What changes in the water cycle mikght take place if the earth's climate becomes hotter? what about colder?

Answer 1

Hotter air can hold more water, so there'll be more vapor and less liquid water. The reverse is true for cooler.

The effect is pretty small. But it's enough to trigger a positive feedback, where the increased water vapor in the air creates even more greenhouse effect. No one knows yet exactly how significant this feedback will be.

Answer 2

The water cycle is largely driven by temperature, the higher the temp the faster the cycle. This is because water enters the water cycle through evapouration, primarily from the seas and oceans.

As the seas and oceans become warmer less energy is required for the molecules of water to break free from being in a liquid state to being in a gaseous state. Consequently more evapouration takes place.

The maximum amount of water vapour in the atmosphere is determined by Saturation Vapour Pressure (SVP), the warmer the air is the higher the SVP and the more moisture it can contain. Once SVP is reached the water vapour is expelled from the atmosphere either by deposition as dew or by condensing into water droplets which fall as precipitation.

With increasing temps comes increased evapouration and therefore increased precipitation. Conversely, as temps fall there is less evapouration and less precipitation. This is one of the primary reasons for monsoons in hot climates and the very dry desert conditions in Antarctica (the snow there has accumulated very, very slowly over millions of years).

Winds are the result of differences in temperatures, as temps change so too do wind patterns, winds are the delivery mechanism for precipitation.

So whilst temp changes affect the rate of precipitation they also affect where it falls. There could be an average global increase or decrease in precipitation but it's not a uniform change. For example, with the current warming we're observing a global increase in precipitation but there are some places that are receiving less rainfall.

Answer 3

Go rent the movie, "day after tomorrow"
It can happen.