| | Precipitation | Snow pack conditions | Data sources | Explanation of terms
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Since the last Drought Report (October 31st, 2006) significant precipitation accumulations were recorded over much of the northern half of the Central Region and much of the Northern and Peace Regions, with the greatest amounts (in excess of 50 mm) being recorded in the western parts of the Northern Region and Southern half of the Peace Region. Across the plains in the Southern Region, precipitation was generally less than 20 mm with several locations in the south reporting less than 10 mm. Across the Central Region, precipitation accumulations ranged form 10 to 20 mm in the south up to 30 to 40 mm in the north. Across the Northern Region precipitation ranged from 30 to 40 mm in the east up to 80 to 90 mm in the far west. Across the Peace Region precipitation was greatest in the south half with amounts ranging from 40 to 90 mm, diminishing to 10 to 20 mm in the extreme north.
Cold season precipitation accumulations to date across most of the north half of the reporting area were generally high, with many areas classified as very high to extremely high. Across the south half of the province, precipitation accumulations graded from high in the Red Deer - Stettler region, to near normal across most of the Southern Region with the central locations, included the City of Lethbridge recording moderately low accumulations.
Precipitation deficits over the over the past year have eased slightly in the driest parts of the Peace Region due to recent precipitation, but pockets of extremely low still exist in the northwest and southeast. Across the Northern and Central Regions, accumulations over the past year have been at least near normal for most areas with several pockets of moderately low in each region. Across the Southern Region, precipitation deficits are increasing, particularly across the west-central areas, where a few pockets of very low are beginning to emerge.
Snow pack accumulations for this time of year are high across most of the Northern and Peace Regions, with several areas grading to extremely high. Across the Central Region and the northern-eastern and western portions of the Southern Region, snow pack accumulations are at least near normal. In the Central parts of the Southern Region fields are generally bare.
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 31st, 2006 Drought Report (Figure 1) - Since the last report, wet winter weather brought more than 30 mm of precipitation across much of the northern parts of the Central Region, and most of the Northern and Peace Regions, with some areas recording well over 80 mm. Lesser amounts of precipitation were recorded across the Central and Southern Regions, with the least amounts (< 10 mm falling in several locations in the extreme south.
Peace Region: Across the region, precipitation accumulations ranged from less than 18.1 mm at the Fort Vermillion RS station to 89.8 mm in the central parts of the region at the Fairview AGDM station. The recent precipitation that fell across most of the southern half of the Peace Region was welcome relief to the extreme deficits of recent months experienced in the north-western and south-eastern parts of the region.
Northern Region: Precipitation accumulations across the region were variable, ranging from 124.2 mm at the Whitecourt A station in the extreme west down to a low of 22.5 mm at the Bodo AGDM station in the southeast. Generally, across the region precipitation was highest in the west, (greater than 40 mm) and lowest in the east (30 to 40 mm).
Central Region: The least amounts of precipitation were recorded over much of the southern half of the region, with several stations reporting about 15 mm. Precipitation amounts increase northward, with the greatest amount recorded at the Battle River Headwaters station (51.7 mm).
Southern Region: Across most of the Southern Region, precipitation totals were less than 20 mm with several stations recording less than 10 mm and the least amount recorded as 3.8 mm at the Onefour CDA station. In the eastern parts of the region, accumulations increased with the greatest amounts recorded at the Medicine Lodge station (43.7 mm). In the west along the foothills and in the mountains, significant precipitation was recorded with many stations recording in excess of 100 mm.
Cold Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2) - The cold season is arbitrarily defined as the period between October 1st, and March 31st. This is a critical period for soil moisture recharge, particularly when the soil is not frozen. During this time, evaporation rates are low and thus precipitation that falls as rain is an important source of soil moisture recharge for the upcoming growing season. In addition, over winter snow pack accumulations can contribute to soil moisture recharge when melt conditions are favourable, but generally snow melt is more important for recharging surface water bodies and ground water stores.
Peace Region: Most of the southern half of the region has received at least high precipitation accumulations to date, with central locations grading to extremely high. Currently, the driest areas in the south half of the region are in the northwest and southeast and are classified as having moderately high accumulations. Hopefully this marks the end of the below normal precipitation accumulations seen in these areas over the past several months. Across the north half of the region accumulations range from moderately high to low in the far north.
Northern Region: Across much of the region, cold season precipitation accumulations to date are classified as at least high with the exception of the extreme east, were accumulations grade down to moderately high. Several pockets of extremely high can be found throughout the region, the larges of which can be found in the west.
Central Region: Cold season precipitation to date across most of the region grades from near normal in the southeast and southwest, up to at least high the north and north central locations.
Southern Region: Throughout most of the region, cold season precipitation to date has been at least near normal, with a large area of moderately low found in the central parts of the region.
Long Term Conditions: 365-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - Precipitation accumulations over the past year were variable across all regions, with recent precipitation in the north half of the region leading to a reduction in the number of areas classified as moderately low or drier. Recent precipitation deficits in the Southern Region have lead to an increase in the size of the areas classified as moderately low, with a few small pockets of very low emerging across the west central parts of the region.
Peace Region: Recent above normal precipitation accumulations have helped to reduce precipitation deficits over the past year, however, large parts of the Peace Region are still experiencing a net annual precipitation deficit. Areas with extremely low accumulations still persist in the northwest and southeast. Continued above normal precipitation is needed in these areas, particularly in the spring to help replenish water supplies.
Northern Region: Generally over the Northern Region, conditions are near normal, with one area in the northeast classified as having moderately low accumulations.
Central Region: Conditions are extremely variable across the region and the reader is encouraged to look at the map for specific details. Much of the region has recorded at least near normal precipitation, with parts of the west classified as moderately low and the highest accumulations relative to normal found in the north, specifically in the central parts of the County of Stettler, which is classified as extremely high.
Southern Region: Conditions are extremely variable across the region and the reader is encouraged to look at the map for specific details. Much of east half and northern parts of the region are near normal. The driest areas can be found in west central parts of the region with a small pocket of extremely low found in the County of Lethbridge and one in the southern part of Cardston County.
Average Precipitation Accumulations for December (Figure 4) - Across the reporting area, on average about 4.7 % of the annual precipitation falls in December. During this month precipitation totals range from 10 to 20 mm across most the Central and Southern Regions, increasing in the west along the foothills. Across the Northern and Peace Regions, precipitation totals typically range between 20 to 30 mm.
Snow pack conditions (Figure 5 and Figure 6)
Modeled snow pack conditions expressed as snow water equivalent (SWE) are shown in Figure 5. Snow pack accumulations relative to long term normal are shown in Figure 6. These maps represent the current snow pack estimates in stubble fields and reflect a 30% precipitation loss due to blowing; in addition to losses due to sublimation and snow melt process.
Peace Region: SWE's are variable across the region, being highest in the southwest and central locations (60 to 70 mm) and lowest in the extreme north (10 to 20 mm). For the south half of the region, these snow pack accumulations are generally classified as very high for this time of year and represent a good source of moisture for the spring melt period Figure 6.
Northern Region: SWE's are variable across the region and are lowest in the east and highest in the west. Across the east SWE's range from 20 to 30 mm, across the center from 40 to 50 mm up to as high as 70 to 80 mm in the west. Across the entire region, snow pack accumulations are at least moderately high, grading to high in the center and extremely high in some areas Figure 6.
Central Region. SWE's are lowest in the south half of the region ranging from 1 to 10 mm and increase to 30 to 40 mm in the extreme northwest. In general across the region, accumulations relative to the long term normal Figure 6 are at least near normal, with parts of the extreme north west grading to high, and parts of the south west and extreme east, grading to moderately low.
Southern Region: The ground is generally snow free throughout much of the central parts of the region Figure 5, a condition that at this time of year is considered to be moderately low, having a frequency of occurring on average one in three years Figure 6. This grades from 1 to 10 mm in the north up to 20 to 30 mm in the far south and in the west along the foothills Figure 5. In the north these conditions are considered to be near normal and in part of the east and south east snow pack accumulations for this time of year are high in a few isolated areas 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 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,
- 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 less than 1 in 25-years |
| very low | drier less than 1 in 12-years |
| low | drier less than 1 in 6-years |
| moderately low | drier less than 1 in 3-years |
| near normal | every 1 in 3-years |
| moderately high | wetter less than 1 in 3-years |
| high | wetter less than 1 in 6-years |
| very high | wetter less than 1 in 12-years |
| extremely high | wetter less than 1 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 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 December 11th, 2006.
Drought analysis is currently scheduled at monthly intervals between October 31st and April 31st, and twice monthly from May 1st to September 30st . This report updates the previous report of October 31st, 2006 |
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