Underestimating lightning risk due to multiple Ground Strike Point flashes

Abstract

This paper presents an analysis of the lightning risk in South Africa using data detected and geolocated between July 2007–July 2016 from the Southern African Lightning Detection Network (SALDN), which is owned and operated by the South African Weather Service. The study specifically examines the Ground Flash Density (GFD) parameter, which is currently used to depict the lightning risk across the country to inform effective lightning protection. The research finds that the GFD parameter may underestimate the actual lightning risk to ground-based infrastructure, people, animals, and plants. A Ground Strike Point (GSP) algorithm is applied to the SALDN dataset to derive a more accurate Ground Strike Point density map of South Africa. The difference map results, obtained by comparing the GSP density with the GFD, reveals that the GFD parameter underestimates the lightning risk across the entire South African landscape, more significantly in areas between Mpumalanga and KwaZulu-Natal provinces. In these regions, the underestimation reaches a magnitude as high as 32 GSPs per square km per year. The study suggests that applying a constant scaling factor to the GFD parameter can serve as a reliable risk estimation tool when sufficient Lightning Detection Network (LDN) stroke data is unavailable or when there are constraints in data processing power and time due to the large dataset.