| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last report June 22, 2008 wide spread thunderstorm activity and hot and dry weather dominated across most parts of the province. Precipitation accumulations in excess of 20 mm were recorded across much of the Northern and Central Regions, the northern portions of the Peace Region and the western parts of the Southern Region. The rest of the reporting area recorded precipitation in the range of 10 to 20 mm, with the exception of most of the eastern-half of the Southern Region and the south-half of the Peace Region, where less than 10 mm of precipitation was recorded.
Average daily mean temperatures, relative to long term normal, during the past 15 days, varied from high to moderately high across most of the eastern half of the plains reporting areas and the central and northern parts of the Peace Region. The rest of the reporting area recorded very high to extremely high, average daily mean temperatures (Figure 6).
Growing season precipitation accumulations to date (April 1 to July 6, 2008) relative to the long term normal, are at least near normal across most of the reporting area, with the exception of an extended area across much of the Northern Region that is classified as having moderately low accumulations and most of the south half of the Peace Region where accumulations of moderately low to extremely low have occurred. Currently, the western Peace Region, with very low to extremely low soil moisture reserves, requires immediate precipitation and a return to seasonable temperature to ease crop stress already set.
At present, large portions of the central and eastern parts the plains reporting areas have soil moisture levels in the range of 25 to 50 mm, thus the capacity of these areas to resist short term dry spells is rapidly diminishing. In the Peace Region, much of the west and parts of the extreme north have soil moisture levels of less than 25 mm. It is critical that these areas receive immediate precipitation to improve crop moisture stress occurring. Modeled soil moisture reserves relative to long term normal are at least near normal over much of the plains areas, with the exception of few pockets and an extended area in the western part of the Northern Region that has moderately low to extremely low soil moisture reserves. In the Peace Region, soil moisture reserves relative to long term normal, were at least near normal in the centre and graded rapidly to extremely low in the west and to low in the north, the driest in the reporting area.
A large selection of related maps can be found at http://www.agric.gov.ab.ca/acis, under the Quick Viewer tab.
Precipitation
Precipitation since the June 22, 2008 Drought Report (Figure 1)
Since the June 22, 2008 report, precipitation patterns have been dominated by wide spread thunderstorm activity binging variable relief to the hot and dry weather that dominated most parts of the province. Precipitation accumulations in excess of 20 mm were recorded across much of the Northern and Central Regions, as well as the northern portion of the Peace Region and the western part of the Southern Region. The rest of the reporting area recorded precipitation in the range of 10 to 20 mm with the exception of most of the eastern half and northwestern parts of the Southern Region and the south half of the Peace Region, where less than 10 mm was recorded. The highest precipitation accumulations were recorded at Wetaskiwin AGCM station (65.8 mm) in the Northern Region followed by Lethbridge A station (62.5 mm) in the Southern Region.
Peace Region: Precipitation accumulations in the northern and central portions of the Peace Region, as well as parts of the south, ranged from 10 to 40 mm. The rest of the region recorded less than 10 mm. Accumulations in the region were greatest at the La Crete AGCM station (33.2 mm, followed by the Fort Vermillion RS (28.3 mm), both located in the north.
Northern Region: Precipitation accumulations across most of the western, southern and eastern parts of the region were in the range of 20 to 30 mm, grading to isolated pockets of 40 to 70 mm range. The rest of the region recorded precipitation in the range of 10 to 20 mm, with the exception of a pocket along the eastern border of the region with less than 10 mm. The highest precipitation was recorded at Wetaskiwin AGCM station (65.8 mm), followed by the Killiam AGDM station (50 mm), both in southern portions of the region and the lowest amounts were recorded at the Rivercourse AGCM station (6.3 mm) in the east.
Central Region: Precipitation accumulations across most of the region were in the 20 to 30 mm range, with some isolated pockets in the 40 to 50 mm range and some other isolated pockets in the 10 to 20 mm range. Sundre A station (46.7 mm) recorded the highest precipitation in the region followed by Leedale AEDN and Battle River Headwaters stations with 45.8 mm each, all located in the western parts of the region.
Southern Region: In general, with the exception of area around the City of Lethbridge, precipitation accumulations across the region graded from 20 to 40 mm in the west and northwest to a vast area in the central and western parts of the plains where less than 10 mm was recorded. The greatest accumulations were recorded at Lethbridge A station (62.5 mm), followed by the Lethbridge Demo Farm station (43.7 mm), both located in and around the City of Lethbridge. Most of this was due to one particularly intense thunderstorm.
Growing Season Precipitation Accumulations relative to Long Term Normal (1961-2005) (Figure 2)
Growing season precipitation accumulations relative to long term normal (April 1 to July 6, 2008) are at least near normal across the reporting area, with the exception of an extended area, and few pockets in the Northern Region that are classified as moderately low and most parts of the south half of the Peace Region with accumulations in the range of moderately low to extremely low, the lowest in the reporting area.
Peace Region: Growing season precipitation accumulations graded from near normal in the north, central and eastern borders of the region to very low and extremely low in the western parts of the region, the lowest in the reporting area.
Northern Region: A broad and complex polygonal area, that stretches across most of the region received a moderately low growing season precipitation accumulations relative to normal, while the rest of the region received near normal.
Central Region: Growing season precipitation relative to long term normal was at least near normal across most of the region with the moderately high and very high accumulation in the south western part of the region.
Southern Region: In general, growing season precipitation accumulations relative to long term normal are at least near normal across most of the region with several small pockets grading to high.
Average Precipitation Accumulations for July (Figure 3)
July marks the beginning of a drying trend in the Southern Region, but remains one of the wettest months in the year (similar to June) across most of the rest of the reporting area. Historically, the first half of July is typically wetter than the last half. For July, precipitation ranges from 30 to 40 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 4 and Figure 5)
Soil moisture levels in the plains reporting areas are generally higher in the west (75 to 125 mm) and grade down to a 25 to 50 mm range across a broad strip that runs from the central parts of the Northern Region, down through most of the eastern half of the Central Region extending through the central and eastern parts of the Southern Region. Across the Peace Region, soil moisture reserves graded from 50 to 100 mm in the central and central-east parts, to less than 25 mm across much of the western and extreme northern parts of the region. With respect to modeled long term normal in the plains reporting areas, reserves are generally at least near normal across the Central, Southern and east-half of the Northern Region, then grade to very low, in the western and northeastern parts of the
Northern Region. In the Peace Region, the central parts of the region are at least near normal, but the reserves across the western and southern extremes of the region are in a very low to extremely low range, the driest in the reporting area.
Peace Region: Across the east central parts of the region soil moisture levels are highest (75 to 100 mm), grading rapidly to below 25 mm across much of the west half and extreme northern parts of the region. Moreover, modeled soil moisture reserves relative to long term normal graded from near normal to moderately high levels in the east central parts of the region to low and very low levels in the north and very low to extremely low levels in the western and south-western parts of the region.
Northern Region: Generally, soil moisture is lowest (25 to 50 mm) in an extended band starting in the west central parts of the region that stretches to the southeastern corner of the region. Elsewhere, soil moisture levels are typically in the 50 to 75 mm range. Relative to long term normal, reserves are generally near normal across most of the eastern half of the region and grade down to very low in the west, low in the northeast and moderately low in the southeast.
Central Region: Soil moisture levels in the region were lowest in the east (25 to 50 mm) grading upwards to 125 mm in the extreme west. Relative to the long-term normal condition are at least near normal, with moderately high-to-high reserves found in the south and west central portions of the region.
Southern Region: Soil moisture levels in the region were lowest across the east half of the region grading to over 125 mm in the extreme northwest. Relative to the long term normal, soil moisture conditions are near normal for the most of the region.
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 Rural Development (ARD) 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 ARD, 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.
Soil moisture
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.
Report prepared by the Drought Reporting Team
Ralph Wright, Daniel Itenfisu and Isabel Simons-Everett
Alberta Agriculture, and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on July 10, 2008.
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 created on June 26, 2008. |
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