| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last Drought Report, July 3, 2006, hot weather has prevailed over much of the province. The extreme heat has been accompanied by significant thunderstorm activity, making precipitation variable across most of the reporting area. With the extreme heat and recent dry weather, crop moisture stress is a concern in many areas, particularly where crops are in, or entering sensitive stages of development. Cooler, wet weather is needed immediately, in many areas, to alleviate crop heat and moisture stress.
In general, over the past 20 days, the Southern Region and the eastern parts of the Central Region were the driest, with less than 10 mm being recorded in most areas. Through the western parts of the Central Region and southern half of the Northern Region less than 30 mm was recorded. North of Highway 16, between Edmonton and Lloydminster, precipitation amounts tended to be higher, ranging from 30 mm to 85 mm. Across the Peace Region, precipitation ranged from less than 20 mm in the south and northwest, to more than 100 mm in the north.
Since the start of the growing season (April 1, 2006), extremely low precipitation accumulations have occurred in the north-western parts of the Central Region affecting Ponoka and Lacombe Counties and to some extent Red Deer County. Elsewhere in the Central Region and over much of the Southern Region, at least near normal accumulations have occurred. In the Northern Region, moderately low accumulations have occurred along the western, northern and southern border areas, and extend up into central locations with some areas grading to low, south of the City of Edmonton and in Flagstaff County. Much of the Peace Region has experienced near normal growing season precipitation with the exception of the north, which has experienced moderately high accumulations, in contrast to parts of the northwest, northeast and south, where moderately low accumulations have occurred.
Across most of the reporting area, soil moisture reserves are rapidly being depleted and are now below 25 mm, a condition requiring immediate precipitation and a return to moderate temperature regimes. Areas with adequate moisture currently exist in and around the City of Calgary, the northern tip of the Peace Region and small pockets in the northern and eastern parts of the Northern Region. However, with crop water use peaking, these areas will also need cooler temperatures and more precipitation soon. Nevertheless, soil moisture reserves relative to the long term normal (1961 to present) over most of the southern third of the reporting area are at least near normal, with reserves quickly grading to extremely low across much of the western half of the Northern Region, and southern half of the Peace Region (a condition occurring on average, less than once in 30-years).
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 July 3, 2006 Drought Report (Figure 1) - Hot and dry weather has continued to dominate weather patterns since the last report, leading to crop moisture stress and rapid depletion of soil moisture reserves over most areas. Precipitation is needed immediately across most areas of the province, except for the northern and eastern portions of the Peace Region, where precipitation in some areas is considered to be in excess.
Peace Region: Precipitation accumulations ranged from 12.9 mm at the Clear Dale AGDM station in the M.D. of Clear Hills to 113.3 at the High Level A station. In general, precipitation was greatest (>100 mm) in the North and least (< 20 mm) in the northwest and extreme south.
Northern Region: Precipitation was quite variable over the region, with the least amounts recorded at the Atmore station (14.8 mm) in the County of Athabasca, 16.7 mm at the Holden AGDM station in Beaver County and 16.3 mm at the Edmonton Int'l A near Edmonton. The greatest amounts of precipitation were recorded in the east at the Lindbergh AGDM station (71.1 mm) in the County of St. Paul, and at the Abee AGDM station (85.3 mm) in the County of Thorhild.
Central Region: The least amount of precipitation was recorded in the east with less than 6 mm falling at a number of stations across the Special Areas, and ranged up to over 40 mm in the City of Calgary. Generally, the western half of the region recoded between 20 to 40 mm, with the exception of a large area around the City of Reed Deer, where 10 to 20 mm was recorded, and across the east half of the region were less than 10 mm was recorded.
Southern Region: Much of the Southern Region recorded less than 10 mm of precipitation, with a few widely scattered pockets receiving between 10 to 20 mm.
Growing Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2) - Despite adequate growing season precipitation to date, a month or so of hot dry weather has lead to concerns of crop moisture stress and reduced potential yields, as crops move into critical stages of development. Precipitation and a return to more moderate temperatures, is needed immediately across most areas of the province.
Peace Region: Growing season precipitation to date has been at least near normal with moderately low accumulations in the northwest, southwest and Southeast. In contrast, moderately high to high precipitation accumulations have occurred across the north.
Northern Region: Across much of the region, growing season precipitation to date has been adequate (at least near normal) with the exception of south and east central areas, and extreme western and northern areas where moderately low to low accumulations have occurred.
Central Region: Several pockets of extremely low precipitation accumulations were recorded, affecting the eastern and western extremes of Ponoka and Lacombe Counties, in addition to very low accumulations in the eastern parts of Red Deer County. Across the eastern and southern half of the region, near normal precipitation accumulations have occurred.
Southern Region: In general, growing season precipitation to date has been at least near normal, with several pockets of moderately high accumulations across the east and north, and a few pockets of moderately low on the west and southwest portions of the region.
Long Term Conditions: 365-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - Generally, the north half of the reporting area has experienced at least moderately low or lower, precipitation accumulations over the past year, with several areas classified as having extremely low precipitation accumulations. In contrast, across the south half of the reporting area, precipitation accumulations have been at least near normal, with many areas grading up to high or more.
Peace Region: Much of southeast portion of the region has experienced extremely low precipitation accumulations over the past 365-days. This grades to low through the central parts of the region and up to near normal in the north and southwest.
Northern Region: Most of the region has recorded moderately low-to-low precipitation accumulations with a few pockets in the north recording extremely low accumulations. In contrast, the eastern portion of the region have recorded at least near normal, grading to high around the town of Lloydminster.
Central Region: Most of the region has recorded at least near normal precipitation, grading up to extremely high in the west. The driest areas are in the northwest, grading to low.
Southern Region: Precipitation accumulations are generally near normal in the southeast, with one exception of moderately low in the extreme southeast, grading to moderately high in the west, and to extremely high across the north.
Average Precipitation Accumulations for August (Figure 4) - Typically the first half of August is wetter than the last half and this month marks the beginning of a drying trend for most of the reporting area, with the exception of the Southern Region, where July tends to mark the start of drier conditions. For August, average precipitation typically ranges from 30 to 40 mm in the southeast, to greater than 70 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) - Current soil moisture levels are below 25 mm throughout much of the reporting area. With hot dry weather, soil moisture reserves of this magnitude are not sufficient to sustain crop water demands. As a result, immediate precipitation is needed, as well as a return to more seasonal temperatures.
Peace Region: The south half of the Peace Region has soil moisture levels less than 25 mm, grading to 50 to 75 mm in the north.
Northern Region: Most of the region has less than 25 mm of soil moisture with the exception of areas in the extreme east, centered on the town of Lloydminster, and a small pocket in County of Thorhild where 50 to 75 mm of soil moisture remain
Central Region: Soil moisture grades from a low of 25 mm in the east to upwards of 50 to 75 mm in the west, along the foothills.
Southern Region: Soil moisture levels are the greatest in the northwest (50 to 75 mm) and grade down to less than 25 mm east.
Long Term Average Soil Moisture Conditions (Figure 6) - At this time of year soil moisture reserves are typically lowest in the eastern parts of reporting area 50-75 mm, grading upwards towards the west to greater than 100 mm along the foothills. The lowest soil moisture conditions in the reporting area are typically found in southeastern parts of the Central Region (20 to 25 mm). Elsewhere, across the Peace Region, normal soil moisture reserves for this time of year are 75 to 100 mm, with the driest areas found in the center (50 to 75 mm).
Current Soil Moisture Reserves relative to Long Term Normal (1961 - 2005) (Figure 7) - Soil moisture reserves computed for the report date (Figure 5), were compared to modeled soil moisture values, using the historical weather data from the same date during the 1961 to current period, and are expressed as a "frequency of occurrence", which shows how often current soil moisture reserves of a similar magnitude have occurred in the past (1961 to 2005).
Over most of the south, one third of the reporting area, soil moisture reserves are at least near normal. Reserves quickly graded to extremely low across much of the western half of the Northern Region, and southern half of the
Peace Region. Soil moisture reserves classified as extremely low occur on average, less than once in 30-years
Peace Region: Soil moisture reserves are highly variable across the Peace Region with extremely low reserves found in the extreme south, and western border areas. Reserves then grade to moderately low in central areas, up to near normal in the north.
Northern Region: Like the Peace Region, reserves are highly variable across the region, ranging from extremely low in the southwestern, central and extreme northeastern areas, to near normal in the east with some similar pockets, found to lesser extent in north central areas.
Central Region: Soil moisture reserves are extremely low in the northwest, grading to moderately low in the north and west, up to near normal in the southern half of the region. However, recent hot weather has been severe enough to overcome normal reserves, with concerns of crop moisture stress prevalent through most of the region.
Southern Region: Soil moisture reserves across most the region are at least near normal, grading to moderately high in north central areas, and down to moderately low along the foot hills. Recent hot weather has been severe enough to exceed the capacity of the soil to provide moisture to crops, despite normal or better reserves in many areas. The result is crop moisture stress, which appears to be prevalent through 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 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,
- The growing season to date
- Winter precipitation to date.
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 dryer, 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:
| extremely low | drier than this, on average, less than 1 once in 30-years |
| very low | drier than this, on average, less than 1 once in 20-years |
| low | drier than this, on average, less than 1 once in 10-years |
| moderately low | drier than this, on average, less than 1 once in 4-years |
| near normal | on average, this occurs 5 in 10-years |
| moderately high | wetter than this, on average, less than 1 once in 4-years |
| high | wetter than this, on average, less than 1 once in 10-years |
| very high | wetter than this, on average, less than 1 once in 20-years |
| extremely high | wetter than this, on average, less than 1 once in 30-years |
Snow pack (reported during the winter season only)
Snow pack snow water equivalents (SPWE) are modeled for stubble fields. SPWE is defined as the equivalent depth of water (mm) that the snow pack contains if it were to be melted. SPWE 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 SPWE.
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 Normal 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 normal. 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 Normal. However, the process is currently unable to account for snow currently existing on the ground and as such is not 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 July 23 2006.
Drought analysis is currently scheduled at monthly intervals between October 31and April 3, and twice monthly from May 1 to September 30 . This report updates the previous report of July 3, 2006. |
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