LTRR-SRP II
description
Transcript of LTRR-SRP II
LTRR-SRP II
THE CURRENT DROUGHTIN CONTEXT:
A TREE-RING BASED EVALUATION OF WATER SUPPLY VARIABILITY FOR THE
SALT-VERDE RIVER BASIN
Dave Meko & Katie HirschboeckUniversity of Arizona - Laboratory of Tree-Ring Research
April 28, 2008Salt River Project, Phoenix, AZ
To update the tree-ring reconstructions of annual streamflow of the Salt-Verde-Tonto Basin through the period of the most recent drought and place it into a long-term, historical context linked to climatic variability
MAIN OBJECTIVE
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 – 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
4. CLIMATIC ANALYSES – Synoptic dendro-climatology studies of observed record to better interpret the reconstructed record
TREE-RING CHRONOLOGY
UPDATING
Tree-Ring Collections
Douglas-fir at Wahl Knoll site, White Mountains , AZ
Tree-Ring Collections
• Collections at 14 Sites in Fall 2005
• Species:
Douglas-fir ponderosa pine pinyon pine
• Some re-collections, some new collections
• Cores only
-113 -112 -111 -110 -109 -108
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34
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37Utah Colo
Ariz NM
Little Colorado R.
Colorado R.
Salt R.
Gila R.
Verde R.
Ton
to C
k.
80 km
1
23
4
5
6
7
8
910
11
12
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Tree-Ring Sites
Black RiverPine Site
Robinson Mt Site
Link to previous LTRR-SRP I study on joint drought (LL HH) in Salt-Verde and Upper Colorado Basins
Tree Ring Widths – the Basic Data
Site 2 - Black River Pine Core 13B
1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750
HH Years LL Year
Narrow rings in dry years, wide rings in wet years
STREAMFLOWRECONSTRUCTION
PROCESS
-113 -112 -111 -110 -109 -108
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37Utah Colo
Ariz NM
Little Colorado R.
Colorado R.
Salt R.
Gila R.
Verde R.
Ton
to C
k.
80 km
1
23
4
5
6
7
8
910
11
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1617
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Tree-Ring Sites
Overview of the Reconstruction Process
Tree Ring Network
Statistical Calibration: regression
Reconstruction Models
Time Series of Reconstructed Streamflow
Observed Streamflow
1920 1930 1940 1950 1960 1970 1980 1990 20000
2
4 Salt+Verde+Tonto, 1914-2007
Year
Flow
(maf
)
1400 1500 1600 1700 1800 1900 2000
100
200
300
400
Year
Flo
w (pct of norm
al)
Reconstructed annual flows, SVT
0.6 0.8 1 1.2 1.4 1.6
1
2
3
y (m
af)
Index
Site2
0.4 0.6 0.8 1 1.2 1.40
2
4
y (m
af)
Index
Site 1
0.6 0.8 1 1.2 1.4
1
2
3
y (m
af)
Index
Site 10
-112 -110 -10832
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R2=0.53RMSE
cv=574.4 kaf
MAE=248.0 kaf
1330-1989 (4 sites)
-112 -110 -10832
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R2=0.69RMSE
cv=466.7 kaf
MAE=179.9 kaf
1451-1982 (10 sites)
-112 -110 -10832
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R2=0.49RMSE
cv=621.5 kaf
MAE=280.6 kaf
1736-2005 (10 sites)
Three Different Models Used(based on different sub-periods)
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
Sub-period reconstructions ultimately blended into final time series of reconstructed streamflow
RESULTS OF THE NEW
RECONSTRUCTION
Annual Reconstructed Flows, 1330-2005
2002 and 1996 have the lowest reconstructed annual flows in the entire record (28% and 30% of normal* respectively)
•Maximum number of consecutive years below normal = 5 (in 1590s and 1660s)
•Longest stretch of consecutive years below normal in recent interval of 1914-2005 is 4 years (in 1950s)
Plotted as % of normal* *normal = defined as 1914-2006 median of observed flows
1400 1500 1600 1700 1800 1900 2000
100
200
300
400
Year
Flo
w (
pct
of n
orm
al)
Reconstructed annual flows, SVT
Median
2002 baseline
5-yr dry spells
Close up of cores from two different trees at Site 10, located near Flagstaff:
// = false ring bands
“Missing” Rings (locally absent on tree where cored)
This core is missing the year 2002 (27 of the 30
trees at this site had no 2002 ring)
This core has a very narrow 2002 “micro-
ring”
(only 3 trees at this site had a
2002 ring)
Missing-Ring Percentage Through Time
2002 was unprecedented for frequency of missing rings
How unusual is such a high % of missing rings?
1400 1500 1600 1700 1800 1900 20000
20
40
60
80
Rin
g M
issi
ng (
%) Missing Rings 2002
1400 1500 1600 1700 1800 1900 20000
200
400
600
800
Year
Num
ber
of C
ores Sample Size
2002
Variations in Time-Averaged Flows
1400 1500 1600 1700 1800 1900 2000
50
100
150
200
Ending year of 6-yr period
Flo
w (
pct
of n
orm
al)
Reconstructed, SVT, 6-yr running mean
80% CI
1999-2004 Baseline
Plotted as % of normal* *normal =median of all 6-year running means
• 14 distinct prior occurrences of flow as low as 1999-2004 average
• 1- 3 occurrences in each century
• Most severe conditions at ~1590 and ~1670
Variations in Length of Intervals Between High Flow / Wet Years
High flows and large floods can occur during periodsof drought and low flows
1950 &1951 1953-1956 narrow rings
1952 wide ring
Wide rings can occur within otherwise
narrow-ring sequences
Floods / High Flows & Reconstructed Flows
High flow / flood “wet years” are tracked reasonably well by Verde River tree-ring reconstruction
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1925 1935 1945 1955 1965 1975 1985 1995 2005
Inst
anta
neou
s P
eak
Flo
w
(cm
s)
0
50
100
150
200
250
300
Mea
n A
nnua
l Flo
w (c
ms)
Instantaneous Peak Discharge
Observed Annual flow
Reconstructed Annual Flow
Note vertically exaggerated scale on this axisVerde River Basin Comparison:
Observed, Reconstructed, & Instantaneous Peak Flows
Length of Intervals Between Wet YearsBased on Observed Flows, 1914-2007
• 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
1920 1930 1940 1950 1960 1970 1980 1990 2000
500
1000
1500
2000
2500
3000
3500
4000Widest gap = 13 yr
Water Year
Flo
w (
kaf)
Recent gap = 9 yr
“Wet Year” =flow above 75th percentile
Length of Intervals Between Wet Years Based on Reconstructed Flows, 1330-2005
Longest interval = 22 years (1382-1403)
Recent interval = 12 years (1993-2004)
1950s interval = 12 years (1953-1964)
10 intervals ≥ 12 years Median interval is 3 years
1400 1500 1600 1700 1800 1900 2000
500
1000
1500
2000
2500
3000
3500
4000Widest gap = 22 yr
Water Year
Flo
w (
kaf)
Recent gap 12 yr
“Wet Year” = flow above 75th percentile
1400 1500 1600 1700 1800 1900 2000
500
1000
1500
2000
2500
3000
3500
4000Widest Pap = 22 yr
Water Year
Flo
w (
kaf)
Gage = SVTN
t=676
Nw
=141
Time Series of Reconstructed Flows, 1330-2005, with Wet Years Flagged
0 1000 2000 3000 4000 50000
0.2
0.4
0.6
0.8
1
Flow (kaf)
F(x
)
CDF of Reconstructed Flows
0.75 quantile 1914-2005: 1710 kaf 1330-2005: 1596 kaf
1914-2005
1330-2005
0 5 10 15 20 250
0.2
0.4
0.6
0.8
1
Gap (yr)
F(x
)
CDF of Gap Between Wet Years
------------------------------------Period M
edia
n0.
90q
Max
1914-20051330-2005
23
89
1222
1914-2005
1330-2005
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 rainfall variations
from latewood width
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Little Colorado R.
Colorado R.
Salt R.Gila R.
Verde R
.
Ton
to C
k
80 km
Latewood Precipitation Signal – Wahl Knoll Example
2 4 6 8 10 12
ONDJFMAMJJAS
Number of Months
End
ing
Mon
th
0
0.05
0.1
0.15
0.2
0.25
0.3
Signal Strength by Seasonal Grouping
Prism Precipitation
Wahl Knoll Latewood Index
1897-2005
Input-OutputModel
• Signal confined mainly to summer
• Maximum of ~30% of variance of July or July+August precipitation explained by modeling
Testing for Latewood Signal of Summer Rainfall
• Total width had signal for annual precipitation, but no signal for summer precipitation
• Latewood width had a weak but significant signal for summer precipitation
SUMMARY: Results encouraging, but summer precipitation signal in partial ring widths is too weak to expect useful reconstruction of summer monsoon variability from this limited site coverage
THE CLIMATIC CONTEXT OF RECENT DROUGHTS& HIGH FLOW EPISODES
The “Big Picture” Global Climate Context
•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
(not shown here) severe tree-ring drought of 1899-1904: mean NH temperatures very low
1880 1900 1920 1940 1960 1980 2000
-2
0
2
T
(de
g F
) NH Mean Annual Temperature
1880 1900 1920 1940 1960 1980 2000
10152025
Flo
w (
maf
) Annual FlowsColorado RLees Ferry
1880 1900 1920 1940 1960 1980 2000
2
4
Flo
w (
kaf) Annual Flows
Salt+Verde+Tonto
NH Temperature Data from NASA/GISS; data are departures from 1951-80 mean based on GHCN met stations
Upper Colorado Flowsnatural flows for Lees Ferry from USBR
Salt-Verde-Tonto Flows from USGS
Horizontal lines for flows are at medians
Link to LTRR-SRP- I
Project
Updated LL and HH years exhibit
anomaly patterns similar to those of the earlier study
700 mb composites of new LL and HH years for Dec-Feb
Low FlowYears in Both SVT & UCRB
High FlowYears in Both SVT & UCRB
Floods / High Flows & Reconstructed Flows
High flow / flood “wet years” are tracked reasonably well by Verde River tree-ring reconstruction
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1925 1935 1945 1955 1965 1975 1985 1995 2005
Inst
anta
neou
s P
eak
Flo
w
(cm
s)
0
50
100
150
200
250
300
Mea
n A
nnua
l Flo
w (c
ms)
Instantaneous Peak Discharge
Observed Annual flow
Reconstructed Annual Flow
Note vertically exaggerated scale on this axisVerde River Basin Comparison:
Observed, Reconstructed, & Instantaneous Peak Flows
0
500
1000
1500
2000
2500
3000
3500
4000
4500
1925 1935 1945 1955 1965 1975 1985 1995 2005
Ins
tan
tan
eo
us
Pe
ak
Flo
w
(cm
s)
Verde River Basin Instantaneous Peak Flows Classified by Synoptic Type
Water Year
Synoptic Convective Tropical Storm
Jan 1993
Mar 1938
Feb 1995
Dec /Jan 2005
Winters of 1978-80
Dec /Jan 1952
Feb 1927 TS NormaSep 1970
1950s convective dominance
Analyzing the reconstruction synoptically:
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1925 1935 1945 1955 1965 1975 1985 1995 2005
0
50
100
150
200
250
300
Instantaneous Peak Discharge
Observed Annual flow
Reconstructed Annual FlowSynoptic Convective Tropical Storm
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1925 1935 1945 1955 1965 1975 1985 1995 2005
0
50
100
150
200
250
300
Instantaneous Peak Discharge
Observed Annual flow
Reconstructed Annual Flow
Both reconstructed & observed annual flows track the magnitude of
the instantaneous peaks best during SYNOPTIC
(winter) events
Analyzing the reconstructionsynoptically:
“Recent Drought” Low flow years in
SVT Dec – Feb
1950s Drought Low flow years in
SVT Dec – Feb
“Recent” High flow years in
SVT Dec – Feb
Synoptic Circulation Patterns for SVT
1950s pattern vs. “Recent Drought” pattern Recent High Flow Year pattern
Verde Basin study: tree-ring record is a good indicator of winter storm
track activity
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1925 1935 1945 1955 1965 1975 1985 1995 2005
Inst
anta
neo
us
Pea
k F
low
(c
ms)
0
50
100
150
200
250
300
Mea
n A
nn
ual
Flo
w (c
ms)
Instantaneous Peak Discharge
Observed Annual flow
Reconstructed Annual Flow
Water Year
Atmospheric Circulation Anomaly Patterns (700 mb)associated with Dry and Wet Intervalsin the Verde Basin
“Current” Drought
1950s+Drought
1978-1980
1996 & 2002
1993
1953-1964
Synoptic Atmospheric Circulation Patterns Linked to Dry and Wet Intervals
Importance of BLOCKING
circulation anomaly patterns:
Blocking leads to the PERSISTENCE of circulation features that produce EXTREMES
drought /
Are streamflow variations cyclic?
Spectrum, 1330-2005 Reconstruction
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
200
400
600
800
1000
1200
1400
BW
Frequency (yr-1)
Rel
ativ
e V
aria
nce
Spectrum
AR(1) Null Continuum95% CI
ENSO footprint?
SUMMARY & CONCLUSIONS
Reconstruction Model Summary
• Ring widths of the new collections have a strong annual runoff signal
•Subset models blended together yield a streamflow reconstruction covering 1330-2005
• The reconstruction explains 49- 69% of the variance of the annual flows
Extreme Single-Year Summary
• The reconstructed 1996 value was the 2nd lowest reconstructed flow since 1330
• The reconstructed 2002 value was the LOWEST reconstructed flow since 1330
• From tree’s perspective 2002 was a year like no other: 60% of 300+ cores were missing the 2002 ring!
CONCLUSIONS
1) Single-year intensity: drought in recent years unsurpassed in long-term tree-ring record (i.e., 1996, 2002)
2) Multi-year intensity: 14 distinct prior occurrences of flow as low as 1999-2004 average
CONCLUSIONS
3) Several intervals between “drought relieving” wet years were longer than any observed in the instrumental record
4) Winter storm track position key factor in drought signature (1950s vs. recent drought)
Final Report will be posted at:
http://fp.arizona.edu/kkh/srp2.htm