| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last drought report, May 31, 2009, precipitation patterns across most of the plains reporting area were dominated by thunderstorm activity and was very much of a "hit and miss" situation. This resulted in variable accumulations, ranging from less that 10 mm through much of the Peace Region, less than 20 mm through parts of the Northern and Central regions, to more than 50 mm across large parts of the Southern Region, and also in several pockets in the Northern and Central Regions. Dry conditions continue to persist during June, which is normally one of the wettest months of the year. Across most parts of the reporting area, crops on ground have been significantly affected by the dry conditions. In addition to moisture stress, frost and abnormally low temperatures during the month of May and early parts of June have significantly hampered crop growth.
Daily mean temperatures relative to long term normal, during the past 15-days, across most of the plains area were moderately high with the exception most of the Southern Region and isolated pockets with near normal temperatures. In contrast temperature regimes across the Peace Region varied from moderately high to extremely high. However, note that the low to extremely low temperatures during the last two weeks of May and the first week of June have delayed down crop development across much of the reporting area (Figure 8).
Growing season (April 1, 2009 to June 23, 2009) precipitation accumulations relative to long term normal to date, range from low to extremely low across much of the Central Region, the central-north, central and southern portions of the Northern Region and the northern and central portions of the Southern Region. Across the Peace Region, accumulations are very low to extremely low across much of the south-half of the region, grading up to low and moderately low across the north half of the region (Figure 2).
The 365-day Precipitation accumulations, relative to the long term normal, have been low to extremely low across most of the reporting area with the exception of east-half of the Southern Region where they ranged from near normal to low (Figure 4).
Modeled soil moisture reserves, relative to long term normal (Figure 7), varied from low to extremely low across most parts the Peace, the Northern and the Central Regions, including the northwestern portion of the Southern Region. Low soil moisture reserves are the result of soil moisture deficits carried over from past growing season, below normal fall precipitation accumulations and low to extremely low precipitation accumulations experienced since the start of the growing season.
A large selection of related maps can be found at http://www.agriculture.alberta.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 May 31, 2009 Drought Report (Figure 1)
Since the May 31, 2009 report, precipitation totals across most of the plains reporting area were highly variable ranging from less than 10 mm to more than 70 mm. Since thunderstorms dominated precipitation patterns, bringing only localized, spotty relief to many areas, the precipitation accumulations depicted on the maps around the circular shaped color zones likely represent localized storm tracks that moved over weather stations and as such, may not adequately characterize local precipitation accumulations.
The central and southern part of the Peace Region recorded accumulations of less than 10 mm, while across the north, accumulations ranged from 10 to 30 mm. In general across most of the reporting area, dry conditions persisted through June, which is normally one of the wettest months of the year. This, in combination with low soil moisture reserves, unseasonable cool temperatures and late frosts, has fueled fears that crop yields will be seriously impacted.
Peace Region: Precipitation accumulations across the southern half and the central portions of the region were less than 10 mm, grading up to 20 to 30 mm range in the north. Precipitation accumulations were the greatest at the La Crete AGCM station (28.7 mm) followed by high Level A station (18.4 mm), both located in the north, while the lowest accumulations were recorded at Teepee Creek AGCM stations (1.2 mm) followed by Peoria AGDM station (1.9 mm), both located in the southwestern portion of the region.
Northern Region: Precipitation accumulations across the extreme western, extreme eastern and the north central portions of the region ranged between 40 to 70 mm with thunderstorms accounting for most of the precipitation. Across central portions of the region accumulations ranged from less the 10 mm to 10 to 20 mm. The greatest precipitation was recorded at Violet Grove CS station (66.7 mm), in the southwest, followed by the Tulliby Lake AGCM station (64.1mm) in eastern part of the region. The least amounts were recorded in Vilna AGCM station (6.7 mm) followed by Andrew AGDM station (8.1 mm) both located in the central northeastern part of the region.
Central Region: Precipitation accumulations across the region varied from 40 to 70 mm in a few isolated pockets scattered across the region, to less than 20 mm with most of the region receiving less than 30 mm. The highest precipitation was recorded at Oyen AGDM station (69.7 mm) in the east, followed by Drumheller East station (56.1 mm) in the south while the lowest was recorded at the Stettler AGDM station (10.6 mm) followed by Big Valley AGCM station (13 mm) both in the central north part of the region.
Southern Region: Precipitation accumulations across most of the region ranged 40 to 60 mm and graded up to 70 to 120 mm across the eastern parts of the region and also along the foothills. The greatest accumulations were recorded at the Medicine Lodge station (123.3 mm) in the east, followed by Porcupine Lookout station (96.4 mm) in the west. The lowest accumulations in the region were recorded at Mossleigh AGDM stations (21.0 mm) followed by Standard AGCM station (21.6 mm) in the northwestern portion of the region.
Growing Season Precipitation Accumulations, April 1 to May 31, 2009 (Figure 2 and Figure 3)
To date, growing season precipitation accumulations are extremely low to very low across much of the Peace, Northern and Central Regions, along with the north-western portions of the Southern Region. Precipitation totals since April 1, have been only on the order of 20 to 50 mm for much of the east-half of the Central Region, the central and southern Peace Region and the south-eastern parts of the Northern Region. Many areas have received upwards of 60 mm, and are classified as low to moderately low; however, many of these areas have seen little or no appreciable precipitation for several weeks on end. Only a few parts of the reporting area have seen near normal or better accumulations over the current growing season, and most of these areas are confined to the extreme eastern and western portions of the Southern Region.
Peace Region: Growing season accumulations range from extremely low (20 to 30 mm) in central portions of the region, grading to very low across most of the south-half of the region (40 to 60 mm) and up to low (50 to 60 mm) across the north-half of the region. In general, growing season totals for this time of year are 50 percent of normal, or less for most areas.
Northern Region: Growing season precipitation across much of the south half of the region ranges from very low to extremely low (30 to 60 mm), grading to low across the north (50 to 80 mm) , north east (50 to 80 mm) and extreme western portions of the region (70 to 120 mm). In general, growing season totals for this time of year are 50 percent of normal, or less for most areas.
Central Region: Growing season precipitation across most of the region range from very low to extremely low. Across the eastern half of the region, growing season totals range from 20 to 50 mm with a few circular pockets showing more than 50 mm. These are likely the result of isolated thunderstorms tracking over weather stations and may not be representative of surrounding areas. Across the west half of the region precipitation totals range from 50 to 70 mm. In general growing season totals for this time of year are 50 percent of normal or less, for most areas with some areas grading to below 25 percent of normal.
Southern Region. Growing season precipitation across the region is highly variable ranging from extremely low in the northwest (40 to 60 mm) to low and moderately low (60 to 110 mm) in the central areas and near normal in the extreme east (100 to 150 mm).
Average Precipitation Accumulations for July (Figure 5)
July marks the beginning of a drying trend in the Southern Region, but remains one of the wettest months in the year (similar to June) across the rest of the reporting area. Historically, the first half of July is typically wetter than the last half. For July, precipitation ranges from 30 to 40 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.
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 low to extremely low across much of the western and central portions of the Peace Region, the Northern and Central Regions as well as the northwestern portion of the Southern Region. Soil moisture reserves across the rest of the reporting area varied, ranging from moderately low to at least near normal.
Peace Region: Soil moisture levels range from 25 to 50 mm across most of the western and central-north portions of the region, grading up to 50 to 100 mm in the eastern and 50 to 75 mm in the northern portions of the region. Soil moisture reserves, relative to long term normal, graded up from very low to extremely low in the western and central-north portions of the region to moderately low to near normal in the southeastern and northern portions of the region.
Northern Region: Soil moisture levels across most of the region were less than 50 mm with much of the south and west-central areas estimated to have less than 25 mm. Relative to long term normal, soil moisture reserves are classified as very low and extremely low across the west half of the region and across much of the south as well. Across the east half of the region soil moisture reserves are generally low with a pocket of near normal north of the town of Lloydminster.
Central Region: Soil moisture levels dropped sharply from the 75 to 100 mm range along the western border of the region to less than 25 mm east of Highway 2. Relative to normal, soil moisture reserves range from very low and extremely low across in the western and northern portions of the region to moderately low across the eastern half of the area with a small pocket of near normal in the extreme southeast.
Southern Region: Soil moisture reserves along the foothills and across most of the southern half of the region are in the 50 to 100 mm range, grading down to less than 25 mm, across the northwestern portions of the region. Relative to long term normal, soil moisture reserves are at least near normal across most of the eastern half of the region and along the foothills, grading down to very low and extremely low in the northwestern portions of the region.
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.agriculture.alberta.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 1
- Cold Season to date- Starting October 1
Selected maps from this series are included in this report.
Precipitation accumulations 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 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 26, 2009.
Drought analysis is currently scheduled at monthly intervals. This report updates the previous report of May 31, 2009. |
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