The continuous circulation of water through the Earth's atmosphere, surface, and subsurface driven by solar energy and gravity. Also called the water cycle.
The hydrologic cycle, also known as the water cycle, describes the continuous movement of water within the Earth system through the processes of evaporation, transpiration, condensation, precipitation, infiltration, runoff, and groundwater flow. Solar energy drives evaporation from oceans, lakes, and land surfaces, while plants contribute through transpiration. Water vapor rises into the atmosphere, cools, condenses to form clouds, and returns to the surface as precipitation in the form of rain, snow, sleet, or hail. Upon reaching the ground, water may infiltrate into the soil, flow overland as surface runoff, or be intercepted by vegetation. Subsurface water may percolate to recharge aquifers, which eventually discharge to streams, lakes, or oceans, completing the cycle. The global water cycle moves approximately 500,000 cubic kilometers of water per year and is a fundamental driver of weather, climate, and ecosystem functioning. Human activities, including land use change, water withdrawals, dam construction, and greenhouse gas emissions, significantly alter components of the hydrologic cycle at local, regional, and global scales.