7:Local climate modifications

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7Local climate modifications
Urbanization Agriculture Deforestation
Climate Change and its Impacts October 16
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Urban heat island, climate change, and the effect
of urbanization

• Urban heat island affects local temperature
  values
• Urbanization is still too small to affect global
  temperature average
• Concern is expressed about urban bias affecting
  global temperature measurements

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Climate of urban areas

• Air pollution
• Radiation balance
• Moisture balance
• Modification of the microclimate

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The radiation balance

• All components of the radiation balance are
  affected by urbanization

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Urban effects on shortwave
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Urban geometry
SHORTWAVE
LONGWAVE
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More urban effects

• What are the effects of atmospheric pollution on
• Longwave energy downward?
• Shortwave energy downward?
• Thermal conductivity

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More urban effects

• Overall solar energy decreases around 5-10
  percent in urban areas.
• Wavelength-dependent Ultraviolet radiation
  decreases up to 90 percent.

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Urban heat fluxes

• Latent heat flux typically much smaller in a city
• Sensible heat flux thus increases
• Also increases due to increased turbulence in
  urban environment

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Combustion

• In wintertime in New York City, for each unit of
  solar radiation received, 2.5 times that amount
  is added to the climate system by combustion of
  fossil fuels.
• Nights in Cincinnati, 25 of the net radiation
  loss is added to the climate system via
  combustion.

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End result urban heat island

• Annual temperature 1C warmer
• Most significant heat island
• At night
• Clear
• Calm
• Winter
• During the week
• Longer growing season (3 weeks)

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Heat island variability over season and time of
day
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Heat island varies from place to place
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Heat island varies from city to city

• Heat islands noted in cities of only 1,000 people

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Sky View Factor and Heat Island
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Heat island varies over time
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Heat island varies vertically
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Urban modification of moisture

• Relative humidity 6 lower
• Greater decreases in summer
• Cloud cover increases 10
• Condensation nuclei
• Anthropogenic moisture sources trivial
• 1/500th of summer POTET
• Fog double

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Urban modification of precipitation

• Up to 10 higher in city
• Up to 33 higher within 50 km of city DOWNWIND

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Urban modification of species

• Change in ecosystem to include non-native species

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Urban modification of precipitation

• Changes by day of week?
• Snowfall 15 less
• Change in days with precipitation?

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Urban streamflow and runoff
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Land-use/land-cover changes

• Significant local effect
• Albedo change
• Moisture balance change
• Regional effects
• Circulation change
• Modifications to atmosphere
• Pollutants
• Moisture

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Land use change across the US
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Effects of agriculture on central US

• Significant irrigation
• Significant changes in regional circulation
• Higher dew points during summer
• Lower maximum, higher minimum temperatures
• Higher precipitation?

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Evapotranspiration differences
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Great Plains agriculture
Oleson et al.
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Great Plains agriculture
Oleson et al. (2004)
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Great Plains agriculture

• North Central US (37-50N) summer

Differences between modern and natural
vegetation model runs
Oleson et al. (2004)
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Saharan/Sahelian/Arabian dust veil

• Significant transport across region due to lack
  of precipitation/ cloud condensation

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Impacts of deforestation in Amazon

• In pasture
• Decreased evapotranspiration
• Decreased net radiation
• Larger temperature range

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Impacts of deforestation in Amazon

• Modeling studies suggest a deforestation of the
  Amazon would create a semi-arid climate.

Mahli et al.
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Differential energy budget across US/Mexico border

• Significant differences due to irrigation and
  land cover