Final answer:
The hydrological cycle is predominantly driven by solar energy, with the Sun as its main energy source for evaporation and sublimation. Gravity also assists by helping precipitate condensed water and directing surface and subsurface water flow back into the oceans.
Step-by-step explanation:
The main source of energy that drives the hydrological cycle is solar energy. The Sun provides the energy needed for the evaporation of water from oceans, rivers, and lakes and for the sublimation of ice into water vapor. When water vapor cools, it condenses into clouds, and gravity then helps the gathered liquid or frozen droplets fall back to Earth as precipitation (rain, snow, etc.). This precipitation can then flow back to the oceans through streams and rivers, infiltrate into the ground as subsurface groundwater flow, or evaporate again to continue the cycle.
During the hydrological cycle, water molecules gain energy during evaporation and sublimation processes, which are initiated by the sun's heat. Conversely, they lose energy during condensation, when they return to a liquid state to form clouds, and during precipitation, when they lose their gravitational potential energy as they fall to Earth.
In summary, the water cycle is an intricate system that balances the water on Earth and is essential for the sustenance of life. The Sun and gravity are the crucial forces that drive this perpetual cycle.