The Water (Hydrologic) The Water (Hydrologic) CycleCycle

• Earth has a limited supply of water.Earth has a limited supply of water.

• This supply is constantly being This supply is constantly being recycled between the oceans, recycled between the oceans, atmosphere, and land.atmosphere, and land.

The Water CycleThe Water Cycle

• During the recycling of water, water enters During the recycling of water, water enters the atmosphere by evaporation and the atmosphere by evaporation and transpiration.transpiration.– Transpiration is the process where living plants Transpiration is the process where living plants

release water vapor to the atmosphere.release water vapor to the atmosphere.

• Of the precipitation that falls on Earth’s Of the precipitation that falls on Earth’s surface.surface.– 50% returns to the atmosphere by evaporation.50% returns to the atmosphere by evaporation.– 18% 18% infiltratesinfiltrates (sinks into) the ground (sinks into) the ground

((groundwatergroundwater).).– 32% is surface runoff that enters lakes and rivers.32% is surface runoff that enters lakes and rivers.

GroundwaterGroundwater• Zone of saturationZone of saturation

– All spaces, cracks and other openings in soil All spaces, cracks and other openings in soil and rock grains become completely filled and rock grains become completely filled with water.with water.

– Water will stop sinking Water will stop sinking into the soil once it into the soil once it has reached a layer has reached a layer of solid rock that it of solid rock that it cannot pass through.cannot pass through.

• The Water TableThe Water Table– Boundary between Boundary between

the zone of aeration the zone of aeration and the zone of and the zone of saturation.saturation.

GroundwaterGroundwater

• The amount of water in the ground and The amount of water in the ground and the movement of water through the the movement of water through the ground are controlled by the ground are controlled by the characteristics of the soil and rock found characteristics of the soil and rock found near the surface.near the surface.

• Almost all materials on Almost all materials on Earth’s surface are porous.Earth’s surface are porous.

PorosityPorosity

• The number of pores in a material The number of pores in a material compared with its volume.compared with its volume.

• The porosity (percent of empty The porosity (percent of empty space) determines how much air or space) determines how much air or water a sample of rock can hold.water a sample of rock can hold.

• Particle size alone doesParticle size alone doesnot affect the porositynot affect the porosityof a soil.of a soil.

PermeabilityPermeability• The ability of a soil to transmit water.The ability of a soil to transmit water.• The rate (how fast water can pass through The rate (how fast water can pass through

a soil) depends on the size of the pores and a soil) depends on the size of the pores and how the pores are connected.how the pores are connected.

• Surface Surface runoffrunoff occurs occurs when rainfall exceeds when rainfall exceeds the permeability of a the permeability of a soil, when a soil is soil, when a soil is saturated, or when the saturated, or when the slope (gradient) of a soil’s slope (gradient) of a soil’s surface is too great to surface is too great to allow infiltration to occur.allow infiltration to occur.

CapillarityCapillarity• The ability of a soil to draw water upward The ability of a soil to draw water upward

into tiny spaces between soil grains.into tiny spaces between soil grains.• Soils composed of very small particles Soils composed of very small particles

show the most capillary uptake.show the most capillary uptake.– This is because these soils have more This is because these soils have more

surface area per unit volume for water to surface area per unit volume for water to cling to them than do soils with large cling to them than do soils with large particles.particles.

• Capillary water moves upward Capillary water moves upward against the force of gravity against the force of gravity because of the attraction because of the attraction between water molecules and between water molecules and the surfaces of the soil particles.the surfaces of the soil particles.

Rainfall and Stream FlowRainfall and Stream Flow

• Streams and rivers do not respond Streams and rivers do not respond immediately to rainfall.immediately to rainfall.

• Most precipitation falls on the ground Most precipitation falls on the ground and then must flow over the land as and then must flow over the land as runoff to reach a stream.runoff to reach a stream.

• A time lag occurs between maximum A time lag occurs between maximum precipitation and maximum precipitation and maximum stream discharge.stream discharge.

Factors Affecting Stream Factors Affecting Stream FlowFlow

• Slow falling precipitation.Slow falling precipitation.• Low gradient of the land.Low gradient of the land.• Vegetation blocks overland flow.Vegetation blocks overland flow.• Large rivers respond slowly Large rivers respond slowly

because most runoff must because most runoff must flow a great distance to reach the rivers.flow a great distance to reach the rivers.

• Small streams and streams in mountain Small streams and streams in mountain areas where the land is steep and rocky areas where the land is steep and rocky respond quickly to rainfall.respond quickly to rainfall.

• Runoff is very rapid and very brief in Runoff is very rapid and very brief in regions with buildings, paved streets, and regions with buildings, paved streets, and parking lots.parking lots.

Watersheds (Drainage Watersheds (Drainage Basin)Basin)

• The geographic area that drains into The geographic area that drains into a particular stream or other body of a particular stream or other body of water.water.

• Bounded by a drainage divide, Bounded by a drainage divide, usually a line of high land, across usually a line of high land, across which streams do not flow.which streams do not flow.

How Heat Energy TravelsHow Heat Energy Travels

•Convection is heat flow by density is heat flow by density currents within a fluid.currents within a fluid.

• Uneven heating of Earth’s surface by Uneven heating of Earth’s surface by the sun causes winds.the sun causes winds.

How Heat Energy TravelsHow Heat Energy Travels

•Conduction is a form of heat flow that is a form of heat flow that occurs when a hot substance comes in occurs when a hot substance comes in contact with a cooler substance.contact with a cooler substance.

• The vibrational energy of the warmer The vibrational energy of the warmer atoms and molecules is transferred atoms and molecules is transferred to the cooler atoms and to the cooler atoms and molecules, making them molecules, making them vibrate more.vibrate more.

How Heat Energy TravelsHow Heat Energy Travels

• Earth’s primary source of energy is the sun.Earth’s primary source of energy is the sun.

• RadiationRadiation is the flow of energy as is the flow of energy as electromagnetic waves, such as visible electromagnetic waves, such as visible light.light.– It is the fastest form of heat transfer.It is the fastest form of heat transfer.– All radiation travels at All radiation travels at

the speed of light, the speed of light, 300,000,000 300,000,000 meters per second.meters per second.

InsolationInsolation• Earth receives nearly all of its energy Earth receives nearly all of its energy

from the sun.from the sun.• The sun’s electromagnetic energy that The sun’s electromagnetic energy that

reaches the earth is called reaches the earth is called insolationinsolation ((ININcoming coming SOLSOLar radiar radiATIONATION).).

• The intensity (strength) of insolation.The intensity (strength) of insolation.depends on several factors:depends on several factors:– AngleAngle– DurationDuration– Type of surfaceType of surface

Angle of InsolationAngle of Insolation

• A measure of how high the sun is in the sky.A measure of how high the sun is in the sky.

• As the sun rises and sets, this angle As the sun rises and sets, this angle changes.changes.

• This angle is measured from the horizon up This angle is measured from the horizon up to the position of the sun.to the position of the sun.

• The noon sun has the The noon sun has the greatest angle of insolation.greatest angle of insolation.

• The angle also changes The angle also changes seasonally.seasonally.

Angle of InsolationAngle of Insolation

• Because Earth is spherical, each Because Earth is spherical, each latitude has a different angle of latitude has a different angle of insolation.insolation.

Duration of InsolationDuration of Insolation

• The length of time (from sunrise to The length of time (from sunrise to sunset), or daylight period, that the sun sunset), or daylight period, that the sun appears in the sky.appears in the sky.

• A section of Earth’s surface receives the A section of Earth’s surface receives the most heat energy when the sun is most heat energy when the sun is highest in the sky and when the duration highest in the sky and when the duration of insolation is the greatest.of insolation is the greatest.

• As the angle of insolation and the As the angle of insolation and the duration of insolation increases, the duration of insolation increases, the temperature at Earth’s surface temperature at Earth’s surface increases.increases.

Variations in Day Length

Variations of Insolation

Absorption of InsolationAbsorption of Insolation

• Upon reaching the Earth’s surface, visible Upon reaching the Earth’s surface, visible light waves are absorbed, scattered, or light waves are absorbed, scattered, or reflected.reflected.

• Light-colored objects reflect most of the light Light-colored objects reflect most of the light that falls on them.that falls on them.

• Dark-colored objects absorb most of the light Dark-colored objects absorb most of the light that falls on them.that falls on them.

• Some of the absorbed energy is changed Some of the absorbed energy is changed into infrared heat waves that reradiated into infrared heat waves that reradiated back into the atmosphere at night.back into the atmosphere at night.

Absorption of Insolation

Reflection of InsolationReflection of Insolation

• When light is When light is reflectedreflected, it bounces off a , it bounces off a surface.surface.

• Clouds reflect about half of the light Clouds reflect about half of the light falling on them.falling on them.

• The lower the angle of insolation, the The lower the angle of insolation, the greater the reflection of solar rays.greater the reflection of solar rays.

• More reflection also occurs when the More reflection also occurs when the land is light in color or covered by snow land is light in color or covered by snow or ice.or ice.

Reflection of Insolation

Terrestrial RadiationTerrestrial Radiation

•Energy waves emitted from Earth’s Energy waves emitted from Earth’s surface are longer in wavelength surface are longer in wavelength than energy waves emitted from than energy waves emitted from the sun.the sun.

•The longer heat waves radiated by The longer heat waves radiated by Earth are absorbed by gases and Earth are absorbed by gases and remain trapped in the atmosphere.remain trapped in the atmosphere.– This process is called the This process is called the

greenhouse effectgreenhouse effect..

Greenhouse Effect

Insolation Temperature LagInsolation Temperature Lag

• A time lag exists between the time of A time lag exists between the time of greatest intensity of insolation and the greatest intensity of insolation and the time of highest air temperature.time of highest air temperature.

• This is because insolation energy is This is because insolation energy is first absorbed by Earth’s surface and first absorbed by Earth’s surface and then reradiated as heat energy then reradiated as heat energy that warms the air.that warms the air.

ClimateClimate

• Unlike weather, the Unlike weather, the climateclimate for a large for a large geographical region is based on the geographical region is based on the atmospheric conditions measured over atmospheric conditions measured over a long period of time.a long period of time.

• The average conditions of temperature The average conditions of temperature and precipitation and the annual and precipitation and the annual distribution of these distribution of these conditions characterize a conditions characterize a region’s climate.region’s climate.

Factors that Affect ClimateFactors that Affect Climate

• LatitudeLatitude– The location is an important The location is an important

factor that determines the factor that determines the average local temperatures.average local temperatures.

• AltitudeAltitude– High-altitude locations have cool High-altitude locations have cool

climates because of the cooling climates because of the cooling of air as it moves to higher of air as it moves to higher elevations.elevations.

• Mountain RangesMountain Ranges– Can modify precipitation and Can modify precipitation and

temperature patterns.temperature patterns.

Factors that Affect ClimateFactors that Affect Climate

• Oceans and Large Bodies of WaterOceans and Large Bodies of Water– Because of its specific heat, water heats up Because of its specific heat, water heats up

and cools down more slowly than land and cools down more slowly than land areas.areas.

– The climates of locations near the ocean or The climates of locations near the ocean or other large bodies of water are more other large bodies of water are more moderate than inland climates.moderate than inland climates.

– Coastal and marine climates Coastal and marine climates are cooler in the summer are cooler in the summer and warmer in the winter and warmer in the winter than are inland climates.than are inland climates.

Factors that Affect ClimateFactors that Affect Climate

• Ocean CurrentsOcean Currents– Air above an ocean current is affected by Air above an ocean current is affected by

the surface temperature of the water the surface temperature of the water – Cool water will cool the air, and warm Cool water will cool the air, and warm

water will warm the air water will warm the air

Factors that Affect ClimateFactors that Affect Climate

• Planetary Wind BeltsPlanetary Wind Belts– Prevailing winds are important in Prevailing winds are important in

determining the effect of ocean currents determining the effect of ocean currents on nearby climates.on nearby climates.

– There are various There are various regions of rising regions of rising (low-pressure systems) (low-pressure systems) and sinking (high-and sinking (high-pressure systems) pressure systems) air currents.air currents.

Factors that Affect ClimateFactors that Affect Climate

• Monsoons producing Rainy weather.Monsoons producing Rainy weather.

• Typical Storm TracksTypical Storm Tracks– US Weather systems US Weather systems

usually move from usually move from west to east.west to east.