A Comparative Study of the Lightning Incidence in Gaborone and Molepolole

The village of Molepolole, in southeastern Botswana, has long been known to experience an unusually high incidence of lightning activity. In an effort to verify this claim scientifically, two CIGRE lightning flash counters with standard antennae were installed at Gaborone and Molepolole in August 1992. This paper presents a summary of the results obtained over the four complete lightning seasons since then. Overall, the lightning ground flash density in Molepolole was 34% greater than in Gaborone. The 25-year mean annual rainfall in Gaborone is 12% more than in Molepolole, while the corresponding figure over the four-year period of observation was 22%. The mean number of ground flashes per mm of rain in Molepolole and Gaborone were found to be 25.5 and 15.5 respectively - a 64% higher figure in Molepolole - suggesting that the difference in lightning activity between the two locations cannot be meteorological or climatological in origin. Various other possibilities, based on topographical and geological causes, are discussed.