October, 1999

Agricultural Climate of Manitoba

This map shows that station density is not the same throughout the agricultural region of the province. Clearly, the data is most reliable in areas that have the highest station densities.

The following examples show how to use the maps in this publication. Climatic parameters are identified on each map by different colours. Each colour represents an area in which the value of a climatic parameter falls within a given range.

For Example, Figure 2  shows the average date of occurrence of the last spring frost at 0° C. To determine this date for Altona (south of the city of Winnipeg, near the Manitoba-U. S. border), note that the zone which Altona is located in is coloured red. Therefore, according to the map’s legend, the average date of the last spring frost at Altona occurs from May 14 to May 19.

For another example, review Figure 30. This map shows the average growing season precipitation for spring wheat. Consider the zone surrounding Souris. This area is coloured light green, and according to the map’s legend, receives 200 to 210 mm of growing season precipitation.

Prepared by:
G.H.B. Ash, D.A. Blatta and B.A. Mitchell, B. Davies
Manitoba Agriculture, Food and Rural Initiatives, Agriculture Resource Section

C.F. Shaykewich and J.L. Wilson
University of Manitoba, Department of Soil Science

R.L. Raddatz
Winnipeg Climate Centre, Environment Canada

Funding provided by:
Manitoba Agriculture, Food and Rural Initiatives
Environment Canada
Covering New Ground - Manitoba's Agricultural Sustainability Initive
University of Manitoba

List of Maps:  Map Limitations | Heat | Moisture                                                                                     

Figure 1: Names and Locations of Weather Stations Used in this Analysis

Heat

Last Spring Frost

Figure 2: Average Date of the Last Spring Frost at 0° C
Figure 3: 25 Percent Risk Date of the Last Spring Frost at 0° C
Figure 4: 10 Percent Risk Date of the Last Spring Frost at 0° C

First Fall Frost

Figure 5: Average Date of the First Fall Frost at 0° C
Figure 6: 25 Percent Risk Date of the First Fall Frost at 0° C
Figure 7: 10 Percent Risk Date of the First Fall Frost at 0° C

Frost-free Length

Figure 8: Average Length of the Frost-free Period Above 0° C
Figure 9: Length of the Frost-free Period Above 0° C at a 25 Percent Risk
Figure 10: Length of the Frost-free Period Above 0° C at a 10 Percent Risk

Accumulation of Growing Degree Days (GDD)

Figure 11: Average Annual Accumulation of GDD Above 5° C
Figure 12: Annual Accumulation of GDD Above 5° C at a 25 Percent Risk
Figure 13: Annual Accumulation of GDD Above 5° C at a 10 Percent Risk
Figure 14: Average Annual Accumulation of GDD Above 10° C
Figure 15: Annual Accumulation of  GDD Above 10° C at a 25 Percent Risk
Figure 16: Annual Accumulation of GDD Above 10° C at a 10 Percent Risk
Figure 17: Average Annual Accumulation of GDD Above 15° C
Figure 18: Annual Accumulation of  GDD Above 15° C at a 25 Percent Risk
Figure 19: Annual Accumulation of  GDD Above 15° C at a 10 Percent Risk

Corn Heat Units (Accumulation)

Figure 20: Average Annual Accumulation of Corn Heat Units
Figure 21: Annual Accumulation of Corn Heat Units at a 25 Percent Risk
Figure 22: Annual Accumulation of Corn Heat Units at a 10 Percent Risk

P-Day (Accumulation)

Figure 23: Average Annual Accumulation of  P-Days
Figure 24: Annual Accumulation of P-Days at a 25 Percent Risk
Figure 25: Annual Accumulation of P-Days at a 10 Percent Risk

Moisture                                                                                                                         

Alfalfa

Figure 26: Average Crop Water Demand to the Second Cut of Alfalfa (mm)
Figure 27: Average Accumulated Precipitation to the Second Cut of Alfalfa (mm)
Figure 28: Average Plant Moisture Stress at the First Cut of Alfalfa (mm)
Figure 29: 25 Percent Risk of Plant Moisture Stress at the First Cut of Alfalfa (mm)
Figure 30: Average Plant Moisture Stress at the Second Cut of Alfalfa (mm)
Figure 31: 25 Percent Risk of Plant Moisture Stress at the Second Cut of Alfalfa (mm)

Spring Wheat

Figure 32: Average Growing Season Crop Water Demand for Spring Wheat (mm)
Figure 33: Average Growing Season Precipitation for Spring Wheat (mm)
Figure 34: Lower 25 Percent of Growing Season Precipitation for Spring Wheat (mm)
Figure 35: Upper 25 Percent of Growing Season Precipitation for Spring Wheat (mm)
Figure 36: Average Soil Moisture Amounts at Planting for Spring Wheat (mm)
Figure 37: 25 Percent Risk of Soil Moisture Amounts at Planting for Spring Wheat (mm)
Figure 38: Average Plant Moisture Stress at Heading for Spring Wheat (mm)
Figure 39: 25 Percent Risk of Plant Moisture Stress at Heading for Spring Wheat (mm) Figure 40: Average Plant Moisture Stress at the Soft Dough Stage of Spring Wheat (mm)

Corn

Figure 41: Average Growing Season Crop Water Demand for Corn (mm)
Figure 42: Average Growing Season Precipitation for Corn (mm)
Figure 43: Average Plant Moisture Stress at the Grain Stage of Corn (mm)

Map Limitations

The maps presented in this publication should be used with some caution. Some parts of the map may not be very reliable because they have few weather stations. For example, next to the Saskatchewan border there are 12 municipalities – Albert, Cameron, Whitewater, Pipestone, Sifton, Glenwood, Oakland, Wallace, Woodworth, Whitehead, Daly, Archie and Miniota – without a single weather station (Figure 1). Values in these areas have been estimated by interpolation of data from weather stations outside the municipalities. As a result, the map is not as reliable in this area as it is in areas with a higher weather station density.

Another important issue is the representativeness of the weather data. This is particularly important when considering location near lakes or rivers. For example, the weather station at Great Falls on the Winnipeg River has a higher heat accumulation than the surrounding area. This is likely the result of a longer frost-free period recorded at that particular weather station. Although there is no question about the accuracy of the observations made at the weather station, the data may not be representative of the surrounding area because the influence of the river on the weather may extend for only a short distance from the river. As a result, the map probably overestimates the thermal values for that area.