2004/05/30 Drought Report for the Agricultural Region of Alberta

Summary

Two main storms during the last two weeks of May resulted in significant precipitation in southwestern and north central Alberta respectively. Precipitation totals exceeding 80mm were reported in Elk Island National Park and in the Waterton area. As a result of spring precipitation, long term drought conditions have eased slightly. The percent of the province in Drought and Drought Alert decreased, whereas the percent of the province in Normal increased since mid May.
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Precipitation during the past 90 days has resulted in a trend toward Normal, or low risk of drought, for most of the province, including many areas currently in Drought status. If this trend persists, long term drought conditions will normalize in a few months. However soil moisture conditions were drier than normal in most of central and western Alberta. There is still immediate need for moisture in the Peace region and in east central Alberta. There is not enough soil moisture reserve to carry the crop through the next two weeks in these areas.

Current Situation

Seasonal drought (Figure 1):

• Approximately 68% of the reporting area of Alberta was in Normal status, 32% was in Drought Alert Status and no areas were in Drought status for seasonal drought (Figure 1).
• In the Peace region only the eastern Peace was in Normal status and the remainder of the region, including the MD of Woodland, was in Drought Alert status.
• A large portion of eastern Alberta including the counties of St. Paul, Flagstaff, Camrose, Minburn, Vermilion River, Wainwright, Provost, Stettler, Paintearth, Red Deer, Kneehill, Starland, Wheatland, Acadia, Newell Forty Mile and Special Areas 2, 3 and 4 were in Drought Alert status.

• In total the 9% of the reporting area was classified as Drought, and no areas were classified as Exceptional Drought, a decrease from 16% and 1% since May 14th, respectively.
• Areas in the Drought included portions of the MD's of Pincher Creek, Willow Creek, and Acadia, and the Counties of Cardston, Lacombe, Red Deer, Stettler, Starland and Cypress Special Areas 2, 3 and 4.
• The areas in Drought Alert include most of southern central Alberta, central and western Alberta and the western peace region.
• Currently 46% of the reporting area is in the Drought Alert category down from 49% reported on May 14th. Approximately 44% of the reporting area is classified as Normal (up from 34% reported on May 14th) and includes northeastern Alberta, the east half of the Peace region and in the south, some Isolated pockets in the counties of Newel and Cypress as well as the M.D. of Rocky View.
• In the Cypress Hills, erroneous precipitation amounts reported during the past several weeks were discovered and corrected; that area now shows Normal, rather than Extreme Drought conditions.

• Recent (90 day) trends toward Normal conditions were observed in most of the Province. Since most of the province was in Drought Alert status, this represents a trend toward improvement in drought conditions.
• Areas currently in Drought Alert, which are showing no trend toward improvement included portions of the Counties of Grande Prairie and Flagstaff. These areas are expected to remain in Drought Alert status, and are expected to remain at risk if current conditions persist.
• Most areas currently in Drought status are trending toward Normal and if conditions persist will move out of risk. Some areas in Drought status are trending toward Drought Alert status. These include the counties of Kneehill and Special Areas 2 and 3. These areas are trending expected toward slight improvement, but are expected to still remain at risk.
• Only a few isolated pockets in the south are trending toward Drought status (-1 to -2) and include the Counties of Cypress and Forty Mile. One small pocket can also be found in the county of Minburn in the northeast. Those areas already in Drought are showing no indication of changing.

• Precipitation in the past 90 days (since March) was Near Normal for the eastern Peace region, north central and portions of west central Alberta, and most of southern Alberta. Precipitation was Below Normal in the northern and western Peace, east central and the southern portion of west central Alberta. Areas that experienced Much Below Normal precipitation included portions of the counties of Woodlands, Flagstaff, Kneehill, Forty Mile, and Special Areas 2 and 3 (Figure 4).
• Most of the precipitation recorded since the last report (May 14, 2004) fell mainly during two storm events. One storm on May 28-30 resulted in 10 - 60 mm of precipitation in central Alberta and the storm of May 20-22 resulted in 10 - 80 mm in southern Alberta, with higher totals in the southwestern mountains and foothills. In total, since May 14 most of central Alberta received 30 - 70 mm, southern Alberta 40 - 80 mm (over 100 mm in the mountains), whereas most of east central Alberta and the Peace region received less than 20 mm (Figure 5).
• Historically May marks the beginning of the wet season in Alberta with much of the province receiving between 30-90 mm of precipitation. However, at this time of year the greatest amount of precipitation (50-70 mm) usually falls on the west half of the province with the rest of the province receiving between 30 and 50 mm of precipitation (Figure 6). Normal rainfall in June would bring even greater amounts of precipitation across the province with a range of 50 to 120 mm of precipitation

• Soil moisture levels were less than 50 mm of plant available water in most of the Peace and east central Alberta regions (Figure 7). This is not enough moisture to carry annual crops through the next two weeks. Pasture conditions in these areas are expected to be even drier.
• Soil moisture levels were in Extreme Deficit in the southern Peace, the northwest, and isolated areas of central Alberta. Spoil moisture levels were Well Below Normal in most of central Alberta, the Peace region and in the southwest (Figure 8).

Seasonal drought (reported during the growing season months only)
Seasonal drought is only reported for two periods, the growing season (May 1 - August 31) and the fall (Sept 1 - October 31). Seasonal drought during the growing season impacts annual crops, hay and pastures but does not necessarily affect livestock water supply. Seasonal drought during the fall can affect hay and pastures. It also affects livestock water supply in the following year by reducing the potential for spring runoff. The ratings are based on the current soil moisture conditions and precipitation departures. Seasonal drought is rated as Normal, Drought Alert or Drought.

Long term (hydrologic) drought
Long term, or hydrologic, drought is a result of the cumulative effect of several dry months. It primarily impacts livestock feed and water supply and may affect annual crops. Hydrologic drought is determined from precipitation totals over a 365-day period using the Standardized Precipitation Index (SPI). Long term drought is rated as either Wet, Above Normal, Normal, Drought Alert, Drought or Exceptional Drought. The SPI is recommended for drought identification by the United States National Drought Mitigation Centre. The long-term drought conditions are reported year-round.
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The trend in long term drought is determined by comparing the 365-day SPI with the 90-day SPI. Where the 90-day SPI value is -1 to +1, then a trend toward moderating conditions is occurring, potentially resulting in Normal status. If the 365-day SPI values for that area are already Normal, then the trend is toward no change. If the 90-day SPI value is -1 to -2, then the area is trending toward Drought Alert status. This could be a deteriorating condition if the current 365-day value is Normal, however it could represent a continuing condition if the area is already in Drought Alert, or an improving condition if the area is already in Drought. Values of the 90-day SPI that are between of -2 to -3 and lower than -3 indicate a trend toward Drought and Extreme Drought respectively. Values of the 90-day SPI that are between +1 and +2, and greater than +2 represent a trend toward Above Average and Wet respectively.

Soil moisture (reported during the growing season months only)
The crop gets the moisture it requires from the reserve of soil moisture, which in turn is replenished by rainfall. Soil moisture is a valuable indicator of drought potential because it shows the reserve of water available to the crop at a given point in time. During peak growing periods, soil moisture reserves are consumed quickly and must be replenished frequently by rainfall. Low soil moisture reserves during these times indicate a high risk of immediate crop stress. Prolonged stress becomes drought, and results in significant unrecoverable yield loss.
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Because the climate varies across Alberta, comparing current moisture levels to normal levels provides a valuable indicator of drought risk that can be applied to all localities and to all times of the season. Below average soil moisture levels, at any time, indicate a need for more rain or snow to restore reserves.
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Soil moisture is measured as millimeters (mm) of plant available water. Plant available water is approximately half of the total water that can be measured in the soil. Soil moisture is monitored from May through October.

Precipitation trends
Long-term cumulative precipitation departures are generated monthly to assess the long-term water status at representative stations in all five regions of the agricultural area of Alberta. Cumulative monthly total precipitation was compared to normal, starting from an arbitrary reference point of January 2001. These departures provide information on how effective recent precipitation trends are in restoring conditions to normal, given that we have had several months of below normal precipitation.
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This helps understand what amount of rainfall is required to offset the drought and dry weather since 2001. When the line slopes down, the precipitation is below normal. When the line slopes up, precipitation is above normal and when the line is flat, precipitation is near normal. From this information, short-term periods of normal or above normal precipitation can be put into perspective with the cumulative effect of conditions since January 2001. For example, in southern Alberta, since the heavy rains in June 2002, precipitation dropped sharply from normal at Cardston, but remained near normal at Medicine Hat until the summer of 2003. The effect of the dry summer of 2003 can be seen in the steeply sloping lines at most stations in all regions. In the southern Peace region, the flat lines indicate a return to near normal precipitation during August 2003, however the cumulative total since 2001 is still below normal for all stations except Ballater.

Report prepared by the Drought Reporting Team
Allan Howard, Ralph Wright, Katherine Altman, and Kris Sabourin,
Conservation & Development Branch & Program
Alberta Agriculture, Food and Rural Development,
Edmonton, AB T6R 5T6
Contact: Ralph Wright
Phone: (780) 427-3594

This report was created on May 6, 2004.

Drought analysis is scheduled at monthly intervals between November 1 and April 30. This report updates the previous report of March 31, 2004.

Precipitation analysis was based on Environment Canada data, with recent data unverified. Amounts may change as data becomes verified.



Figure 1. Extent and severity of seasonal drought in the agricultural region of Alberta, May 30, 2004.



Figure 2. Extent and severity of long-term drought in the agricultural region of Alberta, May 30, 2004

Figure 3. Recent (90 day) trends in drought status in the agricultural region of Alberta, May 30, 2004.

Figure 4. Precipitation departures for the 90 days up to May 30, 2004.

Figure 5. Precipitation (mm) since the last Drought report as of May 30, 2004. The last drought report was May 14, 2004.

Figure 6. Normal precipitation for May. .

Figure 7. Soil moisture as of May 30, 2004.

Figure 8. Soil moisture departure from normal for May 30.