearly values, for instance, is mostly less than 0.1 ∘ C for temperature and 10% for precipitation totals. Recorded temperature values and precipitation totals corresponding to their 1st and the 99th percentiles are well represented by EPISODES too. Comparisons of various climate change signals derived by EPISODES and other downscaling approaches, present high levels of agreement as well. Many more findings referring to evaluation experiments and climate change projections are to be found in the paper as well as throughout the “ Appendix ”.

We develop a new Earth System model configuration framed into the ICON architecture, which provides the baseline for the next generation of climate predictions and projections (hereafter ICON XPP – where XPP stands for eXtended Predictions and Projections). ICON XPP comprises the atmospheric component of the numerical weather prediction (ICON NWP), the ICON ocean and land surface components, and an ensemble-variational data assimilation system, all adjusted to an Earth System model for pursuing climate research and operational climate forecasting. Two baseline configurations are presented: (1) a 160 km atmosphere and a 40 km ocean resolution, and (2) 80 km atmosphere and 20 km ocean resolution. A CMIP DECK (Diagnostic, Evaluation and Characterization of Klima) experimentation framework is used for a first evaluation. ICON XPP depicts the basic properties of the coupled climate. The pre-industrial climate shows a top-of-atmosphere balanced radiation budget and a mean global near-surface temperature of 13.8–14.0 °C. The ocean shows circulation strengths in the range of the observed values, such as the AMOC at 16–18 Sv and the flows through the common passages. The current climate is characterized by a trend in the global mean temperature of ∼ 1.2 °C since the 1850s, similar to reference datasets. Regionally, the hydroclimate differs greatly from observed conditions. For example, the inter-tropical convergence zone (ITCZ) has a double peak and a wet southern subtropical branch across the oceans. Further, the Southern Ocean sea surface temperature has a strong positive mean bias with temperatures up to 5 °C higher than observations. Dynamical processes, such as El Niño/Southern Oscillation (ENSO) performs similarly to CMIP6-like coupled models. Tropical waves and the Madden-Julian Oscillation are well captured, and the 40 km atmospheric configuration has a spontaneous weak quasi-biennial oscillation. The atmospheric dynamics in the northern extra-tropics of both configurations represent well the position of the jet stream as well as the influences of the transient momentum transports and their feedbacks on the jet stream. Overall, ICON XPP performs similarly to climate models performed in CMIP6 making it a good basis for climate forecasts and projections, and climate research.