Water in the Environment

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Atlas 2m thermal infrared image, Atlanta, GA
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Units kW/m2/day Source R. L. Sass, Rice Univ.
, Houston, TX http//www.ruf.rice.edu/sass/UHI.h
tml
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Atmospheric Moisture
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Environmental Significance of Water

• Important component of global energy fluxes
• (latent heat)
• Powerful agent of erosion
• Universal solvent transports nutrients and
  contaminants
  
• Required for biological processes availability
  determines species distributions
  

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Outline

• Hydrologic cycle (water balance)
• Atmospheric moisture (precipitation)
• Clouds and implications for climate change

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1. Hydrologic Cycle
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Hydrologic Cycle
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Water Balance

• Describes the relationship among fluxes of water

Land surface
Oceans
Precipitation
Input
Input
Evaporation Transpiration
Output --
Output
Runoff
Output
Input
Land Precipitation Runoff
Evapotranspiration Oceans Precipitation Run
off Evaporation
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Water Balance

• Describes the relationship among fluxes of water

Land surface
Precipitation
Input
Evaporation Transpiration
Output
Runoff
Output
Land Precipitation - Evapotranspiration Runoff
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2. Atmospheric Moisture
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Atmospheric Moisture

• Amount of moisture held in air depends upon air
  temperature

26 g/kg
15 g/kg
2 g/kg
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Atmospheric Moisture
http//www.weather.com
Dew point temperature Temperature of an air ma
ss at which it is saturated with moisture
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Atmospheric Moisture
http//www.weather.com
Relative humidity Amount of water vapor curren
tly in air relative to what air could hold at
that temperature if saturated
If air on 70o F day held 5 g/kg water,
RH 5/15 33
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Atmospheric Moisture
Who cares?
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Atmospheric Moisture
As air rises, it cools. Cooler air holds less m
ositure
Adiabatic Cooling
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Atmospheric Lifting Mechanisms
Convection local heating
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Atmospheric Lifting Mechanisms
Orographic Lifting topographic barriers
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Atmospheric Lifting Mechanisms
Frontal Lifting cold / warm air masses
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Atmospheric Lifting Mechanisms
Convergence high / low pressure gradients
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Monga Bay, Peru
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Worldwide annual precipitation
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3. Clouds
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Clouds
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Clouds
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Clouds
Cloud form

• Stratiform - horizontal
• Cumuliform - vertical
• Cirroform wispy, ice crystals

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Role of Clouds in Global Climate System
http//www.giss.nasa.gov/research/briefs/delgenio_
03/

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Role of Clouds in Global Climate System
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Role of Clouds in Global Climate System
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Role of Clouds in Global Climate System
Low clouds reflect shortwave radiation
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Role of Clouds in Global Climate System
Global albedo without clouds
Source E. F. Harrisson et al.,
http//eumetcal.meteo.fr/euromet/english/satmet/s8
220/s8220210.htm
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Role of Clouds in Global Climate System
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Role of Clouds in Global Climate System
Global longwave radiation
Source Eugene S. Takle, 2006
http//www.meteor.iastate.edu/gccourse/influ/influ
_lecture_new.html
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Implications of clouds for climate change

• Surface warming may induce more cloud formation
• Clouds reduce incoming shortwave (albedo)
• Clouds increase counterradiated longwave
  (greenhouse gas)
  
• Clouds introduce considerable uncertainty to
  climate change scenarios

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Summary

• Hydrologic cycle describes processes controlling
  fluxes of water
  
• Water balance used to describe relationship
  between precipitation, runoff and
  evaporation/transpiration
  
• Moisture content of air is temperature dependent
  (warmer air holds more moisture)
  
• Air must be cooled for precipitation to occur
  (atmospheric lifting mechanisms)

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Summary (cont.)

• Atmospheric lifting creates clouds.
• Clouds have varying effects on net radiation
• Effects of climate change on cloud formation
  introduces considerable uncertainty into
  predictions