The Hydrologic (Water) Cycle

how water cycle interacts with the atmosphere

Water evaporates from oceans, lakes, and land surfaces into vapor, condenses into clouds, and falls as precipitation.

how water cycle interacts with the hydrosphere

Includes all of Earth’s water—oceans, rivers, lakes, groundwater, glaciers, and even water vapor

how water cycle interacts with the Geosphere

• Water infiltrates soil and rock layers, forming groundwater and aquifers.

how water cycle interacts with the Biosphere

Living organisms take in water for life processes and release it back through respiration, excretion, and transpiration.

Water moves between reservoirs (storage locations such as the ocean, atmosphere, glaciers, and aquifers) via

fluxes (processes like evaporation, precipitation, runoff, and infiltration)

How does temperature affect the water cycle

influences evaporation and precipitation rates

How does warming climate affect the water cycle

increases atmospheric moisture, causing more intense rainfall events and longer droughts.

How does melting ice and reduced snowpack affect the water cycle

alter freshwater storage

El Niño/La Niña affect the water cycle

cycles shift rainfall and drought patterns globally

El Niño

• climate pattern characterized by unusually warm ocean temperatures in the central and eastern tropical Pacific Ocean

• trade winds weaken. Warm water is pushed back east, toward the west coast of the Americas.

La Nina

• a cold event.

• trade winds are even stronger than usual, pushing more warm water toward Asia.

Reservoirs

• represent where water is stored (atmosphere, ocean, groundwater)

Fluxes

represent the rates at which water moves between them (rain, evaporation, infiltration)

outflow > inflow

water is depleted — an unsustainable system

Oceans hold how much of earths water

• 97% of Earth’s water (salty, not drinkable).

How much of earths water is freshwater

3% total — mostly frozen (≈70% in ice caps) or deep underground

How much of earths freshwater is available

• Only about 1% is accessible in rivers, lakes, and shallow groundwater

How much water does the atmosphere contain

• .001% of total water, but it cycles rapidly (average residence time: ~10 days)

characteristics of aquifers

• (porous, permeable rock/sediment layers)

Groundwater depletion cause by

Overuse for irrigation (e.g., Ogallala Aquifer)

Dams and diversions impact on freshwater availability

• Alter natural flow, trap sediment, reduce downstream biodiversity.

How Climate change impacts freshwater availability

• Alters precipitation and recharge rates.

Point sources of pollution

• Pipes, factories, or wastewater discharge.

Nonpoint sources of pollution

• Runoff from farms, cities, or roads

Nutrients (N, P)cause

• algal blooms → eutrophication.

Sediment pollution effects

• cloudy water, habitat loss.

Chemical pollution effects

toxins (e.g., lead in Flint, MI).

Biological pollution effects

pathogens from sewage or animal waste

Agriculture uses how much freshwater

~70%

Industry uses how much freshwater

~20%.

Public/residential uses how much freshwater

• ~10%

Water footprint

Hidden or “embedded” water in products (e.g., 500 gal/lb pork; 700 gal/gal beer).

Growing population, diet, and industrialization increase

water demand

Conservation Strategies for water scarcity

• Low-flow fixtures, leak repairs, shorter showers.

• Smart irrigation and rainwater harvesting.

• Water recycling and graywater use

Technological Solutions for 

Desalination (removing salt from seawater

Dam removal and river restoration to restore flow and habitats

What is desalination, and what’s its main drawback?

Removing salt from seawater; it’s energy-intensive and costly.

Name one household and one agricultural water conservation method

Household: low-flow showerheads.
 Agricultural: drip irrigation.

Clean Water Act (1972)

• Regulates pollutants in U.S. surface waters.

Safe Drinking Water Act (1974)

• Ensures safe public water systems.

UN Declaration (2010)

Access to safe, clean water is a human right

What does the Clean Water Act regulate

Surface water pollution

When did the UN recognize water as a human right?

2010

Which sphere contains groundwater

Geosphere

Which process connects the biosphere and atmosphere

Transpiration

Why is the hydrologic cycle essential to life

It redistributes water, nutrients, and energy across Earth’s systems.