| | Summary | Drought indices | Precipitation | Soil moisture | Explanation of terms
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Summary
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Since the last report (August 15th, 2004), relatively cool, wet weather has persisted over most of the province. As a result, significant precipitation has fallen over much of the province. In the north half of the province, precipitation totals ranged between 50 mm in the northeast to upwards of 200 mm in the Swan Hills and Saddle Hills. In west central and southwestern Alberta, upwards of 150 mm of precipitation was recorded at a number of stations in and along the foothills. Areas not receiving much of the recent precipitation include the M.D of Mackenzie in the northern Peace region (< 40 mm), parts of east central Alberta (10-40mm), and a small pocket in south central Alberta (30-40mm).
As a result of recent precipitation over most of the province, the areas previously classified as Drought Alert have either disappeared completely or diminished in severity and extent. Currently, only one very small area classified as Drought exists in the province. This area occurs in the county of Minburn and is based on precipitation observations recorded in Vegreville. Drought Alert areas currently persist in several locations around the province including the M.D of Mackenzie in the northern Peace and two areas in central Alberta, the largest of which extends from the town of Smokey Lake south to the town of Morrin and stretches as far east as the town of Provost. In eastern Alberta, Drought Alert can be found in an area affecting Special Areas 3 and 4 and the M.D of Acadia. In southern Alberta, the County of Cardston still remains in Drought Alert.
Precipitation during the past 90 days has resulted in a trend toward at least Normal, or low risk of Drought, for most of the reporting area, including all areas currently in Drought Alert status.One exception is the northern Peace region, where the 90-day trend continues to be Drought Alert. If the 90-day trend towards Normal persists, existing long-term Drought Alert conditions will normalize in most areas within in a few months.
Since the last report, soil moisture deficits decreased substantially over most areas of the province, with more than 75% of the province having a least Near Normal or better soil moisture conditions. Areas with Below Normal to Well Below Normal soil moisture reserves can be found in the northern Peace region, parts of north east and central Alberta, extreme western Alberta and some parts of south central Alberta along the Canadian-US border.
Drought Indices
Long term Drought (Figure 1):
In the last Drought report (August 15th, 2004), 0.1% of the reporting area was classified as Drought. Currently only one very small area exists in the county of Minburn at Vegreville. This strongly suggests that surrounding areas currently classified as Drought Alert are close to the Drought category and could rapidly move into Drought if dry conditions were to develop. However, if the current trend persists, improvements should been seen in these locations.
Currently, 7.8% of the reporting area is in Drought Alert, down from 15% reported in the August 15th, 2004 Drought Report. All of the previously classified Drought Alert areas in the west and southern Peace regions have graded to Normal. Most areas previously classified as Drought Alert have decreased in size but still remain. Currently, Drought Alert areas are located in the northern Peace country affecting the M.D of Mackenzie, in east central Alberta, affecting parts of the counties of Smokey Lake, St. Paul, Lamont, and most of the counties of Two Hills, Minburn, Beaver, Camrose, Wainwright, Flagstaff, Stettler, Paintearth, and Starland. Similarly, in the east, Special areas 3 and 4 and the M.D. of Acadia are in Drought Alert. In southern Alberta, two small pockets of Drought Alert remain, one in the county of Forty Mile and the other in the county of Cardston.
The areas classified as Normal have increased since the last report and are now up nearly 4%, accounting for 88% of the reporting area.
A few small pockets of Above Normal areas can be found throughout the province, accounting for just over 4% of the reporting area.
Recent trends (Figure 2):
Over the last 90 days, all areas save for the northern Peace are trending at least towards Normal conditions over the last 90 days. In fact, as fall approaches many areas are currently trending towards Above Normal. These areas include most of the southern Peace county, parts of southwestern Alberta, and a few pockets in other areas. If current 90-day trends persist the northern Peace is expected to stay in Drought Alert status and all other areas in the province will return to at least Normal or, in some cases, towards Above Normal.
Precipitation
Precipitation over last 90 days (Figure 3):
Over the past 90 days, much of northern Peace region has received at least Below Normal precipitation with the exception of the M.D. of Mackenzie and the northeastern tip of the M.D. of Northern Lights, which have received Well Below Normal precipitation. This is a condition that has persisted since the spring of this year. In all other areas of the Peace, at least Near Normal To Above Normal precipitation has been recorded over the last 90 days.
In the rest of Alberta, only one pocket of much Below Normal precipitation persists and this is located in the County of Lakeland. Areas receiving Below Normal precipitation include parts of northeast Alberta, east central Alberta and the central part of extreme southern Alberta. Several small "dots" of Below Normal precipitation are showing in other locations throughout the province indicating that the Near Normal category adjacent locations are likely on the low end of the normal range (Normal = 80-120 % of Normal)
Precipitation totals since the last report (Figure 4):
Since the last report (August 15, 2004) a series of significant storm events have delivered varying amounts of precipitation (10-200 mm) over the province. Most of the activity (>80 mm) occurred over the west half of the province and over most of the Peace country except the extreme northern areas where precipitation has been lacking during much, if not all, of the growing season. Throughout the northeast and central portions of the province, precipitation ranged from 50 to 80 mm. In east central and southeastern Alberta, less than 50 mm of precipitation was recorded, the least amount being at Oyen (16.8 mm)
Precipitation percent of normal for August 2004 (Figure 5):
August precipitation was Much Below Normal to Below Normal in the extreme northern Peace region, all of north east Alberta, and parts of north central Alberta ranging as far south and east as the Special areas 3 and 4. In all other areas, precipitation for the month of August was at least Above Normal. Much Above Normal precipitation occurred in most of southern Alberta, as well as parts of west central Alberta, in an area north and west of Calgary, and also in the Swan Hills and Saddle Hills.
Precipitation normals, month to date (Figure 6):
Heavy rains over much of north half of the province during the first half of September has resulted in at least Near Normal precipitation for much of this area. Again, the exception is the northern Peace country where a continued lack of precipitation drives a desperate need for moisture. For the entire south half of the Peace and parts of the northwest, precipitation totals are Much Above Normal levels for September. In the south half of the province and parts of east central Alberta, more rain will be needed by the end of September to reach Normal monthly accumulations.
Normal precipitation for the month of September (Figure 7):
September marks the end of the wet season in Alberta, which for most of the province starts in May. This is followed by a series of relatively dry months that persist from October to March. Typically in September, precipitation amounts range from as low as 20 mm in east central Alberta to 70 mm in western and northwestern Alberta.
Soil Moisture
Current soil moisture conditions (Figure 8):
In the northern Peace region, soil moisture levels were predicted to be less than 25 mm of plant available water over much of the M.D of Mackenzie and the northeast corner of the M.D. of Northern Lights. In the central Peace region, soil moisture levels increased to 50-75mm, and for most of the south half of the Peace, soil moisture levels are above 75mm with maximum levels being found in the Swan hills of just over 150 mm. For the east half of the rest of Alberta, soil moisture levels were generally below 50 mm with most of east central and extreme southern Alberta showing soil moisture levels below 25 mm. Areas on the map showing less that 25 mm of soil moisture will need further precipitation immediately to help pasture and hay land prepare for over-wintering. However, precipitation at this time could compromise harvesting activities. In the west half of Alberta there is a strong gradient of increasing soil moisture reserves that increases westward towards the foothills. Within In this zone, soil moisture reserves range from 50 - 75 mm just west of a center line running north south through the reporting area, up to about 135 mm in the foothills west on Calgary and Red Deer.
Soil moisture deficits relative to 30-year normals (Figure 9):
The soil moisture map in Figure 8 by itself does not provide a complete picture of soil moisture status in Alberta. At this time of year it is not uncommon for the southeast to have soil moisture levels below 25 mm. Thus many of the red areas in Figure 8 are considered to be statistically average and as such are not true problem areas with respect to historical moisture levels.
Figure 9 shows soil moisture deficits relative to Normal (30 year statistical average). Since the last report (August 15th, 2004) soil moisture deficits have greatly diminished in almost all areas of the province. Currently more than 75% of the mapping area has Normal of better soil moisture reserves for this time of year. However, in the M.D. of Mackenzie, arguably the driest area in the province, soil moisture deficits have eased but continue to persist and currently range between Below Normal to Extreme Deficit. In the rest of Alberta, one small pocket of extreme deficit still remains in the southwest corner of the M.D of Yellowhead. This still marks a vast improvement since the last report.
In the northwest, Below Normal to Well Below Normal soil moisture reserves can be found in the M.D. of Opportunity, and parts of the counties of Lakeland, Athabasca, Thorhild, Smokey Lake, St. Paul and Bonneville. In Central Alberta, soil moisture reserves continue to be Below to Well Below Normal, with improvements or no change seen in most areas. Exceptions include the Counties of Stettler, Starland and Kneehill and Special areas 3 and 4, where soil moisture levels have declined by about one category since the last report of August 15th, 2004 and currently range between Below Normal to Well Below Normal. In the south, soil moisture levels have also improved markedly with Below Normal soil moisture levels being confined to three counties, (Cardston, Warner and Forty Mile).
Explanation of Terms
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.
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.
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.
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.
Report prepared by the Drought Reporting Team
Ralph Wright, Katherine Altman, and Kris Sabourin,
Conservation & Development Branch & Program
Alberta Agriculture, Food and Rural Development,
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556;
This report was created on September 12, 2004.
Figure 1. Extent and severity of long-term drought in the agricultural region of Alberta as of September 12, 2004.
Figure 2. Recent (90 day) trends in drought conditions for the agricultural region of Alberta, as of September 12, 2004.
Figure 3. Precipitation departures in the agricultural region of Alberta for the past 90 days as of Septemer 12, 2004.
Figure 4. Precipitation (mm), since the last drought report, in the agricultural region of Alberta as of September 12, 2004. The last drought report was August 15, 2004.
Figure 5. Precipitation departures for the month of August 2004.
Figure 6. Precipitation departures for the month of September computed as of September 12, 2004.
Figure 7. Average precipitation for September in the agricultural region of Alberta based on thirty years of data (1971-2000).
Figure 8. Soil moisture in the agricultural region of Alberta as of September 12, 2004.
Figure 9. Soil moisture departure in the agricultural region of Alberta from average modeled soil moisture for September 12, 2004. |
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