• Energy Research

AbstractAs an effect of climate change, cities need detailed information on urban climates at decision scale that cannot be easily delivered using current observation networks, nor global and even regional climate models. A review is presented of the recent literature and recommendations are formulated for future work. In most cities, historical observational records are too short, discontinuous, or of too poor quality to support trend analysis and climate change attribution. For climate modeling, on the other hand, specific dynamical and thermal parameterization dedicated to the exchange of water and energy between the atmosphere and the urban surfaces have to be implemented. Therefore, to fully understand how cities are impacted by climate change, it is important to have (1) simulations of the urban climate at fine spatial scales (including coastal hazards for coastal cities) integrating global climate scenarios with urban expansion and population growth scenarios and their associated uncertainty estimates, (2) urban climate observations, especially in Global South cities, and (3) spatial data of high resolution on urban structure and form, human behavior, and energy consumption.

The CORDEX.be project created the foundations for Belgian climate services by producing high-resolution Belgian climate information that (a) incorporates the expertise of the different Belgian climate modeling groups and that (b) is consistent with the outcomes of the international CORDEX (“COordinated Regional Climate Downscaling Experiment”) project. The key practical tasks for the project were the coordination of activities among different Belgian climate groups, fostering the links to specific international initiatives and the creation of a stakeholder dialogue. Scientifically, the CORDEX.be project contributed to the EURO-CORDEX project, created a small ensemble of High-Resolution (H-Res) future projections over Belgium at convection-permitting resolutions and coupled these to seven Local Impact Models. Several impact studies have been carried out. The project also addressed some aspects of climate change uncertainties. The interactions and feedback from the stakeholder dialogue led to different practical applications at the Belgian national level. Keywords: Regional downscaling, Climate impact modeling, Statistical downscaling, Dynamical downscaling, Local Impact Models, Climate change, EURO-CORDEX, Uncertainty estimation, Regional Climate Model, Climate Belgium, Water vapour observations

Abstract Given the long lifespan of buildings it becomes inevitable to assess the impact of climate change when designing building envelopes or retrofitting solutions. Hygrothermal simulations would benefit from using a climate ensemble to account for the large uncertainties that come with modelled climate data. However, this has been rarely done so far, and no state-of-the-art methodology exists to implement ensemble data in hygrothermal simulations. This paper presents the application of a Canadian initial-condition ensemble CanRCM4 LE in hygrothermal (HAM) modelling. A brick-clad wood-stud wall assembly and historical solid masonry wall, before and after retrofitting, are analysed for Ottawa, CA. Variations in the HAM model are studied to evaluate whether the ensemble can be represented by one smaller “reduced” ensemble for different studies. And, the potential of climate-based indices to predict this “reduced” ensemble is studied. Further, the uncertainty of the ensemble is analysed, as well as the climate change signal of the damage functions. It is found that the application of a climate ensemble is highly valuable for HAM modelling, as it is able to account for the high uncertainty of climate change data. To maintain the level of information, it is recommended to perform HAM simulations using the entire ensemble. However, there is potential to select a “reduced” ensemble to represent spread of the climate change signal.

Prompted with the ongoing and projected climate change, a wide range of cities have committed, not only to mitigate greenhouse gas emissions but also to implement different climate change adaptation measures. These measures serve to ensure the well-being of the urban population. In practice, however, the planning of realistic adaptation measures is a complex process. Prior to starting such endeavor, it may therefore be useful to explore the maximum potential benefit that can be gained through adaptation measures. In this work, simple, extreme yet realistic adaptation measures are proposed in terms of changes in albedo and vegetation fraction. The impact of these land-use scenarios is explored by use of the land surface model SURFEX on the summer climate in terms of heat waves and the urban heat island for the city of Brussels. This is done for different periods in the future using the greenhouse gas scenario RCP8.5.

Climate change (CC) has an impact on degradation mechanisms in building envelopes. A climate-based analysis (only using climate variables) or a response-based analysis (based on hygrothermal simulation results) can be performed to assess the CC impact over a large region. Only the latter accounts for building parameters (e.g. material properties, wall composition ...), which is more reliable, though at a high computational cost and not state-of-the-art. It remains unclear whether a climate-based analysis is suitable to study the CC impact on building envelopes. Therefore, we compared a climate-based and response-based analysis by means of 34.560 hygrothermal simulations across Europe and the Mediterranean, including a high number of building parameter variations (i.e. 'cases'). In the north of Europe (Bodo), freeze-thaw damage and wood decay are projected to increase (81% and 68% of the cases, respectively). In the mid-latitudes of Europe (Berlin, Brussels, Milan, and Madrid), there is a decrease in freeze-thaw damage in 66%-78% of the cases. Mould growth and wood decay tend to increase in up to 51% of the cases in Brussels, and decrease in halve of the cases in Madrid. In Cairo, Bouarfa, Valencia, and Athens, the degradation risks remain small. Further, there is a weak Spearman rank correlation (maximum 0.46) between the climate-based and response-based CC impact. The error goes up to 100% when using a climate-based analysis. Moreover, the climate-based analysis is unable to represent the spread of the CC impact between different building parameter variations. The climate-based analysis is only suitable as first assessment.

The 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) reports important evolutions in the climate system. These changes are likely to affect the durability of the built environment. Although many contemporary studies investigate the future energy efficiency of buildings, research on the impact of climate change on the hygrothermal behaviour and degradation of building envelopes is rather scarce. Using climate projections, we studied the advantage of ‘hygrothermal response based‘ analyses over ‘climate based‘ analyses when assessing the impact climate change on facades. This paper presents a sensitivity study on solid masonry wall assemblies, before and after internal retrofitting, using three RCP (Representative Concentration Pathways) projections of the ALARO-0 Regional Climate Model at the grid point of Brussels (BE). The findings suggest the necessity of a ‘hygrothermal response based‘ analysis to study the sensitivity of the building envelope to climate change. Moreover, the largest sensitivity is observed for RCP 8.5, the scenario having the highest projected greenhouse gas concentrations by the end of the century.

AbstractKey messageThe change in forest productivity was simulated in six stands in Wallonia (Belgium) following different climate scenarios using a process-based and spatially explicit tree growth model. Simulations revealed a strong and positive impact of the CO2fertilization while the negative effect of the transpiration deficit was compensated by longer vegetation periods. The site modulated significantly the forest productivity, mainly through the stand and soil characteristics.ContextForest net primary production (NPP) reflects forest vitality and is likely to be affected by climate change.AimsSimulating the impact of changing environmental conditions on NPP and two of its main drivers (transpiration deficit and vegetation period) in six Belgian stands and decomposing the site effect.MethodsBased on the tree growth model HETEROFOR, simulations were performed for each stand between 2011 and 2100 using three climate scenarios and two CO2 modalities (constant vs time dependent). Then, the climate conditions, soils and stands were interchanged to decompose the site effect in these three components.ResultsIn a changing climate with constant atmospheric CO2, NPP values remained constant due to a compensation of the negative effect of increased transpiration deficit by a positive impact of longer vegetation periods. With time-dependent atmospheric CO2, NPP substantially increased, especially for the scenarios with higher greenhouse gas (GHG) emissions. For both atmospheric CO2 modalities, the site characteristics modulated the temporal trends and accounted in total for 56 to 73% of the variability.ConclusionLong-term changes in NPP were primarily driven by CO2 fertilization, reinforced transpiration deficit, longer vegetation periods and the site characteristics.