hydrosphere

The hydrosphere is the collective realm of water on Earth, encompassing all liquid water, ice, and water vapor. It includes oceans and seas, rivers and lakes, groundwater, glaciers and ice caps, and the water contained in the atmosphere. The hydrosphere interacts with the lithosphere, atmosphere, and biosphere as a cohesive Earth system.

Total volume is about 1.4 billion cubic kilometers. About 97% of this water is salt water in the oceans. Freshwater accounts for roughly 2.5% of all water, of which around 68% is in ice caps and glaciers, about 30% in groundwater, and the remainder in lakes, rivers, soil moisture, and atmospheric water.

The hydrosphere is highly dynamic, driven by the hydrological cycle. Evaporation from oceans and land, transpiration by plants, and sublimation introduce water vapor into the atmosphere, where it condenses into clouds and returns as precipitation. Water then moves via surface runoff, river flow, infiltration, and drainage, recharging groundwater and feeding streams. Residence times vary widely, from days to weeks in the atmosphere to thousands of years in deep groundwater or ice sheets.

The hydrosphere plays a central role in climate and life. It regulates climate by storing and transporting heat, shapes landscapes through erosion and sediment transport, and provides habitats and freshwater essential for ecosystems and human uses. It also underpins weather systems, agriculture, industry, and energy production, particularly through hydropower and the provision of water for consumer and ecological needs.

Human activity affects the hydrosphere through water withdrawals, pollution, dam construction, land-use changes, and climate change, which together influence water availability, quality, and the global water cycle.