2010/05/31 Drought Report for the Agricultural Region of Alberta

 
 
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 Precipitation | Soil moisture | Data sources | Explanation of terms
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Since the last drought report (May 4, 2010) several large storm systems have swept through Alberta, bringing significant amounts of precipitation to many areas. Much of the Southern Region received well over 80 mm, with some areas seeing in excess of 150 mm. Across the Central Region, 40 to 70 mm fell. Across the Central Region amounts were variable, ranging from 20 to 30 in the north-east to well over 100 mm in the south-west. Across the Peace Region, accumulations ranged from 20 to 30 mm in the north, up to 60 to 80 mm in the south. Consequently soil moisture conditions across the province have substantially improved to extent that wet soil conditions have slowed seeding in parts of the Southern Region (Figure 1).

Daily mean temperatures during the past 15-days, relative to long term normal were low to very low, south of Highway 16, (4 to 1 degree C below average), while north of Highway 16, it varied from moderately low to low (Figure 2). Over the past 7-days, daily mean temperatures relative to long term normal were generally extremely low to very low, contributing to delayed seed germination and further hampering seeding operations (Figure 2).

Growing season (April 1 to May 31) precipitation accumulations, relative to long term normal, across most of the reporting area were at least near normal. Most areas east of Highway 2 and south of Highway 16 are classified as having high to extremely high accumulations for the growing season, to date: however, some minor exceptions do exist, namely north and south of the City of Calgary, and also in the north-central portions of the Peace Region, where accumulations are classified as being moderately low (Figure 3).

Despite recent rains, the 365-day precipitation accumulations to date, relative to long term normal remain very low and extremely low across the central and western portions of the Northern Region, and across the central and eastern portions of the Peace Region. South of the Trans Canada Highway, accumulations year to date are well above normal with many areas classified as at least high (Figure 4).

Modeled soil moisture reserves relative to long-term-normal, across the reporting area are highly variable, ranging from extremely high in the southern parts of the province, to extremely low west of Edmonton, near the foothills, and across the central-north portions of the Peace Region (Figure 7). In general, soil moisture levels are in excess of 50 mm across the entire area, which is sufficient to give all crops the moisture they need for at least the next few weeks. Across the south, several areas are extremely wet, with excess moisture currently being of concern, particularly where surface drainage is impeded and local ponding is occurring (Figure 6).

A large selection of related maps can be found on the AgroClimatic Information Service (ACIS) http://www.agric.gov.ab.ca/acis under the ACIS maps heading. Note these maps are updated once a week (usually by Wednesday) providing updates between drought reports.

Precipitation

Precipitation since the May 4, 2010 Drought Report (Figure 1)
Since the last drought report (May 4, 2010) significant precipitation (greater than 150 percent of normal) was recorded across most part of the east-half of the reporting area and few other areas. Elsewhere, precipitation accumulation was classified as near or slightly below normal.

Peace Region: Precipitation accumulations across the region graded down from 60 to 80 mm across the south, to 30 to 40 mm across the north. The highest precipitation accumulations were recorded in the south, at the Beaverlodge RCS and Peoria AGDM stations, both with 77.3 mm, while the lowest accumulations were recorded at Hawk Hills AGCM station (29.5 mm) in the north-central portions of the region, followed by Fort Vermilion station (32. 8 mm) located in north. In general, precipitation accumulations relative to long-term-normal, were at least near normal across the region, with the south-half of the region classified as having high accumulations relative to normal for this period.

Northern Region: In general, precipitation accumulations varied from 100 to 120 mm across the southwest corner of the region, to 30 to 40 mm across parts of central-north, and northeast portions of the region. The highest precipitation accumulations were recorded at Battle River Headwaters station (117.9 mm), followed by Breton Plots station (115.9 mm), both in the southwest, while the lowest accumulation were recorded in Andrew AGDM station (28.3 mm) in the center, followed by Lac La Biche climate station (32,5 mm) in the northeast part of the region. Relative to normal, these accumulations range from near normal in the northeast to high and extremely high in the west.

Central Region: Precipitation accumulations varied from 80 to 100 mm across the southwest and northwest, to 30 to 50 mm in several isolated pockets scattered across the region. The highest precipitation accumulations were recorded at Atlee AGCM station (92.3 mm) in the southeast, followed by Rocky Mountain House station (81.1 mm) in the northwest, while the lowest precipitation was recorded in Esther 1 station (36.4 mm) in the east, followed by Halkirk AGCM station (38.7 mm) in central north. In general, precipitation accumulations relative to
long-term-normal since the last report, ranged from extremely high to near normal.

Southern Region: Precipitation accumulations across the region varied from more than 120 mm in several isolated pockets to 50 to 70 mm across the southeast portions of the region. The highest precipitation amounts were recorded at the Medicine Lodge LO station (168.5 mm) in the east, followed by Porcupine Lookout station (176.3 mm) in the west , while the lowest accumulations were recorded at Pakowki Lake AGCM station (50.6 mm), followed by Onefour CDA station (62.9 mm), both in the southeast part of the region. Precipitation accumulations relative to long-term-normal, since the last report, graded from extremely high in the east to very high and high across most of the rest of the region, with the exception of the northwest corner of the region were near normal accumulations fell.

Growing season precipitation April 1 to May 31, 2010 Drought Report (Figure 3)
Growing season precipitation to date across most the reporting area were at leas near normal, with much of the east half the province experiencing unusually wet weather (very high to extremely high accumulations); however, some areas did miss out somewhat, and are classified as having low accumulations. These are confined to the areas just north and south of the city of Calgary and the central-north Portions of the Peace Region, in and around the town of Hawk Hills.

Peace Region: Growing season accumulations relative to long term normal were lest near normal with the exception of a pocket in and around the town of Hawk Hills, in the central north where moderately low accumulations were recorded.

Northern Region: Growing season accumulations relative to long term normal across most of the region varied from several pockets of extremely high in the southeast, to some areas classified as moderately high, in the northeast and western portions of the region.

Central Region: Growing season accumulations relative to long term normal across most of the region varied from extremely high to very high, down near normal in the extreme west and moderately low just north of Calgary.

Southern Region: Growing season accumulations relative to long term normal across most of the region varied from extremely high to very high, with the exception of the extreme southeast (moderately high) and the extreme northwest (normal to moderately low).

Average Precipitation Accumulations for June (Figure 5)
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 southeastern parts of the Peace Region.

Soil Moisture

Soil Moisture in the Agricultural Regions of Alberta (Figure 6 and Figure 7)
Modeled soil moisture reserves relative to long-term-normal, are extremely variable across the reporting area, ranging from extremely high in the southeast, to extremely low west of Edmonton (towards the foothills) and in parts of the northern Peace Region. Soil moisture levels are well over 125 mm across parts of the south, causing excess moisture concerns in some areas. Elsewhere they are generally 50 mm or more, providing most parts of the reporting area with sufficient moisture to get a good start on the growing season.

Peace Region: Soil moisture levels varied from 75 to 100 mm across the west to 50 to 75 mm across the rest of the region, with the exception of a pocket in the central north with 25 to 50 mm reserve. Similarly, modeled soil moisture reserves relative to long term normal graded from near normal in the west to moderately low and low across the rest of the region, with the exception of a pocket in the central north, with very low to extremely low reserves.

Northern Region: Generally, soil moisture levels varied from a high of 100 to 125 mm in few isolated pockets scattered throughout the region, to 50 to 75 mm across about half of the region. Modeled soil moisture reserves relative to long term normal grade from high and moderately high in southeast, to moderately low, along an east to west corridor across the north, dropping to very low in the extreme west; however, it is important to note, that while reserves in the west are classified as extremely low, this is relative to normal, which normally, tends to be one of the wettest areas in the reporting area. All in all, across the region, soil moisture reserves are at least adequate for the time being.

Central Region: Soil moisture reserve levels varied from 100 to 125 mm down to 50 to 75 mm across several widely scattered areas, with the lowest reserves (25 to 50 mm) being found just north of the City of Calgary. Modeled soil moisture reserves relative to long term normal graded from high and moderately high across the southeast to moderately low and low along the western edge of the region. It is important to note that while reserves across the west are classified as below normal, this area, tends to normally be wetter relative to the rest of the region Thus, all in all, across the region, soil moisture reserves are at least adequate for the time being.

Southern Region: Soil moisture reserve across most of the region are well above normal, with many areas being classified as having high to extremely high reserves relative to normal. The only area remaining that is below normal is just south of the city of Calgary where reserves are estimated to be moderately low. Soil Moisture levels across most of the region, grade from more than 125 mm in the western and eastern portions of the region to 75 to 100 mm elsewhere. Only two small pockets of 50 to 75 mm remain, one in the northwest, near Calgary and one in the extreme south east corner of the region. The southern region has experienced unusually wet conditions over the past few months and warm dry weather is needed now to allow access on to many water-logged fields.

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 the GOES/NESDIS. The data undergoes a rigorous 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 a variety of techniques or when available, 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, expressed as a frequency of occurrence, are computed for various periods and can be found on our web site, Ropin' the Web, under the Weather and Market reports title, through the AgroClimatic Information Service. 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 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 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 millimeters (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 1, 2010.

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 May 4, 2010.

 
 
 
 
For more information about the content of this document, contact Ralph Wright.
This document is maintained by Deb Sutton.
This information published to the web on June 2, 2010.
Last Reviewed/Revised on June 15, 2010.