| | Precipitation | Snow pack | Data sources | Explanation of terms
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Since the last drought report (January 31, 2009) precipitation totals varied from the 10 to 20 mm range across most of the southern part of the Peace Region, the northern, western and the southern parts of the plains reporting areas, to a less than 10 mm in the rest of the reporting area. However, relative to the long-term-normal, the southwestern portion of the Northern Region extending in to the Central Region and the northeastern portion of the Northern Region, have very low and extremely low accumulation.
Average daily mean temperatures during the past 15-days, relative to the long-term-normal, varied from moderately low in most part of the Peace, Central and Southern Regions to very low in the rest part of the reporting area (Figure 6).
Cold season precipitation (Oct 1 to March 31) accumulations relative to long term normal, to date, are low to extremely low across a large area spanning the border between the Central and the Northern Regions, gradually grading up to moderately low conditions across most part of the plains reporting area. However, accumulations are least near normal across most of the Peace Region, the northern parts of the North Region, pockets in the south-eastern and south-western parts of the Central Region, and the south-eastern part of the Southern Region.
Modeled snow pack accumulations relative to long term normal are very low to extremely low in the southeastern parts of the Northern Region, extending to the northeastern parts of the Central Region, while low to moderately low accumulations exist over the most parts of the Northern and Central Regions. In contrast, accumulations are near normal across most of the Peace Region, the northern part of the Northern Region, southwestern and southeastern portion of the Central Region, and through 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 produced once a week (usually by Wednesday) to provide updates between drought reports.
Precipitation
Precipitation since the January 31, 2008 Drought Report (Figure 1)
Since the last drought report on January 31, 2009, 10 to 20 mm of precipitation was recorded in the southern part of the Peace Region, and the northern, western and southern parts of the plains reporting area. The rest of the reporting area recorded precipitation less than 10 mm.
Peace Region: Precipitation accumulation ranged from 10 to 20 mm across much of the region, with the exception of the southern part of the region, with less than 10 mm accumulation. The highest precipitation accumulations were recorded at Spring Creek #1 station (21.1 mm) and Valleyview AGDM (14.4 mm) both located in south, while the lowest accumulations of 4.8 mm were recorded at Eaglesham AGCM and Jean Cote SGCM stations both in the central southeastern part of the region. Precipitation accumulations relative to long-term-normal varied from moderately low the low in the southern and north central part of the region to at least near normal condition in the rest of the region.
Northern Region: Precipitation accumulations ranged from 10 to 30 mm along the northern and western portions of the region to less than 10 mm in the rest of the region. The highest precipitation accumulations were recorded at the Paddle River Headwaters station (25.6 mm) and Edson A station (21.5 mm), both in the west, while the lowest accumulations were recorded at Wainwright A station (3.8 mm) followed by Edgerton AGCM station (3.7 mm), both in the east. Precipitation accumulations relative to long-term-normal varied from near normal and moderately low accumulations in the north, central and southeastern part of the region to lows of very low accumulations in the northeast and very low and extremely low accumulations in the southwestern part of the region.
Central Region: Precipitation accumulations varied from a 10 to 26 mm range in the southeastern and western portion of the region to less than 10 mm in the rest of the region. The highest precipitation accumulations were recorded at Oyen AGDM station (25.4 mm) followed by the Sedalia AGCM station (12.1 mm), both in the east, while the lowest was recorded at Big Valley AGCM Station (5.6 mm) in the center, followed by Kessler AGCM station (5.7 mm) in northeast border of the region. The accumulations relative to long-term-normal grade from near normal accumulation in the central, southeastern and southwestern portion of the region to moderately low and pockets of low and very low accumulation in the rest of the region.
Southern Region: Precipitation accumulations varied from 10 to 20 mm range across most of the region, with the exception of portions in the northwest and southeastern corner of the region with less than 10 mm and parts of the foothill area with 40 to 50 mm accumulation. The highest precipitation accumulations were recorded at Willoughby Ridge station (46.1 mm), followed by Pelletier Creek station (44.4mm) both in southwest, while the lowest accumulations were recorded at Onefour CDA station (3.1 mm), followed by Pakowki Lake AGCM station (5.5 mm), both in southeastern part of the region. Precipitation accumulations relative to long-term-normal across most of the region was at least near normal with the exceptions of pockets in the central north and in the west with moderately low or low accumulations.
Cold Season Precipitation Accumulations relative to Long-Term-Normal (1961 - 2005) (Figure 2)
Cold Season precipitations (Oct 1 to March 31) accumulations relative to long-term-normal, to date, are extremely low to very low along the boarder between the Northern and Central Regions. Accumulations range from low to moderately low across much of the plain reporting area and in two pockets in the Peace Region. Most of the
Peace Region, south-western and the south-eastern areas of the Central Region, as well as the south-eastern portion of the Southern Region had at least near normal accumulation.
Peace Region: Across most of the Peace Region, cold season precipitation accumulations are near normal, with the exception of two isolated pockets in the northern and southern parts of the region with moderately low accumulations.
Northern Region: Cold season precipitation accumulations in the region grade from at least near normal across the western and northern parts of the region, to large pockets of very low and extremely low accumulations across the south-central and southwestern parts of the region.
Central Region: Cold season precipitation accumulations in the region graded up from very low and extremely low in central north and northeastern portions of the region to moderately low accumulations across most of the region, with the exception of the southwestern and southeastern corners of the region, with near normal accumulations.
Southern Region: Cold season precipitation accumulations across the region range from near normal accumulation northwestern, central and southeastern areas of the region to moderately low across most of the region and a few pockets of low and very low accumulations.
Average Precipitation Accumulations for March (Figure 3)
March is a typically a dry month across most of the northern half of the reporting area, with precipitation totals ranging from 10 to 30 mm. On average, March is the driest month in the Peace Region, with normal accumulations ranging from 10 to 20 mm. Along the foothills, and across much of the Southern Region, March marks the end of the drier winter period with accumulations ranging from 50 to 60 mm in the extreme south west, up to 30 to 40 mm in the foot hills west and south of Calgary, and around 20 to 30 mm elsewhere in the Southern Region.
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.
Peace Region: SWEs was at least in the 60 to 80 mm range across most of the region grading up to 80 to 90 mm range in the central west and east and most part of the south eastern portion of the region. 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 to moderately low.
Northern Region: SWEs gradually graded from 40 to 70 mm range along the northern and western part of the region to 30 to 40 mm across most part the center and 10 to 20 mm range in the southeastern part of the region. Similarly, the snow pack accumulations relative to long term normal graded from at least near normal condition in the northern and western part of the region to at least moderately low across most of the region and then to very low and as extremely low condition in southeastern portion of the region.
Central Region: SWEs gradually graded from 30 to 40 mm in the west to 10 to 20 mm across most part of the central and eastern portion of the region, with the exception of the southeastern corner with 30 to 50 mm range accumulation. However, the snow pack accumulations relative to long term normal graded from at least near normal in the southwest and southeast to a large area of very low and extremely low in northeastern parts of the region.
Southern Region: SWEs sharply graded down from 40 to 80 mm along most of the foothills to 10 to 30 mm range along a strip of area along the foothill and then up to 20 to 30 and 30 to 40 mm range in the rest of the region, with the exception of a pocket in the east with 40 to 80 mm range. 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 normal.
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 1
- Cold Season to date- Starting October 1
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 March 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 January 31, 2009. |
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