| | Summary | Precipitation | Soil moisture | Data sources | Explanation of terms
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New classification scheme
On May 28th, 2006, a new classification scheme was introduced for the all maps that describe current conditions relative to long-term normals. Over the past several months, it became evident that the maps that employed this scheme were too uniform across the near normal category and yielded sharp breaks across the extreme categories. As a result, the previous maps failed to show sufficient detail. Table 1 shows a comparison between the old scheme and the new scheme. From this point forward (October 31st, 2006) the following scheme will be used for those maps the describe current conditions relative to long-term normal:
Table 1. Revised classification scheme for describing current conditions relative to long term normal.
Description | New Scheme | Old Scheme |
extremely low | drier less than 1 in 25-years | drier less than 1 in 30-years |
very low | drier less than 1 in 12-years | drier less than 1 in 20-years |
low | drier less than 1 in 6-years | drier less than 1 in 10-years |
moderately low | drier less than 1 in 3-years | drier less than 1 in 4-years |
near normal | every 1 in 3-years | every 5 in 10-years |
moderately high | wetter less than 1 in 3-years | wetter less than 1 in 4-years |
high | wetter less than 1 in 6-years | wetter less than 1 in 10-years |
very high | wetter less than 1 in 12-years | wetter less than 1 in 20-years |
extremely high | wetter less than 1 in 25-years | wetter less than 1 in 30-years |
Previous maps using the old scheme will be deleted from our web site at www.agric.gov.ab.ca\acis and replaced with maps using the new scheme. We apologize for any inconvenience.
Summary
Since the last Drought Report (September 30, 2006) significant precipitation was recorded over much of the western parts of the Northern, Central and Southern Regions, and southern half of the Peace Region, with accumulations typically in excess of 40 mm, ranging up to more than 100 mm being recorded across the northwest corner of the Northern Region. In contrast, less than 20 mm was recorded across much of eastern half of the Northern Central and Southern Regions and across the northern tip of the Peace Region.
Cold season (Oct 1to March 31) precipitation accumulations to date, relative to long term normal, across most of the reporting area were generally at least near normal across most of the reporting areas. Over much of the western half of the Northern Region, north-western parts of the Central Region, southern half of the Peace Region and several isolated pockets in the southern half of the Southern Region high to very high accumulations to date were recorded. The lowest accumulations are found across the northern Peace Region where moderately low to low accumulations were recorded.
Precipitation deficits over the over the past year were the lowest in the Peace Region with pockets of extremely low found in north western, west central south-eastern portions of the region. Elsewhere precipitation deficits are highly variable with most areas either in the near normal to moderately low category with several isolated pockets grading down to low.
Soil moisture levels have increased across all regions due to October precipitation and reduced evaporative demand. Soil moisture levels are lowest (25 to 50 mm) across the Peace Region with parts of the extreme northwest and southeast having less than 25 mm. Across most of the Southern Region and the south-eastern Central Region, soil moisture levels range from 25 to 50 mm. Elsewhere, soil moisture levels are over 50 mm with the highest levels found in the north-western parts of the Central Region and south-western parts of the Northern Region were soil moisture levels are greater than 125 mm.
Soil moisture reserves relative to the long term normal (1961 to present) have increased with most areas in the Northern, Central and Southern Regions estimated to have at least near normal. Across the Peace Region reserves have increased, but much of the western parts of the region are still classified extremely low.
A large selection of related maps can be found at www.agric.gov.ab.ca\acis, under the Quick Viewer tab.
Current Situation
Precipitation
Precipitation since the September 30, 2006 Drought Report (Figure 1) - Since the last report, cool, wet weather brought significant accumulations of precipitation (more than 30 mm) to the much of the western parts of the Northern, Central and Southern Regions and the south half of the Peace Region. In contrast, much of the east half of the reporting area and parts of the northern Peace Region recorded less than 30 mm, with several locations reporting below 20 mm.
Peace Region: Precipitation accumulations ranged from less than 5.3 mm across north at the Fort Vermillion RS station, to 56.6 mm in the central parts of the region at the Fairview AGDM station, with the greatest amounts (91.6 mm) recorded in extreme south at the Spring Creek #1 (Moose) station, in the northern parts of the M.D. of Greenview.
Northern Region: Precipitation accumulations ranged from a low of 4.9 mm at the Cold Lake A station in the northeast and graded up through 20 to 40 mm across the central parts of the region to well over 50 m min parts of the west. The greatest amount that was recorded was 101.8 mm at the Little Paddle Headwaters station in the southern part of Woodlands County.
Central Region: The least amounts of precipitation were recorded over much of the east half of the region, ranging from 10 to 20 mm and grading up to 40 to 50 mm in the northwest.
Southern Region: The north-eastern parts of the region were the driest with between 10 to 20 mm recorded at many stations, grading up to 20 to 30 mm across much of the south and west central parts of the region. The greatest accumulations were recorded in the extreme southwest were accumulations were well over 50 mm at many stations.
Cold Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2) - The cold season is arbitrarily defined as the period between October 1and March 31. This is a critical period for soil moisture recharge, particularly when the soils are not frozen. During this time, evaporation rates are low and thus precipitation that falls as rain is an important source of soil moisture recharge for the following growing season. In addition, over winter snow pack accumulations can contribute to soil moisture recharge when melt conditions are favourable, but generally are more important for recharging surface water bodies and ground water.
Peace Region: Most of the Peace Region has received at least near normal cold season perception to date with much of the south half of the region recording high to very high accumulations. The least amount of precipitation was recorded across the northern parts of the region were accumulations grade down to low.
Northern Region: Across much of the region, cold season precipitation to date is at least moderately high with the exception of the extreme northeast were a small pocket of very low can be found in the M.D of Bonnyville. Cold season precipitation accumulations increase westward, grading up to extremely high in the far west.
Central Region: Cold season precipitation to date across most of the region grades from near normal in the extreme east, to moderately high in the south and up to high and very high in north central and north western locations.
Southern Region: The north-eastern parts of the region are classified as having near normal accumulations to date, grading up to moderately high in the south and north central areas, with several pockets in the west and extreme south grading to at least high.
Long Term Conditions: 365-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - Precipitation accumulations over the past year were variable across all regions, with much of the Southern, Central and Northern Regions showing large areas of near normal accumulations interspersed with several large pockets of moderately low to low accumulations. In the Peace Region, accumulations have been much lower, with several areas in the southeast and northwest, classified as extremely low.
Peace Region: A large area of extremely low accumulations is affecting parts of the northwest, central and much of the southwest corner of the region. These areas include the M.D.'s of Clear Hills, Saddle Hills County, Spirit River, Birch Hills County, the M.D.'s of Greenview and Lesser Slave River. These areas are clearly in need of normal to above normal precipitation from now until early spring to help reverse the effects of prolonged dry weather. In the south-western corner of the region conditions improve, grading to moderately low and in the east central parts of the region to near normal. Across the north half of the region, conditions grade from moderately low in the south to near normal in the far north.
Northern Region: Conditions are extremely variable across the region and the reader is encouraged to look at the map for specific details. However, in general along the eastern edge of the region and across parts of the extreme south, extreme west, and the north central areas accumulation are near normal. Elsewhere most of the region is in the moderately low category with a few pockets grading down to very low, one just south of the city of Edmonton and one in the southern parts of Lakeland County.
Central Region: Conditions are extremely variable across the region and the reader is encouraged to look at the map for specific details. Much of the region has recorded at least near normal precipitation with several pockets in the west classified as moderately low, grading down to low. In the east central parts of the region a few pockets of moderately low can be found and in the east and north west moderately high accumulations can be found, with on area in the County of Stettler grading to very high.
Southern Region: Conditions are extremely variable across the region and the reader is encouraged to look at the map for specific details. Much of the region is near normal, grading to low in the northeast, southeast and west-central locations.
Average Precipitation Accumulations for November (Figure 4) - Across the reporting area, on average about 4.3 % of the annual precipitation falls in November. During this month precipitation totals, range from 10 to 20 mm across the east half of the reporting area, grading up to 40 to 50 mm in the foothills in the south west corner of the Southern Region, and up to 20 to 30 mm the northwest corner of the Central Region and the western parts on the Northern Region. Across the Peace Region, on average, 20 to 30 mm or precipitation falls during the month of November.
Soil moisture
Soil moisture in the agricultural regions of Alberta (Figure 5) - Soil moisture levels have increased across most of the reporting area. The driest areas in the Province can be found across much of the Peace Region and east half of the Southern Region, where soil moisture levels are between 25 to 50 mm. The highest soil moisture levels (125 mm) can be found in the north-western parts of the Central Region and the and south-western parts Northern Region.
Peace Region: Across most of the region, soil moisture levels are between 25 to 50 mm, with the exception of the extreme northwest and south-western parts of the region where soil moisture levels are below 25 mm. Above normal precipitation is needed between now and the start of the growing season to restore soil moisture for the coming growing season.
Northern Region: Soil moisture levels are highly variable across the Northern Region, grading from 25 to 50 mm in a small pocket the northeast, up to greater than 125 mm in the southwest. This represents a significant improvement over the conditions that were reported in the last Drought Report.
Central Region: Soil moisture levels grade from a low of 25 mm across the southeast corner of the region, to more than 125 mm across the northwest. This represents a significant improvement over the conditions that were reported in the last Drought Report.
Southern Region: Soil moisture levels grade from 25 to 50 mm across the eastern half of the region, up to 50 to 75 mm in the northwest. This represents a minor improvement over the conditions that were reported in the last Drought Report.
Long Term Average Soil Moisture Conditions (Figure 6) - At this time of the year soil moisture reserves continue increase across all parts on the reporting area due to reduced evaporative demand brought on by harvest and killing frosts. Generally across the reporting area, average soil moisture levels range from 25 to 50 mm over much of the east (excluding the Peace Region) and grade upwards to 75 to 100 mm in the west. Across the Peace Region, normal soil moisture reserves for this time of year typically are in the 50 to 75 mm range with some areas having as much as 50 to 75 mm.
Current Soil Moisture Reserves Relative to Long Term Normal (1961 - 2005) (Figure 7) - Soil moisture reserves computed for the report date (Figure 5), were compared to modeled soil moisture values, using the historical weather data for the same dates during the 1961 to current period, and are expressed as a "frequency of occurrence". This result was mapped, showing how often current soil moisture reserves of a similar magnitude have occurred in the past (1961 to 2005).
Soil moisture over much of the Northern, Central and Southern Regions are at least near normal with large parts of the central and Northern Regions grading to at least high. In contrast, across the Peace Region, conditions are variable grading from near normal in central localities to extremely low across the extreme west, and to very low in a few pockets in the south east.
Peace Region: Soil moisture reserves range from near normal in the center to extremely low along the western and southwest borders of the region. In addition, several pockets of low can be found in the southeast. Across the north reserves range from moderately low to low.
Northern Region: Most of the north half of the region is classified as near normal grading to high and very high across most of the south half of the region.
Central Region: Soil moisture reserves in most parts of the region are at least near normal, grading to extremely high in the northwest.
Southern Region: Soil moisture reserves in most parts of the region are at least near normal with several pockets grading to high across the northwest, north central and eastern parts of the region. The driest areas are currently along the foothills were reserves grade to low, in the M.D.'s of Ranchland and Foothills.
Data Sources:
Near real time weather data
Daily and hourly near-real-time raw weather data is brought in via daily data feeds from Alberta Environment (AENV) and Environment Canada (EC). The data undergoes preliminary QA/QC checks by Alberta Agriculture (AAFRD) staff, assisted by a computer program that flags suspicious and missing values. Suspicious values are checked and verified and daily missing values are filled using archived data from AENV databases or from the EC web site. If daily data is still missing, it is estimated using data from nearby stations. All maps describing current conditions are based on preliminary data that is subject to change under further review by AAFRD, AENV and EC.
Historical weather data
Historical weather data was provided by Environment Canada. . This data was then converted to a 10 km daily gridded weather data set that used all available daily data to generate historical climate and soil moisture normals.
Explanation of Terms
Precipitation accumulations-frequency of occurrence
Precipitation accumulations, expressed as a frequency of occurrence are computed for various periods and can be found on our web site at www.agric.gov.ab.ca\acis, under the Quick Viewer tab. Maps are routinely produced for the following periods:
- 365 days
- 180 days,
- 90 days
- 30 days,
- The growing season to date
- Winter precipitation to date.
Selected maps from this series are included in this report.
Precipitation accumulations for each period are then determined by ranking the precipitation accumulations during similar periods period dating back from 1961 to present. The current accumulation is compared to the ranked values, yielding the frequency of occurrence, based on percentiles. The percentile points were then put into arbitrary but intuitive classification fields that describe the current state as drier, near or wetter than the long term normal. The resulting map thus answers the question "how often does this occur?" The classifications are as follows:
Description | New Scheme |
extremely low | drier less than 1 in 25-years |
very low | drier less than 1 in 12-years |
low | drier less than 1 in 6-years |
moderately low | drier less than 1 in 3-years |
near normal | every 1 in 3-years |
moderately high | wetter less than 1 in 3-years |
high | wetter less than 1 in 6-years |
very high | wetter less than 1 in 12-years |
extremely high | wetter less than 1 in 25-years |
Snow pack (reported during the winter season only)
Snow pack snow water equivalents (SPWE) are modeled for stubble fields. SPWE is defined as the equivalent depth of water (mm) that the snow pack contains if it were to be melted. SPWE is computed from precipitation and subsequent losses due to blowing, sublimation and snow melt processes.
In the model, if precipitation falls when the mean daily temperature is below 2 °C that precipitation is estimated to be in the form of snow. If precipitation if estimated to fall as snow then to simulate drifting, only 70% of the total precipitation is allowed to accumulate resulting in a 30% loss due to snow "blow off". If precipitation occurs as rain on an existing snow pack, it is added directly to the snow pack as SPWE.
Soil moisture (reported during the growing season months only)
Soil moisture is measured as millimetres (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.
The crop gets the moisture it requires from the reserve of soil moisture, which in turn is replenished by precipitation. Soil moisture is a valuable indicator of drought potential because it indicates 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. Poor soil moisture reserves during peak water use 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 during the frost-free season. Current soil moisture levels are compared against soil moisture levels for the same day in each year from 1961 to present. The frequency of occurrence is computed based on the percentile points, using the same method that was used for similar maps that were generated for precipitation. The frequency of occurrence is then plotted using the same class scheme as is used in the long term (hydrologic) drought map (see table above). Soil moisture reserves with a modifier of low, indicate a need for more precipitation to restore reserves.
Soil moisture needed to return to average spring or fall conditions
Soil moisture needed to return to normal spring or fall conditions is computed by subtracting average soil moisture (spring or fall), computed using model runs dating back from 1961 from current soil moisture conditions. This yields the amount of recharge needed to bring current soil moisture levels to average. Historic model runs are then analyzed to determine how many years since 1961 that soil moisture recharge was similar to or greater than that currently needed. The number of years that this occurred is then used to compute the probability of returning to average. However, currently this process is unable to account for snow currently existing on the ground and as such is not as accurate where snow packs exist.
Report prepared by the Drought Reporting Team
Ralph Wright, Daniel Itenfisu and Isabel Simons-Everett
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 31, 2006.
Drought analysis is currently scheduled at monthly intervals between October 31 and April 31, and twice monthly from May 1 to September 30. This report updates the previous report of September 30, 2006. |
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