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Abstract
Introduction
Methodology
Results & Discussions
Error and Uncertainty
Results and Discussions
Results
Our results of the lowest temperature over 30 years can be viewed as:
a
Flash animation.
or as a series of
Static images.
Visually the results are as would be expected, the coldest temperatures are found in northern
and eastern BC with high areas in the south also experiencing low winter temperatures. Coastal areas,
including the Coast Mountains do not exhibit lows temperatures and rarely drop below -30 C. Also, as would be expected,
there is a great deal of variation between years.
With only 30 years of data it is difficult to make any
conclusions on long term temperature trends. However the maps agree with global data with the mildest winters occurring
consecutively from 1998 to 2003 matching the warmest years on records, although 2004 saw a return to lower winter
temperatures. High global average temperature clearly impacts on the distribution of minimum extreme temperature in
Western Canada. Until 1999 no discernable pattern can be seen and show a mixture of cold and mild years, 1987 was the
mildest year outside of this recent period and 1996 was one of the coldest years. The winters of the 1970s were
uniformly cold, with 1979 being the coldest year in the study. Although due to the length of the study, this is not
statistically significant.
Discussions of El Nino effects, Spatial Distribution, Ecological Impacts and Biogeoclimatic Zone.
El Nino Effects
The El Nino Southern Oscillation (ENSO) can be seen to have some impact on observed results.
Typically ENSO events give British Columbia milder and wetter winters due to higher sea surface temperatures.1
ENSO events occurred in 1982/83, 1986-88, 1991/92, 1994/95, 1997/98 and 2002/03.
What is interesting is that while these years are uniformly mild they are usually followed by unusually cold winters
in 1984, 1989, 1996 and 2004. The change in climate is least obvious for the 1997/98 ENSO, possibly because the results
are confused by very low temperatures at the start of 1997. The event was not followed by a cold winter and temperatures
remained mild; the 1997/98 signal was one of the strongest on record.
The spatial distribution
The standard deviations of the results show that the areas which have shown the greatest amount of variation
are southern lowland areas. This may be due to a greater concentration of data points revealing a more accurate
interpolation. If we assume that the areas which show the greatest variation are the most susceptible to change due
to any warming then we can conclude that these areas will exhibit a falling extreme minimum temperature.
Upland inland regions exhibited the greatest range of temperature between years, while southern
coastal regions exhibited the smallest range. Northern Coastal regions show a higher deviation than southern
ones suggesting some variability in sea surface temperatures at higher latitudes. This is possibly an impact of ENSO events.
A hotspot is visible on the
Standard deviation map(or below) in the area north of Carpenter Lake in the Chilcotin Ranges
(about 123 W, 50 N). This area sits in the rain shadow of the Coast Mountains and has a very dry and cold climate,
the average winter temperature is around -12 C.2 Even in an exceptionally mild winter
it is likely that the temperature in this area will drop below the -1.5 C recorded for the Big Creek AUT station at
this site in the raw data. The station became operational in 1995. Closer inspection of the daily data for this station
revealed that very large amounts of data were missing for that year and therefore its results should be disregarded.
Ecological impacts
The following map
shows the areas of BC experiencing temperatures of below -40 C for three years.
The years are selected to show the possible range. The graph
shows the total area in Km^2 which experience
temperatures below -40 C.
The map illustrates that during mild winters vast areas in the south of BC will not drop below -40 C, even at altitude. The sequence of mild winters from 1999 would mean very high winter survivorship rates of the Mountain Pine Beetle in southern areas and explain the recent epidemic. Mountain Beetle also require an average annual mean temperature of above 5.6 C to complete there life cycle.1 The graph below compares the total area (km^2) reaching temperatures below -40 C. The significance of the unusually mild resent period of winters is clear; 4 of the 5 events where less than 10,000 Km^2 experienced temperatures below -40 C occurred. While the area experiencing extreme mild winters may be becoming more common, extreme cold winters are still occurring at reasonable intervals. The interval of the areas increasing over 20,000 Km^2 has fallen from 4 to 6 across the study period, but the severity of the winters appears largely unchanged.
Biogeoclimatic Zones
A shift in the spatial distribution may also impact on the distribution of ecological zones in British Colombia.
Minimum temperatures act as an important limiting factor on the distribution and range of plants species, although of
course precipitation also has a major influence. An interactive map of Biogeoclimatic Zones can seen
here.
Reference
1 Environment Canada
http://www.msc-smc.ec.gc.ca/education/elnino/index_e.cfm
2 British Columbria Government, Ministry of Lands and Agriculture
http://srmwww.gov.bc.ca/dss/initiatives/tourism/tos/chilcotin/chil_res.htm
3 British Columbria Geoclimatic Classification (BEC Web)
http://www.for.gov.bc.ca/hre/becweb/index.htm