Mapping Extreme Hot Weather Events By Adopting Urban Environmental Parameters- a Case Study of Hong Kong

Rapid urbanization in Hong Kong has led to more frequent extreme weather events such as very hot days and hot nights. The Hong Kong Observatory defines days with a minimum temperature of 28°C or above as hot nights and days with a maximum temperature of 33°C or above as very hot days. The annual count of hot nights and very hot days has increased significantly, by 19 and 10 respectively from 1885 to 2015 [1]. The increasing hot weather events can lead to excess energy consumption and an increase in heat-related mortality. However, there is still a very limited understanding of how hot weather varies within the urban environment. This study aims to examine and quantify the spatial variation of very hot days and hot nights across Hong Kong. Urban environment parameters such as the sky view factor, NDVI (Normalized Difference Vegetation Index) and digital elevation models are used to describe the urban morphology.

Hourly air temperature data from 40 Hong Kong Observatory stations from 2011 to 2015 were used for mapping the hot hours. First, the annual mean hot night hours and very hot day hours over the five years were counted based on the observatory data. Second, a geostatistical interpolation algorithm, called kriging, was applied to map the very hot days and hot nights. The kriging interpolation expresses the spatial variation of the property in terms of the variogram, and minimizes the prediction errors which are themselves estimated [2]. In addition, the sky view factor, NDVI and digital elevation model information of Hong Kong were involved in the interpolation process through the use of co-kriging to gain a more comprehensive understanding of the correlation of hot weather and spatial patterns. The spatial distribution of the very hot days and hot nights can thus be mapped and the potentially hot spot areas in Hong Kong identified. Results from the study could support the development of a heat wave warning system to ensure the well-being of the Hong Kong inhabitants.

[1] Climate Change in Hong Kong. from Hong Kong Observatory: http://www.hko.gov.hk/climate_change/obs_hk_extreme_weather_e.htm

[2] Oliver, M. A., & Webster, R. (1990). Kriging: a method of interpolation for geographical information systems. International Journal of Geographical Information System, 4(3), 313-332.