THE CURRENT DROUGHT THE CURRENT DROUGHT IN CONTEXT: A TREE-RING - - PowerPoint PPT Presentation

LTRR-SRP II S

THE CURRENT DROUGHT THE CURRENT DROUGHT IN CONTEXT:

A TREE-RING BASED EVALUATION OF WATER SUPPLY VARIABILITY FOR THE WATER SUPPLY VARIABILITY FOR THE SALT-VERDE RIVER BASIN

Dave Meko & Katie Hirschboeck University of Arizona - Laboratory of Tree-Ring Research

Summary presentation Summary presentation, February 26, 2008 Salt River Project, Phoenix,AZ

MAIN OBJECTIVE

To update the tree-ring reconstructions

• f annual streamflow of the Salt-Verde-

T t B i th h th i d f th Tonto Basin through the period of the most recent drought and place it into a long-term historical context linked to long-term, historical context linked to climatic variability

MAIN PROJECT ACTIVITIES MAIN PROJECT ACTIVITIES

1. UPDATING TREE-RING CHRONOLOGIES – Field collections and laboratory analysis to develop chronologies in the Salt-Verde basin with data through growth year 2005 2 NEW STREAMFLOW RECONSTRUCTION A l i f 2. NEW STREAMFLOW RECONSTRUCTION – Analysis of the new tree-ring chronologies to place the most recent drought in a long-term context 3. EW-LW EVALUATION – Exploration of the seasonal precipitation signal in separate measurement of earlywood and latewood width measurements and latewood width measurements 4. ONGOING CLIMATIC ANALYSES – Synoptic dendro- climatology studies of observed record to better interpret the gy p reconstructed record

TREE-RING CHRONOLOGY CHRONOLOGY UPDATING UPDATING

Tree-Ring Collections

Douglas-fir at Wahl Knoll site, White Mountains , AZ

Tree-Ring Collections

• Collections at 14 Sites

37

Utah Colo

Tree-Ring Sites

Collections at 14 Sites in Fall 2005

• Species:

36 37

Ariz NM Colorado R.

12

p Douglas-fir ponderosa pine

35

L i t t l e C

• l
• r

a d

• R

. V

6 8 9 10 13 18

Robinson Mt Site

p p pinyon pine

• Some re-collections,

ll i

34

R Verde R. Tonto Ck.

1 2 3 4 5 7 14

Black River Pine Site

some new collections

• Cores only

33

S a l t R . Gila R.

80 km 4 11

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Tree Ring Widths – the Basic Data

1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750

Link to previous LTRR-SRP I study Site 1 - Black River Pine Core 13B

HH Years LL Year

• n joint drought

(LL HH) in Salt- Verde and Upper Colorado Basins

HH Years LL Year

Narrow rings in dry years, id i i t wide rings in wet years

STREAMFLOW STREAMFLOW RECONSTRUCTION PROCESS

Overview of the Reconstruction Process

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Tree Ring Network Observed Streamflow

Statistical Calibration: regression

Reconstruction Models Time Series of Reconstructed Streamflow

• w

• f

• r

Reconstructed annual flows, SVT

Three Different Models Used

(based on different sub-periods)

37

1330-1989 (4 sites)

37

1451-1982 (10 sites)

37

1736-2005 (10 sites)

( p )

34 35 36 34 35 36 34 35 36 32 33 34

R2=0.53 RMSE

cv=574.4 kaf

MAE=248.0 kaf

32 33 34

R2=0.69 RMSE

cv=466.7 kaf

MAE=179.9 kaf

32 33 34

R2=0.49 RMSE

cv=621.5 kaf

MAE=280.6 kaf

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• 110
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32

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32

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Tree-ring sites not in model Tree-ring sites in model

*

• Tree-ring sites have variable time coverage
• Uniform time coverage required for a model

S b i d t ti lti t l bl d d Sub-period reconstructions ultimately blended into final time series of reconstructed streamflow

RESULTS OF THE NEW OF THE NEW RECONSTRUCTION RECONSTRUCTION

Annual Reconstructed Flows, 1330-2005

Plotted as % of normal* *normal = defined as 1914-2006 median of observed flows

400 )

Reconstructed annual flows, SVT

5-yr dry spells

200 300

• w (pct of normal)

1400 1500 1600 1700 1800 1900 2000 100 Year Flo

Median 2002 baseline

2002 and 1996 have the lowest reconstructed annual flows

Year

in the entire record (28% and 30% of normal* respectively)

• Maximum number of consecutive years below normal = 5 (in 1590s and 1660s)

y

( )

• Longest stretch of consecutive years below normal in recent interval of

1914-2005 is 4 years (in 1950s)

“Missing” Rings (locally absent on tree where cored)

Close up of cores from two different trees at Site 10, located near Flagstaff:

1999 2000 2001 2004 2005 2003 2002 (missing in this core)

// = false ring bands

This core is missing the year 2002

(27 of the 30 trees at this site

Robinson Mt. AZ ROB 11B 1999 2000 2001 2005 2004 2003 2002

trees at this site had no 2002 ring)

This core has This core has a very narrow 2002 “micro- ring”

Robinson Mt. AZ ROB 22A

(only 3 trees at this site had a 2002 ring)

Missing-Ring Percentage Through Time g g g g

How unusual is such a high % of missing rings?

40 60 80 ssing (%)

Missing Rings

2002

2002

1400 1500 1600 1700 1800 1900 2000 20 40 Ring Mis 200 400 600 800 mber of Cores

Sample Size

2002 d t d f

1400 1500 1600 1700 1800 1900 2000 200 Year Num

2002 was unprecedented for frequency of missing rings

Variations in Time-Averaged Flows

Reconstructed SVT 6 yr running mean

Plotted as % of normal* *normal =median of all 6-year running means

150 200 t of normal)

Reconstructed, SVT, 6-yr running mean 80% CI

1400 1500 1600 1700 1800 1900 2000 50 100 Flow (pct

1999-2004 Baseline

1400 1500 1600 1700 1800 1900 2000 Ending year of 6-yr period

• 14 distinct prior occurrences of flow

as low as 1999-2004 average

• 1- 3 occurrences in each century

M t diti t 1590 d 1670

• Most severe conditions at ~1590 and ~1670

Variations in Length of Intervals Between Hi h Fl / W t Y High Flow / Wet Years

High flows and large High flows and large floods can occur during periods of d ht d l

1952 wide ring

drought and low flows

1950 &1951 1953-1956 narrow rings

Wide rings can occur in

• therwise narrow-ring sequences

Floods / High Flows & Reconstructed Flows

Hi h fl / fl d “ t ” t k d bl High flow / flood “wet years” are tracked reasonably well by Verde River tree-ring reconstruction

5000 300

N t ti ll t d

4000 4500 250

Note vertically exaggerated scale on this axis

Verde River Basin Comparison: Observed, Reconstructed, & Instantaneous Peak Flows

3000 3500

Peak Flow

s)

200

ual Flow

s)

Instantaneous Peak Discharge Observed Annual flow Reconstructed Annual Flow 1500 2000 2500

stantaneous

(cms

100 150

Mean Annu (cms

500 1000 1500

Ins

50

1925 1935 1945 1955 1965 1975 1985 1995 2005

Length of Intervals Between Wet Years

Based on Observed Flows 1914 2007 Based on Observed Flows, 1914-2007

2500 3000 3500 4000 Widest gap = 13 yr af) Recent gap = 9 yr 1000 1500 2000 2500 Flow (ka

“Wet Year” = flow above 75th percentile

• Interval longer in 1950s than during recent drought period

1920 1930 1940 1950 1960 1970 1980 1990 2000 500 Water Year

• Interval longer in 1950s than during recent drought period
• If not for mildly wet 1952, the earlier interval would have

been 25 years

• Median interval is 2 years in the observed record

Length of Intervals Between Wet Years Based on Reconstructed Flows, 1330-2005 Based on Reconstructed Flows, 1330 2005

3500 4000 Widest gap = 22 yr Recent gap 12 yr 2000 2500 3000 3500 Flow (kaf)

“Wet Year” = flow above 75th

1400 1500 1600 1700 1800 1900 2000 500 1000 1500

75th percentile

Longest interval = 22 years (1382-1403)

Water Year

g y Recent interval = 12 years (1993-2004) 1950s interval = 12 years (1953-1964) 10 intervals ≥ 12 years 10 intervals ≥ 12 years Median interval is 3 years

EARLYWOOD LATEWOOD EARLYWOOD-LATEWOOD EVALUATION

Earlywood / Latewood Evaluation

Ring width can be partitioned into parts formed early and late in the growth year

Studies have shown some success at inferring summer inferring summer rainfall variations from latewood width

Testing for Latewood Signal of Summer Rainfall es g o a e ood S g a o Su e a a

• Total width had signal for annual precipitation, but

g p p , no signal for summer precipitation

• Latewood width had a weak but significant signal

f i it ti for summer precipitation SUMMARY: Results encouraging, but summer precipitation signal in partial ring widths is too weak to expect useful reconstruction of summer weak to expect useful reconstruction of summer monsoon variability from this limited site coverage

THE CLIMATIC CONTEXT THE CLIMATIC CONTEXT OF RECENT DROUGHTS OF RECENT DROUGHTS

The “Big Picture” Global Climate Context

1880 1900 1920 1940 1960 1980 2000

• 2

2

ΔT (deg F)

NH Mean Annual Temperature

NH Temperature Data from NASA/GISS; data are departures from 1951-80 mean based on

1880 1900 1920 1940 1960 1980 2000 1880 1900 1920 1940 1960 1980 2000 10 15 20 25 Flow (maf) Annual Flows Colorado R Lees Ferry

GHCN met stations Upper Colorado Flows natural flows for Lees Ferry from USBR

1880 1900 1920 1940 1960 1980 2000 2 4 Flow (kaf) Annual Flows Salt+Verde+Tonto

Salt-Verde-Tonto Flows from USGS

Horizontal lines for flows are at medians

• Recent drought: mean NH temperatures near record highs
• 1950s drought: mean NH temperatures near middle of long-

term warming trend

• Wet late 1970s to early 1980s: mean NH temperatures higher
• Wet period 1915-20: mean NH temperatures low

p p

(not shown here) severe tree-ring drought of 1899-1904: mean NH temperatures very low

Link to LTRR-SRP- I Project Project

Updated LL and HH hibit

Low Flow Years in Both SVT & UCRB

years exhibit anomaly patterns similar to those of similar to those of the earlier study

700 mb composites of new LL and HH years for Dec-Feb High Flow Years in Both Years in Both SVT & UCRB

Synoptic Atmospheric Circulation Patterns Linked to Dry and Wet Intervals

4500 5000 300

Atmospheric Circulation Anomaly Patterns (700 mb) associated with

1993

Patterns Linked to Dry and Wet Intervals

3500 4000

low

200 250 Instantaneous Peak Discharge Observed Annual flow

associated with Dry and Wet Intervals in the Verde Basin

1978-1980 1996 & 2002 1953-1964 2500 3000

us Peak Fl

cms)

150 200

nnual Flow

(cms)

Observed Annual flow Reconstructed Annual Flow 953 96 1500 2000

nstantaneo

(c

100

Mean An (

“Current” Drought 1950s+ Drought 500 1000

In

50 g

1925 1935 1945 1955 1965 1975 1985 1995 2005

Water Year

Synoptic Circulation Patterns for SVT

1950s

Patterns for SVT

Verde Basin study:

Drought Low flow years in SVT Dec – Feb

y tree-ring record is a good indicator of winter storm track activity

1950s pattern vs. “Recent Drought” pattern Recent High Flow Year pattern

track activity

“Recent Drought” Low flow years in “Recent” High flow years in SVT Dec – Feb SVT Dec – Feb

SUMMARY & CONCLUSIONS

Reconstruction Model Summary

• Ring widths of the new collections

have a strong annual runoff signal have a strong annual runoff signal

• Subset models blended together

yield a streamflow reconstruction yield a streamflow reconstruction covering 1330-2005 Th t ti l i 49 69%

• The reconstruction explains 49- 69%
• f the variance of the annual flows

Extreme Single Year Summary Extreme Single-Year Summary

• The reconstructed 1996 value was the 2nd

lowest reconstructed flow since 1330 lowest reconstructed flow since 1330

• The reconstructed 2002 value was the

OWEST d fl i 1330 LOWEST reconstructed flow since 1330

• From tree’s perspective 2002 was a year

From tree s perspective 2002 was a year like no other: 60% of 300+ cores were missing the 2002 ring! g g

CONCLUSIONS CONCLUSIONS

1) Single-year intensity: drought in recent years unsurpassed in in recent years unsurpassed in long-term tree-ring record (i.e., 1996, 2002) 1996, 2002) 2) Multi year intensity: 14 distinct 2) Multi-year intensity: 14 distinct prior occurrences of flow as low as 1999 2004 average as 1999-2004 average

CONCLUSIONS CONCLUSIONS

3) Several intervals between “drought relieving” wet years were longer than any observed in the instrumental record 4) Winter storm track position ) p key factor in drought signature (1950s vs. recent drought) ( g )