Lightning Changes in Response to Global Warming in Rio de Janeiro, Brazil

Physical concepts based on the Clausius-Clapeyron relation and on the thermodynamics and aerosol characteristics associated with updrafts, global climate models assuming different parametrizations and lightning-related output variables, and lightning-related data (thunderstorm days) are being used to infer the lightning incidence in a warmer planet, motivated by the global warming observed. In all cases, there are many gaps to be overcome making the lightning response to the global temperature increase still unpredicted. Values from almost 0% (no increase) to 100% have been estimated, being 10% the most common value. While the physical concepts address only part of the problem and the global climate models need to make many simple assumptions, lightning-relate data have strong time and space limitations. In this context, any new evidence should be considered as an important contribution to better understand how will be the lightning incidence in the future. In this article, we described new results about the occurrence of thunderstorms from 1850 to 2010 (a period of 160 years) in the city of Rio de Janeiro, in the Southeast of Brazil. During this period thunderstorm days were recorded in the same location, making this time series one of the longest series of this type available worldwide. The data support an increase of 21% in the mean annual thunderstorm days during the period, while surface temperature increased by 0.6°C during the period. Considering that the mean annual number of thunderstorm in the beginning of this period was 29, we found an increase of one thunderstorm day per 0.1°C of increase in the surface temperature. Assuming that the number of lightning flashes per thunderstorm remains approximately constant during the period, this number corresponds to an increase in the lightning flash rate of approximately 35% per °C of increase of temperature. In addition, considering that the increase of the global temperature during the period was almost the same that observed in Rio de Janeiro, we can conclude that this increase in the lightning flash rate is due to the global warming with no effect of urban activity. Finally, we found that monthly thunderstorm days and monthly mean surface temperature show a linear correlation with a coefficient of 0.9 along the period.