| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last report on July 27, 2008, dry conditions prevailed across most of the reporting area. Over all, in the agricultural areas, precipitation accumulations were less than 20 mm, with large areas receiving less than 10 mm. The greatest precipitation accumulations, in the range of 20 to 72 mm, were recorded in isolated pockets in the Peace, Northern and Central Regions.
Average daily mean temperatures relative to long term normal during the past 15 days were near normal across most of the Southern and Central Regions, as well as in isolated pockets in the Northern Region, grading to moderately high and high across in the rest of reporting area (Figure 6).
Growing season precipitation accumulation to date (April 1 to Aug 10, 2008), relative to the long term normal, in the plains reporting area are at least near normal across most of Southern and Central Regions and in few scattered pockets in the Northern Region. Two areas of extremely low exist in the Central Region, one affecting the M.D. of Provost and the County of Paintearth, and one in the south-west corner of Special Area 4. Most of the Northern Region has received at least moderately low accumulations, grading to very low in central parts, with the driest area (extremely low) found in Lakeland County in the northeast. Across the Peace Region conditions have been very dry in the south half of the region, with a large area classified as extremely low, affecting the County of Saddle Hills and the M.Ds of Fairview and Spirit River.
Currently, soil moisture reserves across most of the reporting area fall below 25 mm, with the exception of strip along the western boarder of the Central and Southern regions where soil moisture reserves grade up to more than 75. Areas that have reserves that are less than 25 mm, currently have little capacity to resist short-term dry spells and precipitation is needed immediately.
Soil moisture reserves relative to long-term normal were at least near normal across the western and eastern parts of the Central and Southern Regions, as well as in the southern part of the Southern region. Across most of the Peace and Northern Region, reserves were generally moderately low, with large areas grading to very low and several pockets of extremely low. Generally across all parts of the reporting area, normal to above normal precipitation is needed now.
A large selection of related maps can be found at http://www.agric.gov.ab.ca/acis, under the Quick Viewer tab. Note these maps are updated once a week (usually by Wednesday) providing updates between drought reports.
Precipitation
Precipitation since the July 27, 2008 Drought Report (Figure 1)
In the last 14 days, since the last report (July 27, 2008), dry conditions prevailed across most of the reporting area, with precipitation accumulations generally less than 20 mm. Most parts of the Southern and Central Regions, and parts of the Northern and Peace Regions received less than 10 mm. Precipitation accumulations in the range of 20 to 72 mm were recorded in isolated pockets in the Peace, Northern and Central Regions. The Peace Region continues to be the driest in the reporting area.
Peace Region: Precipitation accumulations across the region varied across a range of 20 to 60 mm, with most of the southern and northern parts of the region receiving in the 10 to 20 mm range. The highest precipitation accumulation was recorded at Peoria AGDM station (52 mm), followed by Grande Prairie A station (23.6 mm) both located in south, and the lowest at Fairview AGDM station (4.7 mm), followed by Brownvale AGCM station (5.7 mm) both located in the centre. The Peace Region continues to be the driest in the reporting area.
Northern Region: Precipitation accumulation across the region graded from 30 to 60 mm in isolated pockets in the western, northern and south-eastern parts of the region to 10 to 20 mm across a wide area, including mainly locals that received less than 10 mm. The highest accumulations of precipitation were recorded at Mayerthorpe station (56.8 mm), followed by Glenevis AGCM station, both in the west, and the lowest at Cadogan AGCM station (3.9 mm) followed by Bellshill AGCM station (4.4 mm), both in the south-eastern corner of the region.
Central Region: In general, precipitation accumulation graded from 20 to 50 mm in the north-west down to less than 10 mm across a most other areas. The highest precipitation accumulation was recorded at Prentiss station (42.6 mm), followed by Red Deer A station (31.6 mm) in the west and the lowest at Consort AGDM station (1.5 mm) followed by Kessler AGCM station (0.5 mm), both in the north-eastern part of the region.
Southern Region: Precipitation accumulation rapidly graded from 10 to 30 mm across the extreme west and parts of the southwest to less than 10 mm across the rest of the region. The highest accumulations were recorded at Pelletier Creek station (49 mm), followed by Crowsnest station (24.4 mm), both located in the west, whereas the lowest accumulations (less than 1 mm) were recorded at Rosemary IMCIN and at Brooks ASCHRC stations, both located north-centrally.
Growing Season Precipitation Accumulation relative to Long Term Normal (1961 - 2005) (Figure 2)
Growing season precipitation accumulation relative to long term normal to date, (April 1 to Aug 10, 2008) are at least near normal across most of Southern and Central Regions, and also in isolated pockets in the Northern Region, as well as a small pocket in north-central part of the Peace Region. Accumulations in the rest of the reporting area graded from moderately low to very low, with at least four areas grading extremely low, the largest of which is in the western part of the Peace Region. Here growing season precipitation accumulations this low occur on average less than 1 in 25 years.
Peace Region: Growing season precipitation accumulation relative to long term normal graded from near normal conditions in the north central parts of the region to a moderately low, in the north, to low and extremely low in the southwestern parts of the region, affecting the County of Saddle Hills and M.Ds of Fairview and Spirit River. Here crop moisture stress is reported to be well-advanced and precipitation is desperately needed.
Northern Region: Growing season precipitation accumulations relative to normal across the region was generally moderately low, with some pockets grading from low to very low and one area, in Lakeland County classified as having extremely low accumulations. Several isolated pockets of near normal accumulations exist across the region.
Central Region: Growing season precipitation relative to long term normal was at least near normal across most of the region, with the exception of the northern part of the region, where accumulations grade from moderately low to pockets of very low with two pockets grading to extremely low; one affecting the M.D. of Provost and the County of Paintearth, and one in the south west corner of Special Area 4.
Southern Region: In general, growing season precipitation accumulations relative to the long term normal are at least near normal across most of the region with the exception of two small pockets of moderately low accumulations.
Average Precipitation Accumulation for August (Figure 3)
Historically, the first half of August is wetter than the last half and this month marks the beginning of a drying trend for most of the reporting area, with the exception of the Southern Region, where July tends to mark the start of drier conditions. For August, average precipitation typically ranges from 30 to 40 mm in the southeast, to greater than 70 mm across the western parts of the Northern Region and south-eastern parts of the Peace Region.
Soil Moisture
Soil Moisture in the Agricultural Regions of Alberta (Figure 4 and Figure 5)
Currently, soil moisture reserves across most of the reporting area have been estimated to fall below 25 mm, with the exception of areas in the western border of the Central and Southern Region rapidly grading from the 75 to 100 mm range. Relative to normal, the picture becomes far move complex. With very low reserves found in north eastern parts of the Central Region, the central and western parts of the Northern Region and the northern and southern parts of the Peace Region.
Peace Region: In general, soil moisture reserves in the region fell below 25 mm, with the exception of a pocket in the central south and part of the eastern border the region where reserves grade up to 25 to 50 mm. Modeled soil moisture reserves relative to long term normal grade from near normal in a small pocket in central south, down to low and extremely low across the rest of the region.
Northern Region: Most of the region's soil moisture reserves fall below 25 mm, with the exception of isolated pockets with 25 to 50 mm range. Relative to long term normal, reserves graded from two pockets of near normal in the east to a large area of low and extremely low reserves in the central and western part of the region.
Central Region: Soil moisture levels in the region sharply graded down from a high of above 75 mm in the west to lows of less than 25 mm across most of the central and eastern part of the region. Relative to the long-term normal, reserves graded from a high of at least near normal in the west and part of the east, to very low reserves in the north-eastern portions of the region.
Southern Region: Soil moisture levels in the region sharply graded down from a high of above 75 mm in the west to lows of less than 25 mm across the rest of the region. Modeled soil moisture reserves relative to long term normal grade from near normal reserves in the western, southern and eastern parts of the region to moderately low reserves in the central parts.
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 a preliminary computer assisted QA/QC check performed by Alberta Agriculture and Rural Development (ARD) staff. 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. Maps describing current conditions are based on preliminary data that is subject to change under further review by ARD, 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:
- Past 365-days
- Past 180-days,
- Past 90-days
- Past 30-days,
- Growing season to date -Starting April 1st
- Cold Season to date- Starting October 1st
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 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 | Frequency of Occurrence |
| extremely low | drier than this, on average, less than once in 25-years |
| very low | drier than this, on average, less than once in 12-years |
| low | drier than this, on average, less than once in 6-years |
| moderately low | drier than this, on average, less than once in 3-years |
| near normal | on average, this occurs at least once in 3-years |
| moderately high | wetter than this, on average, less than once in 3-years |
| high | wetter than this, on average, less than once in 6-years |
| very high | wetter than this, on average, less than once in 12-years |
| extremely high | wetter than this, on average, less than once in 25-years |
This same scheme is then used for similar maps of soil moisture and snow pack accumulations so that comparisons can readily be made across the various map types.
Snow pack (reported during the winter season only)
Snow pack snow water equivalents (SWE) are modeled for stubble fields. SWE is defined as the equivalent depth of water (mm) that the snow pack contains if it were to be melted. SWE 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 percent of the total precipitation is allowed to accumulate resulting in a 30 percent 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 SWE.
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 reported on from May through to 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
Alberta Agriculture, and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on August 13, 2008.
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 July 27, 2008. |
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