Hydrology is the scientific study of the movement, distribution, and quality of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A hydrologist studies water’s physical properties, its behavior in nature, and how society uses and affects it.
Water is a unique compound, essential for all forms of life. About 71% of Earth's surface is covered by water, mostly in oceans and other large water bodies. Only 2.5% of this water is fresh, and the rest is saline. Of this fresh water, the majority is frozen in glaciers and polar ice caps or lies too deep underground to be extracted at an affordable cost.
The water cycle, also known as the hydrological cycle, describes the continuous movement of water on, above, and below the surface of the Earth. The cycle illustrates how water changes state between liquid, vapor, and ice at various places in the water cycle, comprising processes such as evaporation, condensation, precipitation, infiltration, runoff, and subsurface flow.
Evaporation is the process of water changing from a liquid to a gas form. This mainly occurs in oceans, rivers, lakes, and soil. The sun’s energy heats water, enabling the molecules to move fast enough to escape as vapor into the air.
In condensation, water vapor in the air cools down and changes back into liquid, forming clouds. This process is the reverse of evaporation.
Precipitation occurs when so much water condenses that the air cannot hold it anymore. Water falls from clouds in the form of rain, snow, sleet, or hail.
After precipitation, some of the water seeps into the ground. Infiltration is the process by which water on the ground surface enters the soil.
Runoff is the movement of water, usually from precipitation, across the land surface towards streams, rivers, lakes, and eventually to the ocean. Runoff can cause erosion and transport nutrients, sediment, and pollutants.
Some of the water that infiltrates will remain in the soil and move as subsurface flow. This water can reappear in springs or contribute to the base flow of rivers.
Freshwater is found in glaciers, ice caps, rivers, lakes, soil, aquifers, and the atmosphere. Despite being a renewable resource, it's unevenly distributed across various regions, leading to abundance in some areas and scarcity in others.
Effective water management involves planning, developing, distributing, and optimizing water resources to meet society’s needs while protecting the environment. It includes irrigation practices, water conservation, pollution control, and building infrastructure like dams and reservoirs for water supply and flood control.
Human activities such as agriculture, industry, and urbanization alter the natural flow of water, affecting its distribution, quality, and availability. Pollution can contaminate water sources, making them unsafe or unusable. Deforestation and urbanization increase runoff, reducing infiltration and groundwater recharge, potentially leading to erosion and decreased water quality.
Hydrology plays a crucial role in understanding and managing Earth’s water resources. By studying the movement, distribution, and quality of water, humanity can better prepare for its future, ensuring sustainable water supply for all forms of life. Understanding hydrology and respecting the principles governing water is fundamental to managing this indispensable resource effectively.
