| | Summary | Current situation | Explanation of terms
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Summary
Since the last report (August 02, 2004), precipitation has generally been light over much of the reporting area (< 30 mm) with the exception of west central Alberta where local weather stations reported up to 120 mm of precipitation due to scattered thunderstorm activity. Other stations reporting significant rainfall include Flat Top Lookout in the Swan Hills (66.3), Hussar in south central Alberta (73.3 mm) and Schuler in southeastern Alberta (48.0 mm). Areas receiving less than 10 mm include the parts of the northern Peace country, nearly all of northeast Alberta and much of southern Alberta.
As a result of relatively light precipitation over most of the province, the areas previously classified as Drought Alert remain relatively unchanged since the last report. Drought Alert areas persist in the northern Peace region along with a few pockets in the western Peace region. In east central Alberta a large area remains in this classification, extending as far east as the border of Special areas 3 and 4. In western Alberta a portion of the counties of Yellowhead and Clear Water are classified as Drought Alert. In southern Alberta a few locations of Drought Alert still persist. Two small pockets classified as Drought currently exist, one in the County of Minburn and one in county of Cardston. This suggests that Drought Alert areas surrounding these locations may be close to the lower end of the Drought classification boundary and as a result could move into the Drought category if much Below Normal precipitation occurs.
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 status. One exception is the northern Peace region where the 90-day trend is towards Drought Alert. If the 90-day trend towards Normal persists, existing long-term Drought and Drought Alert conditions will normalize in most areas within in a few months.
Since the last report, soil moisture deficits appear to be intensifying of most areas of the province. Soil moisture conditions were predicted to be at least as low as Well Below Normal in most of Alberta north of Red Deer with the exception of a few areas of Below Normal or better in the central Peace region, northwestern Alberta and eastern Alberta. In southern Alberta at least Well Below Normal soil moisture conditions are predicted to be occurring in a large area surrounding Calgary and also in the southwest corner of the Province. Within these areas several small pockets of Extreme Deficit can also be found suggesting many of the areas currently classified as Well Below Normal may grade to Extreme Deficit if future precipitation deficiencies occur. If Extreme Deficits persist into the fall, pasture and forage growth may be further impacted as these stands prepare for over wintering.
Current Situation
Long term drought (Figure 1):
- Since the last Drought report the total area classified as Drought has remained largely unchanged and is still at 0.1% of the reporting area. However the locations of these areas have shifted. In the last report, three small pockets were reported; one in the county of Starland, one spanning the border between Special Areas 3 and 4, and one in the county of Cardston. Now, both pockets in Starland and in the Special areas have disappeared, and a new one has emerged in the county of Minburn. The existence of these small pockets suggests that both of these areas are on the low end of the Drought category and that surrounding areas are in the high end of the Drought Alert category. All five areas mentioned here represent areas of low moisture status and further precipitation deficits could well bring about a rapid increase in the areas classified as Drought. However, on the other hand, a return to Normal or even slightly Below Normal precipitation will result in a relative improvement.
- Currently nearly 15% of the reporting area is in Drought Alert, down from 16% reported in the August 02nd, 2004 Drought report. Light rainfall over much of the reporting area has generally reduced or maintained Drought Alert areas in much of the province. Exceptions include the northern Peace country where the Drought Alert area has expended as far south as Manning and in Central Alberta where the northern edge of the Drought Alert area has now extended as far north as the counties of St Paul and Smoky Lake.
- The areas classified as Normal have increased marginally since the last report and are now up nearly 2%, accounting for 84% of the reporting area.
Recent trends (Figure 2)
- The area representing recent (90-day) trends toward Normal conditions stayed largely unchanged since the last report and still represents most of the mapped area. Since 15% of the province was in Drought Alert status, this represents a trend toward improvement in most of the affected areas
- The 90-day trend towards Drought Alert remains in the northern Peace region and affects the M.D. of Mackenzie, and the northeastern corner of the M.D. of Northern Lights. If current 90-day trends persist those areas currently in Drought Alert status are expected to stay in Drought Alert and those areas in Normal are expected to move into Drought Alert.
Precipitation (Figure 3, Figure 4, and Figure 5)
- Most of the northern half of the 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. In other areas of the Peace, Below Normal precipitation was recorded at Fairview, Beaverlodge and the Slave Lake airport. In the rest of Alberta, areas receiving Below Normal precipitation include parts of northeast Alberta, east central Alberta and the central part of southern Alberta. Several small "dots" of Below Normal precipitation are showing in many locations throughout the province indicating that the Near Normal category is likely on the low end of this range (80-120 % of Normal) in many locations. If precipitation in the later half of August proves to be Below Normal for most of the province, expect to see large areas in this category in the next report (Figure 3).
- Since the last report (August 02, 2004) isolated showers delivered varying amounts of precipitation (0-120 mm) over the province. Most of the activity (40-120 mm) was located in west central Alberta and west of Calgary in a zone stretching from Clearwater County in the north to Ranchland County in the south. Other areas receiving significant precipitation include Flat Top Lookout in the Swan Hills (66.3 mm), Hussar in the County of Wheatland (73.3 mm) and Shuler in the county of Cypress (48 mm). Areas receiving less than 10 mm include the northern Peace region, most of northeastern Alberta, and three large areas in southern Alberta. In all other areas of the province, precipitation totals ranged from 10 - 40 mm. (Figure 4)
- August generally marks an end to the heavy rainfall season in most of Alberta with total amounts ranging from 30 mm in the southwest up to 100 mm in the northwest and southeastern Peace region (Figure 4). This compares to ranges of 30-140 mm for July, 50-140 mm for June and 20-60 mm for September. Given current soil moisture conditions, a return to Normal precipitation patterns should result in adequate conditions for harvesting and provide enough precipitation to sustain annual crops.
Soil moisture (Figure 6 and Figure 7)
- Soil moisture levels were less than 25 mm of plant available water for most of the east half of the reporting area and nearly all of Southern Alberta. Similarity almost the entire Peace region was predicted to have less than 25mm of plant available water. Small pockets of less than 25 mm of plant available water also exist in the M.D of Yellowhead and parts of the counties of Woodlands, Barrhead and Lac Ste Anne. For those crops nearing harvest this may not be a problem. However, for pasture, hay lands and those crops that need further precipitation to finish, immediate precipitation is required as soil moisture reserves are extremely low (Figure 6).
- Soil moisture deficits generally grew in magnitude and extend throughout the reporting area. Locations currently experiencing soil moisture levels in the Extreme Deficit category in the Peace are the M.D.'s of Mackenzie, Northern Lights Greenview and the county of Grand Prairie. In the north half of Alberta, isolated pockets in this category can be found in the M.D. of Opportunity, and the counties of Lakeland, Athabasca, Woodlands, Yellowhead, Lac Ste Anne, Wetaskiwin, Camrose, Ponoka and Lacombe. Two small areas in the south can also be found in the M.D. of Pincher Creek and the county of Cardston (Figure 7).
- Well Below Normal moisture reserves are predicted to be present for most of the Peace region and parts of northern, central and northwestern Alberta. In the south, Well Below Normal soil moisture levels were predicted to occur around Calgary and in southwestern Alberta. Currently about one third of the province has Near Normal or better soil moisture reserves. These areas include the Swan Hills, most of eastern Alberta along the Saskatchewan border and south-central Alberta, and much of western Alberta along the foothills (Figure 7).
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 United States National Drought Mitigation Centre recommends the SPI for Drought identification. 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, Allan Howard, 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 August 15, 2004.
Drought analysis is currently scheduled at bi-weekly intervals between May 1 and October 30. This report was generated as a result of a widespread recent precipitation and updates the previous report of August 02, 2004.
Figure 1. Extent and severity of long-term drought in the agricultural region of Alberta, as of August 15, 2004.
Figure 2. Recent (90 day) trends in drought conditions for the agricultural region of Alberta, as of August 15, 2004.
Figure 3. Precipitation departures in the agricultural region of Alberta for he past 90 days as of August 15, 2004.
Figure 4. Precipitation (mm), since the last drought report, as of August 15, 2004 in the agricultural region of Alberta. The last drought report was August 02, 2004
Figure 5. Average precipitation for August in the agricultural region of Alberta based on thirty years of data (1971-2000).
Figure 6. Soil moisture in the agricultural region of Alberta as of August 15, 2004.
Figure 7. Soil moisture departure in the agricultural region of Alberta from average modeled soil moisture for August 15, 2004. |
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