GEOG5839.22, Paleofloods

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This document discusses paleoflood research along the Red River. It provides evidence that past floods along the river were larger than any observed in recorded history. Tree ring analysis reveals details about 3 extremely large floods that occurred in the 17th, 18th and 19th centuries. The tallest scars on trees from these events indicate water levels exceeded any modern floods by 1-3 meters. Studying past flood sizes and frequencies provides important information about the full range of Red River flood risk.

INSURED LOSSES
DUE TO FLOODS EXCEEDED

$6.4 B
IN 2010.

Source: Swiss Re

WORLDWIDE

11,027
PEOPLE WERE
KILLED BY FLOODS.

Source: Swiss Re

Annual losses* due to ﬂoods in the United States 2005

1993

1972

1927

Source: National Weather Service
* adjusted for inﬂation

The 100-year ﬂood refers to a ﬂood that has a 1% chance
of being equaled or exceeded in any single year.

“ NG ”
O
The 100-year ﬂood has come and gone, so, by all rights,

R
Tucsonans should enjoy another century of great Southwest weather.

W
Metropolitan Tucson Convention and Visitor’s Bureau
Sent immediately a er a severe ﬂood

Paleoﬂood hydrology uses physical evidence le behind
on the landscape to make inferences about past ﬂoods
that were not directly observed or recorded by humans.

Photograph: David Snyder

Slackwater deposits Fine-grained sediments laid down by ﬂoodwaters

“
The forts now stand like a castle of romance in the midst of
an ocean of deep contending currents, the water extending
for at least a mile behind them, and they are thereby only
approachable by boats and canoes.”
Francis Heron
Hudson Bay Company, 1826

St.. George and Rannie, Canadian Water Resources Journal, 2003

scarring

microclimatology

injury

“ﬂood rings”

Reading
St. George (2010), Tree rings as paleoﬂood and
paleostage indicators. In Stoﬀel et al., (eds.),
Tree Rings and Natural Hazards.

Photograph: Mark’s Postcards from Beloit

FLOOD SCARS
The timing of the ﬂood can be determined by counting the number
of rings between the scar and the outside ring, and the height of
the scar represents the minimum elevation of high water.

Floods can damage trees by tilting or partial uprooting
or can uproot them completely, causing their death.

Winnipeg

The name Winnipeg is a transcription of
the western Cree word wi-nipe-k meaning
"muddy waters"

Source: U.S. Coast Guard, Lt. Brendan Evans

Grand Forks, North Dakota 1997 ﬂood and ﬁre

How large can Red River ﬂoods get and how o en
do the large ones occur?

Are there geological processes that may be
changing the Red River ﬂood hazard?

What are the geological controls that govern the
character of Red River ﬂooding?

Instrumental and historical estimates of major Red River ﬂoods

Source: St. George and Nielsen, Geographie Physique et Quaternaire, 2002

In hydrology, ﬂood observations reported as having occurred
above some threshold are known as censored data sets.

Photograph: USGS

1979 Red River ﬂood Drayton, North Dakota

St. George et al. (2002), Tree-Ring Research

350 years of Red River ﬂoods

Source: St. George and Nielsen, The Holocene, 2003

TREES AS PALEOFLOOD INDICATORS
Strengths and limitations

Nearly all decisions about water in Minnesota relate either directly or indirectly to data collected by the state’s hydrological observing network. Because most gauges were installed in early 20th century, as a whole the network provides us with roughly a 100-year ‘window’ to estimate flood risks, develop worst-case scenarios for drought, and set maximum allowable withdrawals for aquifers. But when we rely exclusively on observations made during this relatively brief interval, we may inadvertently increase our exposure to hydrological ‘surprises’. In order to make sound decisions about water in Minnesota, we need to expand this window: into the past, drawing upon historical accounts and natural archives; and into the future, via projections from climate and hydrological models. By cultivating a broader perspective on hydrological variability and extremes across the state, we will be better prepared to ensure adequate water supplies and mitigate the impacts of future floods and droughts.

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Trees as flood sensors

Scott St. George

In many settings, trees growing on floodplains provide an important source of indirect evidence that may be used to infer the occurrence, extent, and magnitude of floods prior to direct observations. That evidence may take several forms, including external scars caused by abrasion or impact from floating debris, anatomical changes within the annual growth increment following prolonged stem or root inundation, or tilting or uprooting due to the hydraulic pressure of floodwaters. Likely the most useful characteristic of paleoflood studies based on floodplain trees is their relatively high temporal resolution and dating accuracy compared to most other methods. Dendrochronological methods can routinely date past floods to the year of their occurrence and, in rare cases, can estimate the timing of floods that occur during the growing season to within two weeks. This high degree of chronological control, which is surpassed only by that provided by direct observation or instrumentation, can be used to determine whether floods in separate watersheds were synchronous or offset by several years and test hypotheses that suppose linkages between extreme floods and specific forcing mechanisms. Furthermore, the wide geographic distribution of tree species with dateable rings combined with the broad suite of methods available to examine interconnections between floods and tree growth allow this style of paleoflood hydrology to be applied to many settings that are not suitable for techniques that depend on geological evidence. Future paleoflood research involving tree rings will need to strike a balance between improving our understanding of the biological and fluvial processes that link tree growth to past events, and providing answers to questions about flood dynamics and hazards that are needed to safeguard people and property from future floods.

Expecting the unexpected: The relevance of old floods to modern hydrology

Scott St. George

As one of the most destructive hazards on our planet, floods kill thousands of people and cause billions of dollars in property damage every year. We usually try to gage the risk of future floods by fitting mathematic functions to hydrological data and then extrapolating the upper tail of those distributions. But because large floods are rare and river gage records are short, the conventional approach can sometimes drastically underestimate the threat posed to communities and infrastructure by extreme floods. In this lecture, I’ll argue that paleoflood hydrology — the study of ancient floods as recorded by river and lake sediments, trees, caves, and historical documents — is absolutely essential to judge the real risk of large, rare floods. And I’ll use examples from North America to illustrate how a ‘deeper river memory’ can help people evaluate their own vulnerability to floods, weigh the potential benefits of proposed infrastructure projects, and become more aware of what nature is truly capable of producing.

Noah, Joseph, And High-Resolution Paleoclimatology

Scott St. George

In 1968, Benoit Mandelbrot and James Wallis published an article titled ‘Noah, Joseph, and operational Hydrology’ in the journal Water Resources Research. In it, they argued that hydrological models of the day were not able to estimate the true risk of extreme floods or prolonged drought, and that rare hydrological events were much more common than usually assumed. In this lecture, I’ll review how high-resolution paleoenvironmental archives can help us judge more accurately the risks posed by the ‘Noah’- and ‘Joseph’-style events described by Mandelbrot and Wallis. I’ll give particular emphasis to the environmental information recovered from the rings of ancient trees, and explain how dendrochronology (tree-ring research) has been used to redefine the ‘flood of record’, test potential avenues for long-lead climate predictions, and gage the performance of state-of-the-art climate models.

Long droughts: Using natural climate archives to gage the risks of future “me...

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In the Biblical story of Joseph, following seven years of abundance, the Kingdom of Egypt was confronted by seven years of drought and famine. In the parlance of modern climate science, intervals with several consecutive extremely dry years are described as ‘“megadroughts”. In this short talk, I’ll describe how climate scientists combine clues from natural weather archives (including corals, tree rings, lake sediments, and many other sources) to reveal the history of ancient megadroughts across our planet. And I’ll highlight new research that combines these surrogate drought records with simulations from state-of-the-art climate models to help us better anticipate the risks of unusually persistent droughts during the coming century.

Large-scale dendrochronology and low-frequency climate variability

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Large-scale low-frequency variability has emerged as a priority for climate research, but instrumental observations are not long enough to characterize this behavior or gage its impacts on dependent geophysical or ecological systems. As the leading source of high-resolution paleoclimate information in the middle- and high-latitudes, tree rings are essential to understand low-frequency variability prior to the instrumental period. But even though tree rings possess several advantages as climate proxies, like other natural archives they also have their own particular impediments. In this lecture, Dr. St. George will describe the structure and characteristics of the Northern Hemisphere tree-ring width network, and outline how the fingerprint of decadal and multidecadal climate variability encoded within ancient trees varies across the hemisphere.

Flood rings: Paleoflood evidence in tree-ring anatomy

Scott St. George

How long do we need to watch a river before its behavior holds no more surprises? In this country, instrumental measurements of river stage and discharge stretch back a century or more, but this observed history still provides only a rough guide to the risks of future extreme floods. In this lecture, I’ll outline how paleoflood hydrology expands our perspective on river history by combining historical, botanical, and geological evidence of earlier (and ofttimes unknown) floods. And I’ll explain how we can interpret those physical clues left behind by ancient floods to improve hazard assessments for at-risk communities, support decisions about flood infrastructure, and investigate the long-term effects of climate or land-use changes on flooding. Because what has happened before can happen again, most everyone near a river would profit by keeping a longer memory of old floods.

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Many of the decisions we make about environmental issues are based on experience. Whether we're setting limits for the use of scarce resources, estimating the risks posed by natural hazards, or deciding how to manage protected areas, our plans for the future often reflect our understanding of the past. The problem is that, when it comes to the environment, our society has a fairly short memory. In this presentation, Dr. St. George will discuss how the study of ancient trees is expanding our perspective on the natural history of the northern Plains and helping to answer questions about what the future may hold for Minnesota's environment.

Solar ghosts: Weighing the evidence for sunspot cycles in fossil trees

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In their study of tree rings from the Chemnitz Fossil Forest (Germany), Luthardt and Rößler (2017) claim to identify a regular near-11-yr cyclicity in growth, and present that pattern as evidence of the influence of the Schwabe solar cycle (Usokin and Mursula, 2003) on climate and forest productivity during the early Permian. If correctly interpreted, these fossil tree rings would indicate the sunspot cycle was the dominant influence on interannual variability in Earth’s climate during this period and that it has been a consistent aspect of our Sun’s behavior for at least the past 300 m.y. We argue the fossil tree-ring record from Chemnitz does not constitute reliable evidence of solar activity during the Permian because the individual tree-ring sequences are not correctly aligned (dendrochronologically dated) and, as a result, the mean ring-width composite is not a meaningful estimate of year-to-year variations in tree growth in this ancient forest.

The "Year Without A Summer" was not a year without a ring

Scott St. George

The societal value of historical and paleoflood research in Manitoba, Canada

Scott St. George

Southern Manitoba is one of the most flood-prone regions in Canada, with the Red River of the North being the cause of most significant floods. The realization that the then-recent 1950 flood disaster was dwarfed by the historical 1826 flood led Canadian government officials to set an unusually high design standard for the Red River floodway, a 48-km long diversion built in the 1960s to protect the provincial capital of Winnipeg. And after paleoflood research confirmed new evidence of the 1826 flood, that event was cited as the main justification for expanding the Red River floodway, a $668 billion CAN infrastructure project that began in 2010. Without these insights from historical and paleoflood research, it’s almost certain flood risk estimates would have been unrealistically low and Winnipeg would have adopted a lesser level of flood protection. Because widespread Euro-American settlement in the Pembina Territory (the present-day Red River basin within the United States) did not occur until the 1870s, there are no historical accounts that indicate whether the 1826 flood was also so severe in North Dakota or Minnesota. As a result, the 1997 flood, which was nearly 1.5 times larger than any other previous flood in the US gage record, overwhelmed the dikes protecting Grand Forks and East Grand Forks. By having a deeper understanding of the history of flooding, communities are better able to anticipate future floods, make sound decisions about flood protection and migration, and protect people and their property more effectively.

Guarding against false discovery in large-scale dendroclimatology

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Measurements of tree-ring widths are the most widely-distributed and best replicated source of surrogate environmental information on the planet, and are one of the main archives used to estimate changes in regional and global climate during the past several centuries or millennia. Because the Northern Hemisphere ring-width network is now so large, it is more crucial than ever to ensure our understanding of tree-environment relations is not influenced by decisions to include or exclude certain records. It may be the case that a particular set of ring-width records are, for whatever reason, more tightly coupled to a particular climate factor than other records from the same region or species and, as a result, may be superior estimators of that factor’s past behavior. At the same time, it is known that selecting a small number of predictors from a large pool of potential candidates increases the likelihood of a Type I error. That effect may be particularly relevant to dendroclimatology because the total number of available ring-width records is often much larger than the number of records used to produce reconstructions of large-scale climate features. As an initial step, it would be helpful if paleoclimate reconstructions derived from tree rings described more explicitly the criteria used to select ring-width records as potential predictors and specified those records excluded by that screening. By comparing ring-width chronologies and their relations with climate against the standard set by thousands of records across the hemisphere, we should be better able to distinguish climate signals from proxy noise and produce more accurate reconstructions of climate during the late Holocene.

Seeing the Forest for the Tree(Ring)s

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Every year, trees in temperate and boreal forests go through a cycle of dormancy and activity that produces a new layer of tracheids, fibers and other woody cells around their stem. The end result of this process - a tree ring - is one of the most obvious signs in nature documenting the passage of time and the character of that year’s weather. Measurements of tree-ring widths are the most widely-distributed and best replicated source of surrogate environmental information on the planet and are one of the main archives used to estimate changes in regional and global climate during the past several centuries or millennia. In this lecture, I describe the structure and characteristics of the Northern Hemisphere tree-ring width network, and outline how these data are linked with key aspects of local climate and the global climate system. More generally, by describing the characteristics of the Northern Hemisphere tree-ring width network and the diversity of its relations with varying aspects of the global climate system, this presentation highlights the breadth and quality of environmental information that may be recovered from the width of annual growth layers in temperate and boreal trees.

Decadal variability in tree rings

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Strong variance at decadal and multidecadal timescales is a common feature of most tree-ring width records. But does this aspect of tree growth exhibit such long-memory behavior due to biology, climate, or some combination of the two factors? Understanding the origins of this behavior is crucial for efforts to evaluate the causes of decadal variability in the climate system. Presentation at Johann Gutenburg University (Mainz) on February 16, 2017.

Absent rings are rare in Northern Hemisphere forests outside the American Sou...

Scott St. George

Background/Question/Methods Under environmental stress, boreal and temperate trees will occasionally form a discontinuous layer of wood about their stem, a condition described as a locally-absent (or “missing”) growth ring. Absent rings can potentially cause errors in tree-ring dates and dendroclimatic reconstructions but the frequency, distribution and controls of these features are not well understood at large spatial scales. Furthermore, the recent claim that the Northern Hemisphere tree-ring network contains multiple chronological errors caused by widespread but unrecognized locally-absent rings has been difficult to evaluate because it is not known where or when absent rings have occurred across boreal and temperate forests or what environmental factors cause the development of spatially-extensive absent rings. Here we present a synthesis of locally-absent rings across the Northern Hemisphere during the last millennium based on 2,359 publicly-available tree ring-width records. Results/Conclusions Over the entire dataset, one locally-absent ring was observed for every 240 visible rings. More than half of all records (1,296 of 2,359) did not contain a single absent ring. Absent rings were extremely uncommon at high latitudes; poleward of 50°N, the absent:visible ratio increased from 1:240 to 1:2,500. Absent rings were not widespread during the growing seasons that followed the four largest stratospheric sulfate aerosol injection events of the last millennium, including A.D. 1259 and the “Year Without a Summer” in A.D. 1816 or during the coldest year in the Northern Hemisphere in the last 1,500 years. Because these features have occurred so rarely in high-latitude and high-elevation tree ring-width records, the argument that paleotemperature estimates based on these data contain chronological errors due to unrecognized absent rings is not consistent with field observations. If however the rate of absent-ring formation were to increase in forests outside of the American Southwest, that behavior would represent a response to environmental stress that is without precedent over the last millennium.

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Even after more than a century of coordinated monitoring, instrumental weather observations are still too short to adequately constrain decadal or multidecadal behavior in the Earth’s climate system. Leading climatologists and climate modelers have called for the wider application of high-resolution proxy records to decadal variability and prediction studies, and our community has responded by producing new paleoclimate products that specifically target this type of ‘intermediate-term’ behavior. But we now also know our medium changes that message: the biological and geological systems that encode climate information into natural archives often also alter the original ‘input’, usually due to either seasonal filtering or non-climatic persistence. In this talk, we’ll discuss some of the challenges inherent to the use of high-resolution proxies to study decadal or multi-decadal climate variability, and suggest strategies that might clarify how climate acts on those timescales. And we’ll also present a new theoretical framework that could help paleo-scientists evaluate competing ideas about the causes of decadal- or multi-decadal events known to have occurred during the past one or two millennia.

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When climate science is communicated to the broader public, many of its key findings are shared in the form of conceptual diagrams or information-dense data graphics. In this collaboration, we applied a data sonification approach to express NASA’s global temperature record as a musical composition for the cello. The resulting piece, which we titled ‘A Song of Our Warming Planet’, transformed 133 years of annual global temperature anomalies into a haunting, atonal melody that stretched across almost all of the instrument’s range. Since its release in June 2013, the song has been featured by several national and international media outlets, including the New York Times, the Weather Channel, and National Public Radio, and its accompanying video has received more than 140,000 views from nearly every corner of the world. We are currently preparing a new composition for string quartet that will add a geographic dimension to describe both the pace and place of global warming. We believe the success of our initial sonification project is testament to the power of music to reach audiences who respond less enthusiastically to traditional methods used to communicate climate science. We also imagine this approach could be applied more broadly to allow students to create novel, visceral, and memorable encounters with other aspects of the geophysical sciences.

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Anthropogenic climate change is one of the most challenging problems humanity faces, but public opinion surveys show that many people are skeptical about global warming. In this seminar, Dan Crawford, Scott St. George and Todd Reubold will share their experiences with using music to help climate science reach out to new audiences. Their first collaboration — a music video that reconfigures global temperature data as a cello composition — has been described as “amazing, and eerie” and “an effective tool to show people that our planet is changing.” Join us to learn what global warming sounds like!

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GEOG5839.22, Paleofloods

1. November 27 Paleoﬂoods

2. Source: AP Photo/Carolyn Kaster

3. INSURED LOSSES DUE TO FLOODS EXCEEDED $6.4 B IN 2010. Source: Swiss Re

4. WORLDWIDE 11,027 PEOPLE WERE KILLED BY FLOODS. Source: Swiss Re

5. Annual losses* due to ﬂoods in the United States 2005 1993 1972 1927 Source: National Weather Service * adjusted for inﬂation

6. PAST BEHAVIOR FUTURE RISKS

7. Photograph: skooksie

8. “100-year ﬂood”

9. The 100-year ﬂood refers to a ﬂood that has a 1% chance of being equaled or exceeded in any single year.

10. “ NG ” O The 100-year ﬂood has come and gone, so, by all rights, R Tucsonans should enjoy another century of great Southwest weather. W Metropolitan Tucson Convention and Visitor’s Bureau Sent immediately a er a severe ﬂood

11.

12.

13. Paleoﬂood hydrology uses physical evidence le behind on the landscape to make inferences about past ﬂoods that were not directly observed or recorded by humans.

14. Photograph: David Snyder Slackwater deposits Fine-grained sediments laid down by ﬂoodwaters

15. “ The forts now stand like a castle of romance in the midst of an ocean of deep contending currents, the water extending for at least a mile behind them, and they are thereby only approachable by boats and canoes.” Francis Heron Hudson Bay Company, 1826 St.. George and Rannie, Canadian Water Resources Journal, 2003

16. scarring microclimatology injury “ﬂood rings”

17. Reading St. George (2010), Tree rings as paleoﬂood and paleostage indicators. In Stoﬀel et al., (eds.), Tree Rings and Natural Hazards.

18. FLOOD SCARS

19. Photograph: Mark’s Postcards from Beloit

20. Photograph: NDSU Ag Comm

21. FLOOD SCARS The timing of the ﬂood can be determined by counting the number of rings between the scar and the outside ring, and the height of the scar represents the minimum elevation of high water.

22. INJURY

23. Floods can damage trees by tilting or partial uprooting or can uproot them completely, causing their death.

24. MICROCLIMATE Source: Alex Drainville

25.

26. Photograph: Alex Source

27. Source: ouelle e001.com

28. FLOOD RINGS

29.

30. Winnipeg Manitoba

31. Winnipeg The name Winnipeg is a transcription of the western Cree word wi-nipe-k meaning "muddy waters"

32. Source: Greg Brooks

33.

34. Source: U.S. Coast Guard, Lt. Brendan Evans

35. Source: Greg Brooks

36. Grand Forks, North Dakota 1997 ﬂood and ﬁre

37.

38. Source: Ma hew Bietz

39. Lake Agassiz

40.

41. How large can Red River floods get and how o en do the large ones occur? Are there geological processes that may be changing the Red River flood hazard? What are the geological controls that govern the character of Red River flooding?

42. Instrumental and historical estimates of major Red River ﬂoods

43. Erik Nielsen Manitoba Geological Survey

44.

45. Source: Greg Brooks

46.

47.

48.

49. 2008

50. 1875

51. Source: Erik Nielsen

52. 54 Source: Erik Nielsen

53.

54.

55.

56.

57.

58. “ The forts now stand like a castle of romance in the midst of an ocean of deep contending currents, the water extending for at least a mile behind them, and they are thereby only approachable by boats and canoes.” Francis Heron Hudson Bay Company, 1826 St. George and Rannie, Canadian Water Resources Journal, 2003

59.

60. Source: St. George and Nielsen, Geographie Physique et Quaternaire, 2002

61. In hydrology, ﬂood observations reported as having occurred above some threshold are known as censored data sets.

62.

63. Photograph: USGS 1979 Red River ﬂood Drayton, North Dakota

64. Source: St. George and Nielsen, Geographie Physique et Quaternaire, 2002

65.

66. St. George et al. (2002), Tree-Ring Research

67. How large can Red River floods get and how o en do the large ones occur? Are there geological processes that may be changing the Red River flood hazard? What are the geological controls that govern the character of Red River flooding?

68. 350 years of Red River ﬂoods Source: St. George and Nielsen, The Holocene, 2003

69. TREES AS PALEOFLOOD INDICATORS Strengths and limitations

70. Photograph: David Snyder

71. Redrawn from Stahle (1990)

72. Source: Steﬀano A ardi

73. scarring microclimatology injury “ﬂood rings”

74. GEOG5839 XT C L AS S NE

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