| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last report on July 6, 2008, wide spread thunderstorm activity dominated precipitation patterns across most of the reporting area, with the exception of the west and southwestern parts of the Peace Region, where little precipitation fell. Precipitation accumulations in excess of 20 mm were recorded across much of the plains reporting areas and also in the northern parts of the Peace Region. Most of the south half of the Peace Region recorded precipitation in the range of 10 to 20 mm including two pockets with less than 10 mm. This area continues to be the driest area in the reporting area.
Average daily mean temperatures, relative to long term normal, during the past 15 days, ranged from near normal to moderately low, across most of the area, with some areas ranging up to moderately high (Figure 6).
Growing season precipitation accumulations to date (April 1 to July 27, 2008), relative to the long term normal, are at least near normal across most of Southern and Central Regions, and also in few pockets in the eastern portions of the Northern Region, and in the central and northern parts of the Peace region. An extended area, across much of the Northern Region is classified as having moderately low accumulations interspersed with few pockets of low to extremely low accumulations. Parts of the Peace Region remain extremely dry, with most of the south half classified in the very low to extremely low range. The western Peace Region requires immediate precipitation to ease crop moisture stress that is reported to be well advanced in some areas.
Currently, large portions of the central and eastern parts of the plains reporting areas have soil moisture levels in the range of 25 to 50 mm, with several areas grading down to less than 25 mm; thus, the capacity of these areas to resist short-term dry spells is rapidly diminishing. Soil moisture levels in the Peace Region are below 25 mm, with the exception of an area along the eastern border of the region. It is critical that the Peace Region receive immediate precipitation to alleviate current crop moisture stress.
Modeled soil moisture reserves relative to long term normal are at least near normal across the Southern and Central Regions, grading across the Northern Region to an extended area of moderately low, with several pockets of very low to extremely low. In the Peace Region soil moisture reserve, relative to long term normal, ranged from very low to extremely low, with the exception of a small pocket of near normal in the east central portions of the region.
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 6, 2008 Drought Report (Figure 1)
Since the last report (July 6, 2008), wide spread thunderstorm activity brought significant precipitation to most parts of the reporting area, except the south half of the Peace Region. Most of the plains reporting areas recorded precipitation in excess of 30 mm, with the exception of isolated pockets of 10 to 20 mm range, scattered in the Northern and Central Regions. Most of the southern parts of the Peace Region recorded less than 20 mm (amounts that occur on average less than 1 in 12 years). The Peace Region continues to be the driest in the reporting area.
Peace Region: Precipitation accumulations in the central and the northern parts of the region were in the range of 20 to 80 mm, with the highest recorded at the Hawk Hills AGDM station (79.7 mm), followed by the La Crete AGCM station (45.1 mm), both located in north central parts of the region. The rest of the region recorded less than 20 mm, with the exception of pockets in the southeastern parts of the region where 30 to 40 mm was recorded.
Northern Region: Precipitation accumulations varied across the region ranging from 20 to 40 mm across much of the region, interspersed with isolated pockets of 20 to 30 mm, 50 to 60 mm, 60 to 90 mm and 10 to 20 mm. The highest precipitation was recorded at Tulliby Lake AGCM station (92.9 mm), followed by the Cold Lake A station (88.1 mm), both near the eastern border of the region. The lowest amounts were recorded at the Edmonton Int'l A station (14.3 mm), followed by the Camrose station (16.7 mm), both in south-central part of the region.
Central Region: Across the western and eastern parts of the region precipitation accumulations where generally above 50 mm, grading down to 20 to 40 mm, across a wide spread area running north to south, through the center of the region. The Oyen AGDM station recorded the highest precipitation in the region (105.9 mm), followed by Water Valley station (80.1 mm) in the west.
Southern Region: Precipitation accumulations varied across the region from isolated pockets of 60 to 70 mm south of Lethbridge, to wide areas of 50 to 60 mm and 30 to 40 mm, with a few pockets in the 20 to 30 mm range. The highest accumulations were recorded at Raymond IMICIN station (83.3 mm) followed by Cross Drain 5 station (73.2 mm), both located in the southern parts of the region.
Growing Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005)
(Figure 2)
Growing season precipitation accumulations relative to long term normal to date, (April 1 to July 27, 2008) are at least near normal across most of Southern and Central Regions, and also in the extreme eastern and southern portions of the Northern Region and the central and northern parts of the Peace Region. An extended area across the Northern Region is classified as having moderately low accumulations, with few pockets of low to extremely low accumulations. Across the south western parts of the Peace Region growing season precipitation ranges from very low to extremely low.
Peace Region: In general, growing season precipitation accumulations relative to long term normal graded from near normal conditions, across most parts of the north to low and extremely low accumulations in the western and southwestern portions of the region. Here crop moisture stress is reported to be well advanced and precipitation desperately needed.
Northern Region: Growing season precipitation accumulations relative to normal across the region were generally moderately, with some pockets grading to low and very low. In contrast, the extreme eastern and southern parts of the region were generally near normal.
Central Region: Growing season precipitation relative to long term normal was at least near normal across most of the region with the exception of few pockets of moderately low to low accumulations located in the northwestern and northeastern part of the region.
Southern Region: In general, growing season precipitation accumulations relative to long term normal are at least near normal across most of the region with several small pockets grading to high and very high.
Average Precipitation Accumulations for August (Figure 3)
Historically, the first half of August is wetter than the last half of August, 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 southeastern parts of the Peace Region.
Soil Moisture in the Agricultural Regions of Alberta (Figure 4 and Figure 5)
Currently, soil moisture levels in the plains reporting areas generally grade from 75 mm, in the west down to below 25 mm reserves in the east. In the Peace Region soil moisture reserves fall below 25 mm across most of the region, with the exception of areas along the eastern border of the region. Modeled long-term normal reserves across the Southern Region and most of the Central Region were at least near normal. Across the Northern Region, reserves grade from near normal in the east to very low across large parts of the west, with similar reserves found in the extreme northern and southern parts of the region. In the Peace Region modeled long-term normal reserves ranged from very low to extremely low with the exception of a small pocket of near normal in the east central portions of the region.
Peace Region: Soil moisture reserves in the region fell below 25 mm, with the exception of the east central portions of the region were reserves grade up to 50 to 75 mm. Modeled soil moisture reserves relative to long term normal grade from near normal in a small pocket in the east, down to low and extremely low across the rest of the region.
Northern Region: Most of the Region's soil moisture reserves fall in the 25 to 50 mm range, with an extended band running through the most of the region that grades to below 25 mm. Relative to long term normal, reserves in graded from near normal in the east to a large area of low and extremely low reserves in the western half of the region. Other areas grading to very low are also be found the north-eastern and south-eastern parts of the region.
Central Region: Soil moisture levels in the region graded down from a high of above 100 mm in the west to lows of less than 25 mm in an extended area occupying most of the east half of the region. Relative to the long-term normal, reserves are at least near normal across most of the region with the exceptions of large pockets in the northwestern and northeastern parts of the region where reserves grade from moderately low to very low.
Southern Region: Soil moisture levels in the region graded from a high of 75 to 125 mm in the west to below 25 mm across most of the east-half of the region, with the exception of the Cypress Hills in the southeast that grades up to 50 to 75 mm. Relative to the long term normal, soil moisture reserves are at least near normal across the entire region.
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 1, 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 7, 2008. |
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