First saw this mentioned in the Sept 15 Nat Geo.
Projected increase in lightning
strikes in the United States due to
global warming
http://www.romps.berkeley.edu/pubs/pubs-2014-lightning.htmlHere we propose that the lightning flash rate
per area is proportional to the precipitation rate
times convective available potential energy (CAPE).
Sorry, the formula doesn't paste easily. It's in the PDF at the link...