Transcript Lecture 6: The Hydrologic Cycle EarthsClimate_Web_Chapter.pdf, p. 10, 16-17, 21, 31-32, 34

Lecture 6: The Hydrologic Cycle
EarthsClimate_Web_Chapter.pdf, p. 10, 16-17, 21, 31-32, 34
Components of the Hydrologic Cycle
Evaporation, Condensation, Transport,
Precipitation, Transpiration, Runoff,
Groundwater Flow
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/smry.rxml
Water and the Planets
Earth: the only planet where water
can exist in three forms.
Water is essential to life.
Where Is Water On Earth?
Atmosphere: 0.001%
Ice/Snow 2.0%
Surface Water 0.02%
Water is a vital component
of the climate cycle.
Groundwater 0.58%
Oceans 97.39%
Hydrologic Cycle
Movement of Water Between Stores
1. Most Rapid Movement
In Vapor Phase, in the
Atmosphere
2. Most Water and Energy
Storage
In Liquid Phase, in the
Oceans
3. Most of Water useful to
Humanity
in Rivers, Lakes,
Subterranean Water, and
Ice and Snow, as Fresh
Water
Water Vapor
1. Highly variable spatially
• Near 0% over deserts
•3–4% over tropical oceans/jungles
• Decreases rapidly with altitude;
most is within a few km of the surface
• Decreases rapidly with latitude; at
the equator is 10 times that at the
poles
2. Importance to climate and climate change
* Important part of the water cycle; ocean-toland atmospheric vapor transport balances
land-to-ocean runoff.
* The most important greenhouse gas:
water vapor-temperature feedback.
* Water vapor condenses to form clouds, thus
clouds–radiation feedback. Clouds release
rainfall, reflect solar radiation, and reduce the
infrared radiation emitted by Earth.
Cloud Development
 Causes of a rising air mass
Rising air expands, cools, and
condenses to form cloud
What causes the air to rise?
1. Surface heating and convection
2. Widespread ascent due to convergence
of surface air
Cold Front
3. Orographic uplift
Warm Front
4. Uplift along weather fronts
Steps in Making Precipitation
1. Water vapor in air
2. Air with vapor rises, expands, and cools
3. Vapor condensates around nuclei to
form droplets (clouds)
4. Droplets suspended by atmospheric
upward motion and turbulence
5. Droplets collide and coalesce into drops
in warm clouds and droplets diffuse to
ice crystals in cold clouds
6. Drops/crystals falls as rain/snow
when they are too heavy to be
suspended by upward motion
Orographic Precipitation
Winds blowing moist air toward a mountain will experience
orographic uplift to an elevation where dew point is reached and
clouds are formed.
When the condensed moisture falls as rainfall, the leeward side of
the mountain is kept in a rain shadow.
Topographic Controls on Precipitation
Westerly winds blowing moist air from the Pacific Ocean encounter
several mountain ranges that create patterns of rising air and
precipitation followed by sinking air and warm dry rain shadows.
Global Annual Mean Precipitation
http://www.atmo.arizona.edu/students/courselinks/spring03/atmo421/prec.html
Geographic Distribution of Annual P-E (mm)
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Evaporation excess nearly ubiquitous over sub-tropical oceans, with a sharp contrast at coastal regions.
Equatorial ocean evaporation minimum.
From Paul Houser
Tropical land areas show richest excess in precipitation.
Major desert regions, tundra, and mountainous regions all indicate deficit to marginally-balanced conditions.
Mid-latitude and boreal coastal/maritime environments exhibit adequate precipitation supply over evaporation.
Zonal Mean Precipitation
http://www.atmo.arizona.edu/students/courselinks/spring03/atmo421/prec.html
Precipitation
Precipitation
Various Satellites Are Monitoring Earth’s Water Cycle
Summary:
• 1. What are three most important elements of the hydrological
cycle?
– Evaporation/evapotranspiration, transport, precipitation
• How is water distributed in the earth’s climate system?
– 97% in ocean, 2% in ice, ~0.6% in ground water, 0.02% river/lake,
0.001% in atmosphere.
• How does each form of water (e.g., vapor, liquid and ice)
influence climate?
– Vapor: strongest greenhouse gas, liquid/ice forms clouds and
precipitation, river and ice/snow, which influence albedo of the
earth, sensible and latent heat fluxes.
• How are clouds and rainfall formed?
– Clouds/precipitation are formed by condensation/freeze of the
water vapor in rising motion of the atmosphere either due to
unstable thermodynamic stratification or due to mechanical lifting
by topographic or lower tropospheric wind convergence.