Toward climate-responsive zoning: microscale simulation of building coverage ratio effects on outdoor thermal comfort in a semi-arid city

Urban zoning regulations strongly influence outdoor thermal comfort (OTC) and Urban Heat Island (UHI) dynamics, particularly in semi-arid environments where built-form density amplifies heat exposure. This study investigates the thermal implications of adjusting the Building Coverage Ratio (BCR), the proportion of land occupied by building footprints, within two residential zones of Irbid, Jordan: Zone A (low density) and Zone C (medium density). Using microclimate simulations, BCR values was modified by ±3% and ±6% from regulatory baselines, and results were evaluated for air temperature, mean radiant temperature, wind speed, sky view factor, and Physiologically Equivalent Temperature (PET) under representative summer and winter afternoon conditions. Results demonstrate that modest densification (+3% and +6%) in Zone C reduced SVF and Tₘᵣₜ, lowering PET by ∼0.2°C and raising neutral comfort from 12.5% to 16.8%. In contrast, Zone A exhibited minimal PET change (<0.3°C), and negligible comfort improvement. Seasonal contrasts confirm that BCR effects are meaningful primarily under summer heat stress, while winter differences (<0.1°C) were statistically detectable but thermally insignificant. The results reveal that the microclimatic benefits of densification depend on existing urban density and season, suggesting that design and zoning policies should differentiate between low- and medium-density contexts. The study provides evidence-based guidance for climate-responsive urban planning in semi-arid cities, helping balance development pressures with thermal performance, livability, and public health objectives.