Downscaling ensemble climate projections to urban scale: Brussels's future climate at 1.5 °C, 2 °C, and 3 °C global warming

There is an increasing need to obtain climate projections for cities using an ensemble approach for uncertainty estimation. Yet, current-day computational resources are too limited to dynamically downscale GCM ensembles to urban scale. Here, a recently developed and validated statistical-dynamical computationally-cheap method is employed to downscale ten EURO-CORDEX climate projections over Brussels (Belgium) covering the period 1971-2100. Results show that, under the Paris agreement, summer mean projected temperature in Brussels will rise by 3.6 degrees C to 4.1 degrees C [+ - 0.7 degrees C] on average. The Urban Heat Island (UHI) intensity does not increase under future global warming with even a slight decrease under heatwave (HW) conditions by 0.1 degrees C (+/- 0.1 degrees C). However, the number of HW days is projected to be 30.6% and 158.9% higher for the 2 degrees C and 3 degrees C Global Warming Levels (GWL), respectively, as compared to 1.5 degrees C GWL. The heat stress during HW periods also follows the same trend: compared to a 1.5 degrees C GWL, the number of extreme heat stress days at 2 degrees C (3 degrees C) GWL will increase by 29% (91%) on average inside the city. The results can be used in support of adaptation measures, which should be considered for future resilience of the city of Brussels.