CH 10 Hydrologic cycle

Hydrologic Cycle

The continuous movement of water through evaporation, transpiration, condensation, and precipitation. Example: Water evaporates from oceans, condenses into clouds, and falls as rain that returns to rivers and oceans.

Evaporation

When liquid water changes into water vapor due to heat. Example: The sun heats the ocean surface, causing water molecules to rise into the atmosphere.

Transpiration

The release of water vapor from plants into the atmosphere. Example: Trees in a rainforest release moisture through their leaves, adding humidity to the air.

Condensation

When water vapor cools and turns back into liquid droplets. Example: Clouds form when moist air cools high in the atmosphere.

Precipitation 

When condensed water droplets become heavy enough to fall as rain, snow, sleet, or hail. Example: Rain showers after a warm humid day.

Purification

Evaporation and condensation remove impurities from water. Example: When ocean water evaporates, salt and particles stay behind, creating clean freshwater as rain.

Rain Shadows 

Dry regions on the leeward side of mountains where moist air has already lost its water vapor. Example: The Mojave Desert lies in the rain shadow of the Sierra Nevada mountains.

Groundwater

Water that soaks into the soil and moves through porous layers of rock beneath the surface. Example: Wells tap into groundwater for household use.

Watershed

The land area that channels rainfall and snowmelt into rivers, lakes, and oceans. Example: The Mississippi River watershed drains water from much of the central U.S.

Surface Water

All water found above ground, such as rivers, lakes, and streams. Example: Lake Superior or the Amazon River.

 Aquifers

Layers of rock or sediment that store and transmit groundwater. Example: The Ogallala Aquifer supplies irrigation water to much of the U.S. Midwest.

Recharge Area

The area where water infiltrates the ground and refills an aquifer. Example: Rainfall soaking into sandy soil in rural regions.

Porosity

How much open space a material has for storing water. Example: Sand has high porosity, while clay has low porosity.

Permeability

How easily water can flow through rock or soil. Example: Gravel is more permeable than clay because water moves through it faster.

Unconfined Aquifer 

An aquifer where water seeps directly from the surface above. Example: A shallow water table under open ground.

Confined Aquifer

An aquifer trapped between layers of impermeable rock that recharges slowly. Example: The Floridan aquifer beneath layers of clay and rock.

Surface Subsidence

The sinking of land caused by groundwater being pumped out faster than it’s replaced. Example: California’s San Joaquin Valley has dropped over 30 feet in some areas.

Impervious Surfaces

Roads, roofs, and parking lots that prevent water from soaking into the ground. Example: Urban flooding after heavy rain.

Nonconsumptive Water Use

Water that is used but returned to its source, often after treatment. Example: Cooling water in power plants that’s later released back into rivers.

Consumptive Water Use

Water that is removed from a source and not returned. Example: Irrigation water that evaporates or is taken up by plants.

Desalination

The process of removing salt from seawater to make it drinkable. Example: Desalination plants in the Middle East providing freshwater to cities.

Human Impacts on the Hydrologic Cycle

Humans alter the water cycle through deforestation, urbanization, dams, and pollution. Example: Roads and buildings reduce natural groundwater recharge.

Bottled Water Pros and Cons

Pros: portable, useful in disasters. Cons: high energy use, plastic waste, draws from public water supplies. Example: The U.S. used 46 billion gallons of bottled water in 2023.

Ways to Increase Water Efficiency

Use efficient fixtures, take shorter showers, and reduce dishwashing water use. Example: Low-flow showerheads save gallons daily.

Agricultural Water Efficiency

Drip irrigation and treadle pumps use less water and reduce evaporation. Example: Farmers in dry climates use drip systems to conserve water.