An Introduction to The Hydrologic Cycle An Introduction to The Hydrologic Cycle

Hydrology focuses on the global hydrologic cycle Hydrology focuses on the global hydrologic cycle and the processes involved in the land phase of and the processes involved in the land phase of that cycle. Hydrology describes and predicts:that cycle. Hydrology describes and predicts:

1.1. The spatial and temporal variations of water The spatial and temporal variations of water substance in the terrestrial, oceanic, and substance in the terrestrial, oceanic, and atmospheric compartments of the global water atmospheric compartments of the global water system.system.

2.2. The movement of water on and under the earth’s The movement of water on and under the earth’s surface, the physical, chemical, and biological surface, the physical, chemical, and biological processes accompanying that movement.processes accompanying that movement.

Historical BenchmarksHistorical Benchmarks

Monitoring of river flows started by Egyptians Monitoring of river flows started by Egyptians 3800 3800 B. P.B. P.

Concept of hydrologic cycle, 3000 Concept of hydrologic cycle, 3000 B. P.B. P., King , King Solomon in Ecclesiastes:Solomon in Ecclesiastes:

All the rivers run into the sea; ….. unto the place from whence the All the rivers run into the sea; ….. unto the place from whence the rivers come, thither they return again.rivers come, thither they return again.

Rainfall measuring, 2400 Rainfall measuring, 2400 B. P.B. P. in India. in India.

........

Formal recognition of the scientific status of Formal recognition of the scientific status of hydrology, 1920’s and 1930’s, UGG, AGU…etc.hydrology, 1920’s and 1930’s, UGG, AGU…etc.

Atmosphere

Biomass

Soil moisture

Ground water

Rivers Lakes

Oceans

Glacier

s

Water StorageWater Storage

Water Source Water Volume

(cu. mi.) Water Volume (cu. km)

% of Total Water

Oceans 321,000,000 1,338,000,000 96.5% Total global water

332,500,000 1,386,000,000 --

Last glacial period: Last glacial period: Sea level 400 ft lower than todaySea level 400 ft lower than today

Last inter-glacial period: Last inter-glacial period: Sea level 18 ft higher than todaySea level 18 ft higher than today

3M years B.P.:3M years B.P.:Sea level 165 ft higherSea level 165 ft higher

Changes in Water StorageChanges in Water Storage

Water Storage in the AtmosphereWater Storage in the Atmosphere

0.001%0.001% Water vapor Water vapor CloudsClouds

(water vapor (water vapor condensed on condensed on particulate)particulate)

Global distribution of atmospheric waterGlobal distribution of atmospheric water

Water Water SourceSource

Volume (cu Volume (cu mi)mi)

Volume (cu Volume (cu km)km)

% total % total freshwaterfreshwater

% total % total waterwater

Water in Water in Atmos.Atmos.

3,0943,094 12,90012,900 0.04%0.04% 0.001%0.001%

Total Total Global Global Fresh Fresh WaterWater

8,404,0008,404,000 35,030,00035,030,000 100%100% 2.5%2.5%

Total Total Global Global WaterWater

332,500,00332,500,0000

1,386,000,001,386,000,0000

---- 100%100%

Processes of The Hydrologic Cycle Processes of The Hydrologic Cycle

•EvaporationEvaporation

•TranspirationTranspiration90%90%

10%10%

What percent of the water What percent of the water in the atmosphere comes in the atmosphere comes from evaporation?from evaporation?

What two processes change liquid water into vapor that can ascend into the atmosphere?

EvaporationEvaporation Conversion of Conversion of

water from a liquid water from a liquid into a gasinto a gas

Water transferred Water transferred from surface to from surface to atmosphere atmosphere through through evaporationevaporation

                        

 

Evaporation & the SunEvaporation & the Sun The sun heats up The sun heats up

water in the water in the ocean, rivers, or ocean, rivers, or lakes, turning it lakes, turning it into vapor, which into vapor, which then goes into the then goes into the airair

Evaporation Cont.Evaporation Cont. 80% of evaporation 80% of evaporation

from oceanfrom ocean 20% of evaporation 20% of evaporation

from inland water from inland water and vegetationand vegetation

Winds transport Winds transport evaporated water, evaporated water, influencing humidity influencing humidity around the worldaround the world

Evaporation: As water is heated by the sun, Evaporation: As water is heated by the sun, its surface molecules become sufficiently its surface molecules become sufficiently energized to break free of the attractive energized to break free of the attractive force binding them together, and then force binding them together, and then evaporate and rise as invisible vapor in the evaporate and rise as invisible vapor in the atmosphere.atmosphere.

EvaporationEvaporation

Primary mechanism for surface-to-atmosphere Primary mechanism for surface-to-atmosphere water transportwater transport

Energy breaks bonds that hold molecules togetherEnergy breaks bonds that hold molecules together Net evaporation occurs when the rate of evaporation occurs when the rate of

evaporation exceeds the rate of condensationevaporation exceeds the rate of condensation Removes heat from the environment: Removes heat from the environment: Net Cooling

Global EvaporationGlobal Evaporation

The process of water loss from plants (plants sweating) through stomata.

•passive process that depends on:~humidity of the atmosphere ~the moisture content of the soil

•only 1 % of the water transpired used for growth

•transports nutrients from the soil into the roots and carries them to the various cells of the plant

•keeps tissues from becoming overheated

(Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues.)

TranspirationTranspiration

Transpiration Cont.Transpiration Cont.Environmental Environmental

factors that affect factors that affect transpiration:transpiration:

LightLight TemperatureTemperature HumidityHumidity WindWind Soil waterSoil water

Every day an actively growing plant Every day an actively growing plant transpires 5 to 10 times as much water as it transpires 5 to 10 times as much water as it can hold at one time.can hold at one time.

Condensation is the process of water Condensation is the process of water changing from vapor to liquid. Water vapor changing from vapor to liquid. Water vapor in the air rises mostly by convection. This in the air rises mostly by convection. This means that warm, humid air will rise, while means that warm, humid air will rise, while cooler air will flow downward. As the cooler air will flow downward. As the warmer air rises, the water vapor will lose warmer air rises, the water vapor will lose energy, causing its temperature to drop. The energy, causing its temperature to drop. The water vapor then has a change of state into water vapor then has a change of state into liquid or ice.liquid or ice.

Condensation Condensation

Condensation

& Convection

Condensation

& Convection Warm air risesWarm air rises Air cools and can Air cools and can

no longer hold no longer hold vaporvapor

Process known as Process known as CONVECTIONCONVECTION

Condensation & Cloud Formation

Condensation & Cloud Formation Cooling of water Cooling of water

vapor forms vapor forms CLOUDSCLOUDS

Other ways Other ways clouds are formedclouds are formed ConvergenceConvergence Lifting of air Lifting of air

by frontsby fronts

Precipitation is water being released from Precipitation is water being released from clouds as rain, sleet, snow, or hail. clouds as rain, sleet, snow, or hail. Precipitation begins after water vapor, Precipitation begins after water vapor, which has condensed in the atmosphere, which has condensed in the atmosphere, becomes too heavy to remain in becomes too heavy to remain in atmospheric air currents and falls. Under atmospheric air currents and falls. Under some circumstances precipitation actually some circumstances precipitation actually evaporates before it reaches the surface.evaporates before it reaches the surface.

Precipitation Precipitation

PrecipitationPrecipitation The vapor that accumulates or freezes on condensation nuclei is acted on by gravity and falls to The vapor that accumulates or freezes on condensation nuclei is acted on by gravity and falls to

Earth’s surface.Earth’s surface.

Primary connection in the water cycle that provides for the delivery of atmospheric water to the Primary connection in the water cycle that provides for the delivery of atmospheric water to the EarthEarth

rain, freezing rain, sleet, snow, or hail

Total Precipitable WaterTotal Precipitable Water

The total atmospheric water vapor contained in a vertical column of unit cross-sectional area from the Earth’s surface to the “top of the atmosphere”

SnowSnow Snow is a type of Snow is a type of

precipitation like precipitation like rain but at cooler rain but at cooler temperaturestemperatures

Usually reaches the Usually reaches the ground and staysground and stays

Eventually melts Eventually melts and becomes runoff and becomes runoff in streamsin streams

Rain Rain Type of Type of

precipitation during precipitation during warmer weatherwarmer weather

Occurs when clouds Occurs when clouds become too fullbecome too full

Falls to earth in the Falls to earth in the form of water and form of water and runs off to streams runs off to streams & rivers& rivers

How many gallons of water fall when 1 inch of rain falls on 1 acre of land?

About 27,154 gallons (102,800 liters) of water.

On average, the 48 continental United States receives enough precipitation in one year to cover the land to a depth of 30 inches.

Evaporation v. PrecipitationEvaporation v. Precipitation About equal on a global scaleAbout equal on a global scale Evaporation more prevalent over the oceans than Evaporation more prevalent over the oceans than

precipitationprecipitation Over land, precipitation exceeds evaporationOver land, precipitation exceeds evaporation Most water evaporated from the oceans falls back into Most water evaporated from the oceans falls back into

the ocean as precipitationthe ocean as precipitation 10% of water evaporated from the ocean is transported 10% of water evaporated from the ocean is transported

over land and falls as precipitationover land and falls as precipitation Once evaporated, a water molecule spends ~ 10 days Once evaporated, a water molecule spends ~ 10 days

airborneairborne

Infiltration: A portion of the precipitation Infiltration: A portion of the precipitation that reaches the Earth's surface seeps into that reaches the Earth's surface seeps into the ground through the process called the ground through the process called infiltration. The amount of water that infiltration. The amount of water that infiltrates the soil varies with the degree of infiltrates the soil varies with the degree of land slope, the amount and type of land slope, the amount and type of vegetation, soil type and rock type, and vegetation, soil type and rock type, and whether the soil is already saturated by whether the soil is already saturated by water.water.

InfiltrationInfiltration

Groundwater begins as infiltrationGroundwater begins as infiltration

Precipitation falls and infiltrates into the subsurface soil and rock

•Can remain in shallow soil layerCan remain in shallow soil layer•Might seep into a stream bankMight seep into a stream bank•May infiltrate deeper, recharging an aquiferMay infiltrate deeper, recharging an aquifer•May travel long distancesMay travel long distances•May stay in storage as ground waterMay stay in storage as ground water

Factors affecting infiltrationFactors affecting infiltration

Precipitation (greatest factor)Precipitation (greatest factor) Magnitude, intensity, durationMagnitude, intensity, duration Characteristics (rain, snow)Characteristics (rain, snow)

Soil CharacteristicsSoil Characteristics Clay absorbs less water at a slower rate than sandClay absorbs less water at a slower rate than sand

Soil Saturation Soil Saturation Higher saturation leads to more runoff insteadHigher saturation leads to more runoff instead

Land CoverLand Cover Slope of the Land Slope of the Land

Hills enhance runoff velocityHills enhance runoff velocity EvapotranspirationEvapotranspiration

Plants use soil moisture to grow and transpirePlants use soil moisture to grow and transpire

-Rain water soaks into ground through soil and underlying rock layer.

-Water cleaned as impurities filtered

Subsurface WaterSubsurface Water

As precipitation infiltrates subsurface soil, it forms two zones: Unsaturated -- It includes the capillary fringe and pores

in this zone contain both water and air Saturated -- Water completely fills the voids between

rocks and soil particles

Infiltration replenished aquifersInfiltration replenished aquifers

Slow process -- ground water moves slowly through the Slow process -- ground water moves slowly through the unsaturated zoneunsaturated zone

Recharge Rate determined by precipitation & depthRecharge Rate determined by precipitation & depth An aquifer in New Mexico, if emptied, would take centuries to refill An aquifer in New Mexico, if emptied, would take centuries to refill

whereas a shallow aquifer in south Georgia may be replenished almost whereas a shallow aquifer in south Georgia may be replenished almost immediatelyimmediately

Artificial RechargeArtificial Recharge

Enhanced InfiltrationEnhanced Infiltration Spread water over the land in pits, furrows, ditches or build small dams Spread water over the land in pits, furrows, ditches or build small dams

in creeks and streams to deflect runoffin creeks and streams to deflect runoff

Ground water injectionGround water injection Construct recharge wells and inject water directly into aquifersConstruct recharge wells and inject water directly into aquifers

Surface RunoffSurface Runoff When When

precipitation rate precipitation rate exceeds exceeds infiltration rate, or infiltration rate, or when soil is when soil is saturated, water saturated, water begins to move begins to move down slope on down slope on ground surface.ground surface.

Runoff: When there is a lot of precipitation, soils Runoff: When there is a lot of precipitation, soils become saturated with water. Additional rainfall become saturated with water. Additional rainfall can no longer enter it. Runoff will eventually drain can no longer enter it. Runoff will eventually drain into creeks, streams, and rivers, adding a large into creeks, streams, and rivers, adding a large amount of water to the flow. Surface water always amount of water to the flow. Surface water always travels towards the lowest point possible, usually travels towards the lowest point possible, usually the oceans. Along the way some water evaporates, the oceans. Along the way some water evaporates, percolates into the ground, or is used for percolates into the ground, or is used for agricultural, residential, or industrial purposes.agricultural, residential, or industrial purposes.

Meteorological factors affecting surface (over soil) runoffMeteorological factors affecting surface (over soil) runoff

- Type of precipitation

- Rainfall intensity

- Rainfall amount

- Rainfall duration

- Distribution of rainfall over the drainage basin

- Direction of storm movement

- Precipitation that occurred earlier and resulting soil moisture

- Meteorological conditions that affect evapotranspiration

Physical characteristics affecting surface runoffPhysical characteristics affecting surface runoff

- Land use- Vegetation- Soil type- Drainage area- Basin shape- Elevation- Topography, especially the slope

of the land- Drainage network patterns- Ponds, lakes, reservoirs, sinks,

etc. in the basin, which prevent or delay runoff from continuing downstream

RunoffRunoff

Drains to a creek To a stream

To a river

• To ocean Sometimes runoff drains to a closed lake May be diverted for human uses

Freshwater Flow

About 3% of About 3% of precipitation will precipitation will seep underground seep underground

About 31% will run About 31% will run off into rivers, off into rivers, streams and lakes streams and lakes

About 66% of the About 66% of the water returns to the water returns to the atmosphere through atmosphere through evaporation and evaporation and transpirationtranspiration

A hydrologist is A hydrologist is particularly particularly interested in stream interested in stream flow -- the 31% of flow -- the 31% of precipitation which precipitation which runs off into rivers, runs off into rivers, streams and lakes. streams and lakes.

Watch the following Water Cycle movie Watch the following Water Cycle movie (about 3 min.). Provide a one-page (about 3 min.). Provide a one-page scientific (not too scientific) narrative scientific (not too scientific) narrative describing what is seen in the movie i.e. describing what is seen in the movie i.e. describe the main processes (e.g. describe the main processes (e.g. evaporation, transpiration, precipitation, evaporation, transpiration, precipitation, infiltration, infiltration, runoff…etc). infiltration, infiltration, runoff…etc).

Quiz Quiz