Spatial characteristics of severe storms in Hong Kong

A storm may cause serious damage to infrastructures and public safety. The storm spatial distribution is an important piece of information in drainage system design and landslide hazard analysis. The primary objective of this paper is to quantify the spatial characteristics of three severe storms in Hong Kong. The maximum rolling 4, 24 and 36 h rainfall amounts of these storms are introduced firstly. Then the spatial structure of precipitation represented by semivariograms is analysed in both isotropic and anisotropic cases. Afterwards, the distribution of rainfall in spatial domain is assessed via surface trend fitting. Finally the spatial correlation of detrended residuals is determined through studying the scales of fluctuation along eight directions. The spatial distribution of the maximum rolling rainfall can be represented by a rotated ellipsoid trend surface and a random field of residuals. The principal directions of the surface trend are between 25 and 45°. The scales of fluctuation of the detrended residuals are found between 5 and 25 km according to the semivariograms and autocorrelation functions. The spatial correlations of the maximum rolling rainfall are affected by the rainfall duration. The scale of fluctuation becomes smaller as the rainfall duration increases. Such spatial characteristics are related to the local terrain and meteorology factors.