| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last Drought Report (June 12th, 2006), hot weather has prevailed over much of the province. Across the reporting area an abrupt change in precipitation pattern from north to south exists, with most areas north of Highway 12 receiving below average precipitation and those areas to the south of Highway 12, receiving near normal or better. Across the Peace Region, central locations received less than 10 mm, ranging to a high of 42.2 mm in the southeast. Across the Northern Region, precipitation ranged from a low of 5.7 mm in the Vegreville area, to 20 to 30 mm across much of the central portions, and as much as 50 mm was recorded at a some stations across the north. Across the Central Region, precipitation has been generally adequate, with the least amounts (25 mm) falling in the eastern parts of Lacombe County, grading to as much as 74.5 mm in the east near the Town of Oyen and upwards of 100 mm in the southwest. Heavy thunderstorm activity brought significant precipitation to much of the Southern Region, with several locations recording well over 100 mm of precipitation, with flooding reported in several areas.
Since the start of the growing season, April 1, 2006, much of the province has received at least near normal precipitation, with exceptions in the north western parts of the Central Region where very low accumulations have occurred and scattered pockets of moderately low through the Northern and Peace Regions
Over the long term, the past 365-days, several areas in the Peace Region recorded extremely low precipitation accumulations; with these areas growing rapidly in size since the last report. Across the west half of the Northern Region, moderately low to low precipitation accumulations have occurred, with some areas in the extremely low category. Elsewhere across the reporting area precipitation accumulations have been at least normal, with the northern parts of the Southern Region and eastern parts of the Central Region showing extremely high precipitation accumulations.
Despite near normal growing season precipitation to date, recent hot weather combined with low soil moisture reserves across much of the Peace Region and the west and central parts of the Northern Region have lead to some concerns of crop moisture stress. Precipitation is needed immediately to prevent yield losses due to moisture stress. Currently in the Peace Region, soil moisture reserves are low to extremely low throughout most of the region. In the Northern Region, soil moisture reserves range from moderately low in the center to extremely low in the west. Elsewhere across the reporting area, soil moisture reserves are at least near normal with parts of southern and Central Regions having reserves ranging from moderately high to extremely high.
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 June 12th, 2006 Drought Report (Figure 1) - Over the past week, hot dry weather has settled in across the province, bringing the immediate need for more precipitation, particularly across most of the northern half of the reporting area. In general, the Northern and Peace Region received less than 30 mm, with many areas in the Peace Region receiving less than 20 mm. In stark contrast, the Central and Southern Regions received over 50 mm with several locations in the Southern Region reporting over 120 mm of precipitation.
Peace Region: Precipitation accumulations ranged from a low 8.1 mm at the Peroria AGDM station in Birch Hills County to a high of 42,2 mm at the Ballater Station in the M.D. of Smoky River. With the exception of Ballater, most areas received less than 20 mm with slightly more falling in the north at the Fort Vermillion RS station (28.2 mm).
Northern Region: The least amounts of precipitation were recorded in the center and extreme north east with 5.7 mm recorded at the Vegreville station and 5.2 mm reported at the Cold Lake A station. In addition, much of the east central portions of the region received less than 20 mm of precipitation, grading up to 20 to 30 mm for most of the rest of the region, with the exception of a few widely scattered pockets across the northern half of the region were upwards of 50 mm was recorded.
Central Region: The least amount of precipitation (25.0 mm) was recorded in the north at the Parlby Creek Near Mirror Station in the County of Lacombe, grading up to 111.4 mm at the Calgary Int'l A station in the south west and to 74.7 mm at the Oyen AGDM station in the east
Southern Region: Heavy thunderstorm activity brought variable amounts of precipitation over the region, but generally all areas received adequate precipitation. Several locations reported over 120 mm with localized flooding. Elsewhere, most of locations received at least 50 mm with the least amount (33.5 mm) recorded at the Shuler AGDM station in Cypress County.
Growing Season Precipitation Accumulations Relative to Long Term Normal (Figure 2) - Overall, growing season precipitation to date, has been adequate across most of the reporting areas, with exception in the central and north eastern parts of the Northern Region and north central and south western parts of the Peace Region and the north western parts of the Central Region. Unfortunately, these areas are tend to have low to extremely low soil moisture reserves, thus, recent hot weather has resulted in poor growing conditions, particularly in those crops that are at sensitive stages of development.
Peace Region: Across most of the region at least near normal accumulations with a few pockets of moderately low accumulations. However, recent hot weather coupled with extremely low soil moisture reserves are resulting in poor growing conditions.
Northern Region: Most of the Region has at least near normal precipitation accumulations with few pockets grading down to moderately low. Despite this, recent hot weather coupled with low soil moisture reserves in the central and western parts of the region have resulted in poor growing conditions.
Central Region: Most of the Region has at least near normal precipitation accumulations with some extremely low accumulations western portion of the County of Ponoka and Lacombe. Across the northwest, hot dry weather coupled with low soil moisture reserves have resulting in poor growing conditions. In contrast, the southeast portion of the region has moderately high to very high accumulations.
Southern Region: Most of the region recorded at least near normal precipitation. Recent thunderstorm activity has resulting in significant accumulations over much of the east half of the region, with some parts of the north central portions of the region reporting extremely high accumulations.
Long Term Conditions: 365-Day Precipitation Accumulations Relative to Long Term Normal (Figure 3) - Generally speaking, the north half of the reporting area has experienced at least moderately low 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: Lack of recent precipitation has resulted in an increase in those areas classified as having experienced extremely low precipitation accumulations. These areas are currently centered on the Towns of Manning, Grand Prairie and Valley View, and also parts of Birch Hills County and the M.D's of Big Lakes, Lesser Slave River and Green View.
Northern Region: Lack of recent precipitation has resulted in an increase in those areas classified as having experienced low to extremely low precipitation accumulations. Across the central and western portion of the region, most areas have received at least moderately low accumulations, with several areas in the low category and two pockets in the extremely low category. One in Westlock County, and one centered on the Town of Vegreville. Eastern parts of the region are fairing much better with near normal accumulations grading to high around the town of Lloydminster
Central Region: Most of the region is at least near normal, with the driest areas in the northwest, grading down to low, and the southwest and east grading up to extremely high.
Southern Region: Precipitation accumulations are near normal in the southeast, grading to moderately high in the west, and to extremely high across the north.
Average Precipitation Accumulations for July (Figure 4) - 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 the rest of the reporting area. Historically, the first half of July is typically wetter than the last half. For July in the southeast, precipitation ranges from 30 to 40 mm to greater than 100 mm across the western parts of the Northern Region and southeastern parts of the Peace Region. Across the Peace Region and much of the Northern Regions normal or above normal precipitation, with near normal temperatures, is needed to insure adequate moisture for crop growth and prevent crop losses associated with heat stress.
Soil moisture
Soil moisture in the agricultural regions of Alberta (Figure 5) - Soil moisture levels are low or worse, throughout much of the west half of the Northern Region and almost all of the Peace Region. In contrast, soil moisture levels are adequate to excellent throughout the Central and Southern Region.
Peace Region: Hot dry weather has depleted soil moisture reserves significantly over the past few weeks. Most the Region has less that 25 mm of soil moisture reserves and precipitation is needed immediately. Throughout the central portions of the region, soil moisture is generally between 25-50 mm and under cool conditions crops have only about a week of reserves left. Precipitation is needed immediately to reduce crop moisture stress.
Northern Region: Less than 25 mm of moisture remains in several pockets in the northeast, including one centered on the Town of Vegreville. Precipitation is needed immediately here and a return to cooler conditions will help alleviate severe moisture stress. Much of the region is dominated by soil moisture levels in the 25- 50 mm range, grading to 50-75 mm in the west and up to 100 to 125 mm in the east, centered on the Town of Lloydminster.
Central Region: Soil moisture levels are the greatest in the west, 100-125 mm, and grade down to 50-75 mm in the east half of the region.
Southern Region: Soil moisture levels are the greatest in the west, 100-125 mm, and grade down to 50-75 mm in the southeast.
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 moving westward 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). Across the Peace Region, normal soil moisture reserves for this time of year are typically 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 (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 half of the reporting area, soil moisture reserves are at least near normal. In stark contrast, across the north half of the reporting area soil moisture reserves range from moderately low across most of the Northern Region to extremely low in the Peace Region.
Peace Region: Lack of rainfall in combination with above average temperatures, has lead to significant depletion of soil moisture reserves since the last report. Much of the area is in dire need of cooler temperatures coupled with above average precipitation, as soil moisture reserves are extremely low. In central locations, conditions are slightly better, grading to near normal in the M.D of Smoky River.
Northern Region: Hot dry weather has depleted soil moisture reserves across the region. Reserves are extremely low in the west and extreme north west, grading to moderately low across much the central parts of the region and are at least near normal in the east.
Central Region: Most of the region has at least near normal soil moisture reserves with low reserves found in the northwest and very high reserves found in some parts of the extreme southeast.
Southern Region: Soil moisture reserves across most the region are at least near normal, grading to extremely high in north central areas and downs to moderately low in a few isolated pockets along the foothills.
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 check by Alberta Agriculture (AAFRD) staff, assisted by 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 site or from 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 this 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 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:
| 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 millimeters (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 Policy and Development Branch
Alberta Agriculture, Food and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on July 3, 2006.
Drought analysis is currently scheduled at monthly intervals between October 30 and May 1. This report updates the previous report of June 12, 2006. |
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