|
Any surface receiving the suns ray's will absorb some of the energy
and reflect the rest. Some interesting effects and consequences
for land use are seen below. See sections 5 and 6 on Ecosystems.
And Section 3 on Albedo.
There are three main categories of landscapes:
- natural - forests, water bodies, tundra , natural meadows,
grassland, bog
- managed or changed - planted fields, cleared land, newly
planted forests
- "built" landscapes - roads, buildings, houses,
parking lots, canals, trails, vehicles
Each color and type of roof has a different albedo or reflectivity.
Each agricultural crop and each forest type has a different albedo.
Every change on the landscape made by humans changes the albedo.
Natural changes such as snow cover and ice cover have a great effect
on albedo.
In Ontario, forests were cleared to grow food. The warmest parts of Ontario now have about 3% forest cover left
and they now produce the most food.
Increases in available heat act as a powerful trigger to start
processes in the natural world such as germination and melting.
Temperature increases can also trigger the shut down processes
and systems through overheating or dehydration. The rate of evaporation
of surface water and soil along with evapotranspiration from plants
will increase with warmer temperatures. Plant growth rate may increase.
To help warm the soil sooner in the spring and to prevent flooding
of crops, many farmers have installed drainage systems. Flexible
slotted piping has been buried in a pattern in the field and water
is drained to a channel, and later into a creek, by gravity. Draining the land gives the farmer more growing days.
Water
requires more heat energy per gram to increase its temperature
by one Celsius degree than any other substance. The specific heat
of water is 1 and all other substances are less.
In sunlight, beach sand is always warmer than the water. The sand cools faster than the waterwhen the sun sets. This effect
is also the reason that large bodies of water modify the climate
of the land near them. The Great Lakes, for example. See Ontario
sections for Temperatures.
Corn Heat units are another way of measuring this. Air temperatures
are used.
Southern Ontario Average Annual Corn Heat Units (CHU) Map
Note that Corn Heat Units are in degrees Celsius. This accumulated
value is calculated using the following conditions:
- Start-up of corn growing season: where the mean daily temperature
is > 12.8 oC for three consecutive days during the period
May 11 to July 31.
- End of the season: the first occurrence when the minimum
daily temperature drops below -2.0 oC during the period August
1 to October
15.
Source: Integrated Assessment Mapping Project www.utoronto.ca/imap/
ACTIVITY 1
- What degree of latitude is the southernmost point on this map
of southwestern Ontario? The northernmost point? The total range
of degrees of latitude?
- How many minutes is this in map time?
Changing dates of planting, fertilizing, and harvesting, along with
a change in the demand for irrigation, will have to be part of adaptation
of agriculture to climate change, especially in southwestern Ontario.
Source: MacIver, D. C. and H. Auld (2000). The Changing Atmosphere:
Forest Biodiversity and Productivity in Ontario, Canada. 14th Conference
on Biometeorology and Aerobiology, 14-18 August 2000, Davis, California.
260-261 pg.
ACTIVITY 2 Research
The map above represents land use status
in 2000. Research the increase in area changed to residential
development, that is the
area now covered by "built" environment. Use air photos or municipal
reports in one chosen part of this area or in your own area to
determine the increase in built area since 2000. Option: use
documentation earlier than 2000
Increases in temperatures increase the rate of evaporation from
the soil and evapotranspiration from agricultural crops, managed
forests, and all natural ecosystems.
ACTIVITY 3
Set up a specific heat experiment using
the same volume of water, oil, sand, and soil in each of 4 similar
test tubes. Put a similar
thermometer in each to the same depth. Place all 4 test tubes at
the same time into a larger beaker containing water at room temperature. Heat the large beaker and record the temperatures
of each substance each minute. Graph these results using a separate
line for each substance.
Land use change that replaces agricultural fields with new forests
affects the reflection of sunlight by land surfaces. In Canada
with significant periods of snow cover, this effect can be significant. That is because, in winter, high albedo snow-covered agricultural
fields are replaced by lower albedo forest landscapes.
This can cause a regional warming influence that may be greater
than the benefit of the carbon sinks provided by the new forests.
Source: National Climate Change Process Sinks Table Report
ACTIVITY 4 Research
- What is the annual number of hectares of
forest that are cleared in Canada vs. the number of hectares
that are newly planted? In Ontario? (Reforestation)
- What is the annual number of hectares of
fields or meadows that are planted with new trees in Canada?
In Ontario? (Aforestation)
- What does TC/ha mean? How much carbon dioxide
does this represent?
|
