| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the April 30, 2007 drought report, precipitation was highly variable across the reporting area with no concern for inadequate precipitation. Many areas have received too much precipitation which, combined with low temperatures, has lead to excessive moisture resulting in significant seeding delays. Generally, the least amount of precipitation (less than 30 mm) was recorded in the eastern parts of the Northern, Central and Southern Regions increasing westward, to more than 100 mm.
Growing season precipitation accumulations to date (April 1, 2006 to May 27, 2007), relative to the long term normal, are at least near normal across the entire reporting area, with most areas recording high to very high accumulations. Much of the west half of the Central Region, parts of the Swan Hills and areas surrounding the City of Grand Prairie in the Peace Region have received extremely high accumulations. For most areas of the province lack of moisture is not an immediate concern, in fact, large parts of the province had excessive growing season precipitation to date.
Since the April 30, 2007 report, the 365-day precipitation accumulations relative to long term normal have declined from low to moderately low in the northwestern and southeastern Peace Region and are now classified as very low. However, this does not mark a drying trend since precipitation over the past several months has generally been at least near normal. This serves as a reminder that it is important to refer to more than one map to draw inferences on the moisture situation. The apparent decline compared to the last report, occurs because May of 2006 was above normal and is no longer a part of the current 365-day window (May 28, 2006 to May 27, 2007).
Elsewhere across the reporting area, the 365-day accumulations to date are generally at least near normal with parts of the western and north-central portions of the Central Region, grading up to extremely high. The driest areas are currently in the northeastern parts of the Northern Region and northeastern parts of the Central region (moderately low), and south of the City of Lethbridge in the County of Cardston, along the US border (very low).
The provincial soil moisture survey is now complete and data collected during this exercise has been used to initialize the soil moisture model. This year's survey was significantly delayed due to lingering snow packs in the Peace Region and frozen soils in the Central and Northern Regions. Currently most of the west half of the Central, Northern and Southern Regions has soil moisture levels in excess of 100 mm. Across the eastern portions of these regions soil moisture levels are generally in the 50 to 75 mm range. Across the Peace Region, soil moisture levels grade from more than 125 mm in the southeast to 75 to 100 mm in the north. For this time of year, most of the reporting area is classified as at least near normal, with several areas grading to high or more.
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 April 30, 2007 Drought Report (Figure 1) - Since the last report, precipitation was variable ranging from 10 to 20 mm across the south eastern and north eastern parts of the Northern Region to well over 120 mm in the north western parts of the Central Region and over the Swan Hills.
Peace Region: Overall the Peace Region has received significant precipitation since the last report, ranging from 90 to 100 mm in the southeast down to 40 to 50 mm in the northwest.
Northern Region: Precipitation accumulations ranged from 14.6 mm at the Cadogan AGCM station in the M.D of Provost to 119.5 mm at the Breton Plots Station in the M.D of Brazeau located in the South West. In general, precipitation was lowest (greater than 40 mm) in the east and east-central locations, grading to well over 80 mm in the west.
Central Region: Precipitation accumulations ranged from 22.5 mm at the Consort AGDM station in the northeast (Special Area 4) to 136.6 mm in the southwest (Dickson Dam Auto station in the County of Red Deer). With the exception of the northeast, precipitation ranged from 40 to 60 mm in the east to well over 100 mm in the west. Generally, most of the west half of the region has received sufficient precipitation to hamper seeding efforts and raise concerns of too much moisture. Warmer drier conditions are needed to complete seeding and encourage germination and crop growth
Southern Region: Precipitation accumulations ranged from 21.0 mm at the Pakowki Lake AGCM station in the County of Forty Mile to 108.0 mm at Porcupine Lookout Station in the M.D of Ranch Land. Over all precipitation graded from 20 to 30 mm in the northeast and south east to well over 80 mm in the northwest and west, along the foothills.
Growing Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2) - Growing season precipitation accumulations have been at least near normal throughout the reporting area, grading to extremely high across most of the west half of the Central Region, northern parts of the Southern Region and some western locations in the Northern Region. Across the Peace Region, growing season precipitation to date is at least high with one area centred on the City of Grande Prairie, grading to extremely high.
Peace Region: Most of the region has received at least high growing season precipitation to date. Late snowmelt, in combination with cool wet weather has hampered seeding operations. However, those areas where low fall soil moisture reserves were of great concern are now showing adequate soil moisture reserves.
Northern Region: The lowest amounts of growing season precipitation to date were recorded in the southeastern portions of the region and are classified as moderately low. With this exception, most of the east half of the region ranges from near normal to moderately high, which then grades to high and very high across the west with some locations classified as extremely high. Drier, warmer conditions are needed in these areas to allow seeding to continue.
Central Region: Most of the region has received at least moderately high growing season precipitation to date, with much of the west half of the region classified as extremely high.
Southern Region: Most of the south half of the region has received near normal to moderately high growing season precipitation to date, grading to extremely high in the north central portions of the region.
Long Term Conditions: 365-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - The 365-day precipitation accumulations have continued to improve across most of the reporting area, particularly in the northwestern parts of the Central Region (extremely high) and in the northern parts of the Southern Region, where accumulations are high.
In contrast, 365-day accumulations have decreased in the northwestern portions of the Peace Region and across the northeastern parts of the Northern Region, suggesting a drying trend in these areas. Over the past several months, precipitation has been at least near normal and the apparent drying in these areas is an artefact of the current 365-day window. During May of 2006, accumulations in these areas ranged from high to extremely high. The April 30, 2007, 365-day map included these accumulations, were as the May 27, 2007 map does not, thus it appears that these areas are drying when in fact they are not. This serves as a reminder that it is important to refer to more than one map to draw inferences on the moisture situation.
Peace Region: Most of the Peace Region is now classified as at least near normal with parts of the northwest and southeast grading down to very low. However, precipitation over the past several months in these areas has been at least near normal and as a result, there is no immediate cause for concern.
Northern Region: Accumulations range from moderately low in the northeast and grade upwards to high in the southwest. In the northeast, precipitation accumulations over the past several months has been at least near normal and as a result, there is no immediate cause for concern here.
Central Region: Accumulations in the east range from moderately near normal to high and then grade up to extremely high in the northwest.
Southern Region: Across the Southern Region, 365-day precipitation accumulations are at least near normal with the exception one pocket of very low in Cardston County and one pocket of low in the M.D. of Pincher Creek. The highest accumulations are generally confined to the north and extreme east (Cypress Hills) where they are classified as high.
Average Precipitation Accumulations for June (Figure 4) - June is typically one of the wettest months in the year with precipitation accumulations ranging from 60 to 70 mm in the southeast to greater than 100 mm across the western parts of the Northern Region and southeastern parts of the Peace Region.
Soil moisture
Soil moisture in the agricultural regions of Alberta (Figure 5 and Figure 6) - Lingering snow packs, wet weather and frozen soils delayed the completion of the spring soil moisture survey, which started on April 4, 2007 and was completed on May 14, 2007, two weeks behind the target completion date of May 1, 2007. Sampling started in the southeastern parts of the province and progressed northward. The Peace Region was surveyed during the first week of May, while much of the Northern Region was completed during the second week of May. The soil sampling data was used to initialize the soil moisture model.
Since the fall (October 31, 2006 Drought Report), soil moisture levels have increased dramatically across most of the reporting area, due to the above average precipitation that was received during the cold season and throughout April and May of 2007. Of note is the fact that the previously dry areas in the western parts of the Peace Region have recovered due to near record snow packs and well above average spring rains. In these areas, soil moisture levels are in excess of 100 mm and are classified as having at least near normal soil moisture reserves Figure 6. Currently there are concerns over too much moisture in many parts of the reporting area, with soil moisture reserves that range from very high to extremely high. This, combined with cool temperatures and late melting of snow packs, has hampered seeding activities throughout much of the reporting area.
Peace Region: North of the town of Peace River, soil moisture levels generally range between 75 to 100 mm. The highest soil moisture levels (greater than 125 mm) are found through the central parts of the region, Figure 5. Currently reserves range from near normal across the north up to very high in the centre and again to near normal in the extreme west Figure 6.
Northern Region: Soil moisture levels range from 50 to 75 mm in the northeast and southeast and grade up to more than 125 mm across much of the west Figure 5. Soil moisture reserves range from near normal in the northeast, moderately high in the west and southeast, and up to at least high across central portions of the region, Figure 6.
Central Region: Soil moisture ranges from 25 to 50 mm in a small pocket in the east (Special Area 4) up to more than 125 mm across the entire western half of the region Figure 5. Over all soil moisture reserves for this time of year are generally extremely high, with the exception of the extreme northeast where they grade down to normal, Figure 6.
Southern Region: Soil moisture levels are lowest (50 to 75 mm) in the southeast and grade to more than 125 mm along the foothills in the northwest Figure 5. The south half of the region is mostly at least near normal grading up to extremely high in the north and northwest, 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 Occurence |
| 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 and Program Policy Development and Coordination Branch
Alberta Agriculture and Food
Contact: Ralph Wright; ph 780-427-3556
This report was created on May 30, 2007 and updates the previous report of April 30, 2007.
Drought analysis is currently scheduled at monthly intervals between October 31 and April 31, and twice monthly from May 1 to September 30. |
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