An improved method for calculating urban ground roughness considering the length and angle of upwind sector

Most traditional morphometric methods to calculate urban ground roughness only considered uniform height arrays. However, given the complex arrangement of buildings in real urban districts, traditional methods are no longer sufficient to meet current demands. In this paper, wind tunnel experiments were conducted on roughness elements with diverse arrays to determine the mean wind speed profiles in the investigating position under distinct upwind sectors. The experiment results indicate that as the upwind sector expands, its influence on the mean wind speeds profile diminish as the length r of the upwind sector extends to 750 m and the angle θ of upwind sector reaches 70°. This upwind sector, 750 m in length and 70° in angle, is defined as the minimum upwind sector. Beyond this threshold, additional variations in r and θ do not significantly affect the mean wind speed profile. An improved method for calculating urban ground roughness, considering both uniform height arrays and real urban districts, is proposed based on the wind tunnel experiment results and existing morphometric methods. The efficacy of this improved method has been demonstrated in calculating ground roughness in uniform height arrays. When applied to real urban districts, the method yields optimal results when the calculation area is defined as the minimum upwind sector. Compared to traditional morphometric methods, the improved method offers significant advantages and a new approach to determining ground roughness in urban districts.