| | Precipitation | Soil moisture | Data sources | Explanation of terms
Summary
Since the last report (September 1, 2008), precipitation was highly variable across the reporting area, ranging from less than 10 mm across much of the Central Region and southeastern parts of the Northern Region, to more than 50 mm across large parts of the Southern Region and also across then northern parts of the Peace Region. Temperature regimes (Figure 6) across the reporting area over the past 15-days have been moderately high, providing favourable conditions for harvesting where rainfall accumulations have not been excessive.
Growing season precipitation accumulations relative to long term normal to date, (April 1 to Sep 30, 2008) are at least near normal across the Southern Region, and the south half of the Central Region, with many of these areas grading to moderately high or more. In contrast across the northern parts of the Central Region and most of the Northern and Peace Regions, growing season accumulations were at least moderately low, with several areas grading to low and very low. The driest areas, relative to normal, can be found in the northwestern Peace Region, where two pockets of extremely low accumulations are found.
Currently, estimated soil moisture reserves across much of the plains reporting areas grade from the 25 to 50 mm to below 25 mm, with the exception of areas along the southern foothills and an isolated pocket, in the Southern Region, where reserves at least 50 mm. Across the Peace Region reserves are in the 25 to 50 mm range with the exception of portions in the northern and eastern parts of the region where reserves are in 50 to 75 mm range.
Soil moisture reserves relative to the long-term normal in the plains reporting areas were at least near normal across most of the Southern Region, the western and eastern portions of the Central Region, and in the south-eastern parts of the Northern Region. Soil moisture reserves across the rest of the plains reporting area are classified as being at least moderately low with several large and widely scattered areas that graded to low and very low. Across the Peace Region reserves are near normal in the central and northern parts of the region grading, mainly to moderately low across the rest 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 September 1, 2008 Drought Report (Figure 1)
Since the last report (September 1, 2008), precipitation accumulations of more than 20 mm were received across Peace Region, most parts of the Southern Region and the south central and north central parts of the Northern Region. Areas that received less than 10 mm include the eastern and north-western parts of the Central Region, and the south-eastern parts of the Northern Region. In general, precipitation amounts and distribution have been favourable to harvest operations.
Peace Region: Precipitation accumulations across the region graded from above 40 mm in the north and east, down to 20 to 30 mm across much of the south and west. The highest precipitation accumulations were recorded at High Level A station (76.8 mm), followed by the La Crete AGCM station (62.0 mm) both located in the north, while the lowest accumulation were recorded at the Teepee Creek AGCM station (21.3 mm) which is located in the southern part of the region.
Northern Region: Precipitation accumulations across the region graded from 30 to 60 mm in the central and north central parts of the region to below 10 mm in the southeast and up to 20 to 30 in the western parts of the region. The highest accumulations of precipitation in the region were recorded at Elk Island National Park station (52.3 mm), followed by the Mundare AGDM station (47.0 mm) located in the center, whereas the lowest accumulations (4.7 mm) were recorded both at the Codagan AGCM station in the southwest and the Rivercourse AGCM station in the east.
Central Region: Precipitation accumulations where generally in the 20 to 40 mm range, across the extreme west and south western portion of the region, and grade down to less than 10 mm in the west-central portions of the region (near the City of Red Deer) and across much of the east half of the region. The greatest amounts of precipitation were recorded at Bow Valley station (83.9 mm) in the southwest corner, followed by Drumheller East station (41.0 mm) in the south, while the lowest accumulations were recorded at the Oyen AGDM station (4.6 mm), followed by Consort AGDM station (5.4 mm), both in the eastern parts of the region.
Southern Region: Precipitation accumulations graded from 40 to 70 mm across much of the western and southern parts of the region to 10 to 20 mm across the northern and north-eastern parts of the region. The highest accumulations were recorded at Grassy Lake IMCIN station (76.4 mm) followed by Fincastle IMCIN station (65.1 mm), both located in the center; and the lowest at the Hussar AGDM station (12.0 mm) followed by Standard AGCM station (13.2 mm) both located in the north.
Growing Season Precipitation Accumulation relative to Long Term Normal (1961 - 2005) (Figure 2)
Growing season precipitation accumulations relative to long term normal to date, (April 1 to Sep 30, 2008) are at least near normal across the Southern Region, most of the Central Region, and in a few isolated pockets in the Northern and the Peace Regions. Accumulations across the rest of the reporting area were moderately low or worse, with several areas grading to very low and extremely low. Two large pockets of extremely low can be found in the western Peace Region; and several pockets of very low can be found throughout the Northern Region, the largest affecting several counties just south of the City of Edmonton.
Peace Region: Growing season precipitation accumulations relative to long term normal are at least near normal in parts of the centre and north, and grade to very low and extremely low in the western parts of the region, with the driest areas affecting Saddle Hills County and the M.D’s of Fairview, Spirit River and Clear Hills.
Northern Region: Growing season precipitation accumulations relative to normal across most of the region were moderately low, grading down to very low and, down to extremely low in some isolated pockets, the largest of which is located in the neighbouring counties south of the City of Edmonton. In contrast, a few relatively small and widely scattered, pockets in the region are classified as having near normal growing season precipitation accumulations to date.
Central Region: Growing season precipitation accumulations relative to long term normal were at least near normal across most of the region, with the exception of the northwest and a pocket in the east central portions of the region, where moderately low to extremely low accumulations were recorded.
Southern Region: Growing season precipitation accumulations relative to the long term normal are at least near normal to moderately high, across most of the region, with some widely scattered areas grading to high.
Average Precipitation Accumulations for October (Figure 3)
Across the reporting area, on average about 4.4 percent of the annual precipitation falls in October. During this month precipitation totals, range from 10 to 20 mm across the east half of the reporting area, grading up to 40 to 50 mm in the foothills of the Southern Region, and in the northwest corner of the Central Region and the western parts on the Northern Region. On average, the Peace Region generally receives between 20 to 30 mm of precipitation in the month of October.
Soil Moisture
Soil Moisture in the Agricultural Regions of Alberta (Figure 4 and Figure 5)
Currently, soil moisture reserves across much of the plains reporting area range from 25 to 50 mm, with large parts of the Central, Northern and Southern Regions, grading down to below 25 mm, with the exception of many areas along the foothills and an isolated pocket in the Southern Region, where reserves are at least 50 mm. Across most of the Peace Region reserves are in the 25 to 50 mm range, with the exception of portions in the northern and eastern parts of the region where reserves are in the 50 to 75 mm range. Relative to long-term normal reserves in the plains reporting areas were at least near normal across most of the Southern Region, the western and eastern portions of the Central Region, and the southeastern parts of the Northern Region. This contrasts sharply with in the rest of the reporting area where reserves grade from moderately low to low or in several cases down to very low. Across the Peace Region reserves are near normal in the central and northern parts of the region grading, mainly to moderately low across the rest of the region.
Peace Region: Soil moisture levels across most of the region are estimated to be in the 25 to 50 mm range with the exception of the northern and eastern portions of the region where reserves are in the 50 to 75 mm range. Relative to long-term normal soil moisture reserves grade from near normal in the central and northern portions of the region to moderately low across the rest of the region.
Northern Region: Much of the region’s soil moisture levels are estimated to fall in the 25 to 50 mm range with the exception of portions of the south-western and north-eastern corner of the region where reserves are below 25 mm. Relative to long term normal, reserves are near normal in the south-eastern corner of the region, and grade to low or very low in the north-eastern and south-western parts of the region.
Central Region: Soil moisture levels across most of the region are estimated to fall below 25 mm with exception of the areas along the western borders of the region where moisture levels sharply graded up to the 75 to 125 mm range. Relative to the long-term normal, reserves are at least near normal in the western and eastern parts of the region, grading to low or very low in the central portions of the region.
Southern Region: Soil moisture levels in the region range from above 50 mm in the western and south central portions of the region to less than 25 mm across extreme northern parts of the region. Soil moisture reserves relative to long-term normal across most parts of the region are classified as being at least near normal or better, with the exception in extreme northern parts of the region where they grade down to moderately low or 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 October 3, 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 September 1, 2008. |
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