What is the driving energy of the hydrologic cycle?
Solar energy
The water cycle is driven primarily by the energy from the sun. This solar energy drives the cycle by evaporating water from the oceans, lakes, rivers, and even the soil. Another way that water moves is from plants to the atmosphere through the process of transpiration. As liquid water evaporates or transpires, it forms water vapour and clouds, where water droplets eventually gain enough mass to fall back to Earth as precipitation. The precipitation then becomes run-off or ground water and works its way—over various timescales—back into the surface reservoirs. The water cycle is essentially a closed system, meaning that the volume of water that is in the hydrosphere today is the same amount of water that has always been present in the Earth system.