| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Significant precipitation accumulations have occurred across the Southern Region since the September 9, 2007 report, with the greatest amounts (greater than 40 mm) recorded in the southwest, an area previously suffering from extreme precipitation shortages. Across the Central Region precipitation accumulations ranged from 5 to 10 mm in the east to well over 30 mm in the west. The Northern Region remained dry with generally less than 10 mm recorded in most areas. Across the Peace Region precipitation was lowest in the centre (5 to 10 mm) graded up to 15 to 20 mm in the southwest and to more than 40 50 mm across the north.
Fall precipitation deficits combined with low fall moisture reserves have lead to moisture shortages across the eastern half of the Northern Region and southern half of the Peace Region. Fall is an important time for soil moisture recharge, and moisture received at this time is usually held in the soil and utilized by crops the following spring. These areas need above average precipitation between now and early spring to insure a good start to next years growing season.
Growing season precipitation accumulations, relative to the long term normal, remained largely unchanged since the last report (September 9, 2007). Precipitation for the growing season was 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 southeast portions of the Northern Region and a few pockets in the southern extremes of the Peace Region.
The 30-day precipitation accumulations relative to long term normal as of October 2, 2007 were moderately high to high across the southern half of the Southern Region, near normal across most of the Central Region and moderately low, across much of the Northern region, grading to very low in the. Across the Peace Region accumulations ranged from low, in the centre to high in the extreme northeast.
Soil moisture reserves have improved throughout the Southern Region and now range from 25 to 50 across most of the region, grading up to 50 to 75 mm in the west and southwest. This is a marked improvement over conditions that were reported in the September 9, 2007 report. Elsewhere, soil moisture reserves have remained largely unchanged, with the exception of the central parts of the Northern Region, north-eastern parts of the Central Region and the south-western and north-central parts of the Peace Region where they have declined to less than 25 mm. Currently soil moisture reserves relative to long term normal are at least near normal across the south half of the reporting area and grade down very low across central parts of the Northern Region, and for the most part are moderately low in the Peace Region, with parts of the southwest grading down to very low. The probability of achieving normal spring soil moisture conditions is highly variable across the reporting area, ranging from less than 10 % to greater than 90%. Areas with a less than 20 % chance of achieving normal spring soil moisture conditions include most of the Peace Region, as much of the Northern Region, and parts of the Central 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 September 9, 2007 Drought Report (Figure 1) - Precipitation accumulations ranged from less than 5 mm across large parts of the Northern Region, to well above 60 mm across the south-western parts of the Southern Region. In general, the south half of the Southern Region received more than of 40 mm, the northern parts of the Southern Region and western parts of the Central Region, more than 20 mm, the north-eastern Peace Region more than 40 mm, and much of the Northern Region, less than 10 mm.
Peace Region: Precipitation across the Peace Region ranged from 5.0 mm at the Fairview AGDM station in the centre to 49.3 mm as the Fort Vermillion RS station in the North. In general, the east and southeast was driest, receiving between 5 and 10 mm, grading up to more than 15 mm in the southwest and more than 30 mm across the north.
Northern Region: Precipitation accumulations remained low over most of the region with less than 5 mm recorded at a large number of stations in the east and northwest. Two stations received notable, but isolated, high precipitation accumulations, Breton Plots in the southwest (104.0 mm) and Lac La Biche A in the northeast (60.9 mm).
Central Region: Precipitation accumulations were lowest in the east with several stations recording between 5 to
10 mm, grading up to 15 to 20 mm in the centre and more than 30 mm across the extreme west. The greatest accumulations in the region were recorded at the Bow Valley station (104.2 mm) with several stations in the mountain parks receiving in excess of 70 mm.
Southern Region: Previously extremely dry areas in the southwest and southeast received over 60 mm with many stations recording just over 80 mm. This was welcome relief and much of this moisture went to recharging soil moisture reserves. The lowest accumulations were recorded in the central portions of the region with the Vauxhall CDA station in the M.D of Taber recording the least (12.9 mm). In general, the southwest, southern and much of the eastern parts of the region received more than 40 mm with the driest locations found in the central and north central portions of the region where many station recording less than 25 mm.
Growing Season Precipitation Accumulations Relative to Long Term Normal (1961 - 2005) (Figure 2) - Total growing season precipitation accumulations relative to the long term normal have remained largely unchanged since the last report. The greatest deficits were recorded in the south-western portions of the Southern Region and the southeast portions of the Central Region where one pocket of very low in each was recorded. In the Southern Region, the area of very low can be found in the M.D of Pincher Creek, and in the Northern Region, in Flagstaff County. Other areas with notable growing season precipitation deficits include much of the central and northern parts of the Northern Region (moderately low to low) and the south-western portions of the Peace Region where a pocket of moderately low as also recorded.
Peace Region: Growing season precipitation was near normal across the most of the region, with two areas in the south grading down to low; one in the south-western portion 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 was lowest in the southeast portion 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 were classified as moderately low, with large areas grading down to low. Elsewhere across the region growing season accumulations were generally classified as at least near normal, with parts of the southwest grading up to at least high.
Central Region: Most of the region received at least moderately high growing season precipitation, with much of the west-half of the region classified as high to extremely high. The County of Paintearth received the lowest growing season accumulations and was classified as moderately low to low.
Southern Region: Growing season precipitation deficits across the much of the south-half of the region were classified as at least moderately low, with the driest areas found in the M.D of Pincher Creek (very low). Elsewhere across the Southern Region, precipitation accumulations were classified as near normal and graded to extremely high in the far northern parts of the region.
30-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - Precipitation accumulations over the south-half of the reporting area were at least near normal with much of the south half of the Southern Region grading to moderately high and the extreme south-western and south-eastern portions of the region grading to high. Across much of the Northern and Peace Region 30-day accumulations have been moderately low with several areas classified as low to very low.
Peace Region: Accumulations over the past 30-days have been at least moderately low over much of the south-half of the region with central and south-central areas grading down to low. Across the north, 30-day precipitation accumulations were at least near normal with the extreme northeast grading to high.
Northern Region: Over the past 30-days accumulations over most of the region have been at least moderately low with pats of the west grading down to very low or extremely low. Fall is and important time for soil moisture recharge, and subsequent storage of moisture for the following spring. Large parts of the Northern Region are quite dry. As a result, above normal precipitation is needed between now and early spring in order to insure a good start to next year's growing season.
Central Region: Most of the region received near normal accumulations over the past 30-days, with the exception of the northeast where moderately low accumulations were recorded.
Southern Region: Most of the region has received at least near normal precipitation over the past 30-days with parts of the south and southeast grading up to moderately high.
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.
In October evapo-transpiration rates are low due to killing frosts and precipitation generally falls as rain, going directly to soil moisture reserves. 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, particularly where soil moisture reserves are below normal; in the western half of the Northern Region and over much of the Peace Region where soil moisture reserves are low or worse.
Soil moisture
Soil moisture in the agricultural regions of Alberta (Figure 5 , Figure 6 and Figure 7) - Across much of the south-half of the reporting area, recent precipitation and cooler temperatures have resulted increase in soil moisture reserves, particularly in the Southern Region. In contrast, soil moisture reserves continue to decline in the central parts of the Northern Region, east-central parts of the Central Region and across the south-western and north-central parts of the Peace Region. Across all four regions, significantly large areas have a less than 30% chance of achieving normal soil moisture reserves by spring. In fact, the probability of achieving normal spring soil moisture conditions is less than 10% across much of the northern and western parts of the Northern Region, as well as through many parts of the southern Peace Region.
Peace Region: Soil moisture reserves are generally between 25 to 50 mm across most of the region with parts of the southwest and north-central portions of the region estimated to have less than 25 mm (Figure 5). Soil moisture reserves relative to the long term normal have declined significantly since the last report due to a recent lack of precipitation, which at this time of year typically acts to increase soil moisture reserves. Much of the region has moderately low to low soil moisture reserves with parts of the southwest grading to very low (Figure 6). The probability of returning to average spring soil moisture conditions ranges from more than 50% in the northern portions of the region, down to less than 10% across many parts in the southern half of the region (Figure 7).
Northern Region: Most of the region has between 25 to 50 mm of soil moisture with less than 25 mm found in the central, north-central and extreme south-eastern portions of the region and the greatest amounts found in the northeast (50 to 75 mm) and the extreme southwest greater than 125 mm, (Figure 5). Soil moisture reserves for this time of year are classified as at least near normal across the east half of the region and grade down to very low in the north, and low in the centre and western portions of the region (Figure 6). The probability of returning to average soil moisture conditions by the spring is estimated to be less than 10% across most of the north and northwest with much of the west-half of the region having less than a 20% chance of returning to normal by spring. In contrast, across the extreme northeast, soil moisture reserves are quite good, with some areas having a better than 60% of achieving normal by spring (Figure 7).
Central Region: Soil moisture reserves are generally between 25 to 50 mm across most of the region, with a large area in the northeast grading down to 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 (moderately high) found in the southeast (Figure 6). The probability of returning to normal soil moisture conditions by the spring is estimated to range from less than 20% in the extreme north, to more than 70% across parts of the south east and extreme north west.
Southern Region: Across most of the region, soil moisture levels have improved significantly since the last report (September 9, 2007) and are now at 25 to 50 mm (Figure 5). In general, for this time of year soil moisture reserves for much of the region are at least near normal with parts of the south and southwest grading up to moderately high (Figure 6). The probability of returning to normal soil moisture conditions by the spring is generally less than 30% across the centre and northwest grading up to more than 60% across much of the northern, eastern and southern parts of the region (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 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 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 October 5, 2007.
Drought analysis is currently scheduled at monthly intervals between October 31st and April 31st, and twice monthly from May 1st to September 30th. This report updates the previous report of September 9, 2007. |
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