Katie HirschboeckLaboratory of Tree-Ring Research

The University of Arizonakatie@ltrr.arizona.edu

Some Thoughts On Developing

Climate-Based Scenariosfor Extreme Hydrologic

Events

Hazards Planning and Policy Panel on the Use of Scenarios to Address Natural Hazards Issues

UCOWR / NIWR Annual Conference July 25, 2007

OVERVIEW:

• Process-Sensitive Upscaling

• Flood & Drought Hydroclimatology(causative mechanisms)

• Integrating the Paleo-Record

How do we transfer the growing body of knowledge

about global and regional climate change and variability

to individual watersheds

to develop useful scenarios about hydrologic

extremes?

Key Question:

Key Need: to understand the processes

that deliver precipitation (or the lack thereof)

to individual watersheds, at relevant

time and space scales

from Hirschboeck 2003 “Respecting the Drainage Divide” Water Resources Update #126 UCOWR

(Def): Interpolation of GCM results computed at large spatial scale fields to higher resolution, smaller spatial scale fields,

and eventually to watershed processes at the surface.

ONE APPROACH: DOWNSCALING

PROPOSED COMPLEMENTARY APPROACH:

RATIONALE FOR PROCESS-SENSITIVE UPSCALING:

Attention to climatic driving forces & causes: -- storm type seasonality-- atmospheric circulation patterns

with respect to:-- basin size -- watershed boundary / drainage divide

-- geographic setting (moisture sources, etc.)

. . . can provide a basis for a cross-scale linkage of GLOBAL climate variability with LOCAL hydrologic variations

at the individual basin scale . . .

. . . . including EXTREME EVENTS in the “tails” of streamflow probability distributions,

such as DROUGHTS & FLOODS.

Scenarios are based on a systematic compilation of

watershed-specific information that is used to determine the CAUSES

of spatially and temporally varying hydroclimatic extremes:

PLAN FOR BUILDING SCENARIOS VIA PROCESS-SENSITIVE UPSCALING:

“FLOOD HYDROCLIMATOLOGY”

also“DROUGHT HYDROCLIMATOLOGY”

(see Hirschboeck 1988)

Flow Time Series

A fairly long record with lots of variability . . . .

The long record made the gaging station a candidate for discontinuation in the early 1980s . . .

Flow Time Series

The flood of October 1983

(WY 1984)

What does this time series of floods look like when each event is classified according to hydroclimatic cause?

Santa Cruz at Tucson

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char

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(cf

s)52700 (cfs)

Convective

Tropical Storm

Synoptic

Convective events are the most common, but the largest floods in the record were produced by other mechanisms

Now that we know the underlying causes for flood magnitudes & frequencies, how do we apply this

information to scenario building?

Some hints on scenario-building from the web-based “course” of UA’s Roger Caldwell:

“Anticipating the Future” http://cals.arizona.edu/futures/

• Represent Events by Simple Curves

• Question Assumptions

• Watch for Groupthink and Fixed Mindsets

• Expect Both Surprises & ‘Expected Results’

• Several Solutions are Likely

Santa Cruz River at TucsonPeak flows separated into hydroclimatic subgroups:

Hirschboeck et .al. 2000

Tropical storm Sumer

Convective

Winter Synoptic

All Peaks

Santa Cruz at Tucson

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1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

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Dis

char

ge in

(cf

s)

52700 (cfs)

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Tropical Storm

Synoptic

Schematic climate-basedcurves torepresent PDFs

Events at each point in time emerge from independently,

identically distributed probabilities

The standard “iid”approach assumes stationarity and independent, identically distributed event probabilities

Question (or Re-Examine) Assumptions:

Hirschboeck 1988

Alternative Process-Based Conceptual Framework for Hydrologic Time Series:

Time-varying means

Time-varying variances

Both

Hirschboeck, 1988

Mixed frequency distributions may arise from:

• storm types

• synoptic patterns

• ENSO, PNA, NAM etc., teleconnections

• multi-decadal circulation regimes

Alternative Conceptual Frameworks to Explain How Flood Magnitudes Vary over Time: (Arizona watershed scenarios)

Based on Different Storm Types . . .

Varying mean and standard deviationsdue to different causal mechanisms

When the dominance of different types of flood-producing mechanisms

or circulation patterns changes over time, the probability distributions of potential flooding

at any given time (t) may be altered.

. . . Based on Varying Circulation Pattern Changes . . .

El Nino year

La Nina year

Blocking Regime

Zonal Regime

. . . Based on Low-Frequency Variations and/or Regime Shifts:

A low frequency shift in atmosphere or ocean circulation regime (e.g. PDO)

OR the anomalous persistence of a given regime . . .. . . will lead to different theoretical frequency / probability distributions over time.

Temporal shifts in dominance of circulation regimes, e.g. PNA, NAM / NAO patterns, etc

Abrupt shift from one PERSISTENT regime to another

By definition extreme events are rare . . . hence gaged streamflow records capture

only a recent sample of the full range of extremes that have been experienced by a given watershed.

To build reliable scenarios, the longest record possible is the ideal . . .

especially to understand and evaluate the extremes of floods and droughts!

ADVANTAGES OF INTEGRATING THE PALEORECORD

&

STRATIGRAPHIC PALEO - STAGE INDICATORS

can augment the gaged record of extreme events in watersheds in many locations.

Paleo -information extracted from . . .

TREE RINGS

1900 & 1904 = missing rings

1899 &1902 = narrow rings

1950 &1951 1953 -1956 series of narrow rings

1952 (one wet year)

A TREE-RING CORE FROM THE SALT RIVER BASIN showing ring-width variations in the 1900s

1905 -1908 1914 – 1920 two wet episodes

1899-1904 dry “signature”

pattern 1950’s DROUGHT

Extreme High and Low Flow Years in Upper Colorado & Salt-Verde Basins based on Reconstructed Streamflow* 1521-1964

< 10th Percentile < 25th and ≥ 10th Percentile > 75th and ≤ 90th Percentile > 90th Percentile

Upper Colorado River Basin

(UCRB) ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔

Salt -Verde -Tonto River Basin(SVT)

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Extreme Years of High & Low Streamflow in the Salt-Verde-Tonto River Basin

Extreme High and Low Flow Years in Upper Colorado & Salt-Verde Basins based on Reconstructed Streamflow* 1521-1964

< 10th Percentile < 25th and ≥ 10th Percentile ≥ 25th and ≤ 75th Percentile > 75th and ≤ 90th Percentile > 90th Percentile

Upper Colorado River Basin

(UCRB) ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔

Salt -Verde -Tonto River Basin(SVT)

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* Reconstructed annual water year discharge

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Even in a single tree, the record of

extreme wet and dry streamflow episodes

is evident.

Extreme High and Low Flow Years in Upper Colorado & Salt-Verde Basins based on Reconstructed Streamflow* 1521-1964

< 10th Percentile < 25th and ≥ 10th Percentile > 75th and ≤ 90th Percentile > 90th Percentile

Upper Colorado River Basin

(UCRB) ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔

Salt -Verde -Tonto River Basin(SVT)

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* Reconstructed annual water year discharge

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Extreme High and Low Flow Years in Upper Colorado & Salt-Verde Basins based on Reconstructed Streamflow* 1521-1964

< 10th Percentile < 25th and ≥ 10th Percentile > 75th and ≤ 90th Percentile > 90th Percentile

Upper Colorado River Basin

(UCRB) ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔

Salt -Verde -Tonto River Basin(SVT)

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1670 = missing ring

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wide rings

shift to narrower rings

Tree-Ring core from the Salt River Basin:

COMPARISON OF TWO BASINS:

Extreme High & Low Flow Years occuring in BOTH Basins Together

Upper Colorado Basin

Salt – Verde Basin

Extreme High and Low Flow Years in Upper Colorado & Salt-Verde Basins based on Reconstructed Streamflow* 1521-1964

< 10th Percentile < 25th and ≥ 10th Percentile ≥ 25th and ≤ 75th Percentile > 75th and ≤ 90th Percentile > 90th Percentile

Upper Colorado River Basin

(UCRB) ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔

Salt -Verde -Tonto River Basin(SVT)

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↔ * ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ * ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔

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* Reconstructed annual water year discharge

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↔ HH years (high flow in both basins)

↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ LL years (low flow in both basins)

SV

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* LH = Low in UCRB / High in SVT

1900

1910

1920

1930

1940

1950

1960 HL = High in UCRB / Low in SVT (no occurrences)

500 mb Geopotential Height (m) Composite Anomaly, Oct-Sep water year

Widespread Drought:

LOW FLOW WATER YEARS

Widespread Wet Period

HIGH FLOWWATER YEARS

higher-than-normal pressure over both basins

lower-than-normal pressure over both basins

Atmospheric Circulation Anomalies Driving the Extremes(based on observed record)

HIGHPRESSUR

E

LOW PRESSURE

Using Paleo-stage Indicators & Paleoflood Deposits . . .

-- direct physical evidence of extreme hydrologic events

-- selectively preserve evidence of only the largest floods . . .

. . . this is precisely the information that is lacking in the short gaged discharge records of the observational period

Compilations of paleoflood records combined with gaged records suggest there is a natural, upper physical limit to the magnitude of floods in a given region --- will this change?

Envelope curve for Arizona peak flows

From Hirschboeck et .al. 2000

Verde River, Arizona Peak flows separated into hydroclimatic subgroups:

Tropical storm

Sumer Convective

Winter SynopticAll

Peaks

Verde R. below Tangle Creek

Historical FloodLargest paleoflood(A.D. 1010 +- 95 radiocarbon date)

1993

FLOOD HYDROCLIMATOLOGY evaluate likely hydroclimatic causes of pre-historic floods

By associating seasonal and long-term variations in an individual basin’s stream’s hydrograph . . . with the present mix of storm types and the

synoptic atmospheric circulation patterns which deliver them . . .

SUMMARY

. . . a PROCESS-BASED “upscaling” approach provides a complementary way to bridge the gaps between local, regional, and global scales of climate information when building scenarios . . . .

. . . The circulation patterns associated with:

-- hydroclimatically grouped flood or drought events / PDFs

-- persistent paleodrought episodes -- extreme paleofloods (magnitude or frequency)

. . . can then be linked to other features of the global-scale climate that are

projected to change such as:

-- storm track latitudinal shifts -- circulation/ sea level pressure changes

(e.g. Hadley circulation expansion) -- teleconnections & atmosphere-ocean

circulation regime shifts.

. . . to construct climate-sensitive SCENARIOS

Rising temperatures, changing water balances, seasonal shifts, etc.

HYDROCLIMATICCHANGE

Seager et al. 2007

JJA

Projected IPCC Modeled Precipitation Change:

Hydrologic impact of earlier snowmelt

DROUGHTS

HYDROLOGIC EXTREMES

“Intensification” of the Hydrologic Cycle

Projected increases in droughts & floods

HAZARDS!

FLOODS

FOR ADDRESSING:

THE FFA“FLOOD PROCESSOR”

With expanded feed tube – for entering all kinds of flood data

including steel chopping, slicing & grating blades

– for removing unique physical characteristics, climatic information, and outliers

plus plastic mixing blade – to mix the populations together