| | Precipitation | Soil moisture | Data sources | Explanation of terms
.
Summary
Since the last drought report, June 23, 2009, three major storms, combined with "hit and miss" showers, brought much needed, very significant precipitation across most part of reporting area, improving soil moisture conditions. Most of the reporting areas received precipitation in the range of 50 to 70 mm, while the southwestern, central-north and eastern portion of the Southern Region, as well as scatted pockets in the rest of the reporting area, recorded precipitation in the 80 to 140 mm range. In contrast, the central and eastern portion of the Central Region, as well as the south central border of the Southern Region, recorded 20 to 40 mm, the driest in the reporting area. In general, the storms brought relief to crop condition in most part of the reporting area; however, crops yields in areas where dry condition persisted prior to the first week of July will be seriously impacted.
Daily mean temperatures relative to long term normal during the past 15-days across most of reporting area varied from moderately low (1 to 3° C less) to near normal conditions, with the exceptions of isolated pockets throughout the reporting area with low average temperature. Overall, though moisture conditions have improved in most part of the reporting area, the abnormally low temperatures during the month of May, June and the first two weeks of July have slowed crop development (Figure 8).
Growing season (April 1 to July 19, 2009) precipitation accumulations relative to long term normal, to date, are still in the low to extremely low ranges, across the western, central and central-eastern portion of the Central Region; most of the southern, central and central-north portions of the Northern Region, as well as the northwestern portion of the Southern Region. Accumulation in the rest of the reporting area graded up from low to moderately low, with few pockets of near normal to high accumulation, located in the Southern Region (Figure 2).
The 365-day precipitation accumulations, relative to the long term normal, have been low to extremely low across much of the Central and the Northern Regions, the southeastern and northern portion of the Peace Region, as well as the northwestern portion of Southern Region (Figure 4).
Modeled soil moisture reserves, relative to long term normal (Figure 7) varied from low to moderately low, in most of the Central and Northern Regions, with the exception of extremely low to low and near normal reserves in isolated pockets. Reserves in the Peace Region varied from near normal, in the central-east, southwest and a portion in the north to moderately low to low, across most parts of the region, with the exception of very low to extremely low reserves in the north. In contrast, reserve in most of the Southern Region are at least near normal, with very high to extremely high reserves in the central-east and eastern portion of the region, except a moderately low to low reserves in two pockets, in the south and northwestern portion of the region. Again, the low soil moisture reserves are due to low to extremely low precipitation accumulations experienced since the start of the growing season combined with the below normal fall precipitation accumulations and the soil moisture deficits carried over from past growing seasons.
A large selection of related maps can be found at http://www.agric.gov.ab.ca/acis, under the Quick Viewer tab. Note these maps are updated once a week (usually by Wednesday) providing updates between drought reports.
Precipitation
Precipitation since the June 23, 2009 Drought Report (Figure 1)
Since the last report, June 23, 2009, three major storms brought much needed precipitation across most of the reporting area, improving dry soil moisture conditions. Precipitation total was the lowest (20 to 40 mm), in the central and central eastern portion of the Central Region, extending to the southeastern portion of the Northern Region and along the south border of the Southern Region. In general, accumulations in the rest of the reporting area were variable ranging from 50 to 80 mm with the exception of accumulations in isolated pockets in the range of 80 to 120 mm.
Peace Region: Precipitation accumulations relative to long term normal have been near normal (40 to 70 mm) across most of the region grading up to high and very high (70 to130.9 mm) in the southwestern and the northern corner of the region. Precipitation accumulations were the greatest at High Level A station (130.9 mm), followed by the Fort Vermillion RS station (124.6 mm) both located in the north, while the lowest accumulations were recorded at Jean Cote AGCM station (42.7 mm) followed by Peoria AGDM station (45.3 mm), both located in the south-central portion of the region.
Northern Region: Precipitation accumulations in the region varied from lows of 30 to 50 mm in scattered pockets, to 50 to 70 mm range, across most of the region, and highs of 80 to 176 mm in the extreme west and in isolated pockets and the northeastern portion of the region. The greatest precipitation was recorded at Edson A station (176 mm), followed by Paddle River Headwaters station (124.2 mm) both in the west. The least amounts were recorded in Wainwright A station (32.1 mm) followed by Bellshill AGCM station (40.3 mm), both located in the southeastern portion of the region.
Central Region: Precipitation accumulations across the region gradually graded up from a low of 20 to 40 mm range, in the central and central east part of the region to 40 to 60 mm range to the rest of the region, with the exception of the southwestern and southeastern portions, which recorded highs in the 80 to 150 mm range. The highest precipitation was recorded at Elbow RS station (144 mm) in the southwest corner followed by Pollockville AGDM station (90.7 mm) in central-south while the lowest was recorded at Linden AGCM station (22.7 mm) followed by Three Hills A station (22.8 mm) both in Kneehill County, in the central part of the region.
Southern Region: Precipitation accumulations in the region were the highest as a result of two major storms that crossed the region. Accumulation in the region graded down from highs in the 80 to 120 mm range, across most portion of the southwestern, central, central north and southeastern part of the region to lows of 30 to 50 mm in isolated pockets mainly located in the central south and central northwestern portion of the region. Precipitation accumulation was the highest at Brooks ASCHRC station (110.67 mm), followed by Rosemary IMICIN station (105.3 mm), both located in the central north, and the lowest at Mossleigh AGDM stations (37.4 mm) in northwestern portion of the region.
Growing Season Precipitation Accumulations, April 1 to July 19, 2009 (Figure 2 and Figure 3)
To date precipitation accumulations relative to long term normal in most part of the Central and Northern Regions extending to the northwestern portion of the Southern Region range from low to extremely low, with precipitation totals in the 50 to 125 mm range, the lowest in the reporting area. Precipitation accumulation in the central part of the Peace Region was also low (75 to 100 mm ). Precipitation totals in the rest of the reporting area, mainly, varied from moderately low to near normal accumulation, with pockets in the Southern Region reporting accumulation in the moderately high to high, in the 200 to 300 mm range (Figure 2).
Peace Region: Growing season accumulations graded up from low (70 to100 mm), in the central and southeastern part, to moderately low (100 to 150 m) across most of the region and to near normal accumulation (150 to 175) in the southeastern and northern corner of the region.
Northern Region: Growing season precipitation in the southern, southeastern, and central portion of the region was manly very low (75 to 125 mm), grading up, to low and moderately low (100 to 150 mm) accumulation, with the exception of few isolated pockets of near normal accumulation (200 to 250 mm) located in the western part of the region.
Central Region: Growing season precipitation across the western, central and northeastern portion of the region range from very low to extremely low (45.6 to 100 mm) grading up to low to moderately low (100 to 175 mm) in the southeastern and northwestern portion of the region. Four stations in the special areas recorded precipitations in the 45.6 to 71.3 mm range, the lowest in the reporting area.
Southern Region. Growing season precipitation graded down from moderately high and near normal (125 to 300 mm) accumulation, in most part of the eastern half and western part of the region, to moderately low (100 to 170 mm) to low (100 to 150 mm) to the rest of the region with the exception of very low to extremely low accumulation in the northwestern part of the region.
365-Day Precipitation Accumulations Relative to Long Term Normal (Figure 4)
Average Precipitation Accumulations for August (Figure 5)
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 6 and Figure 7)
In general, modeled soil moisture reserves, relative to long term normal varied from low to moderately low, in most part of the Central and Northern Regions, with the exception of extremely low to low and near normal reserves in isolated pockets. Similarly, in the Peace Region, reserves varied from very low to extremely low, in pockets in the north, to moderately low to low, across most parts of the region and then to near normal reserves in the central-east, southwest and the north portion of the region. In contrast, reserve in most part of the Southern region are at least near normal with very high to extremely high reserves in the central-east and eastern portion of the region, with the exception of two pockets of moderately low to low reserves in the south and northwestern portion of the region. Low soil moisture reserves are mainly caused due to precipitation accumulations deficit experienced since the start of the current growing season combined with the below normal fall precipitation accumulations and the soil moisture deficits carried over from past growing seasons.
Peace Region - Soil moisture reserve varied from the 50 to 75 mm range in the south to 25 to 50 mm and less than 25 mm ranges in the center and northern portion of the region. Soil moisture reserves, relative to long term normal, graded up from very low to extremely low, in isolated pockets in the south, central-west and northern portions of the region to moderately low and near normal reserves in the rest of the region.
Northern Region - Soil moisture levels graded down from 25 to 50 mm range, in the northern part of the region, to less than 25 mm across most of the southern and central portions of the region. Relative to long term normal, reserves in most part of the region were classified as moderately low and low, with the exception of very low reserves, in isolated pockets and near normal reserves along the eastern boarder of the region.
Central Region - Soil moisture reserve across most of the region was below 25 mm grading up to 25 to 100 mm range along the west and south-central and southeastern portion of the region. Relative to long term normal, reserves varied from very low to extremely low, in isolated pockets in the western and northeastern portions of the region, gradually grading up to moderately low and above near normal reserves, along the southeastern portion of the region.
Southern Region - Soil moisture reserves along the Foothills rapidly graded down from 125 mm to 50 mm, and remained at 50 mm across most of the region grading up to the 50 to 125 mm range in the east. Relative to long term normal, soil moisture reserves are at least near normal across most of the region with the exception of moderately low to low reserves in pockets located in the northwestern and central-south portions 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 a preliminary computer assisted QA/QC check performed by Alberta Agriculture and Rural Development (ARD) 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 ARD, 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 Accumulation - Frequency of Occurrence
Precipitation accumulation, 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 accumulation for each period are then determined by ranking the precipitation accumulation during similar 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 Occurrence |
| 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 accumulation 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 percent of the total precipitation is allowed to accumulate resulting in a 30 percent 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 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 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
Alberta Agriculture and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on July 22, 2009.
Drought analysis is currently scheduled at monthly intervals. This report updates the previous report of June 23, 2009. |
|