We all know the water cycle: sunlight evaporates water into the atmosphere, where it forms clouds, which rain water back down to the ground. Have you ever wondered how much energy is involved in this cycle?
We can start to understand the scale by looking at the amount of work involved in a single, smallish rain shower. It will take the same amount of energy to raise that water back up into the atmosphere (not even counting the energy involved in temperature and phase changes).
Estimate the amount of work gravity does on the rain by assuming total precipitation of $1.00\,cm$ of rain falls over a surface area of $100\,km^2$ from a cloud that is $2.00\,km$ above ground.