Combining regional downscaling expertise in Belgium: CORDEX and beyond. Final Report. Belgian Science Policy (BRAIN-be).

ABSTRACT Context In the context of the Paris Agreement, there exists a clear demand from different stakeholders for Climate services in Belgium. However, Belgium currently lacks the fundament for enabling such services. The CORDEX.be project brought together the Belgian climate and impact modelling research groups into one network as the first step towards the realization of climate services. It is based on the international CORDEX (“COordinated Regional Climate Downscaling Experiment”) project but the “.be” indicates it goes beyond for Belgium. The key to the foundation of national climate services is a combination of the existing expertise on high-resolution downscaling, local-impact models, ensemble dynamical and statistical downscaling, combined with links to international initiatives and stakeholder dialogue. This allows to address the propagation of climate change and uncertainty from the global to the local scale combined with a better representation of climate extremes. The climate network consists of nine partners using four upper-air Regional Climate Models and seven Local Impact Models. The CORDEX.be framework and guidelines are based on a user-oriented bottom-up approach. The CORDEX.be framework provides the first building block for a research network which could be extended, both nationally and internationally, with the objective of providing climate services. Objectives The main objectives of the CORDEX.be project were: 1. Contribute to the international climate community by participating to EURO-CORDEX by performing regional climate simulations over Europe. 2. Provide an ensemble of High-Resolution (H-Res) climate simulations over Belgium i.e. to create a small ensemble of high-resolution future projections over Belgium at convection- permitting resolutions. 3. Couple these model simulation to seven local-impact models for impact studies. 4. Present an overview of the ongoing climate modelling activities in Belgium. 5. Provide coherent climate information for Belgium targeted to end-users, backed by: (i) a unified framework for the H-Res climate runs and (ii) uncertainty estimations on the climate change signal; 6. Provide and present a climate-impact report for stakeholders and the general public that highlight the most important results of the project. Conclusions While Belgium does not formally have a national climate centre (Fonteyn, 2013), the CORDEX.be project provides a platform for data exchange and communication among the Belgian climate- 7Project BR/143/A2/CORDEX.be - Combining regional downscaling expertise in Belgium: CORDEX and beyond modelling groups. This is coordinated through the website euro-cordex.be. This website will be maintained and updated with new results and serve as a link between the Belgian activities and the international ones of the CORDEX project. In the context of the CORDEX.be project a wide range of climate model simulations has been performed that are collected on the CORDEX.be data hub at RMI and will serve as the basis of future impact studies. The model simulations are thoroughly validated by comparison with past observations and GNSS-derived products. Different climate impact studies have been performed in the context of CORDEX.be and are presented here. These include the impact of climate change on      extreme precipitation for Belgium; maximum snow height for Belgium; urban parameters for Brussels; including outdoor labor productivity, excess energy consumption and heat stress due to heat waves; agricultural crop performance and yield for Belgium; and biogenic emissions for Europe and Belgium. Focusing on the future period 2070-2100 for the scenario with the largest greenhouse gas emissions (RCP8.5), the most prominent impacts of climate change for Belgium include:         A strong increase in tropical days and heat wave days. An increase in winter precipitation and long extremely wet periods. Intensification of summer precipitation extremes, especially in urbanized areas. The precipitation intensity with hourly time scale and 10-year return period may increase up to 100%. For the Brussels urban environment: o An increase of a factor 3 to 4 in the number of heat waves. o Significant increase of heat stress for people living in the city of Brussels, up to twice as large as in the surrounding rural areas. o Significant impact on the outdoor productivity due to thermal discomfort. More specifically, a doubling of lost working days may be expected. o A doubling of days when air-conditioning is intensively used, impacting the urban energy consumption. An increased variability for biomass production and yields. Average yields for fodder maize and late potatoes will also decline. Severely reduced winter snow height maxima (above 500m altitude). An increase of 51% of biogenic emissions from isoprene with the highest emissions in the Ardennes and Campine forests (disregarding the CO 2 inhibition effect). Indications exist that there will be less hail events but increase of mean hail size. 8Project BR/143/A2/CORDEX.be - Combining regional downscaling expertise in Belgium: CORDEX and beyond A table including the climate change numbers and their uncertainty estimates for Belgium are provided. Based on interactions and feedback with stakeholders, different applications are planned that demonstrate the use of the climate data (e.g. Vanderhoeven et al., 2017).