| | Precipitation | Soil moisture | Data sources | Explanation of terms
.
Summary
Since the last Drought Report (August 13, 2006), hot and dry conditions have prevailed across the reporting area with less than 10 mm of precipitation recorded in many locations, including all of the Peace Region, the eastern parts of the Northern Region, southern parts of the Central Region, and across much of the Southern Region. The greatest amounts of precipitation were recorded just north of the City of Edmonton (40 to 50 mm) and the extreme western parts of the Central Region where upwards of 50 mm was recorded at a few locations.
Due to recent precipitation deficits, growing season precipitation accumulations relative to long term normals across most of the reporting area have declined since the last report (August 13th). The areas with the greatest deficits include much of the Northern Region and Peace Region where accumulations were ranked as moderately low with several pockets in the central parts of the Northern Region ranking as very low and across the Peace Region, parts of the northwest, extreme southern and south eastern areas were ranked as extremely low. Elsewhere, most of the northern Peace and much of the Central and Southern Regions recorded at least near normal growing season precipitation accumulations with several isolated recording moderately low accumulations and the south-western parts of the Southern Region recording extremely low accumulations.
Due to recent dry weather, precipitation deficits over the over the past year have increased across most of the reporting area. Generally, south of the City of Red Deer, year to date accumulations have been at least near normal, with a few exceptions where less was recorded. In contrast, north of Red Deer, precipitation accumulations have been below normal with several areas reporting extremely low accumulations, the largest of which are found in the Peace Region, stretching in a broad band down from the north-western Peace Region into most of the south-eastern Peace Region. Across the Northern Region, most areas have experienced at least moderately low accumulations with two notable pockets of extremely low accumulations occurring, one south of the City of Edmonton and one centered around the town of Vegreville.
Since the last report, soil moisture reserves have decreased signifactly due to hot, dry weather. Most of the reporting area was estimated to have less than 25 mm of plant available water, a condition that could lead to serious moisture shortages next growing season. Fall and spring are typically times of soil moisture recharge and significant amounts of precipitation are needed between now and spring to improve soil moisture conditions and build drought resistance for next growing season.
Since the last report, soil moisture reserves relative to the long term normal (1961 to present) have decreased sharply across most of the Peace Region with most of the areas classified as having extremely low reserves. Similarly in the Northern Region, reserves have declined since the last report, ranging from extremely low in the west to moderately low across most of the north half of the region. Across most of the Central and Southern Regions, soil moisture reserves are near normal grading to moderately low in the western parts of the Central Region and down to low or extremely low in western parts of the Southern Region.
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 August 13, 2006 Drought Report (Figure 1) - Since the last report, hot, dry weather has dominated over the reporting area, bringing precipitation accumulations of less than 20 mm to most areas in the province. The highest amounts were in the 40 –50 mm range and these were confined to areas north of the City of Edmonton, the western parts of Lakeland County and the western parts of the Central Region
Peace Region: Precipitation accumulations were less than 10 mm for the entire region.
Northern Region: Precipitation accumulations were lowest in the east and northwest, with less than 10 mm recorded at a number of stations. This graded to a high of 40 to 50 mm in central locations around the City of Edmonton with 42.6 reported at Edmonton Namao A. Elsewhere throughout the central area of the region, precipitation ranged from 20 to 30 mm.
Central Region: The greatest amounts of precipitation were recoded in the northwest at Leedale AEDM (54.2 mm) grading down to less than 10 mm through most of the southern and southeast portions of the region.
Southern Region: Precipitation was generally below 20 mm throughout most of the Southern Region with less than 10 mm recorded across the north and south along the Canada US border.
Growing season precipitation accumulations relative to long term normal (1961 - 2005) (Figure 2) - Recent dry weather has lead to increasing growing season precipitation deficits. In general, south of the City of Red Deer, growing season precipitation to date has been near normal with several pockets of moderately low scattered throughout parts of the Central Region and southern half of the Southern Region, with some areas in the south-western corner of the Southern Region grading to extremely low. Across the North, growing season precipitation to date has generally been moderately low to low with several locations reporting low to extremely low accumulations to date.
Peace Region: Growing season precipitation accumulations for the north half of the region have generally been normal. In the north-western Peace Region, this grades to extremely low in the M.D. of Clear Hills, in the southwest down to low (County of Grande Prairie), and in the south and south east down to extremely 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 been moderately low with a few areas in the north central and extreme eastern parts of the region reporting near normal. The driest areas are located centrally where areas grading down to very low are found, mostly affecting the Counties of Leduc and Minburn . Other relatively dry areas can be found in the extreme west and northwest where low accumulations have been recorded.
Central Region: Growing season precipitation to date across most of the region has been near normal with several isolated pockets classified as moderately low, and these are mostly confined to the west with a few small areas of the same in the extreme east. Currently the driest area in the region is located in the western part of Red Deer County, where a small pocket classified as having low growing season accumulations to date is found.
Southern Region. Much of this region is reporting near normal growing season precipitation to date, however, most of its growing season precipitation fell during June with July and August receiving well below normal precipitation accumulations. The driest areas in the region are confined to a few pockets in the west half that grade down to extremely low, affecting the M.D. of Pincher Creek and Cardston County. In addition, the extreme southeast corner of the region is classified as moderately low.
Long term conditions: 365-Day precipitation accumulations relative to long term normal (1961 – 2005) (Figure 3) Precipitation accumulations over the past year have generally been near normal south of the City of Red Deer and below normal north of this, with a few pockets grading to extremely low in the central parts of the northern region, followed by much lower accumulations in the Peace Region. Across the Peace Region, there is a broad band in the extremely low category, extending from the northwest corner of the region in the M.D. of Clear Hills all the way down to the southwest corner of the region.
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 Clearhills, 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 above normal-to-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, there has been to a trend near normal across much of the northern tip of the Peace Region.
Northern Region: Most of the region has recorded at least moderately low-precipitation accumulations over the past year, with the west half grading to low and several pockets in the south central and east central areas grading to extremely low, affecting Leduc County, and the County of Minburn. Other dry areas include parts of the northwest affecting an area of Lakeland County and the M.D. of Bonnyville were some areas are classified as having experience low accumulations.
Central Region: Most of the region has recorded at least near normal precipitation with the exception of the northwest where large areas are reporting moderately low, grading down to low in Kneehill county and very low in the western parts of Red Deer County.
Southern Region: Precipitation accumulations are generally at least near normal in most parts of the region grading to moderately high in the center with a few small pockets grading to moderately low in the extreme southeast and southwest.
Average precipitation accumulations for September (Figure 4) - September marks the transition between the wet season (May – August) and the drier winter months (October – March). During this month precipitation totals typically decline significantly, with precipitation totals ranging from just over 20 mm in the Special Areas to less than 60 mm in the Swan Hills and Foothills. Provincially, on average about 9% of the annual precipitation falls in September. September and October are important months for soil moisture recharge in Alberta since moisture losses due to evaporation and plant water demands have been reduced significantly. Fall and spring rains help to replenish soil moisture for the following growing season and thus those areas that are currently abnormally dry will need above average precipitation (post harvest) over the next seven months or so to help build soil moisture reserves for next spring.
Soil moisture
Soil moisture in the agricultural regions of Alberta (Figure 5) - Current soil moisture levels are below 25 mm over most the reporting area, grading to 25 to 50 mm in south west and west central parts of the northern region and up to 50 to 75 mm in the north-western corner of the Central Region. Throughout most of the Central and Southern Regions this represents near normal conditions for this time of year. In contrast, for the northern half of the reporting area current conditions are well below normal for this time of year.
Peace Region: Across the entire Peace Region soil moisture levels less than 25 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: Across most of the Northern Region soil moisture levels are less than 25 mm with the exception of the west central and southwestern portions where soil moisture is slightly higher (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.
Central Region: Soil moisture reserve grades from a low of 25 mm across the east half of the region to a high of 50 to 75 mm in the northwestern corner of the region. Fall and spring rains will need to be at least normal to provide adequate soil moisture for the start of the next growing season.
Southern Region: Across the entire Southern Region soil moisture levels are estimated to be less than 25 mm, a condition that is near normal for this time of year, except in the west along the foothills where normal soil moisture levels are typically 25 to 50 mm greater than this.
Long term average soil moisture conditions (Figure 6) - At this time of the year soil moisture reserves in most parts of the reporting area (excluding the Peace Region) are typically lowest in the central and the eastern parts of each region, overall grading from a high of 75 to 100 mm in the west to less than 25 mm in the eastern half of the Central and Southern Region and to 25 to 50 mm in the eastern half of the Northern Region. In the Peace Region, normal soil moisture reserves for this time of year are 25 to 50 mm in the central parts grading to 50 to 75 mm to the southern and northern portions of the regions.
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 over the Central and Southern Regions are near normal grading to moderately low in the extreme western parts of the Central Region and to very low in the extreme western parts of the Southern Region. Across the Northern Region soil moisture reserves are moderately low, grading to extremely low in the extreme western pats of the region. Across most of the Peace Region, soil moisture reserves are extremely low for this time of year indicating a need for above average precipitation between now and the start of the next growing season.
Peace Region: Soil moisture reserves are extremely low across most of the Peace Region, grading to moderately low in the extreme northern and eastern parts of the region.
Northern Region: Reserves grade near normal in the southeast to moderately low across the central portions of the region and then down to extremely low in the far western reaches of the region. In the east, some areas are classified as low.
Central Region: Soil moisture reserves in most part of the region are at least near normal grading to moderately low along the foothills.
Southern Region: Soil moisture reserves in most part of the region are at least near normal grading to moderately low along the foothills with some foothill areas classified as having extremely low 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 September 9, 2006.
Drought analysis is currently scheduled at monthly intervals between October 3 and April 3, and twice monthly from May 1 to September 30 . This report updates the previous report of August 13, 2006. |
|