| | Precipitation | Soil moisture | Data sources | Explanation of Terms
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Summary
Since the last Drought Report (May 27, 2007), precipitation ranged widely across the reporting area with less than 10 mm recorded across the northern tip of the Peace Region to well over 200 mm in the western parts of the Central Region. Areas that have received relatively low amounts of precipitation include the northern tip of the Peace Region (less than 10 mm), several widely scattered pockets in the Southern Region (30 to 40 mm), and parts of the County of Newell received only 20 to 30 mm. Elsewhere, the County of Paintearth (Central Region) received only 30 to 40 mm and in the Northern Region, two areas of relatively low precipitation accumulation (30 to 40 mm) can be found; one near the town of Mundare and one near Lac La Biche. Precipitation is needed in those areas that have received low precipitation accumulations over the past 30-days to insure the crop moisture stress does not develop.
Growing season precipitation accumulations to date (April 1 to May 27, 2007), relative to the long term normal, are at least near normal across the entire reporting area. Most of the west half of the Central Region, and parts of the Swan Hills have received extremely high accumulations. The lowest accumulations are confined to a few pockets in the south-western corner of the Southern Region and the south-eastern portions of the Northern Region. For most areas of the province, lack of moisture is not an immediate concern. In fact, central parts of the reporting area have had excessive growing season precipitation to date.
Precipitation over the past 30-days has been at least near normal across for most of the region. However, precipitation accumulations in the northern Peace Region (M.D. of Mackenzie) are classified as very low signifying a dire need for precipitation there. Elsewhere, low accumulations can be found in a number small pockets, including the northern parts of the M.D of Big Lakes (Peace Region), the southern parts of Lakeland County (Northern Region) and across the Southern Region in the MDs of Pincher and Willow Creek, and the southern parts of the County of Newell.
Currently most of the western half of the Central, and Northern Regions, as well as the central portions of the Peace Region and northern parts of the Southern Region, have soil moisture reserves that are classified as at least high, with much of the Central Region classified as having extremely high reserves. Soil moisture reserves that are below normal can be found in the northern parts of the Peace Region, currently classified as low, and south-western parts of the Southern Region, classified as low to moderately low. Areas with low or worse soil moisture reserves have generally received below normal precipitation over the past 30-days and are now susceptible to crop moisture stress. Precipitation in these areas is needed now.
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 May 27, 2007 Drought Report (Figure 1) - Since the last report, precipitation across the region ranged widely from less than 10 mm across northern tip of the Peace Region to well over 175 mm in the north-western parts of the Central Region and over the Swan Hills.
Peace Region: Precipitation across the Peace Region has been highly variable, ranging from 7.2 mm at the Fort Vermillion RS station to 81.8 mm at the Peace River A station. With the exception of a few areas, at least 50 mm has fallen across the region with lesser amounts 34.9 recorded at the Beaver Lodge RCS station in the southwest and 28.0 mm recorded at the Peavine Station in the extreme east, in the northern parts of the M.D of Big Lakes.
Northern Region: Precipitation accumulations were the lowest at the Mundare AGDM station (28.7 mm) and Lac La Biche Stations (33.7 mm) and greatest at the White Court A station (165.8 mm). Generally, the lowest accumulations were in the central and north-eastern portions of the region (40 to 60 mm) and highest in the south, southeast and northwest > 100 mm.
Central Region: Precipitation accumulations ranged from 35.7 at the Alliance AGCM station in the County of Paintearth to 243. 6 mm at the Red Deer A station. Over all, the east central portions of the region received the least amounts of precipitation (40 to 70 mm) while the eastern parts of the region received more the 70 mm and the west half of the region more than 100 mm. Currently the biggest concerns to farming operations are from excess moisture, particularly west of Highway 2 between Town of Lacombe and the City of Calgary.
Southern Region: Precipitation accumulations ranged from 25.6 mm at the Rolling Hills AGCM station in the County of Newell to 108.0 mm at the Bassano AGCM station, also in the County of Newell. Generally, most of the region has received at least 40 mm of precipitation, with a few widely scattered pockets receiving less (30 to 40 mm). In these areas, precipitation is needed soon particularly for those crops that do not benefit from irrigation.
Growing Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2)- Growing season precipitation accumulations have been at least near normal throughout most of the reporting area, grading to extremely high across most of the west half of the Central Region, northern parts of the Southern Region and extreme western and southern parts of the Northern Region.
Peace Region: To date, growing season precipitation is at least near normal across the entire region, grading to moderately high across most of the south, with a few locations in the centre and south central portions of the region grading to high. Across the north, the entire areas is classified as near normal, despite less than 10 mm of precipitation falling since the last report Figure 1. Precipitation is needed now across the north, particularly in and around the Hamlet of Fort Vermillion.
Northern Region: The lowest amounts of growing season precipitation to date were recorded in the south-eastern portions of the region where moderately low accumulations have fallen. 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 in the extreme north west and southern portions of the region.
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.
30-Day Precipitation Accumulations relative to Long Term Normal (1961 – 2005) (Figure 3) - The 30-day precipitation accumulations have been at least near normal across most of the reporting area with some exceptions. These areas are generally confined to the extreme southern, south-western and north-central parts of the Southern Region (low to moderately low), the northern and eastern extremes of the Peace Region classified as very low and low, respectively, and several widely scattered pockets of low in the Northern Region.
Peace Region: Most of the Peace Region is now classified as at least near normal. However, one area of concern is beginning to emerge as a large pocket of very low is developing in the north, in and around the Hamlet of Fort Vermillion. Elsewhere moderately low accumulations can be found in the western portions of the County of Grande Prairie near the Town of Beaver Lodge, and one small pocket classified as low can be found in the extreme east parts straddling the Boarder between Northern Sunrise County and the M.D. of Big Lakes.
Northern Region: 30-day accumulations are generally at least near normal across most of the region with three widely scattered and isolated pockets that grade down to moderately low and one small pocket in the south western parts of Lakeland county centred on the Town of Lac La Biche grading to low.
Central Region: 30-day accumulations relative to normal are at least near normal throughout the entire region with the exception of a small pocket of moderately low found in the centre of the County of Paintearth. Of note is the extremely high accumulations found across the Northwest, which includes the City of Red Deer.
Southern Region: Across the Southern Region, 30-day precipitation accumulations range from moderately low to low in the south and east central portions of the region, up to moderately high in the northwest. Low accumulations in the south west are of concern since soil moisture reserves in these parts are classified as moderately low to low Figure 6. These areas need precipitation now to alleviate moisture stress in crops.
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, precipitation ranges from 30 to 40 mm in the southeast, to greater than 100 mm across the western parts of the Northern Region and south-eastern parts of the Peace Region.
Soil moisture in the agricultural regions of Alberta (Figure 5 and Figure 6)
Soil moisture reserves are generally at least near normal across most of the reporting area, with a few areas in the southern parts of the Southern Region, grading to moderately low to low and in the extreme northern parts of the Peace Region grading to low or extremely low. Currently most of the west half of the Central Region has soil moisture reserves classified as extremely high, a condition that may limit trafficability for post season field operations.
Peace Region: North of the Town of Peace River, soil moisture levels generally range between 75 to 100 mm and then decrease to less 25 to 50 mm in the extreme north. The highest soil moisture levels (> 125 mm) are found through the south central parts of the region, Figure 5. Currently reserves range from low to very low across the north, and up to very high in the centre Figure 6.
Northern Region: Soil moisture levels range from 50 to 75 mm in a small pocket in the east and grade quickly up to greater than 125 mm across the west half of the region. Figure 5. Over all, soil moisture reserves range from near normal in the east, to at least high in the west with the greatest reserves relative to normal ranked as extremely high across much of the southwest, Figure 6.
Central Region: Soil moisture ranges from 25 to 50 mm in a small pocket in the east (Special Area 3) up to more than 125 mm across the entire western half of the region (Figure 5). Soil moisture reserves for this time of year are generally extremely high with the exception of northeast where they grade down to normal, Figure 6.
Southern Region: Soil moisture levels are lowest (25 to 50 mm) in the southeast and grade to more than 125 mm in the northwest Figure 5. Most of the region is at least near normal and then grades up to extremely high in the north. However, much of southwest corner of the region is classified as moderately low with one small pocket of low found in the M.D. of Pincher Creek. This coupled with low to moderately low precipitation accumulations over the past 30-days is cause for some concern and precipitation is needed immediately in these areas where agricultural production is rain fed. (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 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 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 & Program
Alberta Agriculture, Food and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on June 26, 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 May 27, 2007. |
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