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Hydrologic cycle
The continuous movement of water through Earth's hydrosphere, including processes like evaporation, condensation, and precipitation.
Storage of Earth's water
In oceans, glaciers, and rocks below Earth's surface; over 99% of Earth's water is in these storage forms.
Freshwater percentage
Less than 3%, with most of it frozen in glaciers and ice sheets.
Ocean volume and atmospheric moisture during an ice age
Ocean volume decreases and atmospheric moisture diminishes as ice sheets grow.
Evapotranspiration
The combined process of water evaporation and plant transpiration from land surfaces.
Primary source of water vapor
The oceans, which provide 86% of all evaporated moisture.
Water vapor residence time
Around 10 days, although it can be shorter.
Precipitation vs. evaporation
Evaporation exceeds precipitation over oceans, while precipitation exceeds evaporation over continents.
Excess precipitation return to ocean
Through surface runoff, which flows back into the sea in streams and rivers.
Role of runoff
Runoff balances excess precipitation over continents, preventing oceans from drying up and land from flooding.
Residence times of water molecules
Water can be stored for thousands of years in oceans, lakes, or glaciers, but moves rapidly through the cycle once in motion.
Energy source for hydrologic cycle
The Sun, which drives processes like evaporation and powers weather patterns.
Latent heat in water vapor
Latent heat is released during condensation, fueling storms and helping transfer energy from the tropics toward the poles.
Global precipitation and evaporation relationship
Over time, global precipitation equals global evaporation, balancing the hydrologic cycle.
Moisture movement from sea to land
Through atmospheric advection (movement of moist air from oceans to land).
World ocean
A single, interconnected body of saltwater covering about three-fourths of Earth's surface, divided into five principal parts: the Pacific, Atlantic, Indian, Arctic, and Southern Oceans.
Pacific Ocean characteristics
It occupies about one-third of Earth's surface, is the deepest, and extends to both polar circles, with most of its area in tropical zones.
Average salinity of seawater
About 35 parts per thousand or 3.5% of total mass, mainly composed of sodium chloride and other salts.
Salinity variation in ocean regions
High salinity occurs where evaporation is high, and low salinity is found near major rivers, in areas with heavy rainfall, or where river discharge is high.
Ocean's increasing acidity
Absorption of CO2 from the atmosphere forms carbonic acid, making the ocean more acidic, which affects organisms that rely on calcium carbonate for their shells.
Ocean water temperature variation
It decreases with increasing latitude, from about 26°C near the equator to around -2°C in polar regions, with warmer water generally on the western side of ocean basins.
Factors influencing seawater density
Temperature, salinity, and depth; high temperatures lower density, while high salinity and greater depth increase density.
Role of ocean currents
Currents create warmer western ocean areas and cooler eastern areas, also leading to upwelling of colder, denser water in some regions.
Desalination
A process to remove salts from seawater to make it drinkable, crucial for providing freshwater in arid regions, though it is energy-intensive.
Types of ocean water movement
Tides, currents, and waves.
Causes of tides
The gravitational attraction between the Earth, Moon, and Sun.
Tide frequency
Nearly every 25 hours, with two high and two low tides.
Flood tide
The period when water rises and reaches high tide.
Ebb tide
The period when water recedes after high tide until it reaches low tide.
Spring tides
Higher than usual tides that happen when the Sun, Moon, and Earth align during full and new moons.
Causes of neap tides
The Sun and Moon are at right angles to each other, reducing tidal range.
Moon's elliptical orbit effect on tides
When the Moon is closest to Earth (perigee), tides are higher; when farthest (apogee), tides are lower.
Cryosphere
The solid portion of the hydrosphere, consisting of the world's ice, second only to oceans as a water storage reservoir.
Land surface ice coverage
Approximately 10 percent.
Types of ice on land
Mountain glaciers, ice sheets, and ice caps.
Water locked in ice feeding rivers
Nearly 900 years at their present flow rate.
Types of oceanic ice
Ice pack, ice shelf, ice floe, and iceberg.
Iceberg above water percentage
Only about 14 percent of an iceberg remains above water.
Composition of oceanic ice
Almost entirely freshwater, as salts from seawater are not incorporated into ice crystals.
Summer sea ice in the Arctic
It has diminished significantly over the last 45 years.
Permafrost
Permanently frozen subsoil found in high-latitude and high-elevation regions, widespread in northern Canada, Alaska, and Siberia.
Active layer of permafrost in summer
Only the upper 30 to 100 centimeters thaws, while the layer below remains frozen.
Thawing permafrost effect on infrastructure
It destabilizes buildings, roads, and pipelines, disrupting transportation and business.
Environmental issue from thawing permafrost
Wet thermokarst conditions, leading to subsidence and oversaturation of the ground.
Coastal erosion rate increase
From an average of 6 meters (20 feet) per year to as much as 20 meters (65 feet) per year by 2010.
Greenhouse gases from thawing permafrost
Carbon dioxide or methane from decomposing organic matter, contributing to greenhouse gas concentrations.
Surface waters percentage of total moisture
Only about 0.02 percent.
Surface waters
They include lakes, wetlands, swamps, and marshes, and are abundant in many regions, providing essential resources.
Lake
A body of water surrounded by land, with no minimum or maximum size. Smaller lakes are often called ponds.
Percentage of nonfrozen surface water in lakes
Well over 90 percent.
Largest freshwater lake by volume
Lake Baikal in Siberia.
Saline lakes
More than 40 percent of lake water on Earth is salty, like the Caspian Sea, which holds most of the world's nonoceanic saline water.
How lakes become saline
Lakes without natural drainage outlets accumulate salts and minerals from inflowing freshwater that evaporates over time.
Ephemeral lakes
Small salt lakes that contain water sporadically and are often dry due to insufficient inflow.
Conditions for lake formation
(1) A natural basin with a restricted outlet, and (2) enough inflow of water to keep it partly filled.
Water drainage in lakes
Most lakes are fed and drained by streams, with one stream usually serving as the drainage outlet.
Distribution of lakes
Lakes are common in glaciated regions where glacial erosion created basins, but some are formed by tectonic faulting or sinkhole collapse.
Geologic changes in lakes
Lakes are temporary features that can fill with sediment from inflowing streams or drain through outflowing streams, leading to their eventual disappearance.
Human impact on lakes
Diverting streams, as seen in California's Mono Lake, and irrigation projects, like those affecting the Aral Sea, can significantly reduce lake sizes.
Consequence of irrigation on the Aral Sea
It shrank to less than 10 percent of its original size, causing the collapse of the fishing industry and environmental issues.
Decline of Lake Chad
Ongoing drought and water diversion projects, reducing it to about 10 percent of its original size.
Reservoirs
Artificial lakes created primarily by the construction of dams for flood control, water supply, and hydroelectric power.
Environmental concerns from dam construction
Altered ecosystems, loss of land, restricted stream flows, and issues like sedimentation affecting reservoir life.
Notable features of Lake Mead
Created by Hoover Dam, it is the largest reservoir in the U.S. and its water levels are affected by Colorado River water allotments.
Controversy of Glen Canyon Dam
Its construction led to the flooding of scenic canyons, sparking opposition from environmental activists like the Sierra Club.
Consequences of fluctuating water levels in reservoirs
They lead to visible 'bathtub rings' and can cause catastrophic dam failures if not managed during extreme weather.
Wetlands
Areas saturated with water that influence soil and plant/animal communities, serving as important ecosystems.
Swamps vs. marshes
Swamps are dominated by trees, while marshes are primarily vegetated with grasses and rushes.
Rivers and streams in the hydrologic cycle
They drain land surfaces and transport water, sediment, and dissolved chemicals seaward, even though they hold a small proportion of the world's water.
Precipitation patterns and rivers
Humid areas have many rivers that flow year-round, while dry areas have fewer, mostly ephemeral streams.
Amazon River
It yields nearly 20 percent of the world's total stream discharge.
Mississippi River significance
It is the largest river in North America, with a drainage basin covering about 40 percent of the contiguous U.S.
Groundwater
Underground water that exists beneath the land surface, primarily originating from precipitation that percolates into the soil.
Movement and storage of groundwater
Groundwater comes from precipitation that seeps down through soil or from lakes and streams.
Porosity
The percentage of total volume of a material (rock or soil) that consists of voids (pore spaces) that can hold water.
Permeability
The ability of rock or soil to transmit groundwater, determined by the size and interconnectedness of the pore spaces.
Aquifers
Moderately to highly permeable rock structures that store and slowly move underground water.
Aquicludes
Impermeable materials, like clay or dense rock, that hinder or prevent water movement.
Zone of Aeration
The upper layer of the subsurface where pore spaces are filled with a mix of water and air.
Zone of Saturation
The layer below the zone of aeration where all pore spaces are fully saturated with water.
Cones of Depression
A phenomenon that occurs when water is withdrawn from a well faster than it can be replenished.
Confined Aquifers
Aquifers that are surrounded by impermeable aquicludes, restricting direct infiltration from above.
Artesian Wells
Wells that tap into confined aquifers, allowing water to rise under pressure to the surface.
Groundwater Pollution
Contamination of groundwater due to polluted surface water seeping into aquifers from sources like industrial waste.
Waterless Zone
The lower limit of the zone of saturation that lacks pore spaces for water.
Groundwater Mining
The rapid extraction of groundwater faster than it can be replenished.
Global Environmental Change
Monitoring groundwater resources is crucial as demand increases and natural recharge rates often cannot keep up.
Ogallala Aquifer
The largest aquifer in the U.S., located under the Great Plains, and a classic example of groundwater mining.
