Evaluation of heat stress mitigation potentials of climate change adaptation measures in cities: Scenario analyses for technical- and nature-based solutions using 3D microclimate modelling

Urban areas are expected to warm significantly more than the global average according to climate projections. This will lead to many adverse effects such as increasing health risks and mortality rates, making climate change adaptation crucial for future urban planning. Identifying effective and suitable adaptation measures requires assessment of cooling potentials, societal acceptance and cost effectiveness based on sound-scientific analyses. High-resolution microclimate modelling and scenario analyses are a promising approach to evaluate thermal effects of climate adaptation measures. A physically-based 3D-gridded ENVI-met model was parameterized based on field measurements and remote sensing data to simulate the microclimate of a 16-ha urban high-density area in Cologne/Germany. The model was successfully validated using a densely-distributed NETATMO sensor network in the study area. We evaluated 92 adaptation scenarios for a 20-year extreme heat event to quantify heat mitigation potentials. Scenarios included technical- and nature-based solutions at buildings as well as in street corridors. Measures were simulated individually and in combinations, across varying idealized and more realistic implementation degrees. Results showed a significant mean air temperature reduction by -3.0 K up to -6.3 K as well as significant mean cooling effects on physiological equivalent temperature (PET) of -4.3 K up to -11.1 K in pedestrian height level, particularly for scenarios with high greenery coverage. Combinations of different nature-based and technical solutions performed better than single measures. Even partial implementations (e.g., 25% greened buildings) provided significant cooling effects in the entire quarter, while high-reflective surfaces and shading structures had limited impact on thermal outdoor comfort.