A Seasonal Resilience Index to Evaluate the Impacts of Super Typhoons on Urban Vegetation in Hong Kong

Urban vegetation plays a vital role in developing sustainable cities via essential urban ecoservices. Potential threats, however, from natural disturbances to urban vegetation and its resilience remain unclear at local scales. Taking the super typhoon Mangkhut in 2018 as an example, this study aimed to develop a resilience index to evaluate the impacts of super typhoons on urban vegetation in Hong Kong at the species level. The typhoon impacts and canopy recovery of four tree species were assessed by integrating field and remote sensing data. First, we discussed the specific influencing factors of the typhoon. Second, we constructed a normalized seasonal difference vegetation index (NSDVI) to identify and characterize the distribution of tree species. Then, a seasonal resilience index was developed at the species level to investigate the severity and recovery of the vegetation after the typhoon. The results demonstrated that strong wind was the leading cause of damage. NSDVI improved tree species identification by more than 10 percent compared with conventional methods. In terms of the resilience analysis, 87.25 percent of the trees were affected by the typhoon. Royal palm (Roystonea regia) performed well among the four species during the typhoon, suffering minor losses. A total of 47.95 percent of the trees recovered to their pretyphoon state two years after the typhoon. The recovery speed of Hainan ormosia (Ormosia pinnata) was the fastest. This research provides a scientific reference for the planning of urban vegetation species to increase their resilience and ability to provide ecoservices despite natural disturbances.