THE STRUCTURE OF DROUGHT 

Ronald StewartUniversity of Manitoba

 

A lot of nothing?

 

To illustrate some aspects of drought's 'structure' (internal features)

OBJECTIVE

The CanadianPrairies

Mackenzie

Saskatchewan

400

500

600

700

850925

1000

300

-2.0-3.0 -1.0 0 1.0 2.0 3.0

PRESSURE (hPa)

FLUX (1011 kg/Pa/month)

VERTICAL MOISTURE FLUX PROFILE

Into the Prairies

Out of thePrairies

 

 

 

  

PDSI- Palmer Drought Severity Index SPI- Standardized Precipitation Index

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COMMON VIEW …

Drought … Not Too Hot

Temperature Precipitation

Summers of 2000, 2001 and 2002

PRECIPITATION-TEMPERATURE ANOMALYAgricultural 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 PRAIRIES2002

ClimatologyLow precipitation events: 52% of total

Sub-drought 2002Low precipitation events: 60% of total

Daily Precipitation Amounts Low precipitation

event:< 10 mm

VIRGA

Summer 2002 - Edmonton

Precipitation Amount Reduction (%)    -49Precipitation (h)                                   123  Virga (h)                                              130 

Cold Lake 24 April 2003• Hail and rain• 243% of monthly

average accumulation

Cold Lake 1-3 October 2005•  Rain and snow• 143% of monthly average

accumulation

PRECIPITATION RATE

45 dBZ maximum

20 dBZ maximum

Annual Variation of calm wind obs at 10-m height drought YR - climatology

-80.0

-60.0

-40.0

-20.0

0.0

20.0

40.0

1999 2000 2001 2002 2003 2004 2005

YEAR

Perc

enta

ge d

iffer

ence

(%)

EdmontonMedicine HatLloyministerPrince AlbertSaskatoonSwift CurrentWinnipeg

OCCURRENCE OF CALM CONDITIONS

DUSTSTORMS 

32 major dust storms in Saskatchewan in 2002

CANADIAN PRAIRIES2002

_________ 900 km ___________

June 6-9, 2002

Palmer Drought Severity Index (PDSI) for agricultural years with severe drought

___ 900 km __

DROUGHT TYPES

• The sustained lack of precipitation can be linked with different 'types'

• A drought can go between 'types'

No precipitation       ... or ... Sprinkles

Virga Chance of catastrophic rain

Steady rain Torrential rate

Hot Cold

Windy Calm

Dusty Clear

Cloud-free Cloudy

Drought has spatial and temporal 'structure'

One can think of it as being of various 'types'

Understanding drought needs to consider such features

SUMMARY