The sun can give you heatstroke, make you dehydrated and too much time in the sun can lead to suntan and possible skin cancer.
Often summer isn't enjoyable as many say they enjoy going to the beach when it is hot, I totally disagree as the beach is often too hot and windy and the sand goes everywhere.
In summer there is more chances of severe natural disaster's such as cyclones, hurricanes and tornadoes as it is windy and there is a higher risk of bushfire's as it is hot.