| | Precipitation | Snow pack | Data sources | Explanation of terms
.
Summary
Since the last Drought Report (October 31, 2008) significant precipitation (20 to 50 mm) was recorded over much of the Peace Region, the northern part of the Northern Region and southeastern part of the Southern Region. Precipitation across the rest of the reporting area was generally less than 20 mm, with a large area extending from the southern part of the Northern Region to the northern part of the Southern Region that received less than 10mm.
Across much of the western parts of the Northern Region and southern parts of the Peace Region, soil moisture reserves going into freeze up were very low to extremely low (see the October 31, 2008 drought report). These areas are currently very dry and above average snow fall and average to above average spring rains will be needed to bring soil moisture reserves back to normal else these areas will likely have moisture stress to start the next growing season.
Average daily mean temperatures during the past 15-days, relative to the long-term-normal, across the plains reporting area were mainly high to very high with some isolated pockets of moderately high and extremely high. Temperatures in the Peace Region were mainly moderately high, relative to the long term normal (Figure 6).
Cold season precipitation (October 1 to March 31) accumulations to date across most of the Peace Region, the northern parts of the Northern Region, pockets in the Central Region and the eastern and central parts of the Southern region were at least near normal. Accumulations in the rest of the reporting area, varied from moderately low to very low, with several pockets grading down to extremely low found in the northwestern parts of the Central Region, and the southeastern parts of the Northern Region.
Modeled snow pack accumulations relative to long term normal condition for this time of year across the Peace Region, the northern parts of the Northern Region and the central and southern portions of the Southern Region are at least near normal, while across the rest of the reporting area snow pack accumulations are moderately low with a few pockets classified as having low 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 October 31, 2008 Drought Report (Figure 1)
Since the last Drought Report (October 31, 2008), significant precipitation accumulations of 20 to 50 mm were recorded over much of the Peace Region, the northern parts of the Northern Region and southeastern parts of the Southern Region. Precipitation across the rest of the reporting area was less than 20 mm with a vast area, extending from the southern parts of the Northern Region to the northern parts of the Southern Region, receiving less than 10 mm.
Peace Region: Precipitation accumulation across the region graded from 30 to 50 mm across the southern half of the region to 20 to 30 mm across the northern parts of the region. The highest precipitation accumulations were recorded at Sprit River Auto station (45.2 mm), followed by the Savanna AGCM station (42.6 mm) both located in the west, while the lowest accumulations were recorded at La Crete AGCM station (20.3 mm) located in the northern portion of the region. Precipitation accumulations relative to long term normal since the last report were near normal for most of the region.
Northern Region: In general, precipitation accumulations graded from 20 to 30 mm across the north to a less than 10 mm across most of the south-half of the region. The highest precipitation accumulations were recorded at the Atmore AGDM station (28.2 mm), followed by the Rich Lake AGDM station (21.7 mm) both located in north, while the lowest accumulations, less than 2 mm, were recorded in three stations in south, all located in Flagstaff County. Precipitation accumulations relative to long term normal since the last report, graded from near normal in the north to very low and extremely low in the south.
Central Region: Most of the region recorded precipitation accumulations less than 10 mm with the exception in the south and mid western corners of the region were precipitation accumulations were in 10 to 20 mm range. Relative to the long term normal, precipitation accumulations graded from near normal in few pockets in the southeast to very low and extremely low in the northwestern portions of the region.
Southern Region: In general, precipitation accumulations graded from 20 to 40 mm across the southeastern corner of the region to 10 to 20 mm across the northwest and less than 10 mm across much of the northern parts of the region and also in a large pocket in the west. The highest precipitation accumulations were recorded at Medicine Lodge station (34.2 mm), followed by the Manyberries AGCM station (30.8 mm), both located in the east. The lowest accumulations were recorded at the Del Bonita AGDM station (5.3 mm) in the southwest, followed by the Brocket AGDM station (6.5 mm) in the western parts of the region. Precipitation accumulations relative to long term normal since the last report, graded from moderately high in the southeast corner to a near normal along most of the eastern half of the region and to, very low and extremely low in a large pocket in the western parts of the region.
Cold Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2)
Cold Season precipitation (October 1, to March 31) accumulations relative to long term normal, to date, across most of the Peace Region and northern parts of the North Region, and pockets in the Central and Southern Regions were near normal while in the rest of the reporting area, accumulations varied from moderately low to very low with a few pockets, located in the Northern, Central, and Southern Regions, grading to extremely low.
Peace Region: Cold season precipitation accumulations across most of the Peace Region are near normal with the exception of few pockets in the southern and northern parts of the region that are classified as having moderately low accumulations.
Northern Region: Cold season precipitation accumulations in the region graded from near normal in the north of very low and extremely low in the southern parts of the region.
Central Region: Cold season precipitation accumulations in the region graded from very low and extremely low in the north to near normal in a few pockets in the south and southeast.
Southern Region: Cold season precipitation accumulations across the region varied from moderately high and near normal in the southeastern and central parts of the region to a moderately low in the northeast and to low and very low in the west and very low and extremely low in the southwester.
Average Precipitation Accumulations for December (Figure 3)
Across the reporting area, on average 4.7 percent of the annual precipitation falls in December. During this month precipitation totals range from 10 to 20 mm across most of the central and Southern Regions, increasing in the west along the foothills. Across the Northern and Peace Regions, precipitation totals typically range between 20 to 30 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.
Peace Region: SWE's varied from 20 to 30 mm in the central, southeastern and northern parts of the region to 10 to 20 mm across the rest of the region. The snow pack accumulations relative to long term normal varied from near normal in the southern and northern part of the region to moderately high in the center.
Northern Region: The only significant snowpack accumulations in the region can be found in the northeastern parts of the region with SWE's in the 1 to 20 mm range. The snow pack accumulations relative to long term normal varied from near normal in the northeastern part of the region to a moderately low and low accumulation in the rest of the region.
Central Region: There are no significant snowpack accumulations in the region, with the exception of southwest corner of the region where SWE's are in the 1 to 10 mm range. Relative to long term normal these snowpack accumulations, or lack there of, across most of the region for this time of year are moderately low, with the exception of the southwestern corner where current conditions are near normal.
Southern Region: Similarly, the snowpack across most of the region was insignificant, with the exception of pockets in the eastern and western part of the region with SWE's in 1 to 10 mm range. Generally, for this time of year this is near normal, with the exception of the northern, eastern and western boarders of the region were snow accumulations for this time of year are moderately low.
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 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 December 8, 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 October 31, 2008. |
|