| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last drought report, March 31, 2009, precipitation was highly variable across the reporting area, ranging from less than 10 mm throughout most of the central and the northern portions of the Southern Region to 40 to 50 mm across the northwestern parts of the Northern Region and upwards of 50 mm along the foothills. Across the Peace Region, precipitation totals were generally in the 10 to 20 mm range.
Daily mean temperatures relative to long term normal, during the past 15-days, were low across most of the reporting area, with the exception of much of the Peace Region and pockets in the Southern Region, where daily average temperatures were classified as moderately low. Seeding operations across most of the reporting have been delayed as a result of cooler than normal temperatures (Figure 7).
Growing season (April 1 to April 30, 2009) precipitation accumulations, relative to long term normal to date, are at least near normal across most of the Peace and the Northern Regions as well as the south and western portions of the Southern Region. In general, growing season precipitation accumulations across the rest of the reporting area graded from moderately low to very low, with much of the Central Region classified as low, with several pockets grading to very low.
The 365-day precipitation accumulations relative to long term normal are classified as low to extremely low across western and southern parts of the Peace Region and also across most parts of the Northern Region extending to the northern parts of the Central Region. Near normal accumulations are generally only found south of Olds, and most of the Southern Region received at least near normal accumulations over the past 365 days.
Modeled soil moisture reserves, relative to long term normal, are low to extremely low across many parts of the reporting area. Extremely low reserves can be found across large parts of the southwestern portions of the Northern Region, and northwestern parts of the Central Region. Much of the western-half of the Peace Region is classified as low to very low, grading to very high in the east and then down to moderately low in the north. At least near normal soil moisture reserves are generally confined to the east-central parts of the Northern Region, southwestern and southeastern parts of the Central Region, southeastern parts of the Peace Region and the southeastern parts of the Southern 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
Growing Season Precipitation Accumulations, April 1 to April 30, 2009 (Figure 1 and Figure 2)
Growing season precipitation totals ranged from 10 to 30 mm across most of the reporting area, to less than 10 mm throughout most of the Central Region and northern portions of the Southern Region and graded up to 40 to 70 mm along the foothills. A few stations in the southern foothills recorded precipitation accumulations that were greater than 100 mm.
Peace Region: Most of the Peace Region received near normal precipitation (10 to 20 mm) with the exception a pocket in the central west with moderately low accumulations. However, the western part of Peace Region is still recovering from last year's drought. The highest accumulation was recorded at Spirit River Auto station (22.4 mm) in the southwest and the lowest at La Crete AGCM station (10.3 mm) in the northern part of the region.
Northern Region: Precipitation accumulations graded from at least near normal across most parts of the region to moderately low and low accumulations in the central-south and southeastern portions of the region. In general, precipitation was highest in northeastern portions of the region and the lowest in the southern parts of the region. The highest precipitation accumulation was recorded at Elk Island National Park station (50.9 mm) followed by St Lina AGCM station (42.3 mm) and the lowest at Lloydminster A station (2.2 mm) in the central-east followed by Bellshill AGCM station (6.1 mm) in the southeast.
Central Region: Most the region has had at least moderately low growing season accumulations to date with a large portion of the region classified as low with some pockets in the east grading down to very low. The highest precipitation was recorded at Battle River Headwaters station (34.3 mm) in the northwest and the lowest at Atlee AGCM station (1.2 mm) in the southeast followed by Oyen AGDM station (1.4 mm) in the eastern parts of the region.
Southern Region: Precipitation accumulations in the plains area graded from at least near normal accumulation (10 to 50 mm) in the western and the extreme southern parts of the region, to moderately low, low and very low accumulations in the north and northeast portions of the region. Along the foothills precipitation ranged from 50 to 120 mm. The highest precipitation was recorded at Porcupine Lookout station (122.6) in the foothills and the lowest at the Brooks ASCHRC station (2 mm) followed by the Schuler AGDM station (2.9 mm) in the east.
Long Term Conditions: 365-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3)
Precipitation accumulations, relative to the long term normal, over the last 365 days have been extremely low across the southern parts of the Northern Region, also affecting the northern parts of the Central Region. Extremely low accumulations have also occurred across most the western half of the Peace Region. North of Olds, at least 60 percent of the reporting area has at least moderately low accumulations; south of Olds, accumulations were generally at least near normal.
Average Precipitation Accumulations for May (Figure 4)
The month of May generally marks the beginning of a significantly wetter period over most of the province, with May accumulations accounting for about 10 percent of the average annual precipitation. In May, the southwestern parts of the Southern Region typically will receive more precipitation than any other area in the province, with average accumulations in the 50 to 80 mm range. In contrast, across most of the Peace Region and eastern portions of the Northern, Central and Southern Regions, average precipitation ranges between 40 to 50 mm.
Soil Moisture
Soil moisture in the agricultural regions of Alberta (Figure 5 and Figure 6)
Modeled soil moisture reserves relative to long term normal, are very low to extremely low across much of the southern parts of the Northern Region, extending through much of the Central Region, and also affecting the northern parts of the Southern Region and the western parts of the Peace Region. In sharp contrast, several areas are at least near normal in each of the four regions, with the largest areas of at least near normal confined to the southern and eastern portions of the Southern Region and the Peace Region.
Peace Region: Soil moisture levels generally varied from a high of 75 to 125 mm in the eastern and central parts of the region to 50 to 75 mm across the rest of the region with the exception of a pocket in the western part of the region with 25 to 50 mm. Modeled soil moisture reserves relative to long term normal are at least near normal in the central and eastern portions of the region, grading down to moderately low throughout most of the rest of the region with the exception of few pockets of low and/or very low reserves in the western parts of the region.
Northern Region: In general soil moisture levels varied from a maximum of 50 to 100 mm across the central and northern portions of the region to 25 to 50 mm across to the rest of the region. Modeled soil moisture reserves relative to long term normal graded from near normal in the central portions of the region to low and extremely low across the western and southern portions of the region, including areas around Lloydminster.
Central Region: Soil moisture levels were in the 100 to 125 mm range, across the extreme western portions of the region, and rapidly grade down to the 50 to 75 mm range east of Highway 2, with much of the eastern half of the region estimated to have 25 to 50 mm of stored moisture. Modeled soil moisture reserves relative to long term normal graded from near normal in the southwestern and southeastern portions of the region to low and very low, across the rest of the region, with extremely low levels found in the northwestern corner of the region.
Southern Region: Soil moisture levels along the foothills grade rapidly from 100 to 125 mm to 50 to 75 mm across much of the southern half of the region. Across much of the northern half of the region, soil moisture levels are in the 25 to 50 mm range with north-central parts of the region grading down to less then 25 mm. Modeled soil moisture reserves relative to long term normal across most of the region are classified as at least near normal with the exception of a north-south corridor along the foothills and much of the of the northern-half of the region where soil moisture levels are classified as moderately low to low with several pockets in the very low to extremely low range.
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 Accumulation - Frequency of Occurrence
Precipitation accumulation, 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 accumulation for each period are then determined by ranking the precipitation accumulation 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 accumulation 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 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 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 May 12, 2009.
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 March 31, 2009 |
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