OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of...
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Transcript of OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of...
![Page 1: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/1.jpg)
OVERLAPPING SCALES and the
ATMOSPHERIC CAUSES OF FLOODS
Katherine K. Hirschboeck Laboratory of Tree-ring
Research University of Arizona
![Page 2: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/2.jpg)
![Page 3: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/3.jpg)
• Overview of atmospheric causes of floods
• Issues related to overlapping scales
• Implications
• Concluding remarks
PURPOSE
![Page 4: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/4.jpg)
Flood studies / observations:
• urban flash flooding; small basin floods in U.S.
• Basin-wide and regional flooding in AZ, LA, and Mississippi RB
• Largest US rainfall-runoff floods
• Global flooding events in the Dartmouth Flood Observatory
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ATMOSPHERIC CAUSES
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CAUSAL ELEMENTS OF FLOODS
• INGREDIENTS
• PROCESS
• PATTERN
• PERSISTENCE
• SYNERGY
![Page 7: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/7.jpg)
INGREDIENTS
after Doswell et al. (1996)
Heavy Precipitation
“The heaviest precipitation occurs where the rainfall rate is the highest for the longest time.”
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INGREDIENTS
High Precipitation Rate (R)• Rapid ascent of air
• Substantial water vapor
• Precipitation efficiency
after Doswell et al. (1996)
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INGREDIENTS
Sustained Duration
• System Movement Speed
• System Size
• Within-System Variations in Rainfall Intensity
after Doswell et al. (1996)
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INGREDIENTS SUMMARY
Heavy Precipitation
High Precipitation Rate Sustained Duration
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Meteorological processes bring these
basic ingredients together
Rainfall rates associated with deep, moist convection are higher than with other rain-producing systems
INGREDIENTS SUMMARY
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CAUSAL ELEMENTS OF FLOODS
• INGREDIENTS
• PROCESS
• PATTERN
• PERSISTENCE
• SYNERGY
![Page 13: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/13.jpg)
PROCESS
Heavy flood-causing precipitation can be associated with a wide variety of storms types: Multicell or supercell convection Squall lines
Mesoscale convective systems
(MCS, MCC)
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PROCESS
Tropical Storms
Extratropical Cyclones &associated Fronts
Snow events w/ Extratropical Cyclones, etc.
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PROCESS
OVERLAPPING SCALES
Mesoscale
Synoptic scale
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precipitation systems which occur at one scale . . . .
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. . . Are strongly interconnected with systems at other scales . . .
. . . and larger scale processes set the stage for activity at smaller scales.
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Scale factors are critical determinants of whether a given atmospheric mechanism will cause a flood.
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PROCESS
Large-scale vertical motions typical do not initiate convection . . .
. . . but there is a connection between synoptic-scale weather systems and deep, moist convection
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PROCESS
Connection:
. . . via moistening and destabilization created by the modest but persistent SYNOPTIC-SCALE vertical ascent ahead of short-wave troughs
Doswell 1987, Doswell et al. (1996)
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Mesoscale Synoptic Scale connection
in meteorology of flash floods
Based on Maddox et al. (1980)
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PROCESS SUMMARY
OVERLAPPING SCALES
Mesoscale
Synoptic scale
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PROCESS SUMMARY
• Linkage across scales does not necessary imply that there is a seamless process continuum in the nature of flood-causing storm systems• Distinct processes tend to concentrate around discrete and disparate states
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CAUSAL ELEMENTS OF FLOODS• INGREDIENTS
• PROCESS
• PATTERN
• PERSISTENCE
• SYNERGY
![Page 25: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/25.jpg)
Mesoscale
Macroscale
Synoptic scale
![Page 26: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/26.jpg)
PATTERN
> Correlation fields > Composites> Principle components
![Page 27: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/27.jpg)
Flooding in La Paz County, Arizona
October, 2000
![Page 28: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/28.jpg)
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Composite pattern Cutoff Low Floods in
AZ
Correlation pattern for peak October streamflow
Agua Fria River
western AZ
L
H
L
LH
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PATTERNOctober ‘00 composite anomaly pattern
October W. AZ peak streamflow pattern
(Similar to PNA teleconnection
pattern)
H
L
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Teleconnections & indices
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PATTERN SUMMARY
• Most floods in studies could be linked to one of several flood-producing synoptic-scale and/or larger-scale patterns
• Patterns change regionally and seasonally
• Frameworks for forecasting and “backcasting”
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PATTERN SUMMARY
• Pattern alone not always sufficient as causal explanation
• If ingredients are not in place, heavy precipitation / flood may not develop
• If ingredients are in place, a benign pattern may yield anomalous flooding (flash floods)
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CAUSAL ELEMENTS OF FLOODS
• INGREDIENTS
• PROCESS
• PATTERN
• PERSISTENCE
• SYNERGY
![Page 35: OVERLAPPING SCALES and the ATMOSPHERIC CAUSES OF FLOODS Katherine K. Hirschboeck Laboratory of Tree-ring Research University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649d955503460f94a7df60/html5/thumbnails/35.jpg)
PERSISTENCE
Flooding in the Mississippi River Basin
Spring 1973
Hirschboeck (1985)
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PERSISTENCE
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PERSISTENCE
Flooding in Arizona - Winter 1993
House and Hirschboeck (1997)
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PERSISTENCE
“ moistening and destabilization created by the modest but PERSISTENT synoptic-scale vertical ascent ahead of short-wave troughs”
Doswell 1987, Doswell et al. (1996)
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PERSISTENCE SUMMARY
• Persistence of INGREDIENTS (e.g., deep moist convection environment) most important at small scales (flash floods)
• Persistence of PATTERN most important at larger scales (basin-wide / regional floods)
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PERSISTENCE SUMMARY
• In the largest and most extreme floods studied, PERSISTENCE was always a factor
• Persistence bridges meteorological and climatological time scales
• Persistence = underlying factor in atmosphere / basin synergy
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CAUSAL ELEMENTS OF FLOODS• INGREDIENTS
• PROCESS
• PATTERN
• PERSISTENCE
• SYNERGY
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SYNERGY
SYNERGY = A combined action or operation; a mutually advantageous conjunction or compatibility of distinct elements
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From Doswell et al. (1996)
> slow movement of system> large area of high R along motion
vector> both occurring together (as in d)
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The ways in which precipitation is delivered in both space and time over drainage basins of different size strongly influence the occurrence and type of flood event.
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Source: National Severe Storms Lab
Orography = a key factor in synergistic flood development
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SYNERGY SUMMARY
Synergistic relationships between:
> meteorological & climatological processes; > basin size, shape, and orientation; > orography
were factors in many of the extreme flood peaks, esp. in small basins
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Synergistic factors can both supercede the influences of PATTERN
. . . or enhance the influences of PATTERN
SYNERGY SUMMARY
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IMPLICATIONS
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KEY QUESTION:
Can flood-causing mechanisms be analyzed as a process continuum . . .
. . . using statistical techniques, (e.g. “upscaling” or
“downscaling”) . . .
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. . . Or do they concentrate around discrete scales?
Are there limits in space and time to our ability to transfer causal-process information observed at one scale to that of another?
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Can processes and scale relationships observed in the gaged record be applied over longer time scales?
• assess paleoflood causes
• develop climatic forecasts for floods
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Tropical Cyclone 05B, 10-29-99, very heavy rain, winds 135 knots, second cyclone in two weeks
BANGLADESH
INDIABURMA
(MYAMAR)
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Year 1999 Large Floods
Source: Dartmouth Flood Observatory
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Year 2000 Large Floods
Source: Dartmouth Flood Observatory
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1997 – 2000 Composite of Large Floods
Source: Dartmouth Flood Observatory
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Temporal clustering in global floods, (based on number of reported
floods 1975-99)
Source: Dartmouth Flood Observatory
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Temporal clustering in largest U.S. rainfall / runoff floods (in different size drainage areas)
Hirschboeck (1987)
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Mesoscale
Macroscale
Synoptic scale
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CONCLUDING REMARKS
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Concluding Remarks
• INGREDIENTS
• PROCESS
• PATTERN
• PERSISTENCE
• SYNERGY
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Concluding Remarks
Flood events tend to be discontinuous and episodic in time . . . . . . and clustered in space
. . . in response to varying states of the
atmosphere
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Concluding Remarks
Across all scales, the persistence of a precipitation system is a key element for generating exceptionally large floods
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Concluding Remarks
Circulation features which enhance persistence tend to occur as discrete time / space anomalies that are not easily captured by upscaling or downscaling techniques.
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Concluding Remarks
Most major floods are characterized by a synergistic combination of atmospheric, hydrologic, and drainage-basin factors that intensify the event and “tip the scales” beyond what might be expected in a smoothly telescoping process continuum.
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