A parametric optimisation study of urban geometry design to assess outdoor thermal comfort

Over the last two decades, urban geometry has been shown to be a key determinant of the microclimatic con-ditions in urban areas. This study uses the Ladybug-tools, the plugins of Grasshopper3D to optimise building heights, street widths and orientation to maximise outdoor thermal comfort, represented by the diurnal average Universal Thermal Climate Index (UTCI). In the hot-arid climate of Cairo, Egypt, the optimised parameters of symmetrical and asymmetrical urban canyons are compared with the Egyptian Construction Act's design reg-ulations. The results show a strong negative correlation between the height-to-width (H/W) ratios and the output UTCI, with R-2 = 0.71, and much stronger (R-2 = 0.91) if east-west orientations are excluded from the results, exceeding correlations previously reported for Cairo. Maximum UTCI reductions due to changing H/W and orientation approach similar to 6 degrees C. Considerable variation is shown in the strength of the correlation between UTCI and the asymmetrical H/W ratio of each flank, with R-2 = 0.81 for Southeast side compared to R-2 = 0.4 for Northwest side. Design recommendations are given urban planners based on using the optimised parameters that at least achieve a UTCI reduction benchmark that exceeds those resulting from using the regulations' thresholds.

Automated summary

Urban geometry plays a crucial role in determining microclimatic conditions, with adjustments in building heights, street widths, and orientations significantly impacting outdoor thermal comfort in hot-arid climates such as Cairo, Egypt. Strong negative correlations were found between height-to-width ratios and UTCI outputs, with noticeable reductions in UTCI achievable through changes in H/W ratios and orientations. Recommendations for urban planners highlight the importance of using optimized parameters to exceed regulatory thresholds and improve thermal comfort levels in urban environments.