Cities attract 40% more lightning strikes than the surrounding countryside..and it's all due to the heat they emit. A 12-year study carried out in Houston and the surrounding countryside shows that the city area was hit by lightening, on average, 7 times a year, whereas in the countryside there were only 2 hits a year. The difference between the country and the city was more pronounced at mid-day in the summer and autumn. But why do cities attract lightning? The researchers from Texas A&M university have shown that this is not because the tall city buildings attract lightening, but because heat rising from the city buildings adds energy to storms overhead. This can turn rainstorms into thunderstorms. Air pollution from the many oil refineries in the region also adds to the problem. Particles emitted from the refineries attract water droplets to form clouds. This "lightning map" will help power companies find the right spot to put their transformers.