Overview

The data are made available as Dbase files, and may be viewed with database or spreadsheet software such as FoxPro, QuattroPro, or Lotus 1-2-3. Each variable's data file includes a key field called DISTRICT which is the ecodistrict id number, and provides a linkage to the ECODISTRICT GIS coverage available on this site. This coverage is also available as an ARCVIEW shape file near the bottom of this page. The data can thus be viewed spatially using ARCVIEW 3.0 or a similar GIS.

Temperature and Precipitation

Monthly air temperature and precipitation variables (TMAX, TMIN, TMEAN, RAIN, SNOW and TOTALP) were interpolated using the Thiessen polygon method (generated using the GRASS GIS V.GEOM module). The Thiessen polygons were overlayed with Ecodistrict polygons, and an area-weighted value generated for each Ecodistrict. (Area-weighted polygon to polygon overlays were done using ARCINFO GIS based methods developed by AAFC and Pole Star Geomatics called PARS.) Polygons of stations which were more than 350 metres above the lowest elevation of each Ecodistrict were eliminated from the weighting procedure to avoid using stations at high elevations in mountainous terrain (e.g. in British Columbia) which were not considered to be representative of agricultural land. In a few cases where no representative climate stations were available, data for the Ecodistrict is indicated as missing (data field is filled with -999's). The amount of missing data varies with the variable and month, but affects at most about 16 out of the 1021 Ecodistricts. Separate Thiessen coverages were developed for temperature and for precipitation for each month to make use of all available station data.

Other Measured Variables

These variables (VP, WI, SH, SR and DP as defined in the table below) were interpolated using gridded surface interpolation methods, since the density of climate stations was generally inadequate for using the Thiessen approach. A grid with 1.5 minute Latitude and Longitude spacing was generated using the inverse distance method to weight the four stations nearest to each grid cell (using the GRASS GIS R.SURF.IDW2 module). For the variables extrapolated using this method, each monthly variable has a maximum, minimum and mean value determined for each Ecodistrict (i.e. the maximum is the highest, minimum is the lowest and mean is the average of all grid point values found within the district).

Derived Variables

Average monthly and annual Thornthwaite PE values and Water Deficits (WD) were computed using methods described by Thornthwaite and Mather (1957). WD values were estimated for soils with 100, 150, 200 and 250 mm available water-holding capacity using both the Penman and the Thornthwaite PE estimates. A precipitation surplus/deficit was computed by subtracting the PE from TOTALP (i.e. TOTALP-PE) using both the Penman and the Thornthwaite PE calculations.

Annual growing degree-days (GDD) above base temperatures of 0, 5, 10 and 15 degrees Celsius (GDD0, GDD5, GDD10 and GDD15) were computed from the monthly mean air temperature data. Brooks (1943) interpolation procedure was used to generate daily mean air temperatures from monthly values and daily growing degree-days were calculated by subtracting the base temperature from the mean daily temperature (negative values were set to zero). Daily values were summed to obtain the annual total. Calculating GDD from mean daily air temperatures involves some error near the start and end of the accumulation period, since the temperature averages include days when the temperature was below the base value. However, this procedure has been commonly accepted as being of sufficient accuracy (Chapman and Brown 1966).

The date of the growing season start (GSS) and end (GSE) were determined by the first and last day of the year when the mean daily air temperature equals or exceeds 5 degrees Celsius. This is generally considered to coincide with the growing period for perennial forage crops (Chapman and Brown 1966). Growing season length (GSL) was computed as GLS=GSE-GSS+1, where GSE and GSS are calendar (Julian) days.

Effective growing degree-days (EGDD) are GDD above 5 degrees Celsius adjusted for growing season and day length and are used in rating the suitability of land for spring-seeded small grains (Pettapiece, 1995).  EGDD were computed from monthly temperature normals using the procedures outlined by Pettapiece, with the following modifications: i) since observed values of average fall frost dates were not available in the database, a procedure described by Sly et al. (1971) was used to estimate the average date of the first fall frost, on which seasonal accumulations of EGDD were ended; ii) a mathematical equation was fitted to the graph in Fig. A.1, page 67 of the Pettapiece (1995) report, which was then used to compute the daylength factor (DLF).  EGDD are determined by multiplying seasonal GDD sums by the DLF, which ranges from 1.0 at latitudes of 49 degrees N or lower, to 1.18 at latitudes of 61 degrees N or higher.
 

Related Data

NOTES

REFERENCES

Chapman, L.J. and Brown, D.M. 1966. The climates of Canada for agriculture. Canada Land Inventory Report No. 3, Environment Canada, Lands Directorate, Ottawa. 24pp. + maps.

Environment Canada. 1994. Canadian Monthly Climate Data and 1961-1990 Normals on CD-ROM. Environment Canada, Atmospheric Environment Service, Downsview, Ontario.

Jensen, M.E. (ed.) 1973. Consumptive use of water and irrigation requirements. Amer. Soc. Civil Engineers, New York, N.Y.

Kirkwood, V., Dumanski, J., Bootsma, A., Stewart, R.B. and Muma, R. 1989. The land potential data base for Canada - User's handbook. Agriculture Canada, Research Branch, Land Resource Research Centre, Tech. Bull. 1983-4E. 53 pp.

Pettapiece, W.W. (ed.) 1995.  Land Suitability Rating System for Agricultural Crops. 1. Spring-seeded small grains.  Agriculture & Agri-Food Canada, Research Branch, Centre for Land and Biological Resources Research, Tech. Bull. 1995-6E, 90 pp. + maps.

Sly, W., Robertson, G.W. and Coligado, M.C. 1971.  Estimation of probable dates of temperatures near freezing from monthly temperature normals, station elevation, and astronomical data.  Canada Department of Agriculture, Research Branch, Plant Research Institute, Agrometeorology Section, Ottawa, Tech. Bull. 79, 21 pp.

Thornthwaite, C.W. and Mather, J.R. 1957. Instructions and tables for computing potential evapotranspiration and the water balance. Drexel Institute of Technology, Publications in Climatology Vol X, No. 3, Centerton, New Jersey. 311 pp.

van Diepen, C.A., Rappoldt, C., Wolf, J. and van Keulen, H. 1988. CWFS Crop Growth Simulation Model WOFOST Documentation, Version 4.1. Centre for World Food Studies, Wageningen, The Netherlands. 299 pp.

ACKNOWLEDGEMENTS

Date Modified: 1999.02.16		Important Notices
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