| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Since the September 9, 2006 Drought Report significant precipitation was recorded over much of the Northern and Central Regions with the greatest amounts (more than 120 mm) being recorded across the southwest corner of the Northern Region. In contrast, the Peace and Southern Regions remained relatively dry with less than 30 mm recorded at most stations.
Growing season precipitation accumulations relative to long term normals across most of the reporting area have improved since the last report (September 9), particularly across the Northern and Central Regions with most areas in the Northern Central and Southern Regions recording near normal precipitation amounts. The areas with the greatest deficits include much of the Peace Region where accumulations were ranked as moderately low through much of the central areas, grading to low in the south and south west and to extremely low in the northwest. Other areas with notable deficits include a few small pockets in the south-western portions of the Southern Region where areas grading to extremely low can be found.
Precipitation deficits over the over the past year have decreased since the last report, with most areas, except the Peace Region, reporting near normal precipitation, interspersed with several widely scattered pockets grading down to at least moderately low. Across the Southern Region, there has been an increase in the number and size of the areas classified as having moderately low precipitation accumulations. Across the Peace Region, precipitation deficits are classified as at least moderately low with several areas grading to extremely low, the largest of which, stretches in a broad band down from the north-western Peace Region into most of the south-eastern Peace Region.
Since the last report soil moisture levels have increased significantly across all regions, except in the Peace Region where they have only improved slightly. Across the Southern Region soil moisture levels range from 0 to 25 mm in the southeast to 50 to 75 mm in the northwest. Across the Central Region soil moisture ranges from 25 to 50 mm the southeast to 100 to 125 mm the northwest. Across the Northern Region soil moisture ranges from 100 to 125 mm in the southwest down to 25 to 50 mm in the northeast. Currently soil moisture levels are the lowest in the Peace Region with most of the areas dominated by levels in the 0 to 25 mm range with the exception on the north where soil moisture levels are between 25 to 50 mm
Since the last report soil moisture reserves relative to the long term normal (1961 to present) have increased with most areas in the Northern, Central and Southern Regions estimated to have at least near normal reserves. Across the Peace Region reserves have increased as well, however, much of the region has low reserves, with parts of the west grading down to extremely low.
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 September 9t 2006 Drought Report (Figure 1) - Since the last report, cool, wet weather brought significant accumulations of precipitation (> 80 mm) to the much of the Northern and Central Regions and to a lesser extent in the Southern and Peace Regions, with several locations recording between 10 to 20 mm.
Peace Region: Precipitation accumulations ranged from 10 to 20 mm across north central areas and increased to 20 to 30 mm across the north and southern parts of the region. The greatest amount of precipitation was recorded at the Grande Prairie A. station (35.0 mm), and the least amount was recorded at the Manning AGDM station (11.0 mm)
Northern Region: Precipitation accumulations ranged widely throughout the region with the least amounts recorded in the north (30 to 40 mm) and the greatest amounts in southwest (> 90 mm). In general precipitation was the highest in the south half of the region with more than 50 mm recorded at most stations and lowest in the north half of the region with less than 50 mm recorded at most stations. The most precipitation was recorded at the Violet Grove CS station (130.8 mm) in the southwest and the least amounts recorded at the Dapp AGDM station (28.9 mm) in the northwest.
Central Region: The greatest amounts of precipitation were recorded in the northwest (> 80 mm) grading down to less than 30 to 40 mm throughout most of the south and southeast. The most precipitation was recorded at the Battle River Headwaters station (112.1 mm) in the northwest and the least amounts recorded at the Drumheller East station (28.8 mm) in the extreme south.
Southern Region: Precipitation generally ranged from 60 to 70 mm in the extreme northwest down to 10 to 20 mm across large parts of the south central portions of the region. The most precipitation was recorded at the Strathmore IMCIN station (62.4 mm) in the northwest and the least amounts recorded at the Bow Island station (11.1 mm) in the east central portion of the region.
Growing Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2) - Recent precipitation has improved growing season precipitation accumulations across most the Central and Northern Regions, with most areas recording at least near normal precipitation. In contrast, relatively dry conditions have persisted in the Peace Region with much of the east half of the region experiencing at least moderately low accumulations, grading down to extremely low in north-western areas. In the Southern Region conditions remain much the same, with most areas classified as near normal.
Peace Region: Growing season precipitation accumulations for the north half of the region have generally been normal. In the northwest, this grades to two pockets of extremely low, in the M.D. of Clear Hills, in the southwest down to low (County of Grande Prairie), and similarly in the south and southeast down to low in the M.D. of Greenview and the M.D. of Big Lakes.
Northern Region: Across much of the region, growing season precipitation to date has greatly improved since that last report and now is at least near normal with a few small isolated pockets areas in the northeast and central portions of the region, classified as moderately low.
Central Region: Growing season precipitation to date across most of the region has been near normal with four pockets at least moderately high across the north half of the region and a few isolated small pockets of moderately low in the southwest.
Southern Region: Much of the region is classified as near normal, however, most of this precipitation fell during June, with July and August receiving well below normal precipitation accumulations. In the southwest, a few pockets grading to extremely low exist, affecting localized parts of the M.D. of Pincher Creek and Cardston County.
Long Term Conditions: 365-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - Precipitation accumulations, over the past year, are variable across all regions with much of the Southern, Central and Northern Regions showing large areas of near normal accumulations interspersed with several large pockets of moderately low to low accumulations. In the Peace Region, accumulations have been much lower with large parts in the south east and north west, classified as extremely low
Peace Region: A large area of extremely low accumulations is affecting parts of the northwest, central and much of the southwest corner of the region. These areas include the M.D. of Clear Hills, M.D. of Fairview, Saddle Hills County, the M.D. of Spirit River, Birch Hills County, the M.D.'s of Smoky River, Big Lakes, Greenview and Lesser Slave River. These areas are clearly in need of normal to above normal precipitation from now until early spring to help reverse the effects of prolonged dry weather. Elsewhere, in the southwest corner of the region, conditions improve, grading to a small pocket of near normal west of the City of Grande Prairie. In addition across much of the northern tip of the Peace Region conditions are near normal.
Northern Region: Just over half of the region is classified and near normal with several large areas grading down to moderately low in west-central and northeast-central areas. One pocket of very low can be found south of the City of Edmonton affecting Leduc County.
Central Region: Most of the region has recorded at least near normal precipitation with the exception of parts of the west half of the region were two large areas grading to moderately low can be found and one pocket, grading to low southwest of the City of Red Deer.
Southern Region: Precipitation accumulations are generally at least near normal in most parts of the region grading to moderately low and low in the southwest. Elsewhere in the east half of the region three pockets grading to moderately low can be found.
Average Precipitation Accumulations for October (Figure 4) - Across the reporting area, on average about 4.4 % of the annual precipitation falls in October. During this month precipitation totals range from 10 to 20 mm across the east half of the reporting area, grading up to 40 to 50 mm in the foothills of the Southern Region, the northwest corner of the Central Region and the western parts on the Northern Region. Across the Peace Region generally 20 to 30 mm falls during the month of October.
Precipitation received in October generally falls as rain and goes directly to soil moisture reserves because evapotranspiration rates are low due to killing frosts. Therefore, October is historically an important month for recharging soil moisture reserves for the following growing season. Above normal precipitation for October will be needed, where soil moisture reserves are below normal, particularly in the Peace Region where soil moisture reserves are critically low.
Soil moisture
Soil moisture in the agricultural regions of Alberta (Figure 5) - Soil moisture levels have rebounded significantly across much of the Northern and Central Regions and to a lesser extent across the Southern Region but basically remains the same (low) across the Peace Region. The driest areas in the Province can be found across much of the Peace Region where soil moisture levels are below 25 mm, followed by the Southern Region (25 to 50 mm). The highest soil moisture levels (100 to 125 mm) can be found in the north-western parts of the Central Region and south-eastern parts Northern Region.
Peace Region: Across most of the region, soil moisture levels are less than 25 mm, with the exception of the northern tip of the region where soil moisture levels range from 25 to 50 mm. Above normal precipitation is needed between now and the start of the growing season to restore soil moistures for the coming growing season.
Northern Region: Soil moisture levels are highly variable across the Northern Region, grading from 25 to 50 mm in the northeast, up to 100 to 125 mm in the southwest. This represents a significant improvement over the conditions that were reported in the last Drought Report.
Central Region: Soil moisture levels grade from a low of 25 mm across the southeast half of the region, to a high of 100 to 125 mm northwest. This represents a significant improvement over the conditions that were reported in the last Drought Report.
Southern Region: Soil moisture levels grade from less than 25 mm across the south-eastern parts of the region, up to 50 to 75 mm in the northwest. This also represents a marked improvement over the conditions that were reported in the last Drought Report.
Long Term Average Soil Moisture Conditions (Figure 6) - At this time of the year soil moisture reserves begin to increase across all parts on the reporting area due to reduced evaporative demand brought on by harvest and killing frosts. Generally across the reporting area, average soil moisture levels range from 25 to 50 mm over much of the eastern parts (excluding the Peace Region) and grading upwards to 75 to 100 mm in the west. In the Peace Region, normal soil moisture reserves for this time grade up from 25 to 50 mm in a small pocket in the central parts to 50 to 75 mm in the rest 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". This result was mapped, showing how often current soil moisture reserves of a similar magnitude have occurred in the past (1961 to 2005).
Soil moisture over much of the Central and Southern Regions and Northern Regions are at least near normal with large parts of the central and Northern Regions grading to high. In contrast, across the Peace Region, conditions are extremely variable grading from moderately low in the southeast and northern parts to extremely low in the west and southwest.
Peace Region: Soil moisture reserves are highly variable with only a few small pockets of normal. Reserves are moderately low throughout the north, extreme east, and central parts of the region. These rapidly grade to extremely low along the western edge affecting the M.D. of Northern Lights, Clear Hills, M.D. of Fairview, Saddle Hills County, County of Grande Prairie and the M.D. of Green View. Above normal precipitation is needed between now and next spring to bring these levels to near normal.
Northern Region: Reserves are at least near normal throughout the entire region, grading to moderately high in the south half of the region and up to high in the southeast.
Central Region: Soil moisture reserves in most parts of the region are at least near normal, grading to extremely high in north central locals (east of the City of Red Deer), and to high in the extreme northeast.
Southern Region: Soil moisture reserves in most parts of the region are at least near normal, with several pockets grading to moderately high in the north half of the region.
Probability of Returning to Average Fall Soil Moisture Conditions (Figure 8) - The amount of soil moisture recharge needed to bring current soil moisture conditions up to the long term average fall (November 1st) levels was compared to modeled recharge rates that occurred in the past (1961-2005) for a similar period. The probability of returning to normal conditions is then computed from the number of years between 1961-2005 that soil moisture recharge rates had equalled or exceeded those currently required to bring soil moisture levels to average.
Throughout most of the Central and much of the Northern Region there is a better then 90 % chance that soil moisture levels will reach average conditions by November 1, 2006. Across the Southern Region, the probability of reaching normal fall conditions is extremely variable ranging from less than 20 % in the southeast and west, up to 90 to 100% in the north. Across the Peace Region there is less than a 10% chance of attaining average fall soil moisture conditions.
Peace Region: The entire Peace Region has a less than 10% chance of attaining average fall soil moisture conditions. Significant precipitation is needed between now and spring in order to recharge soil moisture levels to average conditions. If this does not happen then soil moisture reserves may be insufficient to get crops through short-term dry spells next growing season. As a result, at least near normal, and extremely well timed precipitation events will be needed during the 2007-growing season in order to prevent moisture stress in crops.
Northern Region: Most of the southern and eastern parts of the region have a better than 90% chance of achieving normal fall soil moisture conditions. In contrast, across much of the north several areas have less than a 10% chance of attaining normal conditions by November 1, 2006.
Central Region: Most of the regions has a better than 90% chance of achieving normal fall soil moisture conditions. The exception is in the south central areas where there is 20 to 30% chance that normal fall soil moisture conditions will be achieved. This area is centered on the town of Drumheller.
Southern Region: Large areas on the north have a better than 90% chance of achieving average fall soil moisture conditions. The chances rapidly decrease for the south half of the region where conditions are highly variable but are generally less than 50% with several pockets in the west and southeast having less than a 20% chance or reaching normal fall soil moisture conditions by November 1, 2006.
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 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
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 September 30, 2006.
Drought analysis is currently scheduled at monthly intervals between October 31and April 31, and twice monthly from May 1 to September 30 . This report updates the previous report of September 9, 2006 |
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