Trends and Changes in Extreme Weather Events
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Trends and Changes in Extreme Weather Events: An assessment with focus on Alberta and Canadian Prairies By Madhav L. Khandekar October 2002 Pub. No. I/927 ISBN: 0-7785-2428-0 (Printed Edition) ISBN: 0-7785-2429-9 (On-line Edition) Web Site: www.gov.ab.ca/env/info/infocentre/publist.cfm Disclaimer Alberta Environment funded this study for the Climate Change Research Users Group. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. The author, not the publisher, is responsible for the conclusions and opinions expressed. Any comments, questions or suggestions on the content of this document may be directed to: Science and Standards Branch Alberta Environment 4th Floor, Oxbridge Place 9820 – 106th Street Edmonton, Alberta T5K 2J6 Fax: (780) 422-4192 For additional copies, please contact: Information Centre Alberta Environment Main Floor, Great West Life Building 9920 – 108th Street Edmonton, Alberta T5K 2M4 Phone: (780) 944-0313 Fax: (780) 427-4407 Email: [email protected] SUMMARY This report examines recent studies on trends and changes in extreme weather events in Canada and assesses these studies in the context of global warming. The assessment suggests that extreme weather events (hot spells, extreme precipitation events, thunderstorm/tornadoes and ice storms) do not show an increasing trend anywhere in Canada, or over the Canadian prairies at this point in time. On the Canadian prairies, extreme cold spells and winter blizzards are definitely on the decline during the past 40 years. In the higher latitudes of the northeast, from Baffin Bay to Labrador, extreme cold spells have increased in the last 50 years. The total precipitation has increased everywhere in Canada but this increase is mainly due to increase in low to moderate intensity events. The Canadian prairies have experienced drought conditions during the mid-1980s and more recently during 1998/99 and in 2001. These drought patterns appear to be primarily governed by the phase of the ENSO (El Nino-Southern Oscillation) cycle. Canada as a whole is not getting hotter, but less cold. Canada as a whole is getting a little wetter. On the Canadian prairies, low intensity precipitation events have increased in the last 50 years, and for Alberta, summer precipitation has increased by about 10 per cent. Thunderstorms and tornadoes are not increasing on the prairies at this point in time. There is a considerable variability (and uncertainty) in many of the climate model projections of extreme weather occurrences, particularly in regard to the timing of the occurrences. Based on the careful evaluation of available studies, it appears that the likelihood of increased incidences of extreme weather events during the next ten to twenty years over any region of Canada is very small at this time. The present database in Canada, with respect to several extreme weather events like thunderstorms (with or without tornadoes), severe windstorms, hail and lightening is not adequate for assessment of long term trends and changes. Many of these extreme weather events have been monitored and suitably archived only during the last 25 years or so. A few studies reported recently suggest that some of the extreme weather events like severe tornadoes and windstorms may have declined in frequency, following the dust bowl years of the 1920s and 1930s over the Canadian prairies. In higher latitudes, the Canadian database on extreme precipitation and stream flow is also inadequate for long-term trend analysis. There is a definite need to critically assess the available data and develop special techniques for assessing long-term trends in many of the extreme weather elements. Trends and Changes in Extreme Weather Events – An Assessment with Focus on Alberta and Canadian Prairies i ACKNOWLEDGEMENTS Several discussions and e-mail communications with a number of researchers from the Meteorological Service of Canada (MSC) have provided useful input in preparation of this report. I am pleased to acknowledge useful input form the following people: Amir Shabbar, Lucie Vincent and Xuebin Zhang (MSC/Toronto) on precipitation and temperature variability; James Cummine, Bevan Lawson, Mike Noonan and Richard Raddatz (MSC/Winnipeg) on convective activity/tornado counts and winter blizzards over the prairies; Barry Bonsal (MSC/Saskatoon) on extreme temperature variability over the prairies, and Bob Kochtubajda (MSC/Edmonton) on tornado counts for Alberta. Mr. Alf Warkentin (Manitoba Water Resources) provided useful material on the Red River flood of April 1997. My special thanks to Dr. Keith Hage (Professor Emeritus, University of Alberta) for providing useful material from his studies on prairie tornadoes and windstorms. Many thanks to Prof. Stanley Changnon (Illinois State Water Survey/University of Illinois) for his valuable input based on his 50-year long experience in climate and extreme weather. Thanks are also due to Prof. Gerhard Reuter (University of Alberta) for discussion on convective activity in Alberta and for reviewing the report, and to Prof. Edward Lozowski for arranging my lectures at his extreme weather course. The Library facilities of MSC in Downsview (Ontario) are gratefully acknowledged. Finally, I wish to express my gratitude to my wife Shalan for her valuable help during the preparation of this report. Madhav L. Khandekar Unionville, Ontario Trends and Changes in Extreme Weather Events – An Assessment with Focus on Alberta and Canadian Prairies ii TABLE OF CONTENTS SUMMARY..................................................................................................................................... i ACKNOWLEDGEMENTS..........................................................................................................ii LIST OF TABLES ....................................................................................................................... iv LIST OF FIGURES ...................................................................................................................... v 1.0 INTRODUCTION............................................................................................................. 1 1.1 Global Warming and Extreme Weather: A Brief Overview.................................. 1 1.2 Global Warming and Extreme Weather: Media and Public Perception................. 2 1.3 Scope and Purpose of the Present Study................................................................. 3 2.0 EXTREME WEATHER: PRECIPITATION AND TEMPERATURE ..................... 5 2.1 Introduction ............................................................................................................. 5 2.2 Precipitation ............................................................................................................ 5 2.2.1 Droughts and Floods ................................................................................. 11 2.3 Temperature .......................................................................................................... 16 2.3.1 Extreme Hot and Cold Spells.................................................................... 19 3.0 EXTREME WEATHER: THUNDERSTORM, TORNADO, HAIL, WIND............ 27 3.1 Introduction ........................................................................................................... 27 3.2 Thunderstorms and Tornadoes.............................................................................. 27 3.3 Hail........................................................................................................................ 31 3.4 Wind...................................................................................................................... 34 4.0 EXTREME WEATHER: BLIZZARDS, ICE STORMS AND OTHER LARGE-SCALE STORMS ............................................................................................ 37 4.1 Introduction ........................................................................................................... 37 4.2 Blizzards................................................................................................................ 37 4.3 Saguenay (Quebec) Flood, July 1996 ................................................................... 38 4.4 Red River Flood, April 1997................................................................................. 40 4.5 Ice Storms & Freezing Precipitation ..................................................................... 43 5.0 SUMMARY AND CONCLUDING REMARKS.......................................................... 46 5.1 Summary of Important Findings ...........................................................................46 5.2 Extreme Weather and IPCC Projections: Present and Future.............................. 47 5.3 Data Gaps and Future Research Needs ................................................................. 47 6.0 CONCLUSION................................................................................................................ 49 7.0 REFERENCES................................................................................................................ 50 Trends and Changes in Extreme Weather Events – An Assessment with Focus on Alberta and Canadian Prairies iii LIST OF TABLES Table 1 Estimates of confidence in observed and projected changes in extreme weather and climate events ..................................................................................... 2 Table 2 Decadal mean maximum summer (Jun-Aug) temperature values at selected locations