| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last Drought Report, April 11, 2007, significant amounts of precipitation were recorded across the central portions of the Southern, Central and Northern Regions, with most areas receiving between 40 to 60 mm of precipitation. Elsewhere accumulations generally ranged between 5 to 20 mm.
Growing season (April 1, 2006 to April 30, 2007) precipitation accumulations to date, are at least near normal across the entire reporting area. Of particular note is a broad band stretching across the central portions of the Southern, Central and Northern Region that is classified as high to extremely high. One isolated pocket classified as low straddles the border between Special Area 4 and Special Area 3. In the Peace Region growing season precipitation accumulations are generally near normal, with some areas classified as moderately high.
The 365-day precipitation accumulations relative to long term normal in the north-western Peace Region have continued to improved since the last report (April 11, 2007) and now range from a small pocket of moderately low in the southeast, near the town of Valleyview, to a small pocket of very high near the town of Ballater. Elsewhere across the Peace Region 365-day precipitation accumulations are near normal, with a few areas in the northwest and southwest that grade down to moderately low. Across the Northern Region accumulations over the past 356 days are generally at least near normal, with a few widely scattered pockets grading to moderately low. Across the Central Region most areas are classified as having at least near normal precipitation accumulations over the past 365-days, with a few pockets in south-west that grade down to moderately low, and a few pockets in the north that grade up to very high. Across the southern half of the Southern Region, the 365 day precipitation accumulations have remained largely unchanged since the last report (April 11, 2007), with a few pockets in the southwest grading down to very low. Elsewhere in the Southern Region conditions are generally at least near normal.
Due to above average cold season and April precipitation accumulations, soil moisture levels have increased significantly since the report issued at fall freeze up (October 31, 2006). The unusually high snow pack accumulations in the western Peace have turned much of this area around from extremely low, as reported in the October 31, 2006 Drought Report, and now are classified as extremely high. However, severe deficits still exist in some parts of the northern Peace region, with soil moisture reserves grading to extremely low in some areas. Elsewhere through out the central parts of the reporting area, several areas classified as having extremely high soil moisture reserves can be found, prompting the concern that seeding dates will be delayed if cool wet weather persists.
A large selection of related maps can be found at www.agric.gov.ab.ca\acis, under the Quick Viewer tab.
Current Situation
Precipitation
Precipitation since the April 11, 2007 Drought Report (Figure 1) - Since the last report, significant amounts of precipitation fell across the central parts of the Northern, Central and Southern Regions, with many areas receiving between 40 to 60 mm. Accumulations of less than 20 mm were common most other places, including in the Peace Region.
Peace Region: Across the region, precipitation accumulations ranged from 2.8 mm in the extreme north at the High Level A station, up to 24.5 mm at the Grand Prairie A station. In general, most of the region received 10 to 20 mm.
Northern Region: Precipitation accumulations ranged from 6.6 mm at the Bodo AGDM station in the County of Vermillion River, up to 87.6 mm at the Breton Plots station in the County of Brazeau. Much of the south-central, southern and southwestern portions of the region received between 40 to 60 mm, with the least amounts recorded in the east (10 to 20 mm).
Central Region: Precipitation accumulations ranged from 56.9 mm at the Graigmyle AGCM station in Starland County and 58.0 mm at the Battle River Headwaters station in Lacombe County, down to 0.5 mm at the Esther station in Special Areas 3. Most of the central parts of the region reported 40 to 60 mm with precipitation totals, dropping to 15 to 20 mm in the east and southwest.
Southern Region: Precipitation accumulations ranged from 60.1 mm at the Standard AGCM station in Wheatland County and 56.1 mm at the Rosemary IMCIN station in the County of Newell, down to 3.4 mm at the Del Bonita AGDM station in Cardston County. Generally, through the central and north central parts of the region precipitation ranged from 40 to 60 mm, dropping of to 10 to 25 mm in the east and across much of the of the west.
Growing Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2) - Growing season precipitation accumulations relative to long term normal have been at least near normal throughout the reporting season, grading to extremely high across central parts of the Northern, Central and Southern Regions.
Peace Region: Most of the region has received at least near normal growing season precipitation to date, with some areas grading to moderately high in the southwest and north central parts of the region.
Northern Region: Most of the region has received at least near normal growing season precipitation to date, grading to extremely high in the east central and south-western portions of the region.
Central Region: Most of the region has received at least near normal growing season precipitation to date. Large parts of the north, north-western and south-central parts of the region are classified as extremely high with the exception of one small pocket straddling the boarder between Special Areas 4 and 3 that is classified as low.
Southern Region: Most of the region has received at least near normal growing season precipitation to date. Throughout much of the central parts of the region, large areas are classified as least high grading to extremely high in the east central and northern parts of the region.
Long Term Conditions: 365-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - Precipitation accumulations over the past year were variable across all regions, with most areas reporting at least near normal accumulation. This marks a steady improvement since the April 11, 2007 report, however, several isolated pockets grading to moderately low are still present across all regions, with some pockets grading down to very low, found in the southwestern parts of the Southern Region.
Peace Region: Most the region is at least near normal, with one pocket of low found in the extreme southeast corner of the region in the M.D. of Greenview, just south of a small pocket that grades to high in the centre of the M.D of Smokey River. Elsewhere, areas grading to moderately low can be found in the western parts of the County of Grande Prairie, south-western parts of the M.D. of Clear Hills and the across north central parts of the region.
Northern Region: 365-day accumulations are at least near normal, with several relatively small pockets that grade down to low, which can be found in the northern and central parts of the region. The area with the greatest accumulations is centred on Elk Island National Park and is currently classified as high.
Central Region: Much of the region has recorded at least near normal precipitation over the past 365-days, with three small pockets in the southwest portions of the region that are classified as moderately low. The highest accumulations can be found in the northern parts of the region where several locations are grading to very high.
Southern Region: Across the Southern Region, 365-day precipitation accumulations are variable, but for the most part, are at least near normal with the exception of the southwest portions of the region were two pockets can be found that grade down to extremely low. In contrast, across the east, in the Cypress Hills high accumulations can be found, along with several pockets across the north that grade to moderately high.
Average Precipitation Accumulations for April (Figure 4) - May generally marks the beginning of a significantly wetter period over most of the province, accounting for about 10 percent of the average annual precipitation. In May, the south-western parts of the Southern Region, typically 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 across the eastern portions of the Northern, Central and Southern Regions, average precipitation ranges between 40 to 50 mm, increasing westward to upwards of 70 mm along the foothills.
Soil Moisture
Soil moisture in the agricultural regions of Alberta (Figure 5 and Figure 6) - The spring soil moisture survey is well underway, however, progress has been impeded by frost, lingering snow packs and wet weather, delaying the May 1st target date. The survey should be completed during the second week of May, weather permitting. Normally, the spring soil moisture survey is used to initialize the soil moisture model, which provides the most accurate representation of spring soil moisture conditions possible. However, in the absence of the spring soil moisture survey, the soil moisture maps presented here have been generated from winter model runs and may change when the model is reinitialized in the next week or so.
Since the fall (October 31, 2006 Drought Report), soil moisture levels have increased dramatically across most of the reporting area, due to the above average precipitation received during the cold season and in April 2007. Notably, previously dry areas in the western parts of the Peace Region have recovered significantly due to near record snow packs and now have soil moisture levels in excess of 125 mm, with some of these areas grading to extremely high (Figure 6). However, much of the north half of the Peace Region remains relatively dry, with soil moisture levels ranging between 25 to 50 mm which, for this time of year, is classified as ranging from low to extremely low, relative to the long term normal.
Peace Region: North of the town of Peace River, soil moisture levels are generally between 25 to 50 mm, grading sharply upwards across the M.D. of Fairview and Birch Hills County to above 125 mm across much of the south (Figure 5). Currently reserves range from extremely low in parts of the north, through to extremely high in the southwest. Preliminary field reports suggest that this map is largely accurate; however there are some indications that the model may have over estimated soil moisture recharge in the south due to snow melt over the heavier clay soils where snow packs were particularly deep. A drought report will be issued following the completion of the spring survey and the soil moisture maps will be updated (Figure 6).
Northern Region: Soil moisture levels range from 50 to 75 mm in the northeast and grade up to more then 125 mm across much of the west (Figure 5). Overall, soil moisture reserves range from moderately low in a small pocket in the northeast, otherwise they are at least near normal, grading up to extremely high across much of the west and also in small pocket in the central part of the region (Figure 6).
Central Region: Soil moisture ranges from 25 to 50 mm in the south east, to more than 125 mm in the north west (Figure 5). Soil moisture reserves relative to long tern normal are generally at least moderately high, grading to extremely high in the northwest (Figure 6).
Southern Region: Soil moisture levels are lowest (25 to 50 mm) in the extreme southeast and grade to more than 125 mm along the foot hills in the extreme south west (Figure 5). Most of the south half of the region is at least near normal except for a small pocket of low in the southeast corner of Cardston County. Across the north half of the region soil moisture reserves are moderately high, ranging to very high through parts of the County of Newel and Cypress County (Figure 6).
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 (AF) 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 after further review by AF, 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 Accumulations-Frequency of Occurrence
Precipitation accumulations, 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 accumulations during similar periods 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 Occurence |
| 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 accumulations 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% of the total precipitation is allowed to accumulate resulting in a 30% 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
Conservation & Development Branch & Program
Alberta Agriculture, Food and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on April 30, 2007.
Drought analysis is currently scheduled at monthly intervals between October 31 and April 31 and twice monthly from May 1st to September 30th. This report updates the previous report of April 11, 2007 |
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