a thunderstorm is a kind of storm & a storm is a source of heavy rain ->  a thunderstorm is a source of heavy rain  a thunderstorm is a source of heavy rain & rain causes bodies of water to increase amount of water they contain ->  a thunderstorm can cause bodies of water to increase amount of water they contain  a thunderstorm can cause bodies of water to increase amount of water they contain & when a body of water receives more water than it can hold , a flood occurs ->  a thunderstorm can cause bodies of water to flood  a thunderstorm can cause bodies of water to flood & a stream is a kind of moving body of water -> a thunderstorm can cause a stream to flood