| | Summary | Drought indices | Precipitation | Explanation of Terms
Summary
Since the December 31, 2004 Drought Report, precipitation totals have been variable across the province. Parts of northwestern and southern Alberta received less than 10 mm, while the northern tip of the Peace Region recorded upwards of 50 mm. In extreme southwestern Alberta, Waterton Park Gate reported 211 mm.
Relative to the 1971-2000 normals for the month of January, much of northwestern Alberta as well as several other pockets scattered throughout southern, central and western Alberta received Much Below Normal precipitation. Most of the Peace Region received at least Near Normal precipitation with the northern tip, an area in dire need of moisture, receiving Much Above Normal precipitation for the second month in a row. Some other areas (primarily in the west) also received Near Normal precipitation. For the rest of the province, many localities received Below Normal to Much Below Normal precipitation.
Areas classified as Drought Alert since the last report increased in east central Alberta, and remained largely unchanged elsewhere. Drought Alert areas currently persist in a few localities across the province, including east central Alberta, parts of Special Areas 3 and 4 and few locations in southwestern Alberta.
Given the January precipitation totals of Below to Much Below Normal precipitation throughout most of Alberta, with the exception of the Peace Region, the 90-day trend toward Drought Alert exists across much of northern Alberta, and most of the west half of southern Alberta. Within these areas, the 90-day trend indicates a progression towards Drought conditions in a few isolated localities. On a more positive note, much of the rest of the province, including the Peace Region, is trending to at least Normal or low risk of Drought. If the current 90-day conditions persist, Drought and/or Drought Alert conditions will begin to increase in size, particularly in the north and southwest portions of the province.
The snow pack in stubble fields is considered to be much below average to below average throughout most of Alberta. Notable exceptions occur in the north tip of the Peace and extreme southwest and southeastern portions of the province were Much Above Normal snow packs are predicted to occur. Elsewhere in the Peace Region, many areas are expected to have Near to Above Normal snow cover for this time of year. .
Drought Indices
Long-term Drought (Figure 1)
Currently 6.2% of the reporting area is in Drought Alert, an increase of nearly 3% over that reported in the December 31, 2004 Drought Report (3.4%). Most of this increase occurred in east-central Alberta across an area that now extents from the County of Smokey Lake in the north down to the County of Starland in the south. Other areas of Drought Alert can be found straddling the border between Special Areas 3 and 4 and two small pockets in southwestern Alberta, one in the M.D. of Pincher Creek and one in the County of Cardston. Two other small and isolated areas of Drought Alert can be found in the County of Thorhild and Lacombe, suggesting the large area of Drought Alert in east central Alberta may be on the verge of rapid expansion if dry conditions persist. Of note is the fact that the Peace Region is currently free of any Drought or Drought Alert areas.
The areas previously classified as Normal have decreased by about 2% since the last report, now standing at 82.9% of the reporting area. This decrease has been due to a corresponding increase in the Drought Alert category and increases in the Above Normal and wet category that currently stand at 9.8% and 1.1% respectively.
Recent trends (Figure 2)
For the month of January, below to Much Below Normal precipitation throughout most of the reporting area, with the exception of the Peace Region, has resulted in a 90-day trend toward Drought Alert in much of northern Alberta, and most of the west half of southern Alberta and parts of south central and west central Alberta. In both the counties of Westlock and Minburn, precipitation deficits over the past 90 days are pushing conditions towards Drought. If these trends persist over the next few months, those areas currently classified as Normal will tend towards Drought Alert and those areas classified as Drought Alert will trend towards Drought.
On a more positive note, much of the rest of the province, including the Peace Region, is trending to at least Normal or low risk of Drought. In addition, the north tip of the Peace Region is now showing a trend towards Above Normal conditions, which is a welcome relief from the very dry conditions experienced here throughout most of the 2004 growing season.
Precipitation
Precipitation over last 90 days (Figure 3)
For the northern tip of the Peace Region the 90-day precipitation totals have now shifted from Normal to Much Above Normal. However, the period represented by this 90-day time frame (November 3 to January 31) typically only accounts for about 15% of the total annual precipitation in this Region and it remains to be seen whether or not this precipitation is sufficient to alleviate dry conditions resulting from extreme precipitation deficits experienced during the 2004 growing season. For the remainder of the Peace Region, the western areas have received Much Above Normal precipitation, and central and eastern areas from Near Normal to Above Normal precipitation. Two exceptions exist where Below Normal precipitation has been received, centred around the towns of Manning and Valleyview.
The rest of the province reported Below Normal and Well Below Normal precipitation. Near Normal precipitation was reported in localized areas west of Edmonton stretching across to the foothills along highway 16, in a few small areas in south central Alberta, and in the extreme southwest and southeast. The November 3 to January 31 period typically accounts for only about 15% of the total annual precipitation across the province, and as such, deficits or surpluses reported for this time frame generally do not account for much of the annual total precipitation
Precipitation totals since the last report (Figure 4)
Since the December 31, 2004 Drought Report, accumulations of precipitation ranged from less than 10 mm in parts of southern and northwestern Alberta to upwards of 50 mm in the northern tip of the Peace Region with the most, 211 mm, being recorded in extreme southwestern Alberta at Waterton Park Gate. However, the majority of the Peace Region received somewhat less than the northern tip of the region with totals ranging between 20-40mm. Most other areas in the province received between 10-30 mm with up to 40 mm being reported in the western portion of the province.
Precipitation percent of normal for January 2005 (Figure 5)
January precipitation expressed as a percent of normal was variable across the province and similar to the Precipitation Departures for the Past 90-Days in Alberta (Figure 3). Much Below Normal precipitation was recorded in the northeast, the central parts of southern Alberta, and the extreme southern portions of the Peace Region. Several pockets of Normal precipitation were recorded throughout the region, the largest of which can be found in the Peace Country and another smaller but significant area east of Edmonton stretching west towards the foothills along highway 16. Large areas of Below Normal precipitation were recorded throughout most of the reporting area with the exception of the Peace Region where precipitation was generally Normal or better. However, from a yearly perspective, these deviations from Normal do not account for a significant proportion of the yearly precipitation totals as January is historically a relatively dry month, accounting for about 5% of the total annual precipitation. As a result, the map shown in Figure 5 tends to lead the reader into thinking that significant shortages or surpluses exist in several areas of the province, when in fact, total deviations from Normal may be only several mm of total precipitation.
As the dry season progresses (October through to March) the categories on the monthly Precipitation Departures maps become very sensitive to small deviations in total precipitation amounts. Over the year these seemingly large monthly deviations tend to have a relatively small impact on total yearly precipitation deviations (Figure 1). However, it is desirable to see Normal or better precipitation patterns across the province given the serious deficits consistently experienced in many areas of the province over the past few years.
Normal precipitation for the month of January (Figure 6)
January is typically a dry month across the province with total precipitation amounts ranging between 10 30 mm for most areas excluding the foothills where Normal precipitation totals exceed 30 mm.
Snow pack conditions (Figure 7)
Modeled snow pack conditions are shown in Figure 7. This map represents the current snow pack water equivalents (SPWE) in stubble fields and reflects a 30% precipitation loss due to blowing, in addition to losses due to sublimation and snow melt process. Note that only a portion of the snow water is expected to contribute to the spring soil moisture reserves as much of the initial melt occurs over frozen or partially frozen soils and hence, goes directly to runoff.
Warm weather at the end of January resulted in significant melting of snow in the south and some parts of the west. SPWEs range from less than 1 mm across most of the west half of southern Alberta stretching north west of Calgary well into Clearwater County. For central and northwestern parts of the province the snow pack is expected to contain between 10-25 mm of SPWE. In and around Edmonton and stretching west to the foothills along highway 16, SPWEs are predicted to be between 25-50mm. In much of central and eastern Alberta, SPWEs are predicted to be between 10-25 m. The highest SPWEs are expected to be found in the Peace Region (25-75 mm) with the northern tip of the Peace Region containing more than 75 mm of SPWE.
Snow pack conditions percent of normal (Figure 8)
During the melt in November much of the early winter snow pack disappeared. Warm weather, particularly at the end of January, caused further melting in southern and western areas, which resulted in further reduced snow packs in open areas. The melt, coupled with Below Normal precipitation in many areas since November (Figure 3), excluding the Peace Region, has resulted in current snow pack conditions that are estimated to be much below to Below Normal. In the Peace Region, the snow pack is variable with respect to Normal, ranging from much Below Normal in southern regions to Much Above Normal in the northern tip of the Peace Region.
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. |
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