Water molecules inside a cloud are constantly changing colliding each other, creating electrostatic charges. Usually positive charges are on the top part of the cloud and the negative ones in the bottom. Stathistic studies made all over the world shown that 95% of the clouds has negative charge in the bottom.

When there is a charge excess, these look for a gorund way generating a lightning, who always comes in high temperature, tension and stream, and can cause injuries and even death. Also they can cause serious damage in electronic and electrical equipment.