| | Precipitation | Snow pack conditions | Data sources | Explanation of terms
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Since the last drought report (December 11th, 2006), less than 20 mm of precipitation was recorded across most of the reporting area.
Cold season precipitation accumulations to date relative to long term normal, across most of the north half of the reporting area were generally at least moderately high, grading to extremely high, across the north-western and north-eastern portions of the Northern Region and central parts of the Peace Region. Across the south half of the region, cold season precipitation accumulations relative to normal grade from moderately high in the Red Deer Stettler area, to near normal across most of the Southern Region with central locations, including the City of Lethbridge, recording moderately low accumulations, and parts of the extreme south east reporting low accumulations.
Precipitation deficits over the over the past year have remained largely the same since the last report (December 11th, 2006), despite low precipitation accumulations since then. This is because December is typically a dry month, accounting for only to about 4 to 5% of the total average annual precipitation accumulations. Across the agricultural region, the driest areas can be found in parts of the Peace Region, with some pockets of extremely low persisting 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 some pockets of moderately low found in each region. Across the Southern Region, precipitation deficits are greater, particularly across the west central areas and extreme southeast where some areas are classified having low to very low accumulations to date.
Snow pack accumulations for this time of year are at least moderately high across most of the Northern and Peace Regions, with some areas grading to extremely high. Across the Central Region, conditions are variable ranging from low in the east and southwest and up to very high in an isolated pocket in the northwest. Across most of the Southern Region, snow pack accumulations are low to moderately low with many areas being free of snow.
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, precipitation accumulations have been low, with most areas recording less than 10 mm.
Peace Region: Across the region, precipitation accumulations were less than 10 mm in most areas except the central Peace, where 10 to 20 mm was recorded.
Northern Region: Precipitation accumulations across the region were generally less than 10 mm with the exception of the extreme east, where accumulations ranged between 10 to 20 mm.
Central Region: Since the last report, most the Central Region received less than 10 mm or precipitation.
Southern Region: Most of the Southern Region received less than 10 mm with greater accumulations in the east around the Cypress Hills (20 to 30 mm) and in the west along the foothills (30 to 40 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 soils are 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 following growing season. In addition, over winter snow pack accumulations can contribute to soil moisture recharge when melt conditions are favourable, but generally snowmelt water 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 moderately 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 near normal accumulations. Across the north half of the region accumulations range from near normal in the south to low in the far north.
Northern Region: Across most of the region, cold season precipitation accumulations to date are classified as at least moderately high with several locations throughout, grading up to extremely high.
Central Region: Cold season precipitation to date across most of the region grades from near normal in the south half of the region, up to moderately high in the north, with a few pockets of high in the north west.
Southern Region: Throughout much 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, and a pocket of low developing in the extreme southeast.
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, and remain largely unchanged since the last report was issued (December 11th, 2006).
Peace Region: 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 soil moisture and surface 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: Much of the region has recorded at least near normal precipitation with parts of the west, classified as moderately low with the highest accumulations relative to normal found in the north and north east, specifically in the central parts of the county of Stettler, which is classified as high.
Southern Region: 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 several pockets grading to low, and one small pocket of very low found in the southern part of Cardston County. Another area of concern (classified as low) exists in the southeast corner of the region.
Average Precipitation Accumulations for January (Figure 4) - January is a typically a dry month, with on average about 4.9 % of the annual precipitation falling. During this month precipitation totals, range from 10 to 20 mm across most the central and Southern Regions, increasing to 30 to 40 mm in the west along the foothills. Across the Northern and Peace Regions, precipitation totals typically range between 20 to 30 mm, except in the south half of the Peace Region where between 30 to 40 mm is typically recorded.
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, which 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 (70 to 80 mm) and lowest in the extreme north (10 to 20 mm). For much of the south half of the region, these snow pack accumulations are generally classified as at least 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 being lowest in the east central areas (20 to 30 mm) and highest in the extreme west 80 to 90 mm. Across most of the region, snow pack accumulations relative to long term normal are at least moderately high, grading to extremely high in parts of the center, north west and extreme north east (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 west half of 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. For much of the east half of the region, accumulations relative to the long term normal are moderately low, grading to low in the extreme southeast.
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, to low, Figure 6. Snow packs exist in the foothills and up in the Cypress Hills with some accumulations extending along the eastern edge of the region (Figure 5).
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 and Food (AAF) 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. All maps describing current conditions are based on preliminary data that is subject to change after further review by AAF, 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 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 is 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 and Food
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on January 5th, 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 December 11th, 2006 |
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