Nature-Based Solutions for Urban Microclimate Resilience in Hot Arid Regions

Urban areas in hot-arid regions face extreme temperatures, water scarcity, and deteriorating air quality, intensified by rapid urbanization and climate change. In the Greater Cairo Region, road-network redevelopment has reduced street greenery, increasing the need for strategies that compensate for lost shade, cooling, and ecosystem services. This study evaluates nature-based solution (NBS) configurations in a road-widened street corridor in Zahraa El Maadi, Cairo, Egypt. Seven ENVI-met 5.9.0 scenarios, varying in tree-canopy, grass, green-roof, and water coverage, were compared over a 24 h peak-summer period. Air temperature (Ta), wind speed (WS), relative humidity (RH), and physiological equivalent temperature (PET) were assessed at three pedestrian-level receptors at 12:00, 16:00, and 20:00, and i-Tree MyTree was used to estimate complementary carbon, runoff, and air-quality co-benefits for a representative Ficus microcarpa tree. Scenarios with greater tree-canopy cover generally produced lower pedestrian-level Ta, with reductions of approximately 0.4–1.6 °C depending on receptor location and time of day. A one-at-a-time sensitivity analysis of air-temperature forcing (±2 °C) and inflow wind speed (3.0 and 6.0 m/s) showed that the higher-tree-canopy scenario was cooler than the no-vegetation reference in only 21 of 36 comparisons, so its advantage depended on forcing condition, location, and time. The maximum-NBS scenario was not consistently the best performer, highlighting the influence of urban morphology and NBS placement. Water features increased RH but did not consistently reduce PET, while green roofs and grass provided limited direct pedestrian-level benefits. Overall, NBS reduced but did not eliminate heat stress. The study proposes a decision matrix that links site assets, microclimate simulation, ecosystem-service assessment, and water demand, including greywater reuse and efficient irrigation, to support NBS planning in hot-arid urban redevelopment.