Question

How are some changes both desirable and undesirable

Answer 1

Let us take the example of rain. Excess of rain can cause flood due to the rise in water in water bodies and causes a lot of damage to the economy of the people.
Also it is very helpful for us. There are numerous household chores that are done with the help of water. It is also used as a raw material in industries.It is also the source of oxygen for aquatic animals.