2010/03/31 Drought Report for the Agricultural Region of Alberta

 
 
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 Precipitation | Data sources | Explanation of terms

.Summary

Since the last drought report (February 28, 2010), at least near normal precipitation accumulations (15 to 35 mm) were recorded across the south-half and the north corner of the Peace Region, the northeastern corner of the Northern Region, as well as in parts of the foothills and the southeastern corner of the Southern Region; however, precipitation accumulations across the rest of the reporting area were generally less than 10 mm, which is less than 50 percent of normal.

The month of March was unusually warm relative to normal (4 to 8 oC above average), with average daily mean temperatures, classified as being extremely high (1 in 25 year event), across most of the reporting area (Figure 2). These relatively warm temperatures led to the early melting of snow packs across many parts of the reporting area. To date most of the reporting area is snow free, with the exception of the southwestern portion of the Peace Region.

Cold season precipitation (Oct 1 to March 31) accumulations relative to long term normal were at least near normal across the central portion of the Southern Region, but elsewhere across the rest of the reporting area, it graded down to low and very low, with a few isolated pockets of extremely low accumulations in the Central and Northern Regions (Figure 3).

The 365-day precipitation accumulations relative to long term normal were at least near normal in the southern foothills, and in the south-west, central and eastern portions of the Southern Region, while the 365-day accumulations across the rest of the reporting were very low and extremely low throughout most of the Northern Region, and the western and northern-half of the Central Region, as well as in the eastern-half of the Peace Region (Figure 4).

Currently, modeled soil moisture reserves, relative to long-term-normal, vary from very low to extremely low (less than 25 mm) across most parts of the Northern and Central Regions, and also across the western and southern portions of the Southern Region (Figure 6). Only a few areas in Alberta are currently near normal. These areas are in the south-eastern portions of the Southern Region and also in the north-western portions of the Peace Region. Unless significant precipitation is seen over the next several weeks, soil moisture reserves will remain critically low, increasing the risk of moisture stress, in the event of dry weather. This year it is critical that at least near normal precipitation patters return, particularly through the months of May to July, which are usually the three wettest months of the year.

A large selection of related maps can be found through the AgroClimatic Information Service, on the home page of Ropin' the Web under the Weather and Market reports title. Note these maps are updated once a week (usually by Wednesday) providing updates between drought reports.

Precipitation

Precipitation since the February 28, 2009 Drought Report (Figure 1)
Since the last drought report (February 28, 2010) at least near normal precipitation accumulations were recorded only in the western Peace Region, the northeast corner of the Northern Region, as well as the western and eastern parts of the of the Southern Region; however, precipitation accumulation across the rest of the reporting area was generally below 50 percent of normal.

Peace Region: Precipitation accumulations across the region varied from 15 to 22 mm across the southwestern and northern portions of the region, grading down to 5 to 10 mm in the north-central parts of the region. The highest precipitation accumulations were recorded at Cleardale AGDM station (21.7 mm) in the west, followed by the Fort Vermillion RS station (20.8 mm) located in the north, while the lowest accumulations was recorded at Hawk Hills station (1.7 mm) followed by Manning AGDM station (2.5 mm) both in the north-central parts of the region. Precipitation accumulations, relative to long-term normal were near normal in the south and north, grading down to low and very low in north-central portion of the region.

Northern Region: Precipitation accumulations graded from a high of 30 to 35 mm in the northeastern corner of the region to a low of less than 5 mm across most of the western portions of the region. The highest precipitation accumulations were recorded at Rich Lake AGDM station (33.0 mm), followed by Lac La Biche A station (30.5 mm) both in the northwest corner, while the lowest accumulation of 1.7 mm were recorded at Mayerthorpe station in the west. Precipitation accumulations relative to long-term normal varied from near normal in the northwestern corner of the region to low and very low in the southwestern portions of the region.

Central Region: Precipitation accumulations for the region graded from 10 to 15 mm across the central-east and west to less than 5 mm across the rest of the region, including few scattered pockets with no precipitation. The highest precipitation accumulations were recorded at Water Valley station (8.2 mm) followed by Hespero AGCM station (6.2 mm) both in the west, while no precipitation was recorded in Delburne AGCM, Three Hills A, and Old College AGDM stations all in the west-central portions of the region. Precipitation accumulations relative to long-term normal graded from moderately low and low in the east-central to very low and extremely low to the western portions of the region.

Southern Region: Precipitation ranged from more than 30 mm across the foothills and more than 20 mm in the east, grading down to a 10 to 15 mm across most of the southwestern, north-central and the eastern portions of the region. Elsewhere in the region, many areas received less than 5 mm. The highest precipitation amounts were recorded at the Beauvais station (30.6 mm) followed by Chapel Rock station (19.5 mm) both in the foothills, while the lowest accumulations of less than 1 mm was recorded at Schuler AGDM station in the east, followed by Pakowki lake AGCM station (1.9 mm) located in southeast portion of the region. Precipitation accumulations relative to long-term normal were near normal across the east, and in parts of the foothills, grading down to low and very low across the rest of the region.

Cold Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3)
Cold Season (Oct 1 to March 31) precipitation accumulations relative to long term normal across some parts of the Southern Region were at least near normal, grading to moderately low and low to across the rest of the of the region. Elsewhere in the reporting area, Cold season precipitation accumulations were generally low, with several areas classified as very low and extremely low.

Peace Region: Cold season precipitation accumulations graded from moderately low in the western and northern portions of the region, to low and very low across the rest of the region.

Northern Region: Cold season precipitation accumulations graded from moderately low to very low with the exception of few isolated pockets of extremely low.

Central Region: Cold season precipitation accumulations graded from moderately low across the south, to low and very low across most of the rest of the region, with the exception of two pockets of extremely low.

Southern Region: Cold season precipitation accumulations across much of the central east to west corridor of the region as well as few scattered pockets were at least near normal, grading to moderately low and low accumulations across the rest of the region.

Average Precipitation Accumulations for April (Figure 5)

April generally marks the end of the dry season in most parts of Alberta, with precipitation normally increasing to 30-40 mm over much of the province, with the exception of the southwest where 50-60 mm is average. In the Peace Region, dry weather typically persists throughout April with average accumulations ranging from 10 to 20 mm and improving in May, when monthly precipitation amounts average about 40 mm.

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 Alberta Environment (AENV) databases or from the Environment Canada (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 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 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 April 13, 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 February 28, 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 April 8, 2010.
Last Reviewed/Revised on April 30, 2010.