Compound Tropical Cyclone Heat (TC‐Heat) Hazard in Hong Kong: Amplifying Urban Heat Extremes With Storm Position‐Driven Peripheral Warming and Urban Footprint

• Published in: Journal of geophysical research. Atmospheres 2024-11, Vol.129 (21), p.n/a
• Main Authors: Chang, Jeffrey Man‐Hei, Lam, Yun Fat, Wong, Yat‐Chun, Hon, Kai Kwong
• Format: Article
• Language: English
• Subjects: Advection; Air circulation; Air flow; Air temperature; Atmospheric circulation; Breeze circulation; Circulation patterns; Cities; Climate and weather; Climate change; Climate models; Climatic analysis; Climatic data; Coastal circulation; Coasts; compound hazard of tropical cyclones and heatwaves; Cyclones; Data analysis; Emergency warning programs; Extreme heat; Extreme high temperatures; Extreme weather; Global climate; Hazards; Heat; Heat transfer; Heat transport; Heavy rainfall; High temperature; Hot weather; Hurricanes; HYSPLIT backward trajectory; Meteorological conditions; MODIS; Rainfall; Sea breeze circulation; Sea breezes; Storms; Subsidence; tropical cyclone; Tropical cyclones; Urban areas; urban thermal advection; Urbanization; Weather; Weather conditions; Weather forecasting; Wind
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2024JD041037

Compound hazards involving tropical cyclones and extreme heat (“TC‐heat”) have rarely been examined in prior research. Peripheral subsidence associated with cyclones can warm an area to varying degrees, depending on the cyclone's strength and position. Meanwhile, the peripheral airflow also overwhelmed the land‐sea breeze circulation system in coastal cities and favored downwind urbanized heat advection on the Southern China coastline. Here, we systematically applied ERA5 global reanalysis data, local surface‐level observations, MODIS‐based land‐cover data and HYSPLIT backward trajectories to evaluate how the position of distant TCs may divert the monsoon system and foster the surface heat advection from upwind urban agglomerate amplifying air temperature in downwind coastline. The analysis suggests when a distant TC is situated in a favorable area (the vicinity of Taiwan and Luzon Strait) at roughly 500–1,250 km to the east of Hong Kong, it forms a unique meteorological condition which allows the surface heat transport from the Greater Bay Area to Hong Kong, reflecting that regional build‐up of heat could be an important mechanism for producing local heat extremes. Plain Language Summary Rapid urbanization and global climate change bring us new hazards through compound extreme weather events in urban society. Tropical cyclones (TC) are known to bring violent wind and heavy rain upon arrival, while in distant they can also send very hot weather conditions (called TC‐heat events) to regions under its subsidence airflow. This study shows the combined effect of heat from upwind urban areas in coincidence with the TC‐induced subsidence could bring even higher temperatures to the downstream cities like Hong Kong. Comprehensive analysis with global climate data, local weather observations, and backward simulation models were used to further understand how the location of TC may adverse the wind circulation patterns in inland areas and contribute to a larger extreme heat threat to the coastal cities. This can facilitate the early forecast and warning for the potential occurrence of such TC‐heat compound hazard, potentially benefitting public preparedness and response in combating extreme heat and cyclone influences. Key Points High temperature events occur when distant Tropical Cyclone (DistTC) located at 500–1,250 km from Hong Kong Surface heat can be built‐up in inland China cities, transport to Hong Kong as downwind footprint and contribute to the temperature