Wind weakening in a dense high-rise city due to over nearly five decades of urbanization

Decades of urbanization can lead to significant wind reduction in urban areas. At the King's Park meteorological station in the heart of the Kowloon Peninsula Hong Kong, a wind speed reduction of 0.6 m/s per decade was observed from 1968 to 1995, and -0.16 m/s per decade from 1996 to 2017. We obtained data on the changing three-dimensional urban morphology of Kowloon during the period of 1964-2010, and conducted computational fluid dynamics simulations on historical wind environment considering the prevailing winds. The wind speed and its loss were calculated as both intrinsic and comprehensive spatial averages within an elevation of 200 m. The results show that the overall mean wind speed in the studied urban areas gradually decreased due to the continuous urban development and elevation in building height. The total wind loss ratios at three representative locations have increased from less than 10% to greater than 20% during the study period. The total wind loss ratio may increase to about 40% by 2050 if the current weakening trend continues. The average wind speed at pedestrian level has significantly declined, and local acceleration of wind was only observed in some local areas. However, such accelerated airflow is only maintained around a few blocks of buildings. Our study demonstrates the impact of urbanization on the wind weakening in Hong Kong and reveals the importance and need of factoring in urban air ventilation into the design of urban morphology.