In order to write about natural disasters, you must decide what your focus is going to be. What is it about natural disasters that you are going to convey to your audience? You could talk about the causes of a type of natural disaster: why do tornadoes form? how do they cause the damage that they do? what can be done to protect oneself and ones property in the a face of a tornado. You could ask yourself and then answer those types of questions for any kind of natural disaster.
You could write your essay about the financial reprecussions of natural disasters -- for the individual, for businesses, for insurance companies, and for the government of the area affected.
You could write your essay about why people choose to live in areas that are especially susceptible to natural disasters. Why do people live near known fault lines? Why do people live in areas known to flood regularly? Why do people live where hurricane's are a regular threat?
A good paragraph should have a topic sentence that makes the subject of the paragraph clear, and then the body of the paragraph should provide the examples and explanation of the examples to help show what ever it is that the paragraph is trying to prove.