THE STRUCTURE OF DROUGHT
Ronald Stewart
University of Manitoba
A lot of nothing?
OBJECTIVE
To illustrate some aspects of drought's
'structure' (internal features)
The Canadian
Prairies
VERTICAL MOISTURE FLUX
PROFILE
300
PRESSURE (hPa)
400
500
600
Out of the
Prairies
Into the
Mackenzie
Prairies
700
850
925
1000
-3.0
Saskatchewan
-2.0
-1.0
0
1.0
FLUX (1011 kg/Pa/month)
2.0
3.0
---
PDSI- Palmer Drought Severity Index
SPI- Standardized Precipitation Index
COMMON VIEW …
Drought … Not Too Hot
Precipitation
Temperature
Summers of 2000, 2001 and 2002
PRECIPITATION-TEMPERATURE ANOMALY
Agricultural Years (Sept-Aug) Edmonton
Monthly temperature anomalies:
agricultural region of the Prairies
CLOUD AMOUNT
2001
___________ 900 km ____________
WATER AND ENERGY CYCLING
Many factors affect the cycling
of water and energy during
drought
CANADIAN PRAIRIES
2002
Daily Precipitation
Amounts
Low precipitation
event:
< 10 mm
Climatology
Low precipitation
events: 52% of total
Sub-drought 2002
Low precipitation
events: 60% of total
VIRGA
Summer 2002 - Edmonton
Precipitation Amount Reduction (%) -49
Precipitation (h)
123
Virga (h)
130
PRECIPITATION RATE
45 dBZ maximum
Cold Lake 1-3 October 2005
• Rain and snow
• 143% of monthly average
accumulation
Cold Lake 24 April 2003
• Hail and rain
• 243% of monthly
average accumulation
20 dBZ maximum
OCCURRENCE OF CALM CONDITIONS
Annual Variation of calm wind obs at 10-m height
drought YR - climatology
Percentage difference (%)
40.0
20.0
Edmonton
0.0
Medicine Hat
Lloyminister
-20.0
Prince Albert
Saskatoon
-40.0
Swift Current
Winnipeg
-60.0
-80.0
1999
2000
2001
2002
YEAR
2003
2004
2005
DUSTSTORMS
32 major dust storms in
Saskatchewan in 2002
CANADIAN PRAIRIES
2002
_________ 900 km ___________
June 6-9, 2002
___ 900 km __
Palmer Drought Severity Index (PDSI) for agricultural
years with severe drought
DROUGHT TYPES
• The sustained lack of precipitation can be linked with different 'types'
No precipitation
... or ...
Sprinkles
Virga
Chance of
catastrophic rain
Steady rain
Torrential rate
Hot
Cold
Windy
Calm
Dusty
Clear
Cloud-free
Cloudy
• A drought can go between 'types'
SUMMARY
Drought has spatial and temporal 'structure'
One can think of it as being of various 'types'
Understanding drought needs to consider such features