Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last Drought Report (July 23, 2006) several storm events resulted in much needed precipitation across the Central, Northern and parts of the Peace Regions, with precipitation accumulation ranging from near normal to extremely high. Stations in the county of Lacombe, Red Dear and Stettler recorded the highest precipitations in the reporting area with an average of 126.3 mm and a maximum of 199.3 mm. On the contrary, most of the Southern Region and the southeast corner of the Peace Region were the driest, recording a moderately low to very low precipitation accumulation.
Growing season (April 1, 2006 to date) precipitation accumulation across most of the reporting area has been adequate (near normal) with exception of a moderately low accumulation in the western and southern portions of the Peace Region and an extended area stretching through portions of the counties west, south and east of the city of Edmonton, as well as in the western and northern part of the Northern Region. Moreover, pockets of low to moderately low and moderately high-to-high precipitation accumulations exist in most of the reporting area with the exception of the Peace Region.
Precipitation accumulations over the past year across most of the Peace and Northern Regions range from moderately low-to-low, with several pockets classified as having very low to extremely low precipitation accumulations. In contrast, across most of the Central, Southern, and the eastern part of the Northern Regions precipitation accumulations have been near normal and moderately high, with few pockets of high to extremely high accumulations.
Since the last report, soil moisture reserves have improved across most of the reporting area, especially in the Central, Northern and portions of the Peace Regions. Current soil moisture levels are below 25 mm or in the 25 to 50 mm range throughout much of the reporting area, with the exception of the northwestern part of the Central Region (50 to 125 mm) and a pocket in the east border of the Northern Region. Most areas with below 25 mm moisture reserve need immediate precipitation to ease crop moisture stress.
Soil moisture reserves relative to the long term normal (1961 to present) over most of the of the reporting area, except the Peace Region, are at least near normal grading to high and very high reserves at three isolated extended areas. Reserves also grade to low or extremely low across the western portions of the Southern Region. In much of the western half of the Northern Region, and most of the Peace Region, soil moisture range from moderately low to low then to very low and extremely low (a condition occurring on average, less than once in 30-years) reserve levels in the central west and south portion of the region resulting in crop moisture stress.
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 July 23, 2006 Drought Report (Figure 1) - Several storm events resulted in much needed precipitation across the Central, Northern and most of the Peace Region, with precipitation accumulation ranging from near normal to extremely high. Stations in the Counties of Lacombe, Red Dear and Stettler recorded the highest precipitation in the reporting area for the period, with an average of 126.3 mm and a maximum of 199.3 mm. On the contrary, most of the Southern Region and the southeast corner of the Peace Region were the driest, recording moderately low to very low precipitation accumulation.
Peace Region: Precipitation accumulations ranged from a low of 12.0 mm at the Spring Creek #1 station in the M.D. of Smoky River to 60.5 mm at Fairview AGDM station in M.D. of Fairview. In general precipitation was greatest in the central and northwest and the least in the southwest and southeastern corners of the region.
Northern Region: Precipitation accumulations ranged from 33.9 at Smoky lake AGDM in Smoky Lake County and 34.2 mm at Rich Lake AGDM stations in Lakeland County to 94.9 mm at Wainwright A station in M.D. of Wainwright followed by 86.4 mm at Elk Island Nat Park station in M.D. of Elk Island.
Central Region: The highest amount of precipitation in the reporting area was recorded in Red Dear (124.0 mm at Red Deer A), Lacombe (199.3 mm at Prentiss, 133.8 mm at Parlby Creek, 122.4 mm at Lacombe CDA) and Ponoka (112.0 mm at Magee Lake) counties extending to the County of Stettler (146.0 mm at Stettler AGDM). Precipitation accumulation decreased to a low of 20 to 30 mm range in the south and southeastern part of the region.
Southern Region: In general, precipitation decreased from the northern part of the region to the south along the southeast and southwest line. Precipitation accumulations ranged 32.3 mm at Strathmore (IMCIN) station in the Wheatland County, to a low of 1 mm at Onefour CDA in the southeast corner of the region.
Growing Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2) - Growing season precipitation accumulation to date across most of the reporting area has been adequate (near normal), with exception of a moderately low accumulation in the western and southern part of the Peace Region, as well as the south central part of the Northern Region (portions of the counties west, south and east of the City of Edmonton). Isolated pockets of moderately high-to-high and moderately low accumulation also exist in the south half of the reporting area.
Peace Region: Growing season precipitation accumulation in most part of the region has been near normal with the exception of a moderately high accumulation in the north corner and a moderately low accumulations in the central and south western and south eastern corners of the region.
Northern Region: Across much of the region growing season precipitation to date has been near normal, with the exception of an area with moderately low-to-low and very low accumulations in Leduc, Parkland, Strathcona and Beaver County and the Counties of Wetaskiwin, Camrose, and Minburn. Moreover, an isolated pocket of moderately low accumulation exists in northern corner of M.D. of Bonnyville.
Central and Southern Regions: Growing season precipitation across most of the regions have been near normal with several isolated pockets of moderately high and high and moderately low and low accumulations.
Long Term Conditions: 365-Day Precipitation Accumulations relative to Long Term Normal (1961 – 2005) (Figure 3) - Precipitation accumulations, over the past year across most parts of the Peace and Northern Regions range from moderately low-to-low, with several pockets classified as having very low to extremely low precipitation accumulations. In contrast, across most of the Central, Southern, and the eastern part of the Northern Regions precipitation accumulations have been near normal and moderately high, with few pockets of high to extremely high accumulations.
Peace Region: The southeast and the central west portions of the region and a pocket area in the central part have experienced extremely low to very low precipitation accumulations over the past 365-days. These accumulations grade to low, moderately low and then to near normal in the north and southwest portions of the region.
Northern Region: Most of the region has recorded moderately low-to-low precipitation accumulations with a few pockets of extremely low accumulations. In contrast, the eastern and southeastern portions of the region have recorded at least near normal, grading to extremely high around the town of Lloydminster.
Central Region: Most of the region has recorded at least near normal precipitation, grading up to moderately high and then to extremely high in two pockets in the central north and eastern part of the region. A small pocket with moderately low accumulation exists in the western part of the Red Deer County.
Southern Region: Precipitation accumulations are generally at least near normal in most part of the region grading to moderately high in the central part and then to very high and extremely high accumulation in the central north. Two pockets with moderately low accumulation exist in the extreme southeast of the region.
Average Precipitation Accumulations for August (Figure 4) - Historically, the first half of August is typically wetter than the last half and typically this month marks the beginning of a drying trend for most of the reporting area, with the exception of the Southern Region, where July tends to mark the start of drier conditions. For August, average precipitation typically ranges from 30 to 40 mm in the southeast, to greater than 70 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 5) - Current soil moisture levels are below 25 mm and in the 25 to 50 mm range throughout much of the reporting area. Precipitation since the last report has improved soil moisture reserves in most parts of the Northern and Central Regions. Soil moisture reserves in the central and western part of the Central Region are the highest in the reporting area, with reserves ranging from 50 to 125 mm.
Peace Region: The Peace Region has soil moisture levels less than 25 mm, with the exception of 20 to 50 mm reserves in the northern corner. Precipitation is needed to reduce crop moisture stress.
Northern Region: Most of the region has less 25 to 50 mm of soil moisture, with three large pockets of less than 25 mm reserve areas in the central west, north and central east of the region. Soil moisture reserves are 50 to 75 mm in a pocket centred on the town of Lloydminster in the east corner of the region.
Central Region: Soil moisture reserves grade from a high of 75 to 100 mm in the northwest to less than 25 mm to the east.
Southern Region: Soil moisture reserves in most part of the region are less than 25 mm, with the exception of the northwest corner where the reserve grades to 75 to 100 mm.
Long Term Average Soil Moisture Conditions (Figure 6) - At this time of the year, soil moisture reserves in most part of the reporting area (excluding the Peace Region) are typically lowest in the central and eastern parts of the regions, grading from a high of 75 to 100 mm in the west to less than 25 mm or 25 to 50 mm to the east. The lowest soil moisture conditions in the reporting area are typically found in southeastern parts of the Central Region and the central and eastern part of the Southern Region. In the Peace Region, normal soil moisture reserves for this time of year are 25 to 50 mm in the central part grading to 50 to 75 mm to the south and north part of the region.
Current Soil Moisture Reserves relative to Long Term Normal (1961 – 2005) (Figure 7) - Soil moisture reserves computed for the report date (Figure 5), were compared to modeled soil moisture values, using the historical weather data for the same dates during the 1961 to current period, and are expressed as a “frequency of occurrence”, which shows how often current soil moisture reserves of a similar magnitude have occurred in the past (1961 to 2005).
Soil moisture relative to the long term normal over most of the of the reporting area, except the Peace Region, are at least near normal grading to high and very high reserves at three isolated extended areas. Reserves also grade to low or extremely low across the west portions of the Northern and Southern Regions. Soil moisture reserves in most parts of the Peace Region are moderately low grading to low, very low and then to extremely low in the central west and south portion of the region resulting in crop moisture stress, which appears to be prevalent through these portion of the region.
Peace Region: Soil moisture reserves relative to normal are variable across the Peace Region with extremely low reserves found along the south and central west border, grading to near normal level in an extend areas in the central and northern portions
Northern Region: Reserves grade from high and very high pocket area in the east to near normal level through to the west and then to moderately low level across most of the west half portion of the region.
Central Region: Soil moisture reserves in most part of the region are at least near normal grading to high and very high levels in two extended areas located in the central north and southeast portion of the region.
Southern Region: Most of the soil moisture reserves relative to normal across the region are near normal, with the exception on of the western border where it grades to low and very low moisture reserves.
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 preliminary QA/QC checks by Alberta Agriculture (AAFRD) staff, assisted by a computer program that flags suspicious and missing values. 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. All maps describing current conditions are based on preliminary data that is subject to change under further review by AAFRD, 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:
- 365 days
- 180 days
- 90 days
- 30 days
- The growing season to date
- Winter precipitation to date.
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:
| extremely low | drier than this, on average, less than 1 once in 30-years |
| very low | drier than this, on average, less than 1 once in 20-years |
| low | drier than this, on average, less than 1 once in 10-years |
| moderately low | drier than this, on average, less than 1 once in 4-years |
| near normal | on average, this occurs 5 in 10-years |
| moderately high | wetter than this, on average, less than 1 once in 4-years |
| high | wetter than this, on average, less than 1 once in 10-years |
| very high | wetter than this, on average, less than 1 once in 20-years |
| extremely high | wetter than this, on average, less than 1 once in 30-years |
Snow pack (reported during the winter season only)
Snow pack snow water equivalents (SPWE) are modeled for stubble fields. SPWE is defined as the equivalent depth of water (mm) that the snow pack contains if it were to be melted. SPWE 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 SPWE.
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 monitored from May through 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 Normal 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 normal. 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 Normal. However, the process is currently unable to account for snow currently existing on the ground and as such is not 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 August 13, 2006.
Drought analysis is currently scheduled at monthly intervals between October 31and April 31, and twice monthly from May 1to September 30. This report updates the previous report of July 23, 2006. |