2008/05/31 Drought Report for the Agricultural Region of Alberta

 
 
Download 768K pdf file ("alberta_drought_report_for_agriculture_y2008_m05_d31.pdf")PDF
(768K)
     Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
 
 
 
 Precipitation | Soil moisture | Data sources | Explanation of terms
.
Summary

Since the last report (April 27, 2008), several episodes of precipitation have brought relief to most of the previously dry areas in the province. The main concerns now are excessive wetness in the western parts of the Central Region and some lingering dry areas in the northern Peace Region.

Since the April 27, 2008 report significant amounts of precipitation (more than 75 mm) were recorded across much of the Southern Region, the western portions of the Central and Northern Regions, and across the central and southern parts of the Peace Region. The rest of the reporting area recorded precipitation in the 25-50 mm range. In general, precipitation accumulations across the reporting area ranged from a high of 473 mm at Spionkop Creek station in the southern part of the province to lows of 25.2 mm at Dupree station in the Northern Region and 25.5 mm at Hemaruka AGCM station in the Central Region.

Growing season precipitation accumulations to date (April 1 to May 31, 2008) relative to the long term normal, are at least near normal across the reporting area with the exception of a few isolated pockets with moderately low accumulations. Moreover, most parts of the Southern Region and parts of the Central, Northern and the Peace Regions recorded accumulations ranging from moderately high to high. Overall, May precipitation has greatly improved soil moisture reserves for cropping.

The provincial spring soil moisture survey was completed on May 12, 2008 and the data from the survey was used to initialize the soil moisture model. The survey was delayed due to frozen soils and adverse weather conditions. Currently, large parts of the Northern, Central and Southern Regions, have soil moisture levels in excess of 75 mm, however, an area grading from 25 to 50 mm stretches down from the southern parts of the Northern Region to Special Areas in the Central Region.. Across most of the Peace Region, soil moisture levels are estimated to be in the 50 to 75 mm range, with the exception of the central and eastern parts of the region which are in the 75 to 125 range, and in the extreme north where soil moisture levels grade down to 25 to 50 mm.

Soil moisture reserves relative to long term normal are at least near normal over large parts of the reporting area, with several isolated pockets in the plains showing high and very high reserves. However, the Peace Region remains the dry relative to the long term normal, with some areas in the extreme north and in the Saddle Hills classified as having very low reserves relative to normal.

A large selection of related maps can be found through the AgroClimatic Information Service (ACIS).

Precipitation

Precipitation since the April 27, 2008 Drought Report (Figure 1)
Since the last drought report (April 27, 2008) significant amounts of precipitation (greater than 75 mm) were recorded across the western parts of the plains regions and into the mountains and foothills. Some stations in the foothills and mountains record more that 240 mm. Precipitation accumulations were lowest (25 to 50 mm) across much of the eastern parts of the Northern Region, extending down into the Special Areas and also across the much of the southern and northern parts of the Peace Region.

Peace Region: Precipitation accumulations across the northern and much of the southern half of the region ranged from 25 to 50 mm, while in the central and the south-western parts ranged from 50 to 100 mm. Precipitation accumulations in the region were greatest at the Peace River A station (97.4 mm) located in the central part of the region, followed by the Notikewin LO station (74.6 mm) located in the west central part of the region. The lowest accumulation was recorded at La Crete AGDM (27.3 mm) and the Fort Vermillion RS station (29.4 mm ) located in the north.

Northern Region: Precipitation accumulations in the western half of the region were in the range of 50 to 100 mm, while most of the eastern half of the region was in the 25 to 50 mm range. The highest precipitation was recorded at stations in the west; House Mountain LO AFS station recorded 124.8 mm and Goose Mountain LO AFS station recorded 102.7 mm. In contrast, the lowest amounts were recorded in the northeast at the Lac La Biche A station (27.1 mm) followed by Dupre AGCM station (25.1 mm).

Central Region: Precipitation accumulations across the region graded from more than 150 mm in the extreme southwest corner with amounts in the west well over 100 mm recorded at the Water Valley station (117.6 mm ) and at the James River RS station (113.8 mm). Across central portions of the region, precipitation ranged from 50 to 100 mm with the least amounts being recorded in the east at the Sedalia AGCM (27.9 mm) and Kessler AGDM (31.2 mm) stations.

Southern Region: Precipitation accumulations across the region ranged from well over 200 mm in the west to lows of 50 to 75 mm in the southeast. The greatest accumulations were recorded at the Spionkop Creek station in the mountains (415.6 mm), followed by Waterton Red Rock Station (293.1 mm) and Akamina station (255.1 mm), while the least amounts were recorded at the Irvine AGCM station (45.9 mm) in the east.

Growing Season Precipitation Accumulations relative to Long Term Normal (1961-2005) (Figure 2)
Growing season precipitation accumulations relative to long term normal to date, (April 1 to May 31, 2008) were at least near normal across most of the reporting area, with the exception of few scattered pockets classified as having moderately low accumulations.

Peace Region: Most of the region has received at least near normal growing season precipitation with the exception of small areas, one in the west and the other in north, which have received moderately low accumulations to date. Of note is the fact that very high accumulations were recorded near the town of Peace River.

Northern Region: Most of the region has received at least near normal growing season precipitation to date, with the exception of a pocket in the north classified as moderately low accumulation. Across parts of the west and northwest, accumulations are classified in the moderately high to high range.

Central Region: Most of the south and south-western portions of the region received moderately high to high precipitation accumulations, while the rest the region received at least near normal growing season precipitation accumulations, with the exception of few pockets in the east that are classified as having moderately low accumulations.

Southern Region: Most of the plains areas have received moderately high growing season precipitation accumulations, with the exception of a several pockets of near normal and a few pockets in the west and east that grade to very high.

Average Precipitation Accumulations for June (Figure 3)
June is typically one of the wettest months in the year with precipitation accumulations ranging from 60 to 70 mm in the southeast to greater than 100 mm across the western parts of the Northern Region and south-eastern parts of the Peace Region. In the coming weeks, near normal, well timed precipitation accumulations will be needed to sustain soil moisture reserves in those areas that are classified as having near normal or lower soil moisture reserves.

Soil Moisture (Figure 4 and Figure 5)

Soil moisture levels throughout most of the reporting area have improved since the last report, due to several significant precipitation events during the month of May. However, as evapotranspiration demands increase with increases in vegetation cover, soil moisture reserves will drop sharply and additional precipitation will be needed soon in order to maintain near normal reserves.

Peace Region: Soil moisture levels in most of the region were in 50 to 75 mm range with the exception at the center with estimated reserve in the 75 to 125 mm range, and in the extreme north where reserves were estimated to be in the 25 to 50 mm range. Relative to long term normal soil moisture reserves were at least near normal in the center, but graded down to very low in the north and extreme western portions of the region with large parts of the south and north, grading down to moderately low.

Northern Region: In general, soil moisture levels in the region graded from 75 to 100 mm in the west, north and northeast parts of the region to 50 to 75 mm in the southeast with the exception of one pocket, grading down to the 25 to 75 mm range. Modeled soil moisture reserves relative to long term normal ranged from at least near normal conditions across much of the region, to high and very high across parts of the east, and down to moderately low in several widely scattered pockets throughout the region.

Central Region: Soil moisture levels in the region graded from more than 125 mm in the west, down to the 25 to 50 mm range in the east. Modeled soil moisture reserves relative to long-term normal across most parts of the region were at least near normal, with most of the western and southwestern portions of the region classified as being in the moderately high to extremely high categories.

Southern Region: Soil moisture levels in the region graded from more that 125 mm in the west down to 75 to 125 mm in the south and down to 50 to 75 mm level in the northeastern parts of the region. Relative to long term normal, soil moisture reserves are at least near normal with the exception of two isolated pockets in the southwest that grade down to 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 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 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 normalon 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 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 June 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 April 27, 2008.
 
 
 
 
For more information about the content of this document, contact Isabel Simons-Everett.
This information published to the web on June 4, 2008.
Last Reviewed/Revised on March 26, 2012.