| | Precipitation | Snow pack conditions | Data sources Explanation of terms
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Summary
Since the last drought report, December 31, 2006, precipitation ranged from less than 10 mm in the extreme southeast to 120 to 150 mm in the Swan Hills. Other areas experiencing significant accumulations since the last report include the northwestern Peace Region (80 to 100 mm) and the western parts of the Southern Region (80 to 120 mm).
To date, cold season (October 1 to March 31) precipitation accumulations relative to long term normal ranged widely throughout the reporting area from extremely low in the southeast to extremely high in several locations with most of, but not all of, these areas located in the northern half of the reporting area. So far during the cold season several areas in the south half of the Peace Region have received at least high accumulations, along with several locations scattered through out the Northern Region. Throughout most of the Central Region cold season accumulations have generally been near normal, with a few pockets grading to moderately low and one in northeast, grading to low. Across the Southern Region, accumulations have been highly variable grading to extremely low in the southeast, moderately low in central locations, along with a few small pockets grading to least very high in the west, south central and eastern portion of the region.
Long term conditions (365-day precipitation accumulations relative to long term normal) in the northwestern Peace Region improved significantly since the December 31st report and are now up from extremely low to moderately low. However, one pocket of extremely low still persists in the northeastern part of the M.D of Greenview (southeast Peace Region). Across the Northern Region accumulations over the past 356-days have improved since the last report and are now at least near normal, with several areas grading to very high and a few areas in the south and south east, grading to down to moderately low or low. Across the Central Region, most areas are classified as having at least near normal precipitation accumulations over the past 365-days with a few pockets grading down to moderately low. This represents a minor improvement in those areas in the west that were previously classified in the last report as having moderately low accumulations. Across the Southern Region, 365-day precipitation accumulations have generally improved since the last report with most areas classified as near normal. However, two notable exceptions exist in the extreme south where very low accumulations were recorded, one in southern parts Cardston County and one in southern parts of Cypress County.
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 across much of the southeast and parts of the west up to near normal across most of the west half of the region. Across most of the Southern Region, snow pack accumulations for this time of year are near normal with many areas being largely 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 December 31, 2006 Drought Report (Figure 1) - Since the last report, precipitation accumulations have been highly variable across the reporting area, ranging from 2.2 mm at the Onefour CDA station in the extreme southeast to 127.5 at the Goose Mountain LO -AFS station in the Swan Hills.
Peace Region: Across the region, precipitation accumulations where lowest in the North, ranging from 34.0 mm at the Fort Vermillion RS station to more than 90 mm at several stations in the northwest.
Northern Region: Precipitation accumulations ranged from 10 to 20 mm across the southeast to 50 to 60 mm in the extreme west and parts of the extreme northeast.
Central Region: Since the last report, most the Central Region received between 20 to 30 mm with lower amounts (10 to 20 mm) recorded in the northeast and east central portions of the region, with the greatest amounts (30 to 40 mm) recorded in the south west.
Southern Region: Precipitation was highly variable across the region with the least amounts recorded in the extreme southeast at the Onefour CDA station (2.2 mm) grading up to 20 to 40 mm across the central portions of the region, with more than 50 mm across much of the west. The most amount of precipitation was recorded near Claresholm (120.9 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 1, and March 31. 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 and western locations grading to very high. 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 near normal with several locations in the west, central and extreme north east, grading up to extremely high. In contrast, the extreme southeast and south-central parts of the region have received low accumulations over the cold season.
Central Region: Cold season precipitation to date across most of the region is near normal with a few pockets of moderately low in the west and one pocket grading to low in the extreme northeast.
Southern Region: Cold season precipitation is highly variable across the region, ranging from extremely low in the southeast (Cypress County), moderately low in central locations and up to moderately high in parts of the west.
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 improvements across most areas since the December 31, 2006.
Peace Region: The northwest and southeastern parts of the region are still experiencing net annual precipitation deficits, particularly in the southeast, near the town of Valleyview, where extremely low accumulations exist. However, in the northwest, the area previously classified as extremely low is now being classified as low due to high precipitation accumulations over the past few months. Elsewhere across the central and northern parts of the region long-term accumulations are near normal, with parts of north central and extreme southern areas classified as having low 365-day accumulations.
Northern Region: In this region conditions are near normal with one part of the northeast and one small pocket in the south central area, classified as having moderately low accumulations.
Central Region: Much of the region has recorded at least near normal precipitation over the past 365-days with a few isolated and widely scattered pockets classified as moderately low.
Southern Region: 365-day precipitation accumulations have generally improved across the region since the last report, with most areas classified as near normal. Two notable exceptions exist in the extreme south where very low accumulations were recorded, one in southern parts of Cardston County and one in southern parts of Cypress County.
Average Precipitation Accumulations for March (Figure 4) - March is a typically a dry month, across most of the north half of the reporting area, with precipitation totals ranging from 10 to 30 mm. On average, March is the driest month in the Peace Region with normal accumulations ranging from 10 to 20 mm. Along the foothills, and across much of the Southern Region, March marks the end of the drier winter period with accumulations ranging from 50 to 60 mm in the extreme south west, up to 30 to 40 mm in the foot hills west and south of Calgary and around 20 to 30 mm elsewhere in the Southern Region
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 percent precipitation loss due to blowing, in addition to losses due to sublimation and snow melt process.
Peace Region: SWEs are highest in the southwest and southern parts of the region (greater than 100 mm), grade down to 70 to 80 mm in north-central locations (70 to 80 mm) and are lowest (40 to 50 mm) in the extreme north (Figure 5). For much of the west and extreme southern parts of the region, these snow pack accumulations are generally classified as being at least very high with some areas grading to extremely high for this time of year. In these areas, these snow packs represent a good source of moisture for the spring melt period Figure 6. Across central locations snow pack accumulations are generally classified as moderately high and grade down to moderately low in the north.
Northern Region: SWEs are lowest in the extreme southeast (20 to 30 mm), between 40 to 60 mm in the east and central portions of the region and are highest (greater than 90 mm) in the northwest and across parts of the northeast (Figure 5). Across most of the region, snow pack accumulations relative to long term normal are at least near normal, grading down to very low in the extreme southeast and up to extremely high in the northwest and extreme northeast portions of the region. Figure 6.
Central Region. SWEs are lowest in the south central and south western parts of the region ranging from 10 to 20 mm and increase to 40 to 50 mm in the extreme northwest (Figure 5). In general, across the west half of the region, accumulations relative to the long term normal are at least near normal, grading down to low across most of the east half of the region with the extreme south east classified as having low snow pack accumulations for this time of year (Figure 6).
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 near normal, Figure 6. Snow pack exists in the west along foothills and up in the Cypress Hills, with some areas classified as having extremely high accumulations for this time of year Figure 5. However, high winds and warm chinook temperatures forecast over the next few days should melt significant amounts of snow where snow packs still exist.
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 (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 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 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 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 March 6, 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 December 31, 2006 |
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