| | Precipitation | Snow pack | Data sources | Explanation of terms
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Summary
Since the last Drought Report (February 28, 2009) precipitation totals across the agricultural areas of the Province generally varied from 10 to 30 mm, with some isolated areas recording less than 10 mm, the largest of which covers most of the eastern-half of the Southern Region. The foothills area in the south recorded precipitation amounts ranging between 40 to 90 mm. Precipitation accumulations relative to long-term-normal across most of the reporting area were generally near normal, with several widely scattered pockets grading to moderately low, and with the exception of the foothills between Hinton and Waterton Park where accumulations were moderately high to high.
Average daily mean temperatures during the past 15-days, relative to the long-term-normal, varied from moderately low across most parts of the Northern and Central Regions and the western parts of the Peace Region to near normal across the rest of the reporting area (Figure 6).
Cold season precipitation (Oct 1 to March 31) accumulations relative to the long term normal was highly variable across the region. However, in general, across large parts of the reporting area, accumulations were at least moderately low with the lowest accumulations (very low to extremely low) found across a large area spanning the border between the Central and the Northern Regions, as well as in a few locations in the Southern Region. In contrast, isolated pockets grading to at least high can be found in all regions, except for the Peace Region.
Modeled snow pack accumulations relative to long term normal are in general, near normal across most parts of the reporting area with the exception of isolated pockets with moderately high to very high accumulations. However, since snow packs are rapidly retreating, maps of snow packs can be misleading at this time of year when used as an indicator of overwinter accumulations.
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 February 28, 2009 Drought Report (Figure 1)
Since the last drought report (February 28, 2009) precipitation totals varied from 10 to 30 mm across most of the reporting area to less than 10 mm across much of the eastern-half of the Southern Region. In contrast, along the foothills in the south, precipitation ranged between 40 to 90 mm; however, precipitation accumulations relative to long-term-normal across the reporting area were generally at least near normal, with the exception of several widely scattered and isolated pockets of moderately low accumulations.
Peace Region: Precipitation accumulation ranged from 20 to 40 mm in the northwest, and in the northern corner of the region to 10 to 20 mm across of the central portions of the region to less than 10 mm around the Town of Peace River. The greatest precipitation accumulations were recorded at Savanna AGCM station (32.3 mm) and Spring River Auto station (28.3 mm), both located in the northwest, while the lowest accumulations were recorded at Jean Cote SGCM station (7.9 mm) in central west and Hawk Hills AGCM station (8.4 mm) in center, respectively. Precipitation accumulations for this period, relative to long-term-normal across the region were at least near normal.
Northern Region: Precipitation accumulations varied from 30 to 50 mm across the northeastern portions of the region to less than10 to 20 mm across most of the region, with the exception of few pockets showing less than 10 mm of accumulation. The highest precipitation accumulations were recorded at Cold Lake station (42.2 mm) followed by Dewberry AGCM (31.5 mm) both in the northeast, while the lowest accumulations were recorded at Bodo AGCM station (4.0 mm) followed by Ribstone AGCM station (5.8 mm) both in the southeast corner of the region. Precipitation accumulations relative to long-term-normal across most of the region were at least near normal, with the exception of few isolated pockets of moderately low accumulations.
Central Region: Precipitation accumulations varied from 20 to 50 mm in the western portions of the region to 10 to 20 mm across most other parts of the region with the exception of less than 10 mm of accumulation, along the eastern border of the region. The greatest precipitation accumulations were recorded at James River RS station (35.3 mm) followed by Water Valley station (34.3 mm), both in the west, while the least was recorded at Esther Station (1.8 mm) followed by Acadia Valley AGCM station (9.4 mm), both along the eastern border of the region. Accumulations relative to long-term-normal grade from moderately high in the west to near normal across most of the rest of the region, with the exception of a few pockets of moderately low accumulations.
Southern Region: Precipitation accumulations varied from 40 to 90 mm in the foothills to 20 to 30 mm across most of the western-half of the region and to less than 10 mm across the rest of the region, with the exception of a pocket in the southeast in 20 to 30 mm range. The highest precipitation accumulations were recorded at Porcupine Lookout station (83.6 mm), followed by Pekisko station (80.7mm) both in Foothills, while the lowest accumulations were recorded at Rush Lake station (5.1 mm) in the south, followed by Brooks ASCHRC (6.4 mm) in the central part of the region. Precipitation accumulations relative to long-term-normal across most of the region were at least near normal with the exceptions of three isolated pockets with moderately low accumulations, located in the central north, central south and in the western parts of the region.
Cold Season Precipitation Accumulations relative to Long-Term-Normal (1961 - 2005) (Figure 2)
Cold season precipitation (Oct 1 to March 31) accumulations relative to long-term-normal were highly variable across the reporting area, but for the most part were at least moderately low with the lowest accumulations (extremely low to very low) found across a wide area along the border between the Northern and Central Regions along with some localized areas of the same in the Southern Region. Accumulations range from low to moderately low across much of the plains reporting area and in two pockets in the Peace Region. Most of the Peace Region, the south-western and the south-eastern part of Central Region, as well as isolated pockets in the Southern Region are with at least near normal accumulation.
Peace Region: Across most of the Peace Region, cold season precipitation accumulations were generally near normal across much of the region, with the exception of parts of the northern and the south-western portions of the region where moderately low accumulations were recorded.
Northern Region: Cold season precipitation accumulations in the region were highly variable, grading from extremely high in the northeast, to extremely low in the south and south east.
For the most part however, accumulations were at least moderately low to low, with the much of southern and southwestern parts of the region being classified as having very low and extremely low accumulations.
Central Region: Cold season precipitation accumulations in the region ranged from very low and extremely low across much of the north-half of the region, to low and moderately low accumulations elsewhere, with the exception of at least near normal accumulations in the southwestern and southeastern corner of the region.
Southern Region: Cold season precipitation accumulations were generally moderately low to low across most of the region with the exception of few isolated pockets ranging from very low to at least near normal.
Average Precipitation Accumulations for April (Figure 3)
April generally marks the end of the dry season in most parts of Alberta, with precipitation normally increasing to 30-40 mm over much of the province with the exception of the southwest where 50-60 mm is average. However, in the Peace Region dry weather typically persists throughout April, with average accumulations here ranging from 10 to 20 mm and improving in May, when monthly precipitation amounts average about 40 mm.
Snow pack conditions (Figure 4 and Figure 5)
Modeled snow pack conditions expressed as snow water equivalent (SWE) are shown in Figure 4. Snow pack accumulations relative to long term normal are shown in Figure 5. These maps represent the current snow pack estimates in stubble fields and reflect a 30 percent precipitation loss due to blowing; in addition to losses due to sublimation and snow melt process.
Note that during the early spring, maps showing snow pack accumulations should not be used as an indicator of over winter accumulations since snow packs can change rapidly due to melt conditions and sudden spring snow storms.
Peace Region: SWEs were at least in the 60 to 80 mm range across most of the region grading up to 80 to 90 mm in the central-west and southeastern parts of the region and grade down to 40 to 50 mm in the north. The snow pack accumulations relative to long term normal are generally near normal to moderately high with the exception of a small pocket in the north that grades down to moderately low.
Northern Region: SWEs graded from 70 to 80 mm in the central north, and the northeastern parts of the region, down to 30 to 40 mm across most of the central and central western parts of the region and to 10 to 30 mm across the rest of the region, with the exception of less than 10 mm of SWEs in the southeastern and southwestern part of the region. However, the snow pack accumulations relative to long term normal are at least near normal across most of the region grading up to moderately high in the northeastern portion of the region.
Central Region: SWEs varied from 30 to 50 mm across the northwestern parts of the region to less than 10 mm across most of the western-half of the region and snow free across the rest of the region. Snow pack accumulations relative to long term normal were at least near normal across most of the region with moderately high accumulations along the western parts of the region.
Southern Region: Snow packs are still present in the foot hills and the Cypress hills with SWEs upwards of 80 mm in these areas. Snow pack accumulations relative to long term normal across most of the region are at least near normal.
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 accumulations 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 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 April 9, 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 February 28, 2008. |
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