Spatial and temporal patterns of lightning strikes in the eastern Lesotho Highlands, southern Africa

Abstract

The lightning climatology of alpine regions is not well known, in particular spatial patterns of the altitude and facing direction of rock surfaces affected by cloud-to-ground lightning strikes. This study describes the spatial and temporal variability of mesoscale lightning flash climatology of the eastern Lesotho Highlands, southern Africa, during the period 2006–2011, based on data from the South African Weather Service (SAWS). Three study sites located within 8 km of each other show different temporal and elevational patterns of flash density, likely related to the trajectory and properties of incoming weather systems. Lightning flash density does not precisely match with land surface hypsometry at the three sites; rather, flashes occur preferentially at higher elevations that correspond to locations with exposed bedrock summits. We also compare spatial patterns of lightning flash density from the SAWS database with evidence for lighting strike impacts on bedrock surfaces in the field. Strike impacts, based mainly on geomorphological criteria, are identified within a very narrow elevational range which is determined largely by geological factors. The mesoscale lightning flash climatology cannot be used as a predictor of strike impact location or frequency. This has implications for both lightning hazard risk and the rate of alpine debris production by lightning strikes.