RURAL DEVELOPMENT INSTITUTE RESEARCH BRIEF SPRING 2016

RESEARCH BRIEF

Agricultural Climate: Conditions & Trends

This Research Brief summarizes research conducted as
part of the Columbia Basin Rural Development Institute’s Regional Food Systems project. Trends and conditions were calculated in accordance with established
methodologies for climate data analysis. For detailed
information on these methodologies, contact the RDI.

BACKGROUND AND RATIONALE
Our region’s climate, and projected changes related to
temperature and precipitation regimes, are important
factors influencing the long-term sustainability of
the Columbia Basin-Boundary food system. Research
to inform climate change adaptation efforts was
identified as an important information need in the
various agricultural plans in place for the Columbia
Basin-Boundary region1. In addition, the RDI’s
advisory committee for the Regional Food Systems
Project prioritized the need for an updated analysis of
the climate variables commonly used by farmers to
determine agricultural practices.

In 1981, the government of British Columbia
released a report that characterized the climatic
capability of various locations for agriculture2.
Using historic climate data, the report classifies a site’s
agricultural capabilities based on its thermal and
moisture regimes. Classes range from 1d to 7.
A lower number indicates potential for a wider
range of crops, with higher numbers indicating less
potential. Each classification also includes a subclass
which relates to the climate variable that limits the
potential of the site. In our region, the three subclasses
of note are A - potential is limited by the climatic
moisture deficit, F - length of the frost free period, and
G - the number of growing degree days. While each
site is assigned two classifications—one based on its
thermal characteristics and one based on its moisture
characteristics—the higher classification can only
be achieved with active management of moisture
limitations. Since, in our region, agricultural potential
is primarily limited by a lack of moisture availability,

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the thermal classification can only be realized with
adequate irrigation. The 1981 classifications for sites
in our region are summarized in Table 1.
The various classes are associated with a range of
possible crops that can be produced under those
climatic conditions, assuming no other significant
agricultural limitations (e.g., soil type). For example,
class 7 has no potential for agriculture, class 5 only
has potential for forage crops, class 3 is associated
with “strawberries, raspberries, potatoes, lettuce,
peas, spinach, cauliflower, cabbage, cereal grains
and forage crops”, and class 1 has the potential for
a full range of crops from tree fruits to asparagus to
filberts.
Despite relying on climate data that is now over 30
years old, Basin-Boundary farmers still look to the
1981 classifications to determine certain agricultural
practices. This report provides an analysis of the
various climate variables that inform the climatic
capability classifications. Uncertainties surrounding
the analysis methodologies behind the 1981 report
unfortunately prohibit a direct comparison between
the data discussed in this report and that which
informed the original classifications. However, our
analysis of data trends can help farmers understand
how the capabilities of their land have shifted,
and may continue to shift in the near term due to
changes in the region’s climate.

OVERVIEW OF METHODS
The BC climatic capability classification scheme
relies on three derived climate variables: seasonal
climatic moisture deficit, annual growing degree
days, and annual frost free period. Calculation of
these variables requires input of three observed
variables (i.e., seasonal precipitation, minimum
daily temperature, maximum daily temperature)
and calculation of two additional variables (i.e.,
daily mean temperature, seasonal potential
evapotranspiration).

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For variables that could be calculated with monthly
data, inputs were acquired from Environment
Canada’s Adjusted and Homogenized Canadian
Climate Database (AHCCD) and supplemented
with estimated data from the University of British
Columbia’s Climate BC application to generate a
complete dataset. For variables that required daily
data for their calculation, inputs were acquired from
Pacific Climate Impacts Consortium’s data portal.
Data from the same Environment Canada stations
were gathered from the AHCCD and Pacific Climate
Impacts Consortium sources.
Wherever possible, the same calculation methods
described in province’s 1981 publication were
used for our analysis. However, in some cases
where a method was not fully described, we made
assumptions based on best practices in climate data
analysis. The influence of these assumptions on the
analysis prohibits comparison of our results with the
original classifications.
Our analysis involved the only five sites for which
current AHCCD data with good completeness
are available for our region: Cranbrook, Creston,
Fauquier, Golden, and Kaslo.

CURRENT CONDITIONS
Table 2 summarizes average values for key
agricultural climate variables for the most recent
30 years of data available (1984-2013). Given the
diverse geography of the Basin-Boundary region,
it is not surprising that values vary significantly
depending on the community in question.
Cranbrook, Creston, and Golden exhibit a generally
drier climate, with lower seasonal precipitation and
a higher overall climatic moisture deficit. Creston,
Fauquier, and Kaslo exhibit a generally warmer
climate, with a higher number of growing degree
days and a longer frost free period. The frost free
period is approximately a month longer in these
communities than in Cranbrook and Golden.

Table 1: 1981 climatic capability classifications for agricultural sites in the Basin-Boundary region

Table 2: 1984-2013 average values for agricultural climate variables

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Table 3: Trends for agricultural climate variables. “.” indicates no statistically significant trend.

TRENDS
Table 3 summarizes the direction and magnitude
of trends in key agricultural climate variables.
Two time periods are reported—one since the
beginning of the weather record for the relevant
station (ranges from 1908 to 1913), and one over
the standard period 1965-2013. The 1965-2013
period was selected as it minimizes the influence of
natural climate cycles on the analysis. Using longer
or shorter periods, or periods with different start or
end dates, may generate results that are skewed by
the impact of one or more of these cycles (e.g., the
Pacific Decadal Oscillation).
Results are more conclusive for variables that
influence a location’s thermal regime than for the
moisture regime variables. All statistically significant
trends for growing degree days are positive, with
trends being steeper in the more recent time
period. Since the early 1900s, growing degree days
have increased by a range of 151 degree days per
century in Fauquier to 442 degree days per century
in Creston (Figure 1). Cranbrook, Creston, Fauquier,
and Golden show positive trends in the length of
the frost free period since the early 1900s, with
those stations showing increases of 55 to 57 days
per century. No statistically significant trends were
calculated for the length of the frost free period

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since 1965. This movement toward a higher thermal
class is consistent with near-term projections of a
summer warming trend in the Regional District of
Central Kootenay, Regional District of East Kootenay,
and Columbia-Shuswap Regional District3.
All significant trends for seasonal precipitation are
positive (Figure 2), though results show only one
significant trend for the 1965-2013 time period.
Since the early 1900s, seasonal precipitation has
been increasing at a rate of 43 millimetres per
century in Golden to 165 millimetres per century
in Fauquier.
These findings are inconsistent with near-term
projections of a decrease in summer precipitation,
but may be explained by the influence of the
spring and fall months included in the growing
season calculations (May and September). Regional
projections for both the spring and fall are for an
increase in precipitation.
Results for the seasonal potential
evapotranspiration variable are mixed, with two
of three trends since the beginning of the weather
record being negative, and all three trends since
1965 being positive. These results suggest high
variability in the dataset, with a lack of a clear, timeindependent linear trend for most stations.

Figure 1: Annual growing degree days, including trends, since beginning of weather record. Note no significant
trend was calculated for Golden.

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Figure 2: Seasonal precipitation (mm), including trends, since beginning of weather record.

All stations show a significant trend toward a lower
climatic moisture deficit since the beginning of
the weather record, and no clear trend since 1965.
Since seasonal climatic moisture deficit is equal to
the difference between seasonal precipitation and
seasonal potential evapotranspiration, it appears
that any increases in potential evapotranspiration
have been more than offset by increases in seasonal
precipitation.

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IMPLICATIONS

KEY TERMS

The transition to an agricultural climate with
increased growing degree days and a longer frost
free period suggests potential for growing a wider
variety of crops in the region. That said, data show
that an enhanced thermal regime continues to be
accompanied by a moisture regime which severely
limits agricultural potential. Despite long-term
trends toward a lower climatic moisture deficit,
current conditions for this variable remain indicative
of an agricultural climate that lacks sufficient natural
input of seasonal precipitation to permit cultivation
of a wide range of crops. These conditions require
that adequate irrigation be available to realize the
capabilities associated with a higher thermal class.
A recent analysis of stream flow data for our region
indicates that peak and late-summer stream yield
is generally declining4. Since many agricultural
producers in our region depend on surface water
for their irrigation source, these findings collectively
point to the possibility of future water availability
challenges for our region’s agriculture industry.

Seasonal precipitation: The total amount of precipitation, in millimetres, falling during the growing season
(May – September).

Our study of regional agricultural climate trends
is limited in scope and detail. Additional research
could confirm if our findings are consistent with
results for other stations and further investigate
the impact of these trends on current and future
agricultural activities. An enhanced understanding
of the driving factors behind certain trends (e.g.,
the specific timing of increased precipitation during
the growing season) would also assist with crop
management decisions.

Annual frost free period: The number of consecutive
days in a calendar year with minimum daily temperature greater than 0 degrees Celsius.

The RDI thanks Charles Cuell and Mel Reasoner for their
advice on the analysis methodologies used to generate
results for this report.

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Seasonal potential evapotranspiration: The amount
of water, in millimetres, that would evaporate or
transpire from a standardized crop surface if sufficient water were consistently available. Our potential
evapotranspiration calculations considered maximum
temperature, minimum temperature and solar radiation.
Seasonal climatic moisture deficit: The difference
between seasonal precipitation and seasonal potential evapotranspiration; the amount of supplementary
water needed to maintain moisture in the soil.
Annual growing degree days: The difference, accumulated annually, between daily mean temperature
and the standard base temperature of 5 degrees Celsius. The period of accumulation starts and stops with
the first and last consecutive 5-day period when daily
mean temperature is greater than 5 degrees Celsius.

REFERENCES
1.

Columbia Basin Rural Development Institute,
2015. “Knowledge Brief: Agricultural Planning”.
http://www.cbrdi.ca/wp-content/uploads/
CommonThemesAGplans_final.pdf

2.

British Columbia Ministry of Environment, 1981.
“Climatic Capability Classification for Agriculture in
British Columbia”. http://www.alc.gov.bc.ca/assets/
alc/assets/library/agricultural-capability/climatic_
capability_for_agriculture_in_bc_1981.pdf

3.

Pacific Climate Impacts Consortium, 2013.
“Plan2Adapt”. https://www.pacificclimate.org/
analysis-tools/plan2adapt

4.

Columbia Basin Rural Development Institute, 2014.
“Trends Analysis: Stream Flow”. http://www.cbrdi.ca/
wp-content/uploads/TA-StreamFlow-2014-Final.pdf

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