| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last drought report (August 20, 2007), precipitation patterns and daily temperature regimes have generally been at least near normal across most the region, with the exception of most of the eastern and south-western portions of the Southern Region where precipitation deficits have continued.
Precipitation across the reporting area was quite variable. Accumulations ranged from less than 5 mm in the south-eastern portions of the Southern Region to more than 60 mm across the north western portions of the Southern Region, the western parts of the parts of the Central Region, north-eastern parts of the Northern Region and north-central portions of the Peace Region. Relatively warmer, drier weather will be needed across much of the province to finish crops and ensure that harvesting operations are not hampered. Areas that currently have below normal soil moisture reserves will hope for and benefit from above average fall rains, as most of this moisture will be stored for the next growing season.
Growing season precipitation accumulations to date, relative to the long term normal, have been highly variable across the reporting area, ranging from very low in the south-western portions of the Southern Region to extremely high across the extreme northern parts of the Southern Region and north western parts of the Central Region. Areas with less than near normal accumulations include much of the south half of the Southern Region, the central and south east portions of the Northern Region and a few pockets in the southern extremes of the Peace Region.
Since the August 20, 2007 drought report, 30-day precipitation accumulations relative to long term normal have remained below normal across the southern half of the Southern Region. Recent improvements occurred in the north-central Peace Region where 30-day accumulations now range from near normal to moderately high. Short-term precipitation deficits continue in parts of the Counties of Athabasca, Thorhild, Flagstaff and Paintearth.
Soil moisture reserves have remained at less than 25 mm across most of the Southern Region however, in most other areas, with cooler temperatures and recent precipitation, have started to recharge. Soil moisture reserves relative to long term normal are at least near normal across most areas, with the exception of the south-half of the Southern Region, the western-half of the Northern Region and the extreme southern parts of the Peace Region were reserves range from moderately low to low. The probability of achieving normal spring soil moisture conditions is highly variable across the reporting area and ranges from less than 10 % to greater than 90%. Areas with a less than 30 % chance of achieving normal spring soil moisture conditions include parts of the Southern and Northern Peace Region, much of the west half of the Northern Region, as well as parts of southern half 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 20, 2007 Drought Report (Figure 1) - Precipitation accumulations ranged from less than 5 mm across most of the eastern half of the Southern Region to well over 60 mm across several widely scattered locations across the reporting area. Areas that received more than 60 mm include the north-central Peace Region, parts of the Swan Hills, the north-eastern parts on the Northern Region, and the north-western parts of the Southern Region. The south half of the Southern Region remained mostly dry, with many stations rerecording less than 15 mm.
Peace Region: Precipitation across the Peace Region ranged from 19.2 mm at the Peoria AGDM station in Birch Hills County to 74.1 mm at the Manning AGDM station in Northern Sunrise County. Most of the region received more than 25 mm or precipitation with the north central portions of the region receiving more than 50 mm.
Northern Region: Precipitation accumulations ranged from 15.0 mm at the Little Paddle Headwaters station in the west (Woodlands County) to 76.4 mm at the Cold Lake A station in the east (M.D of Bonnyville). The north-western and west-central areas were driest, receiving less than 25 mm and the southwest and northeast were the wettest, receiving upwards of 40 mm.
Central Region: Precipitation was generally lower in the east, ranging from 12.3 mm at the Consort AGDM station in Special Area 4 and higher in the northwest with 56.1 mm recorded at the Rocky Mtn. House A station located in Mountain View County.
Southern Region: The eastern part of the region was the driest with many stations recording less than 5 mm of precipitation. In contrast, the northwest portions of the region received the greatest amounts of precipitation with 63.1 mm recoded at the Mossleigh AGCM station in Vulcan County and 92.7 mm recorded at the Pekisko station in the M.D of Foothills. The south-half of the region recorded less than 15 mm, with the exception of the extreme southwest where more than 20 mm was recorded at some stations in the southwest of Cardston County, an area that has been extremely dry over the past several weeks.
Growing Season Precipitation Accumulations Relative to Long Term Normal (1961 - 2005) (Figure 2) - Growing season precipitation accumulations relative to the long term normal have remained largely unchanged since the August 20, 2007 report, with some exceptions; deficits continued to worsen across the southern half of the Southern Region with parts of the southwest grading down to very low and extremely low and in the south-eastern parts of the Northern Region a small pocket of very low is beginning to emerge in Flagstaff County.
Peace Region: To date, growing season precipitation is at least near normal across the most of the region, with two areas in the south grading down to low; one in the south-western area of the County of Grande Prairie and the other in the north-eastern portion of the M.D. of Greenview.
Northern Region: Growing season precipitation is lowest in the southeast of the region, with a small pocket of very low emerging in Flagstaff County. Other below normal areas include north and north-central portions of the region which are still classified as moderately low, with several pockets grading down to low. Elsewhere across the region growing season accumulations are at least near normal, with parts of the southwest and northeast grading up to at least high.
Central Region: Most of the region has received at least moderately high growing season precipitation to date, with much of the west-half of the region classified as high to extremely high. Currently the driest area in the region, classified as moderately low, is confined to the County of Paintearth.
Southern Region: Precipitation deficits continue to grow across the much of the south-half of the region with most of this area classified as receiving at least moderately low growing season accumulations to date, with the driest areas found in the M.D of Pincher Creek, currently classified as extremely low, and parts of Cardston County which are classified as very low. Above normal precipitation will be needed between now and the spring to bring soil moisture reserves back to average spring conditions.
30-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - With the exception of the west-half of the Northern Region, 30-day precipitation accumulations have generally improved over most areas, including the south western portions of the Southern Region, however, 30-day accumulations in the southwest are still low to moderately low, which is an improvement from the very low accumulations reported for the 30-day period dated back from the August 20, 2007 drought report.
Peace Region: Most of the region has reported at least near normal accumulations.
Northern Region: Most of the west half of the region has experienced moderately low accumulations over the past 30 days, while the east-half is classified as at least near normal with parts of the northeast grading to at least high.
Central Region: The south western parts of the region are the driest and accumulations over the past 30 days are classified as moderately low. Most other parts of the region have received at least near normal accumulations, with parts of the extreme east grading up to at least high.
Southern Region: Dry conditions continue to prevail across the south-half of the region, with many locations grading down to low. Currently the lowest 30-day accumulations were encountered in the extreme southeast where a small pocket of very low is beginning to emerge. The south west, continues to remain dry, however, accumulations over the past 30 days are now low to moderately low, with is better than the very low accumulations that were reported for this area in the August 20, 2007 drought report.
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 , Figure 6 and Figure 7) - Recent precipitation and cooler temperatures have resulted in a slight increase in soil moisture reserves across most parts of the reporting area with the exception of the south-half of the Southern Region where reserves are still below 25 mm. In the fall, with the onset of harvest and cooler temperatures, evaporative demand is reduced significantly and recharge between now and freezing is expected to occur, providing that at least normal precipitation accumulations are observed. Several locations across the reporting area are estimated to have less than a 30% probability of achieving average spring soil moisture conditions by spring (May 1, 2008). These areas include, but are not limited to: much of west half of the Northern Region, parts of the northern and the extreme southern Peace Region, and parts of central and southern Alberta.
Peace Region: Soil moisture reserves are generally between 25 to 50 mm across most of the region (Figure 5). Soil moisture reserves relative to the long term normal are generally near normal for most of the region, but do grade down to low in the extreme north, the southwest and the extreme southern parts of the region. (Figure 6) The probability of returning to average spring soil moisture conditions ranges from more than 50% in the central and north central portions of the region, down to less than 30% across the north and over much of the southwest and southeast (Figure 7).
Northern Region: Soil moisture levels are generally between 25 to 50 mm across the central portions of the region and grade up to 50 to 75 mm in the northeast and southwest, with the extreme southwest and southeast, grading up to 75 to 100 mm (Figure 5). Soil moisture reserves are generally at least near normal across the east half of the region and grade down to moderately low in the north and northwest portions of the region with one pocket grading down to low, just east of the City of Edmonton (Figure 6). The probability of returning to average soil moisture conditions by the spring is estimated to be less than 30% across most of the north and north-west and improves to more than 80% across the east (Figure 7).
Central Region: Soil moisture reserves are generally between 25 to 50 mm across most of the region, with a few scattered pockets of less than 25 mm and conditions in the extreme west grading up to as high as 75 to 100 mm (Figure 5). Soil moisture reserves relative to the long term normal are generally at least near normal across the entire region, with the greatest reserves (high) found in the east (Figure 6). The probability of returning to average soil moisture conditions by the spring is estimated to range from less than 30% in the extreme north, to more than 80% across parts of the east.
Southern Region: Most of the region has soil moisture levels that are less than 25 mm (Figure 5). At this time of year soil moisture reserves for most of the region are generally below 25 mm, but historically they do tend to increase through the fall, provided that at least near normal precipitation patterns are observed. Currently, the southwest and south-eastern parts of the region are classified as having moderately low reserves, with several isolated pockets grading down to low. Through central portions of the region, reserves are classified as normal and grade up to moderately high across parts of the north (Figure 6). The probability of returning to normal soil moisture conditions by the spring is generally less than 40% across the south-half of the region with several areas having less than a 30% chance of achieving average spring conditions. Across the north the chance of reaching average spring conditions is estimated to be higher than 40%, with parts of the north having a 70 to 80% chance of achieving average spring soil moisture conditions (Figure 7).
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 (AF) 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 AF, 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:
- 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 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:
| Description | Frequency of Occurence |
| 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 accumulations 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% 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 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
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 12, 2007.
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 August 20, 2007. |
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