| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last drought report (June 24, 2007), hot and dry weather has prevailed over much of the region bringing with it concerns of crop moisture stress. This is particularly true across much of the Southern Region where soil moisture reserves are low, and maximum daily temperatures have been extreme, exceeding 35°C in some areas.
Across the reporting area, precipitation ranged from less than 10 mm in much of the Southern Region and pockets of the Central, Northern and Peace Regions, to well over 60 mm in the western parts of the Northern Region and northern parts of the Peace Region. Across all areas, a return to more seasonable temperatures is required. In areas with low soil moisture reserves, precipitation is needed immediately to prevent crop moisture stress from intensifying.
Growing season precipitation accumulations to date (April 1, 2006 to July 14, 2007), relative to the long term normal, are at least near normal across most of the reporting area with the exception of the southern-half of the Southern Region, a few pockets in the Northern Region and the southwest corner of the Peace Region where accumulations range from moderately low to low. In contrast, much of the western-half of the Central Region has extremely high growing season precipitation accumulations to date. However, many areas are suffering moisture stress due to hot and dry conditions. As a result, Figure 2 should be interpreted with caution and does not necessarily reflect those areas that are suffering most from short-term precipitation deficits coupled with unseasonably high temperatures.
Over the past 30-days, precipitation accumulations relative to normal ranged widely across the reporting area, with the driest areas found in the south-western parts of the Southern Region (extremely low) and south-western parts of the Peace Region (very low). Many areas in the northern and western Peace Region are in the low to moderately low category, and most of these areas currently have below normal soil moisture reserves, making them particularly vulnerable to extremely high temperatures that can lead to serious heat stress in crops.
Despite recent hot weather, much of the reporting area still has soil moisture reserves that are near normal. However, soil moisture reserves are moderately low, to low across most of the south-half of the Southern Region and south-western portions of the Peace Region. Cooler temperatures and immediate precipitation is needed in these areas. In contrast, central portions of the Central Region still have high to very high soil moisture reserves that, given the absence of recent precipitation, are depleting rapidly in the face of extreme heat. Areas with low or worse soil moisture reserves have generally received below normal precipitation over the past 30-days and are susceptible to serious crop moisture stress, particularly at this time of year when many crop species are entering critical stages of development.
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 24, 2007 Drought Report (Figure 1) - Since the last report, precipitation accumulations across large parts of the reporting area were less than 20 mm, with much of the southern-half of the Southern Region recoding less than 5 mm. This combined with record temperatures has lead to significant heat stress in many crops.
Peace Region: Precipitation across the Peace Region ranged from 5.7 mm in the southwest at the Beaver Lodge RCS station to 66.3 mm at the Manning AGDM station near the village of Manning. In general, the southwest and west were the driest, with less that 20 mm recorded, and the north was the wettest, with many areas recording more than 50 mm. In the northern parts of the region, this precipitation was needed as previous precipitation accumulations had been low.
Northern Region: Precipitation accumulations were the lowest in the south-central parts of the region, with many stations reporting less than 20 mm. Elsewhere precipitation accumulations were quite variable, with most central parts of the region receiving 20 to 50 mm and the western and eastern parts of the region receiving 50 to 80 mm, with the exception of two pockets of greater than 80 mm.
Central Region: Precipitation was highly variable across the region ranging from 11. 4 mm at the COP upper station near the City of Calgary to 66.0 mm at the Consort AGDM station in Special Area 4. Across most of the region precipitation accumulations were less than 40 mm with the some locations in the northwest, northeast and south-central portions of the region receiving more than 50 mm.
Southern Region: Precipitation accumulations across most of the south half of the region were less than 5 mm, with the greatest amounts (73.1 mm) being recorded at Standard AGCM station in Wheatland County. Most of the south half of the region recorded less than 10 mm with some parts of the north and northeast receiving upwards of 40 mm. Low precipitation accumulations in the south half of the region coupled with unseasonably high temperatures is threatening many crops that are not irrigated. Precipitation and a return to cooler temperatures are needed immediately.
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 with the exception of; southern parts of the Southern Region, which grade down to low and moderately low; several widely scattered pockets of moderately low in the Northern Region; and one area of moderately low, in the extreme south-western corner of the Peace Region.
Peace Region: To date, growing season precipitation is at least near normal across the most of the region, with the extreme southwest area of the County of Grande Prairie, that grades down to moderately low. Here, precipitation accumulations over the past 20 days (Figure 1) have been less than 10 mm, and with the extreme heat crop moisture stress is a significant concern.
Northern Region: Most the region is reporting at least near normal growing season precipitation to date, with the exception of a few widely scattered pockets grading down to moderately low. Despite this, extreme temperatures have resulted in a need for precipitation soon and a return to more seasonable temperatures.
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. However, hot dry weather is rapidly depleting soil moisture reserves and a return to more seasonal temperatures is desired.
Southern Region: Much of the south half of the region has received moderately low growing season accumulations to date, grading to near normal through the centre and up to extremely high in the north-central portions of the region. Despite this, recent hot dry weather has been of significant concern in the south half of the region where soil moisture reserves are low and crops are entering critical growth stages. Some reports of significant moisture stress have been received and precipitation is needed immediately along with cooler temperatures.
30-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - 30-day precipitation accumulations have been highly variable across the reporting area, ranging from extremely low in the southwest to extremely high in the southeastern parts of the Northern Region. Large parts of the Northern, Southern and Peace Regions have received at least moderately low accumulations that, combined with above average temperatures, has lead to some concerns over crop moisture stress, particularly in the southern half of the Southern Region and the extreme south western parts of the Peace Region.
Peace Region: The south-western portions of the Peace Region have received very low to low accumulations over the past 30-days and this combined with high temperatures, and moderately low to very low soil moisture reserves puts the region in desperate need of precipitation and a return to more seasonable temperatures. Elsewhere in the Peace Region, 30-day accumulations range from moderately low to very highl.
Northern Region: Many parts of the Northern Region have 30-day precipitation accumulations ranked as moderately low. This typically is not a cause for concern, however these accumulations have been accompanied by extreme heat. As a result, a return to more seasonable temperatures and near normal precipitation accumulations is needed soon.
Central Region: Most of the region has seen at least near normal accumulations over the past 30-days with the exception of a few areas that are classified as moderately low. Soil moisture reserves are being used rapidly and a return to more seasonable temperatures is needed soon.
Southern Region: Across the Southern Region, 30-day precipitation accumulations range from extremely low in the southwest and south-central portions of the region, up to near normal in the northwest and northeast and high in the extreme north central portions of the region. Hot and dry weather over the past several days has prompted significant concern with respect to crop moisture stress, particularly across the south half of the region where soil moisture reserves are generally low (Figure 6), prompting the desperate need for immediate precipitation.
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. Precipitation averages during this month range 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 much of the reporting area with the exception of the south half of the Southern Region and the south-western portions of the Peace Region. In contrast, soil moisture reserves are moderately high to very high across the south-central parts of the Central Region and north-central parts of the Southern Region. Those areas with moderately low or lower soil moisture reserves are in desperate need of precipitation now.
Peace Region: Soil moisture reserves range from 25 to 50 mm (very low) in the extreme southwest, up to 75 to 100 mm (moderately high) in the centre and then down to 50 to 75 mm (near normal) in the north (Figure 5 and Figure 6).
Northern Region: Soil moisture levels range from 50 to 75 mm in the southeast and grade up to 100 to 125 mm across the west half of the region, Figure 5. Over all, current soil moisture levels are generally at least near normal across the region (Figure 6).
Central Region: Soil moisture ranges from less than 25 mm in the east (Special Area 3) up to more than 125 mm across the extreme north western parts of the region Figure 5. Over all, soil moisture reserves for this time of year are generally at least near normal, grading up to very high in the central and south-central parts of the region Figure 6.
Southern Region: Soil moisture levels are less than 25 mm across the east and over much of the south half of the region. The greatest reserves (100 to 125 mm) are found in the extreme west along the foothills. Over all, soil moisture reserves are classified as moderately low to low across the south half of the region and grade up to very high in the far northern parts of the region, with one pocket of extremely high in the eastern parts of Wheatland County. The south half of the region is particularly dry and hot weather has resulted in reports of serious crop moisture stress in non-irrigated fields. Precipitation is needed across the south half of the region immediately to prevent further heat damage to crops.
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 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 July 17, 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 June 24, 2007. |
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