Lightning and fire weather in eastern coastal fynbos shrublands: seasonality and long-term trends

Daily weather data (since 1939) from four localities in the south-eastern, coastal part of the Cape Floral Kingdom ('south-eastern-CFK') were used to calculate daily fire danger indices (FDIs). Cloud-to-ground lightning strike distributions (2006-10) were explored for geographical and temporal trends. Low or moderate fire danger conditions were the norm year round, and even large fires occurred under these conditions. Lightning occurred throughout the landscape at fairly low densities (mean -0.4 strikes km(-2) year(-1)) and in all seasons, increasing somewhat during summer. Lightning presence increased with increasing rainfall, relative humidity, temperature and wind speed. Lightning seasonality in the south-eastern-CFK did not differ from that in the south-western-CFK. Our results provide evidence of a largely aseasonal fire regime in eastern coastal fynbos shrublands: FDIs peaked in winter (due to low rainfall and hot, dry katabatic winds) but were not associated with a winter fire regime; lightning and the co-occurrence of lightning and elevated FDIs were aseasonal and were correlated with the incidence of lightning-ignited fires throughout the year. The implication for management is that season of burn is largely unimportant. Mean annual FDI increased significantly over the study period, a trend which is likely to manifest in increased frequency and severity of fire, some of which has already been observed.