| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
This past October was dry, relative to average. Most of the agricultural areas within the reporting area received less than 20 mm since that last report (October 2, 2007). Although, on average, precipitation accumulations in October are far less than what is typically received during the active growing season months, October remains a very important month for recharging soil moisture reserves for the coming growing season, and for many areas that recharge did not occur.
To date, cold season (Oct 1to March 31) precipitation accumulations relative to long term normal have been near normal across most of the southern half of the Southern Region and the extreme northern and southern parts of the Peace Region. Elsewhere, cold season accumulations to date have been at least moderately low, with several areas grading to at least low. Currently, the lowest cold season accumulations are found across the north-western parts of the Northern Region and central parts of the Peace Region where they grade to extremely low. These are emerging areas of concern as soil moisture reserves in these areas are classified as low to very low.
Recent precipitation deficits, combined with low soil moisture reserves following the growing season, have lead to significant soil moisture shortages across much of the west half of the Northern Region and across many parts of the Peace Region. In some of these areas, soil moisture reserves are classified as very low, and are estimated to be this depleted on average only once in 12 years. In addition, large parts of both regions are estimated to have less than 10 percent chance of achieving normal conditions by spring (May 1, 2008). Since the window for fall recharge is rapidly diminishing, particularly across the north half of the reporting area, above average snowfall and early spring precipitation are needed to develop some capacity to resist short-term dry spells next growing season.
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 October 2, 2007 Drought Report (Figure 1) - Precipitation accumulations continued to be low in most areas, except along foothills and further west into the mountains. In the agricultural areas precipitation accumulations were generally below 20 mm, with several areas receiving less than 10 mm.
Peace Region: Precipitation across the Peace Region ranged from 4.8 mm at the Peace River A station to 25.1 mm at the Grande Prairie A station. Across the central portions of the region, less than 10 mm of precipitation was recorded, grading to 20 to 25 mm across the extreme north and southern portions of the region.
Northern Region: Precipitation accumulations ranged from 3.0 mm at the Dapp AGDM station North of Edmonton to 38.4 mm at the Lac La Biche A station in the northeast. Most of the central portions of the region received less than 10 mm, with more than 20 mm recorded in the in the extreme west and 10 to 15 mm across the parts of the east.
Central Region: Precipitation accumulations ranged from 4.0 mm at the Pollockville AGDM station in Special Areas 2 to 22.5 mm at the Battle River Headwaters station in Lacombe County. Precipitation accumulations were lowest in the east and south (5 to 10 mm) and greatest in the west and northwest (greater than 20 mm).
Southern Region: Precipitation accumulations tended to be higher than the other regions, ranging from 3.6 mm at the Brooks Station to well over 40 mm along the foothills. The driest parts of the region were found in the north where less than 10 mm was recorded, increasing to 15 to 20 mm in the south and southeast with the greatest amounts (greater than 40 mm) recorded in the extreme west along the foothills.
Cold Season Precipitation Accumulations Relative to Long Term Normal (1961 - 2005) (Figure 2) - To date, cold season precipitation (Oct 1 to March 31) accumulations relative to the long term normal were highly variable across the reporting area, ranging from near normal across the south-half of the Southern Region and the northern and south-western parts of the Peace Region, down to extremely low across parts of the central Peace Region and north-central parts of the Northern Region.
Peace Region: Cold season precipitation to date, ranged from near normal in the extreme southwest and northern parts of the region, down to very low or extremely low across central parts of the region. Currently the driest areas in the region are found in the M.D of Fairview and in a relatively large pocket straddling the border between Northern Sunrise County and the M.D. of Big Lakes. These areas are of concern, as soil moisture reserves were classified as very low going into freeze up. Above average precipitation will be needed in these areas over the coming winter and into the spring in order to replenish soil moisture reserves for next growing season.
Northern Region: Cold season precipitation is classified as at least moderately low across most of the region, with several areas grading down to low or very low, with one pocket of extremely low found in the Counties of Westlock and Barrhead. Soil moisture reserves are depleted across the region and above average precipitation will be needed between now and well into the spring in order to insure that moisture reserves are adequate to supply moisture in the face of short-term dry spells over then next growing season.
Central Region: Cold season precipitation is moderately low across most of the region, with several widely scattered pockets grading to low. However, soil moisture reserves tend to near normal across much of the region with some areas grading to moderately low.
Southern Region: Cold season predication to date ranges from moderately low across the north half of the region, up to near normal across much of the south.
Average Precipitation Accumulations for November (Figure 3) - Across the reporting area, on average about 4.3 percent of the annual precipitation falls in November. During this month average precipitation ranges from 10 to 20 mm across the east half of the reporting area, grading up to 40 to 50 mm in the foothills in the south west corner of the Southern Region, and up to 20 to 30 mm the northwest corner of the Central Region and the western parts on the Northern Region. Across the Peace Region, on average 20 to 30 mm of precipitation falls during the month of November.
Soil moisture in the agricultural regions of Alberta (Figure 4, Figure 5 and Figure 6)
Soil moisture reserves are relatively uniform across most of the reporting area and are in the range of 25 to 50 mm. For most of the Southern Region and southeastern portions of the Central Region, these levels are classified as near normal for this time of year. Elsewhere, reserves of this magnitude are classified as at least moderately low with large parts of the western half of the Northern Region and central parts of the Peace Region, grading down to low or very low. Given current soil moisture reserves across large parts of the Central, Northern and Peace Regions, there is a less than 20 percent probability that precipitation received between now and spring will be sufficient to bring soil moisture reserves up to average conditions. It is highly likely that next years crops may not have adequate soil moisture reserves to withstand short duration dry spells. Therefore, during the next growing season, well-timed average to above average precipitation will be needed in these areas to insure good crop growth.
Peace Region: Soil moisture reserves are generally between 25 to 50 mm across most of the region (Figure 4). Soil moisture reserves relative to the long term normal have declined steadily since the last report, due to the fact that the recharge that typically occurs at this time of year has not happened. As a result, much of the region is classified as having at least moderately low to low soil moisture reserves with some areas in the west-central and northern portions of the region, grading down to low (Figure 5). Across most of the region, the probability of returning to average spring soil moisture conditions is less than 20 percent with many locations estimated to have less than a 10 percent chance of achieving normal conditions (Figure 6).
Northern Region: Soil moisture reserves are generally in the 25 to 50 mm range across most of the region with parts of the northeast and southwest grading up to 50 to 75 mm and parts of the north and extreme southeast grading down to less than 25 mm (Figure 4). Since soil moisture recharge has been minimal, moisture reserves across most of the region are at now classified as at least moderately low, with parts of the central, north-central, and extreme west, grading down to very low. In contrast, along the eastern edge of the region, reserves are generally at least near normal (Figure 5). The probability of returning to average soil moisture conditions by the spring is estimated to be less than 20 percent across most of the region (with the exception of the east) with large parts of the north and west estimated to have less than a 10 percent probability of achieving normal conditions (Figure 6).
Central Region: Soil moisture reserves range from less than 25 mm in east-central areas to more than 50 mm in the west, along the foothills, although most of the region is characterized as having reserves in the range of 25 to 50 mm (Figure 4). This translates to near normal conditions for much of the region, with much of the north and west central parts of the region classified as moderately low (Figure 5). The probability of returning to normal soil moisture conditions by the spring ranges from more than 40 percent in the south east, to less an 20 percent across most of the north half of the region, with the exception of the foothills were probabilities improve to well over 60 percent in the extreme west (Figure 6).
Southern Region: Across most of the region, soil moisture reserves are generally between 25 to 50 mm, but grade up to more than 50 mm in the southwest and west along the foothills (Figure 4). For this time of year soil moisture reserves for much of the region are at least near normal, with a few isolated pockets in the central and western portions of the region grading to moderately low and parts of the south and southeast grading up to moderately high (Figure 5). The probability of returning to average soil moisture conditions by the spring ranges from more then 50 percent in the south and eastern parts of the region to less than 30 percent in the central and northern parts of the region, with a few areas in the central and western parts of the region having less than a 10 percent chance of achieving normal conditions by spring (Figure 6).
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 percent of the total precipitation is allowed to accumulate resulting in a 30 percent 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 November 14, 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 October 2, 2007. |
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