| | Current situation | Precipitation | Soil moisture | Explanation of terms
Throughout October 2005, relatively dry warm weather prevailed over most of the province aiding harvesting efforts. The Peace Region was the driest, with parts receiving Much Below Normal precipitation, in contrast to other areas of the province where precipitation totals ranged from Above Normal over the east half of the province to Near Normal for much of the west half of the province.
Since the start of the growing season (April 1, 2005), most of the province received at least Normal precipitation, with the exception of the Peace Region and central parts of the Northern Region, where Below Normal precipitation was recorded. Across much of southern Alberta, and along the eastern half of the province, growing season precipitation ranged from Above to Much Above Normal.
In the Northern Region, since the last report, areas classified as Drought Alert have diminished slightly due to Near and Above Normal precipitation while the Drought area in the Sturgeon County has expanded to some extent due to Below Normal precipitation. In addition, the area of Drought Alert in the southern Peace Region has expanded slightly. Elsewhere in the reporting area, Normal and Above Normal conditions exist, with large areas in the foothills of the Southern Region reporting Wet conditions.
The 90-day trend in drought conditions across most of the Southern and Central Region is Above Normal while most of the Northern Region is trending towards Normal with the exception of an extended area in the central part of the region leaning towards Drought Alert. In the northern, central and southern parts of the Peace Region the current trend is towards Drought Alert, while the remainder of the area is trending towards a Normal condition.
Soil moisture reserves have generally increased across all parts of the reporting areas with the largest increases occurring across much of the Southern, Central and the western and eastern parts of the Northern Region. This was in response to recent precipitation and a corresponding decrease in evapotranspiration demands. Currently, soil moisture deficits across most of the Peace Region and the central parts of the Northern Region are Well Below Normal, with some parts of the northern and southern Peace Region experiencing Extreme Deficits.
Areas with Well Below Normal or lower soil moisture reserves will need Well Above Normal precipitation over winter and into early spring to insure adequate moisture for reseeding and adequate moisture to resist short-term dry spells during the 2006 growing season.
Current Situation
Drought indices
Long-term Drought (Figure 1) - Since the last report (September 18, 2005), Near and Above Normal precipitation in the central eastern and western parts of the Northern Region has decreased the Drought Alert area from 7.3 % to 5.9 % of the reporting area and the pocket area of Drought in the County of Barrhead has disappeared. Due to Below Normal precipitation, the Drought area in Sturgeon County has slightly expanded. Similarly, in the Peace Region Much Below Normal precipitation in the south part of the region has resulted in the expansion of the Drought Alert there. Drought Alert areas in the Northern Region include Sturgeon and Westlock counties, and parts of County of Anthabasca and Thorhild; Strathcona, Leduc and Parkland counties, and the County of Camrose and pockets in the counties of St. Paul, Minburn and along the border between the County of Two Hills, Minburn and Lamont County. Elsewhere, areas are reporting Normal to Above Normal, with areas in foothills reporting Wet conditions.
Recent (90-day) trend in long-term Drought conditions (Figure 2) - Across much of the Southern, Central and the southeastern parts of the Northern Regions, Much Above Normal precipitation, received since the end of July has resulted in a 90-day trend towards Above Normal with a number of isolated pocket reporting Normal to Wet conditions. The 90-day trend in most parts of the Northern and the northern part of the Central Region is towards Normal with the exception of an extended area in the central parts of the Northern Region trending towards Drought Alert, which covers parts of five counties north of the city of Edmonton. Similarly, Much Below Normal precipitation since the end of July, across much of the Peace Region, has resulted in a 90-day trend towards Drought Alert that extended from north to south in addition to an isolated pocket in the southeast. The rest of Peace Region is trending towards Normal conditions.
Precipitation
Precipitation since the September 18th, 2005 Drought Report (Figure 3) - Since the last Drought Report, isolated precipitation events delivered precipitation ranging from 5 to 187.9 over the reporting area. In the Southern Region, precipitation was greatest in the foothills areas with 187.9 mm being recorded at Spionkop Creek station, grading to about 18 mm in the northern central parts of the region, increasing to about 26 mm to the east with the exception of at Medicine Lodge (11.6 mm), just south east of the City of Medicine Hat. In the northern half of Central Region, precipitation was relatively high, ranging from 20 to 40 mm range, with amounts of 55.3 mm at Stettler and 48.2 mm at Olds College. The rest of the region received an average of 16 mm with the lowest amounts being recorded at Drumheller (12.2 mm). In the Northern Region, precipitation in the west and east part of the region ranged from 30 to 52 mm with the greatest amounts (52.0 mm) recorded at Cold Lake. The rest of the region recorded between 10 to 40 mm with the lowest amounts (16.6 mm) being recorded at the Edmonton Namao Station. Across most of the Peace Region, precipitation ranged from 10 to 20 mm with the exceptions of the western and eastern parts of the south half of the region where 20 to 40 mm were recorded and at Manning where the least (5.0 mm) amount was recorded.
90-day precipitation departures (Figure 4) - Over the past 90-days, precipitation over most of the Southern and Central Regions as well as the southeastern portion of the Northern Region was Much Above Normal with the exception of a few isolated pockets reporting Near and Above Normal precipitation. In the southeast corner of the Southern Region, precipitation graded from Above Normal to Below Normal. Similarly in the Northern Region the 90-day precipitation departures graded form Much Above Normal in southeast to Below Normal in the extended area north of the Sturgeon County. Across most of the Peace Region, precipitation over the past 90-days was Below Normal with the central, northern, and three isolated pockets in the southern parts recording Much Below Normal precipitation.
Growing season precipitation (GSP) to date (Figure 5 and Figure 6) - GSP across the reporting area varied widely from 1086.20 mm at Spionkop Creek, in the Foothills of the Southern Region, to a low of 170.7 mm at Manning in the Peace Region.
In the Southern Region, the GSP in the foothill areas ranged from 700 -1100 mm, with the greatest amounts recorded at Spionkop Creek (1086.2 mm), and Pincher Creek (989.0 mm). Across the central parts of the Southern Region GSP precipitation ranged from 550 mm in the west near Lethbridge falling to 350 along the eastern boarders of the M.D. of Taber, County of Warner and County of Newell. The eastern parts of the Southern Region received low amounts of precipitation ranging from 200-250 mm at the southeast around Onefour (208.1 mm) to 300-350 mm through County of Forty Mile and Cypress County. Similarly the GSP in the Central Region ranged from 450 to 700 mm in the west, along the foothills, down to 300 to 500 mm elsewhere with the exceptions of a few isolated pockets receiving 200 to 300 mm, with the lowest amount recorded in Drumheller (242.0 mm) and near the town of Esther (269.6 mm) in the east. In the Northern Region, the central areas around the county of Sturgeon and Strathcona, received GSP, ranging from 250 to 350 mm compared to the 350 to 500 mm across most other areas in the region. The greatest amounts of GSP in the Northern Region were recorded at Lloydminster (511.6 mm) and at Cold Lake (493.9 mm). Across the Peace Region GSP ranged from 200 to 300 mm with greater amounts recorded across the western and the eastern locations ranging from 300 to 400mm. Elsewhere in the Peace Region the least amount of GSP (170.7 mm) was recorded at Manning, whereas the highest (410.4 mm) was recorded at House Mountain.
Across most of the Peace Region, GSP expressed as a percent of Normal (Figure 6), was Below Normal while the western and the eastern parts are Near Normal. Similarly, in the Northern Region the central portion recorded Below Normal GSP, while the rest of the region reporting Near Normal, with the exception of the extreme eastern areas, reporting Above to Much Above Normal. In the Central Region the GSP expressed as a percent of Normal, in general, grades from Near Normal in the west to Above Normal in the center and then back to Above Normal in the eastern parts of the region. In the Southern Region, GSP grades from Much Above Normal in the northwest to a Near Normal in the southeast.
Precipitation departures for the month of October (Figure 7) - October precipitation in the North, Central and Southern Regions ranges from Much Above Normal to Near Normal with the exception of few isolated pockets reporting Below Normal precipitation. In contrast, most of the Peace Region received Much Below Normal precipitation with the exception of the west and two isolated pockets in the north and southwest that received Near Normal to Below Normal precipitation.
Normal precipitation for the month November (Figure 8) - Provincially, on average about 4.8 % of the annual precipitation falls in November. During this month precipitation totals, range from 10 to 20 mm across the east half of the reporting area, 20 to 30 mm through the Peace Region and upwards of 40 to 50 mm in the southwestern foothills.
Soil moisture
Soil moisture in the agricultural regions of Alberta (Figure 9) - Soil moisture reserves across most of the Northern, Central and Southern regions, increased since the last report, as a result of Near to Much Above Normal precipitation. With the end of the growing season and the onset of freezing nighttime temperatures, evaporative demand is low. Thus, since the soil has not yet frozen, most of the incident precipitation is contributing to the increases in soil moisture, even in the Peace Region where marginal soil moisture gains were computed to occur, despite Much Below Normal precipitation for this time of year.
In the Southern and Central Regions soil moisture reserves graded from more than 125 mm in the foothills, to 50 to 100 mm in the east with the exception of the southeastern corner of the province with less than 50 mm reserve. The excess soil moisture in the western half of the region has made harvesting difficult.
In the centre of the Northern Region, a large area with less than 25 mm soil moisture has disappeared and now stands at 25 to 50 mm of reserve. Soil moisture level across the remainder of the region grades to above 100 mm in the east, delaying harvesting operation. Since the last report, in the central and the northern part of the Peace Region, a large area with a soil moisture reserve level below 25 mm has diminished in size, but only marginally. All other areas of the Peace Region are reporting low soil moisture reserves (25 to 50 mm).
Overall, areas with less than 50 mm of soil moisture in both the Peace and Northern Regions require at least Above Normal precipitation over the fall, winter and early spring in order to establish soil moisture reserves that are sufficient to resist short-term dry spells during the early part of the next growing season. If above normal temperatures and precipitation persist into mid to late November, some soil moisture replenishment may occur.
Current soil moisture departures (Figure 10 and Figure 11) - Soil moisture deficits are computed relative to Normal, which is the 30-year statistical average taken from the years 1971-2000 (Figure 10). In the Peace Region, most areas are reporting Well Below Normal soil moisture reserves with the exception of the extreme south and parts of the north where Extreme Deficits are found and the northwest, where Near Normal conditions are reported (Figure 11).
Across most of the central and northern parts of the Northern Region soil moisture reserves are Well Below Normal, but rapidly increase to Above Normal and then to Extreme Surplus in the east and southwestern portions of the region. Across most of the Southern and Central Regions, soil moisture reserves range from Well Above Normal to Extreme Surplus except for a small area in the southeastern part of the Southern Region where Below Normal condition are found.
Probability of returning to normal spring conditions (Figure 12) - The amount of precipitation recharge needed to bring current soil moisture conditions to 30-year average spring (May 1) levels was compared to recharge rates that has occurred in the past (1971-2000) for similar period. The probability of returning to Normal conditions is then computed from the number of years, between 1971-2000, that soil moisture recharge rates has equaled or exceeded those currently required to bring soil moisture levels to average.
The computed probability of achieving normal spring soil moisture is less than 20% for the Peace Region and most of the North Central parts of the Northern Region. In these areas a Much Above Normal precipitation will be required between now and spring to bring soil moisture reserves to a point where short duration dry spells can be tolerated without undue crop moisture stress.
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 from precipitation totals over a 365-day period using the Standardized Precipitation Index (SPI). Long term Drought is rated as either Wet, Above Normal, Normal, Drought Alert, Drought or Exceptional Drought. The United States National Drought Mitigation Centre recommends the SPI for drought identification. Long term drought conditions are reported year-round.
The trend in long term drought is determined by comparing the 365-day SPI with the 90-day SPI. Where the 90-day SPI value is -1 to +1, then a trend toward moderating conditions is occurring, potentially resulting in Normal status. If the 365-day SPI values for that area are already Normal, then the trend is toward no change. If the 90-day SPI value is -1 to -2, then the area is trending toward Drought Alert status. This could be a deteriorating condition if the current 365-day value is Normal, however it could represent a continuing condition if the area is already in Drought Alert, or an improving condition if the area is already in Drought. Values of the 90-day SPI that are between of -2 to -3 and lower than -3 indicate a trend toward Drought and Extreme Drought respectively. Values of the 90-day SPI that are between +1 and +2, and greater than +2 represent a trend toward Above Average and Wet respectively.
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)
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. Low 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. Below average soil moisture levels, at any time, indicate a need for more precipitation to restore reserves.
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.
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 the 1971-2000 period, 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 during the 1971-2000 period 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 October 31, 2005.
Drought analysis is currently scheduled at monthly intervals between October 30 and May 1. This report updates the previous report of September 18, 2005 |
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