| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last Drought Report (July 14, 2007), hot weather dominated much of the region bringing isolated and sometimes severe thunderstorm activity, particularly west of Highway 2 and across parts of the Peace Region. This, in combination with adequate soil moisture reserves, has supplied sufficient moisture to sustain crop growth in most areas despite high temperatures. Dry conditions have prevailed across much of the Southern Region bringing with it severe crop moisture stress. Currently wide spread, significant precipitation and a reprieve from excessive heat are needed across all areas to maintain good crop growth.
Since the July 14, 2007 report, precipitation accumulations were less than 5 mm across much of the Southern Region, central parts of the Central Region, eastern parts of the Northern Region and north-central parts of the Peace Region. The extreme western parts of the Northern and Central Regions, as well as in the western and northern parts of the Peace Region, recorded amounts in excess of 40 mm.
Growing season precipitation accumulations to date (April 1, 2006 to July 28, 2007) relative to the long term normal are generally at least near normal across most of the reporting area, with the exception of the southern-half of the Southern Region, much of the north-eastern parts of the Northern Region and the south-western Peace Region. In these areas growing season precipitation accumulations relative to long term normal are rapidly declining and are now classified as ranging from moderately low, to low. In contrast, south-western parts of the Northern Region, the western half of the Central Region and northern parts of the Southern Region have experienced moderately high to extremely high growing season precipitation accumulations to date.
Over the past 30-days precipitation accumulations relative to long term normal were at least moderately low across most of the reporting area, with much of the southern half of the Southern Region, northern parts of the Central Region and eastern half of the Northern ranging from very low to extremely low. For these areas in the Northern and Central Region, soil moisture reserves have been adequate to sustain crop growth, however soil moisture reserves become depleted and crops will be susceptible to moisture stress if precipitation is not received soon. In the Southern Region crop moisture stress is occurring and precipitation is needed now.
Soil moisture reserves are depleting rapidly due to the recent hot weather and high evaporative demand from well-established crops. Reserves across the reporting area are highly variable and range from extremely low in parts of the Southern Region, eastern parts of the Central Region and north-eastern parts of the Northern Region, to very high in the northern parts of the Southern Region, and extreme south-western parts of the Northern Region. Large areas in the North, Central, and Peace Regions still have at least near normal soil moisture reserves, however timely precipitation is needed in these areas to ensure good crop growth.
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 14, 2007 Drought Report (Figure 1) - Since the last report, thunderstorm activity has dominated the precipitation patterns across the reporting area, bringing with it "hit and miss" precipitation. As a result many areas may have received more or less precipitation than has been reported here.
Precipitation accumulation across much of the east half of the reporting area has been less than 10 mm, with many locations recording less than 5 mm. The greatest precipitation accumulations (greater than 35 mm) were recorded west of Highway 2 between Edmonton and Calgary, across the Swan Hills, and in the western, eastern and northern parts of the Peace Region.
Peace Region: Precipitation across the Peace Region ranged from 1.3 mm at Manning AGDM station near Manning to 61.4 mm at the Spirit River Auto station in the Saddle Hills. The driest areas in the region were concentrated in the central and north-central portions of the region (5 to 10 mm) as well as west of the City of Grande Prairie (15 to 20 mm). Areas that received the most precipitation were the northwest, (30 to 60 mm), the northern tip (40 to 50 mm) and the south eastern portions of the region (30 to 50 mm).
Northern Region: Precipitation accumulations were the lowest across the east and southeast with a number of stations recording less than 5 mm, and ranged up to 90.3 mm at the Violet Grove CS station in the extreme west. Most of the east-half of the region received less than 15 mm of precipitation, grading up sharply across the west-half of the region where precipitation totals were typically well over 25 mm.
Central Region: Precipitation was highly variable across the region ranging from less than 5 mm across most of the central parts of the region to upwards of 40 mm in the west and 30 mm in the southeast.
Southern Region: Most of the region received less than 5 mm of precipitation, with the exception of the southeast, the extreme north and the northwest where 20 to 30 mm was recorded. Areas that had little precipitation and that are not irrigated are experiencing crop moisture stress and yield reductions. These areas are in dire need of precipitation and a return to cooler temperatures.
Growing Season Precipitation Accumulations Relative to Long Term Normal (1961 - 2005) (Figure 2) - Growing season precipitation accumulations relative to the long term normal have been decreasing rapidly across then south half of the Southern Region, north eastern parts of the Northern Region and south-western parts of the Peace Region where they now rank as being moderately low to low. These areas are in need of precipitation and a return to more seasonable temperatures now. Elsewhere accumulations are at least near normal with much of the
Central Region, the south-western parts of the Northern Region and the northern parts of the Southern Region classified as moderately high to extremely high.
Peace Region: To date growing season precipitation is at least near normal across the most of the region, with an area confined to the extreme southwest of the County of Grande Prairie that grades down to low. Here, precipitation accumulations over the past 14 days (Figure 1) have been between 15 to 20 mm, just enough to ease concerns over crop moisture stress, however precipitation is needed in this area now to ensure an adequate moisture supply for crops.
Northern Region: The northeast is drying out rapidly and growing season precipitation to date now ranges from moderately low to low. A pocket of low to very low is developing in the southeast, affecting parts of the M.D.'s of Wainwright and Provost. Precipitation is needed here immediately to maintain adequate moisture supplies for crops. Elsewhere, growing season precipitation is at least near normal, and grades to extremely high in the southwest.
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 high to extremely high.
Southern Region: Much of the south half of the region has received moderately low growing season accumulations to date with a few pockets in the southwest grading to low. Across the northern half of the region, precipitation ranges from near normal up to extremely high in the far north. Most the region needs precipitation now to salvage those crops that have not yet been damaged by moisture stress.
30-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - 30-day precipitation accumulations have decreased significantly since the last report (July 14, 2007) and are now classified as at least moderately low across much of the reporting area, with many locations classified as very low to extremely low. Fortunately, for the most part, soil moisture reserves have been sufficient to compensate for well below normal precipitation accumulations, however soil moisture reserves are depleting rapidly and widespread precipitation is needed across most areas.
Peace Region: Most of the south-western portions of the region have had at least moderately low to low accumulations over the past 30-days, with one pocket west of the City of Grande Prairie grading to very low. Precipitation is needed in these areas now to alleviate crop moisture stress and to ensure good growing conditions. Across much of the south eastern and northern parts of the region, 30-day accumulations are classified as at least near normal.
Northern Region: Across the eastern-half of the region 30-day precipitation accumulations are ranked as being very low to extremely low, particularly in the southeast. Here, soil moisture reserves are depleted prompting and immediate need for precipitation and a return to cooler conditions in order to prevent the development of serious crop moisture stress. Throughout the central parts of the region, precipitation accumulations are moderately low, grading up to near normal in the west and moderately high in the extreme southwest.
Central Region: Most of the region has had at least moderately low accumulations over the past 30-days, with several areas grading down to extremely low in the centre and northeast. Soil moisture reserves have been adequate to over come these precipitation deficits and crops appear to have had adequate supplies of moisture, however precipitation is needed soon to ensure that moisture stress does not develop.
Southern Region: Most of the region has had at least low accumulations over the past 30-days with several areas grading down to extremely low in centre and west. Extreme heat and low precipitation accumulations are affecting crop growth, and it has been reported that yields are affected. Wide spread precipitation and a return to cooler temperatures are needed now.
Average Precipitation Accumulations for August (Figure 4) - Historically, the first half of August is wetter than the last half of August 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 south-eastern parts of the Peace Region.
Soil moisture in the agricultural regions of Alberta (Figure 5 and Figure 6)
High temperatures and below normal precipitation accumulations have lead to a rapid decrease in soil moisture reserves across much of the reporting area. Across most of the east-half of the reporting area and up in the south-western tip of the Peace Region, soil moisture reserves are less than 25 mm resulting in a situation were crops will not be able to tolerate high heat and low precipitation accumulations. Precipitation in these areas is needed now.
Peace Region: Soil moisture reserves are variable across the region, ranging from less than 25 mm (low) in the extreme southwest, up to 75 to 100 mm (near normal) in west-central and eastern locals. Across central portions of the region, soil moisture reserves range from 50 to 75 mm (near normal) and across the north from 25 to 50 mm (moderately low to low) (Figure 5 and Figure 6). Those areas where reserves are less than 50 mm require precipitation soon to ensure that crop moisture stress does not develop.
Northern Region: Soil moisture levels are lowest (less than 25 mm) in the east and grade up to more than 125 mm in the extreme southwest (Figure 5). Across the eastern half of the region, several pockets of very low accumulations, relative to long term normal, are developing and immediate precipitation and a return to cooler temperatures are needed now to prevent crop moisture stress from developing further (Figure 6). Elsewhere across the region, soil moisture reserves relative to the long term normal are at least near normal.
Central Region: Across the eastern half of the region, soil moisture reserves are below 25 mm, grading up to 50 to 75 mm in the centre, and reach a maximum of 100 to 125 mm in the northwest (Figure 5). In the northeast, areas of low to extremely low soil moisture reserves relative to long term normal are beginning to develop, in contrast to most of the rest of the region which is classified as at least near normal. (Figure 6). Where soil moisture reserves are less than 25 mm, precipitation and a return to cooler temperatures are needed now to prevent moisture stress from worsening.
Southern Region: Most of the region has soil moisture levels that are less than 25 mm, with the exception of the northwest where soil moisture reserves grade up to 75 to 100 mm (Figure 5). Across the region several pockets of externally low reserves relative to long term normal are developing (Figure 6), resulting in serious crop moisture stress and reduced yield potential, particularly in late seeded crops and canola and pulse crops. Most of the Southern Region is in dire need of precipitation and a return to more seasonable temperatures.
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 is 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 July 31, 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 July 14, 2007 |
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