| | Summary | Drought Indices | Precipitation | Soil moisture | Explanation of terms
.
.Introduction
A new classification scheme has been introduced for the all maps that describe current conditions relative to the long-term normal. This permits direct comparisons between different maps and provides a more intuitive description of how often certain conditions are likely to occur. The classification system is as follows:
| Class or Condition | Frequency of Occurrence | Probability of Occurrence |
| extremely low | drier than this less than 1 in 30-years | 0.033 |
| very low | drier than this less than 1 in 20-years | 0.050 |
| low | drier than this less than 1 in 10-years | 0.100 |
| moderately low | drier than this less than 1 in 4-years | 0.250 |
| near normal | similar to this 5 out of 10-years | 0.500 |
| moderately high | wetter than this less than 1 in 4-years | 0.250 |
| high | wetter than this less than 1 in 10-years | 0.10 |
| very high | wetter than this less than 1 in 20-years | 0.050 |
| extremely high | wetter than this less than 1 in 30-years | 0.033 |
A large selection of related maps can be found at www.agric.gov.ab.ca\acis, under the Quick Viewer tab.
Summary
Much of the reporting area continued to receive adequate precipitation during the first half of June. Since the June 12th, 2006 Drought Report,, significant precipitation has fallen over many previously dry areas. Specifically, the northern Peace Region at Fort Vermilion received 71.9 mm, the southeast corner of the Southern Region recorded more than 70 mm, and central parts of the Central Region recorded 20 to 40 mm. In general, precipitation totals were highest in the eastern parts of the Southern and Central Region, (> 50 mm) with the least amounts of precipitation (< 20 mm) recorded in the western Peace Region, the northeastern parts of the Northern Region and areas in and around the City of Calgary.
Over the past 365-days, several areas in the Peace Region recorded extremely low precipitation accumulations, however, recent precipitation has greatly improved soil moisture reserves for cropping over initial spring conditions. Across the central parts of the Northern Region, moderately low precipitation accumulations have occurred over the past 365 days. Elsewhere across the reporting area, precipitation accumulations have been at least normal with some parts of the Southern, Central and the extreme eastern parts of the Northern Region having extremely high precipitation accumulations.
Since the start of the growing season, April 1, 2006, much of the province has received at least near normal precipitation with the exception of the western parts of the Central and Southern Region where several pockets of moderately low precipitation accumulations were recorded, with a few of these areas in the Central Region grading to very low.
Soil moisture reserves are at least near normal across most of the reporting area, with the exception of the southern parts of the Peace Region (moderately low to low) and the north central Peace Region (extremely low), where recent precipitation has been sufficient to prevent crop moisture stress across most of these areas. Normal to above normal, well-timed precipitation events are needed in these areas to prevent crop moisture stress and further increase soil moisture reserves.
Current Situation
Drought Indices
Long Term Drought: 365-Day Precipitation Accumulations Relative to Long Term Normal (Figure 1) - The Long Term Drought Index map, based on the Standardized Precipitation Index (SPI), seen in reports prior to the 2006 growing season, has been discontinued and is now replaced by a similar, but more intuitive descriptor of long term precipitation patterns (Figure 1). This new method compares precipitation accumulations over the past 365-days against the ranked precipitation accumulations during the same period, for all years through 1961 to present. The percentile for the current accumulations is then computed and expressed as a frequency of occurrence, relative to the long term normal. This provides a more intuitive assessment of current conditions by answering the question, "how often does this occur?".
Peace Region: In general, conditions are improving since the last report. A large pocket of extremely low precipitation accumulation in the extreme north has disappeared because of more than 70.0 mm of recent precipitation here. Two pockets of extremely low accumulations remain, one in the center, and one in the north. These areas quickly grade to the low category, with much of rest of the Peace Region being classified as moderately low, with the exception of the west, which is classified as near normal.
Northern Region: Conditions are generally improving since the last report. Across much of the western half of the region, precipitation accumulations are ranked as moderately low, with the exception of one pocket of low. Across the east half of the region, precipitation accumulations are at least near normal, with the extreme eastern locations, around the town of Lloydminster, reporting very high precipitation accumulations.
Central Region: The northern parts of the Cenral Region recorded near normal precipitation accumulations, grading to high across the east half of the region with a few pockets of extremely high in the east. Note that since the last report, significant decreases in the extremely high category have occurred because the record-breaking rains during early June 2005 are not included in this time span.
Southern Region: Precipitation accumulations are near normal in the southeast, grading to moderately high in the west, with two small pockets of extremely high reaming, one in the County of Newell and one in the M.D. of Pincher Creek. Note that since the last report, significant decreases in the extremely high category have occurred because the record-breaking rains during early June 2005 are not included in this time span.
Precipitation
90-Day Precipitation Accumulations Relative to Long Term Normal (Figure 2) - Across most of the reporting area precipitation accumulations over the last 90-days have been at least near normal, with the driest locations being found in the extreme western parts of the Central and Southern Regions were isolated pockets of low to very low accumulations exist.
Peace Region: Across most of the region, at least near normal accumulations were recorded, with central and northern parts recording moderately high accumulations.
Northern Region: Moderately high precipitation accumulations dominate most of the west half of the region, with three pockets of high showing up. Across the east half of the region, accumulations were at least near normal, with a few pockets of moderately high accumulations.
Central Region: Most of the east half of the region recorded moderately high precipitation accumulations, with a few pockets of high. Across the west half of the region, accumulations graded from near normal to low in the extreme west, with two pockets of very low; one west of Calgary and one north west of Red Deer affecting small parts of Ponoka and Lacombe Counties.
Southern Region: Most of the region recorded at least normal precipitation, with the exception of a few pockets of moderately low accumulations in the west.
Precipitation since the June 12th, 2006 Drought Report (Figure 3) - In general, most locations across the province received adequate precipitation as cool wet weather prevailed. Most notable were significant accumulations that occurred in previously dry areas, bringing much needed moisture. These areas include, the northern Peace Region at Fort Vermilion (71.9 mm), the southeast corner of the Southern Region (> 70 mm), and west central parts of the Central Region (20 to 40 mm).
Peace Region: Precipitation accumulations ranged from 71.9 mm at the Fort Vermillion RS station in the north to 7.4 mm at the Cleardale AGDM station, and 6.2 mm Beaver Lodge CDA station in the west. Western parts of the region received less the 20 mm, central parts 20 to 30 mm and eastern parts 30 to 40 mm, with the greatest amounts (> 70 mm) being recorded in the north.
Northern Region: Precipitation accumulations ranged from more than 40 mm in the west to less than 20 mm in the northeast, with the least amounts (16.3 mm) recorded at the Lindbergh AGDM station in the County of St Paul and at Cold Lake A station (17.6 mm) in the M.D of Bonneville.
Central Region: The greatest amounts of precipitation were recorded in the east (50 to 60 mm), with the least amount (10 to 20 mm) recorded near the City of Calgary.
Southern Region: The greatest amounts of precipitation were recorded in the southeastern parts of the region at the Medicine Lodge station (79.0 mm) and at the Onefour CDA station (65.2 mm). Central parts of the region received 30 to 40 mm with the least amounts recorded just north of the city of Lethbridge (20 to 30 mm).
Growing season precipitation (GSP) to date (Figure 4) - Overall, growing season precipitation to date has been adequate across the reporting area with the least amounts being recorded in the western half of the Central Region.
Peace Region: Precipitation ranged from 50 to 75 mm in the northcentral areas to over 125 mm in the west. Since the start of the growing season, most areas have received at least 75 mm, an amount sufficient to compensate for extremely low soil moisture reserves.
Northern Region. In general, growing season precipitation has been adequate across the region. In the west, where soil moisture reserves were the lowest going into spring, growing season precipitation has been the greatest ranging from 125 to 175 mm. Elsewhere in the region precipitation ranged from 75 to 125 mm.
Central Region: The west half of the Central Region recorded some of the lowest growing season accumulations across the reporting area, with several locations recording between 50 to 70 mm, however, adequate soil moisture reserves have helped offset some of these precipitation deficits. The east half of the region recorded between 100 to 125 mm that, for most areas, is at least near normal.
Southern Region: Across most of the region, growing season precipitation ranged from 75 to 125 mm, which is near normal.
Growing Season Precipitation Accumulations Relative to Long Term Normal (Figure 5) - Precipitation accumulations for the growing season to date were very similar to those reported for the 90 precipitation accumulations as there is only 16 days difference between the two maps. It is, however, worth mentioning again that the western parts of the Central Region have precipitation accumulations that are moderately low, with some areas in the very low category. These immediate shortages have been offset by good soil moisture reserves and crop soil moisture stress remains minimal, providing crops have germinated.
Normal Precipitation Accumulations for June (Figure 6) - June and July are typically the wettest months in the year. Precipitation accumulations in June range from 60 to 70 mm in the southeast to greater than 100 mm across the west parts of the Northern Region and southeastern parts of the Peace Region. Historically, the latter half of June is typically wetter than the first half, except for eastern parts of the central region were the latter half of June tends to be slightly drier than the fist half of the month. If near normal precipitation falls across all regions, then soil moisture reserves should be at least average across most of the reporting area.
Soil Moisture
Soil moisture in the agricultural regions of Alberta (Figure 7) - Soil moisture conditions are generally good throughout the reporting area due to at least near normal precipitation since the last report. Generally, the greatest amounts of precipitation fell were it was needed most (northern Peace Region and south eastern Alberta).
Dry winter conditions experienced across the south half of the reporting area have been alleviated due to good soil moisture carry over from the fall. In the north, extremely dry conditions over the past year or so have been alleviated somewhat as a result of significant precipitation accumulations this spring. Continued precipitation is needed in the Peace Region, particularly across the north to build sufficient soil moisture reserves to withstand short-term dry spells that may occur during the remainder of the growing season. Areas with less than 50 mm of soil moisture require at least Above Normal precipitation over the next few weeks to build soil moisture reserves for the growing season ahead.
Peace Region: June rains have brought much needed relief to most of the areas that had low soil moisture levels. Most of the south half of the region has 75 to 100 mm of plant available water grading to greater than 125 mm in the west. Soil moisture declines over the north half of the region ranging from 75 to 100 mm, with some areas in the north estimated to have between 50 to 75 mm.
Northern Region: Most of the region has soil moisture levels greater than 125 mm, with a few large pockets in north and southwest in the 100 to 125 mm range.
Central Region: Most f the region has soil moisture levels of greater than 125 mm, with large pockets in the center in the 100 to 125 mm range.
Southern Region: Most of the region has soil moisture levels greater than 125 mm, with a large pocket in the southeast in the 100 to 125 mm range.
Long Term Average Soil Moisture Conditions (Figure 8) - The long-term average soil moisture conditions are shown in Figure 8. Note that 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 direst areas found in the center (50 to 75 mm).
Current Soil Moisture Reserves Relative to Long Term Normal (Figure 9) - This map replaces the soil moisture departure map seen in reports prior to 2006 growing season and uses the same classification scheme as the precipitation maps that describe current accumulations relative to the long term normal. Soil moisture reserves computed for the report date (Figure 7) 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 reporting area, soil moisture reserves are at least near normal, with some exceptions in the Peace Region where drier fall, winter and early spring conditions have resulted in some areas with extremely low reserves.
Peace Region: Soil moisture reserves through the central parts are near normal grading to moderately low in the south with small areas of very low in the extreme southwest. Across the north, areas of extremely low reserves exist north of Manning, grading to near normal in the extreme north, thanks to over 70 mm of recent precipitation.
Northern Region: Most of the southeast is reporting high reserves, with a small pocket of extremely high reserves. Across the rest of the region, soil moisture reserves are generally near normal, with a few small areas classified as moderately low in the extreme western and northern areas of the region.
Central Region: Much of the east half of the region has high reserves, grading to extremely high in the southeast. Across the west half of the region, reserves are moderately high, grading to near normal along the western border.
Southern Region: Soil moisture reserves are extremely high in the west, grading to near normal in central locations and then increasing upwards again to extremely high in the northeast.
Explanation of Terms
Long term (hydrologic) drought
Long term, or hydrologic, drought is a result of the cumulative effect of several dry months. It primarily impacts livestock feed and water supplies and may affect annual crops. Hydrologic drought is determined by ranking the precipitation accumulations during the same 365-day 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:
| Class or Condition | Frequency of Occurrence | Probability of Occurrence |
| extremely low | drier than this less than 1 in 30-years | 0.033 |
| very low | drier than this less than 1 in 20-years | 0.050 |
| low | drier than this less than 1 in 10-years | 0.100 |
| moderately low | drier than this less than 1 in 4-years | 0.250 |
| near normal | similar to this 5 out of 10-years | 0.500 |
| moderately high | wetter than this less than 1 in 4-years | 0.250 |
| high | wetter than this less than 1 in 10-years | 0.10 |
| very high | wetter than this less than 1 in 20-years | 0.050 |
| extremely high | wetter than this less than 1 in 30-years | 0.033 |
Precipitation Accumulations-Frequency of Occurrence.
Precipitation accumulations, expressed as a frequency of occurrence are computed for various periods. They are computed using the same technique and same time frame (1961 to current) that was used for the Long term (Hydrologic Drought Index) and share the same class scheme (see table above). The only difference being the period of length, over which precipitation accumulations were computed.
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
Alberta Agriculture, Food and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on June 12, 2006.
Drought analysis is currently scheduled at monthly intervals between October 30 and May 1. This report updates the previous report of May 28, 2006. |
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