| |
August 6, 2003
The hot and very dry weather during July has resulted in deteriorating crop conditions throughout the province. By July 27, rain was needed immediately and 73% of the agricultural area of Alberta was put in Drought Alert status for growing season drought. The continuing dry weather during the past week has resulted in 94% of the agricultural area of Alberta now being in Drought Alert status (Figure 1).
Longterm drought conditions showed a slight deterioration since July 27, with southwestern Alberta, the Whitecourt - Westlock area, and isolated areas in central Alberta and the Peace region in Drought Alert status. Localized areas in Drought status were around Cardston and Whitecourt.
Seasonal (growing season) drought
Analysis of the 2003 growing season to August 4 showed soil moisture reserves were less than 25mm in most areas east of Highway 2, through most of the northwestern Alberta, and parts of southern, central and the northern Peace region (Figure 2). This is considered insufficient for the next week's crop moisture demand. The remainder of the agricultural area of province has less than 50mm of moisture reserve, which is expected to provide enough moisture for about a week. Crops are at a critical stage and rainfall is needed immediately to maintain yield potential and avoid growing season drought. Crop damage from moisture stress has been reported from Camrose to Red Deer.
Precipitation in the past 90 days (since May 7) was less than 80% of normal in all areas except parts of the Northeast region and the northern Peace region (Figure 3). The west half of southern Alberta, a large area from the MD of Clearwater to Special Area 3 and local areas around Whitecourt and Fairview had less than 50% of normal precipitation.
Growing season drought impacts annual crops and pastures but does not necessarily affect livestock water supply. All areas where moisture conditions were below 25 mm or where the 90-day precipitation departure was below 80% of normal were classified as Drought Alert for growing season drought.
Long term (hydrologic) drought
Hydrologic drought is determined from the 365-day Standardized Precipitation Index (SPI) map (Figure 4). The map shows that Drought Alert conditions persisted in southwestern Alberta, the Whitecourt - Westlock area, and isolated areas around Wainwright, Esther, Lacombe, Three Hills, Beaverlodge, Fairview and High Level. The Lacombe and Three Hills areas were not in Drought Alert status the previous week. Local areas around Whitecourt and Cardston remained in Drought status. Hydrologic drought primarily impacts livestock feed and water supply and may affect annual crops.
Figures 5 to 9 show the longterm cumulative departure from normal from January 2001 through July 2003 at representative stations in each region. Since January 2001, the greatest precipitation shortages, over 400 mm below normal, were at Cardston, Wainwright and Beaverlodge. The least departures were at Ballater and Medicine Hat. All stations except Ballater were below normal for the period.
In southern Alberta, since the heavy rains in June 2002, precipitation dropped sharply from normal at Cardston, but remained near normal at Medicine Hat until the summer of 2003. Precipitation at Lethbridge and Brooks was slightly below normal since July 2002. At Cardston, July 2003 was the 4th driest July since 1923 and the driest since 1960. The effect of the dry summer of 2003 can be seen in the steeply sloping lines at most stations in all regions.
Precipitation analysis was based on Environment Canada data, with recent data unverified. Amounts may change as data becomes verified.
Drought analysis is scheduled at two-week intervals so long as Drought Alert status is in effect in Alberta. Analysis will become weekly if areas in Drought status increase in size.
This report updates the previous report of July 27, 2003.
Report prepared by the Drought Reporting Team
Allan Howard, Ralph Wright, and Doug Sasaki
Conservation & Development Branch
Alberta Agriculture, Food and Rural Development,
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph (780) 427-3556 |
|