Abstract
Introduction
and Background
Data
Methods
Results
Discussion
Conclusion
References
Contact
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Methods
GDD Calculations
Layers:
Soil
Texture, Proximity to Water, Proximity to Roads, Slope, EGDD
Analysis:
Multicriteria Evaluation
GDD Calculations
The best way to calculate growing degree days is to use daily mean
temperature values. Equipped with that data and a decided base
temperature (5º C for this project), here is what you do:
Tmean-Tbase = Daily GDD
for example, a day with a mean temperature of 22 degrees Cº contributes
17 GDDs.
Then, sum the Daily GDD to get the GDDs for the year. To get Effective
GDDs, you calculate a DLF or “day length factor” that accounts for the
different sunlight hours at different latitudes. I found that for the
Yukon, the DLF ranges from 18% in Whitehorse (near the BC border) to
22% in Dawson City (farther north, near the arctic circle). I chose to
use 18% across the Yukon, as this would underestimate the values.
Further, I did not have mean daily temperatures, so I estimated with
the mean monthly values I had. This inevitably leads to some error.
However, I compared EGDD values calculated from monthly temperatures
and the reference map of EGDD from 1990, and I found that the main
effect of using monthly values was to decrease the overall variability
between values and either underestimate or match the reference values.
I talk more about this in the discussion section.
Layers:
(click on maps for large images)
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Soil Texture:
This map was created by joining polygons from
the Land Potential
Database of Canada with corresponding data in an attribute table called
Soil
Inventory. The data joined included characteristics of soil texture,
with the
categories “Clayey,” “Sandy,” “Loamy,” and blank areas which appear to
mostly
correlate with densely glaciated, mountainous regions (such as the
bottom left
corner) or lakes (Kluane Lake is the little forked shape in bottom
left). The
layer was then converted to raster and reclassified into five classes
of
ascending desirability (shown by darker brown) to prepare it for the
weighted
overlay analysis.
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i !
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Proximity to Water: This map was created from a line map of the
drainage networks in
the Yukon. A path distance analysis was run with a base raster of
derived from
a polygon of the Yukon Territory, and the distance map was reclassified
into
five classes with the darkest regions showing areas close to some kind
of
river. Unfortunately, time and metadata constraints meant I couldn't
find a way
to separate major rivers from creeks. This will be further addressed in
the discussion
section.
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i mage2
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Proximity to Roads: This map was created similarly to the water
map, with major roads
as the network from which path distance was calculated. There was a
limit to
the extent of the calculated map, and I'm not sure where this arose
from. I
redid the analysis many times and made sure to use the Yukon territory
as the
base raster, and did not assign a maximum distance, but there continued
to be a
limit. This will also be discussed in the discussion
section.
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imag e3
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Effective Growing Degree Days Reference
Map: This map
reflects effective growing degree
days based on the EGDDs calculated by NRCAN. To build it, I joined the
ecodistrict polygons to the EGDD attribute table, used a symbology of
quantities, and assigned 5 discrete classes based on the classes
described in
the background
section.
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image!
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Slope:This
map was created from a 90m DEM of the Yukon Territory. Slopes were
calculated
with Spatial Analyst and reclassified into five classes according to
flat
slopes (0-5º), moderately flat slopes (5-10º), moderate slopes
(10-15º),
moderately steep slopes (15-25º), and very steep slopes (25º-89.9). The
un-equal interval is a result of the functionality of steep slopes:
past a
certain point they will be unlikely to be stable and will be equally
difficult
to work with whether they are at 35º or 75º. Therefore I grouped all of
the
higher slopes into the single lowest class.
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image!
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Effective Growing Degree Days Present
Day: Each of
the following maps were created in the following way:
Using Excel, I started with mean monthly
temperature values for each ecodistrict. I then built calculated tables
using
If/Then statements that summed all values above 5º for each month,
multiplied
those values by 30 to estimate the number of days in each month, and
multiplied
that value by 1.18 in order to obtain Effective GDD
for the latitude
around Whitehorse (info from Infarmation bulletin). For the 2050 and
2100 values, I first
recalculated
the mean monthly temperature tables to be 3º higher and 6º higher,
respectively, and then carried out the same analysis. Temperature increases are based
on this map for 2050 and
this map for 2100 .
I also performed a minor error analysis to
show that the majority of the calculated EGDD Present Day values
underestimated
rather than overestimated EGDD (which is good given that more EGDD is
better,
and an underestimate won't tend to raise false hopes). A graph of this
can be
found in the discussion section.
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image
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EGDD 2050 |
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EGDD 2100
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m
age!
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Analysis: MCE
The MCE itself was fairly simple. Each of
the above maps had 5 classes, and I reclassified them all to a simple 1
to 5
system in order to make them comparable. Then I performed a weighted
overlay
using these weights:
EGDD:
40%
Rivers: 25%
Slope: 15%
Roads: 10%
Soil:
10%
Justification for weights:
EGDD is the most
important factor, the
factor which cannot be changes by human manipulations and has
historically been
one of the biggest limitations in the North.
Water is a highly
limiting resource in the
dry Yukon, and is second most important.
Slope is classed as
third most important
because of the rough terrain typical of the Yukon, and well as the
uncertainty
present in the road and texture layers that make them less valuable as
criteria.
Roads: From personal
experience I know
there are many more roads than shown on the main road map, including
mining and
logging roads. I believe remoteness is a general problem in the Yukon
which
will be delt with if the drive for access is strong enough.
Texture: These
classes were defined on a
rather broad scale, and don't necessarily reflect the localized
characteristics
of the soil. Further, there is also the possibility of greenhouses
which would
decrease the necessity for good soils.
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