| | Summary | Drought indices | Precipitation | Soil Moisture | Explanation of Terms
Summary
Since the last report (September 12, 2004), relatively warm dry weather has prevailed over most of the province aiding in harvesting efforts. Precipitation totals ranged from 0-10 mm in much of south, south central and eastern Alberta and up to 60 mm in the central peace region.
Areas classified as Drought Alert since the last report have remained largely unchanged. Drought Alert areas currently persist in several locations around the province including the M.D of Mackenzie in the northern Peace, two areas in central Alberta, the largest of which extends from the County of Two hills southward as far as the county of Starland and a far west and east as Camrose and Wainwright, respectively. In the 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, about half of 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 with one exception being 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 should normalize in most areas within in a few months.
Warm dry weather since the last report, has resulting in an increase in soil moisture deficits over most areas of the province. Soil moisture reserves are estimated to be Well Below Normal in a broad band stretching through the central portions of the province including the Special areas, isolated parts of western Alberta and the northern tip of the peace region. Within these areas Extreme Deficits are estimated to occur in the northern peace and extreme western Alberta. In contrast, much of the southern and central peace region are Above to Well Above Normal with some areas in Extreme Surplus.
Drought Indices
Long-term Drought (Figure 1)
Since the last Drought report (September 12, 2004) the small area around Vegreville previously classified as Drought has disappeared.
Currently 7.6% of the reporting area is in Drought Alert, roughly the same as was reported in the September 12th, 2004 Drought report (7.8%). These areas are located in the northern Peace country affecting the M.D of Mackenzie, in east central Alberta, affecting parts 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 remained largely the same and currently stand at 86% of the reporting area. In addition, a few small pockets of land classified as Above Normal can be found through out the province accounting for just over 6% of the reporting area.
Recent trends (Figure 2)
Over the last 90 days, all areas save for the northern tip of the Peace region and a small pocket in the county of Wainwright are trending at least towards a Normal condition. Both of which are currently experiencing a trend towards Drought Alert. In the case of the northern peace, the current long-term Drought Alert area is larger and over laps that of the 90-day Drought Alert trend suggesting slow improvement in this area. In east central Alberta, most of the large area currently in Drought Alert (Figure 1) is trending towards Normal, save for the previously mentioned pocket in the county of Wainwright, which is currently trending towards Drought Alert.
Precipitation
Precipitation over last 90 days (Figure 3)
Over the past 90 days, the tip of the northern peace region has received Below Normal precipitation with one small area of much Below Normal (49.6%) reported at High Level. In all other areas of the Peace, at least Near Normal to Above Normal precipitation has been recorded over the last 90 days with most of the area reporting at least Above Normal. Several small circular areas of Below Normal precipitation can be found scattered through out Alberta. These areas are centered on weather stations and suggest that the adjacent areas in the Near Normal category are sitting near the low end of the category range. Future precipitation deficits in these areas could lead to rapid increases in the areas classified as Below Normal. Larger areas of Below Normal precipitation can be found in east central Alberta and a number of isolated pockets in southern Alberta
Precipitation totals since the last report (Figure 4)
Since the last report warm dry weather has dominated over most of the province with total amounts ranging between 0-10 mm in much of south central and eastern Alberta. In the north half of the province and up into the peace region precipitation totals ranged from 10 - 60 mm with most of the precipitation falling in the Saddle and Birch Hills areas. The northern peace region, a notably dry area in previous months area received between 10 to 40 mm of rainfall.
Precipitation percent of Normal for September 2004 (Figure 5)
September precipitation ranged from Below to much Below Normal for most of the southern half of Alberta. In contrast, relatively wet weather in the northern half of Alberta, resulted in large areas of Much Above Normal precipitation. Some promise exists for the northern tip of the Peace region where Near Normal precipitation was recorded, a phenomenon that has not been observed for a number of months.
Normal precipitation for the month of October (Figure 6)
October marks the start of the dry season for most of Alberta, which typically spans the October to March over winter period. With the exception of the foothills, monthly precipitation totals during the October to March period range from 10mm to 30 mm.
Soil Moisture
Current soil moisture conditions (Figure 7)
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 of just over 150 mm being found in and around the Swan Hills. 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 levels that increases westward, towards the foothills with maximum amounts of 135 mm estimated to occur the foothills west of Red Deer.
By itself, Figure 7 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 much of the red area shown in southeastern Alberta is considered to be statistically average and as such is not an anomaly with respect to historical moisture levels.
Soil moisture deficits relative to 30-year normals (Figure 8)
Figure 8 shows soil moisture deficits relative to Normal (30 year statistical average). Since the last report (September 12th, 2004) soil moisture deficits have grown, particularly throughout the central, north central and southern parts of the province. Well Below Normal soil moisture reserves are present in most of central, north central and south central Alberta. In addition Well Below Normal soil moisture can be found in western Alberta and the northern tip of the Peace River region. Within these two areas, localized areas of Extreme Deficit are persisting suggesting that those adjacent areas of Well Below Normal are approaching the Extreme Deficit category. Well Above Normal soil moisture levels are estimated to occur in much of the Southern half of the peace region, extending into northwestern Alberta. In addition, other parts of the province with at least Well Above Normal soil moisture reserves can be found west of the towns of Red Deer , Lethbridge and surrounding Medicine Hat.
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, 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 October 03, 2004.
Drought analysis is currently scheduled at bi-weekly intervals between May 1 and October 30. This report updates the previous report of September 12, 2004. |
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