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 of annual streamflow of the Salt-Verde- T Tonto Basin through the period of the t B i th h th i d f th 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. 2 NEW STREAMFLOW RECONSTRUCTION – Analysis of NEW STREAMFLOW RECONSTRUCTION A l i f 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 Tree-Ring Sites • Collections at 14 Sites Collections at 14 Sites Utah Colo 37 37 Ariz NM in Fall 2005 Colorado R. • Species: p 36 12 8 13 L � Douglas-fir i t t l e 18 C o 6 l o r Robinson a d o � ponderosa pine p p 35 R Mt Site 10 9 . V Verde R. 5 � pinyon pine 7 14 Black River Tonto Ck. 1 Pine Site 34 • Some re-collections, 3 2 4 4 some new collections ll i R R . t l a S 11 Gila R. 33 • Cores only 80 km -113 -112 -111 -110 -109 -108
Tree Ring Widths – the Basic Data 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 Site 1 - Black River Pine Core 13B Link to previous LTRR-SRP I study HH Years HH Years LL Year LL Year on joint drought (LL HH) in Salt- Narrow rings in dry years, Verde and Upper Colorado Basins wide rings in wet years id i i t
STREAMFLOW STREAMFLOW RECONSTRUCTION PROCESS
Overview of the Reconstruction Process Tree-Ring Sites 16 Utah Colo 37 17 15 Ariz NM Colorado R. 23 20 36 36 12 12 21 21 Little Colorado R. 22 8 13 24 18 6 25 35 10 9 Verde R. Tonto Ck. 5 7 14 19 1 34 3 2 4 Salt R. 11 33 G i a l R 80 km . 4 Salt+Verde+Tonto, 1914-2007 F low (m af) 2002 (missing in this core) -113 -112 -111 -110 -109 -108 1999 2000 2001 2003 2004 2005 2 0 Robinson Mt. AZ ROB 11B 1920 1930 1940 1950 1960 1970 1980 1990 2000 1999 1999 2000 2000 2001 2001 2002 2002 2003 2003 2004 2004 2005 2005 Year Year Tree Ring Network Observed Streamflow Robinson Mt. AZ ROB 22A Site2 3 maf) y (m 2 2 1 Statistical Calibration: regression Site 1 0.6 0.8 1 1.2 1.4 1.6 4 Index y (maf) 2 Site 10 0 0.4 0.6 0.8 1 1.2 1.4 3 y (maf) Index 2 1 0.6 0.8 1 1.2 1.4 Index Reconstruction Models Time Series of Reconstructed Streamflow Reconstructed annual flows, SVT 400 ) l a m r o n 300 f o t c p w ( 200 o l F 100 1400 1500 1600 1700 1800 1900 2000 Year
Three Different Models Used (based on different sub-periods) ( p ) 1330-1989 (4 sites) 1451-1982 (10 sites) 1736-2005 (10 sites) 37 37 37 36 36 36 35 35 35 34 34 34 34 34 34 33 33 33 R 2 =0.53 R 2 =0.69 R 2 =0.49 RMSE cv =574.4 kaf RMSE cv =466.7 kaf RMSE cv =621.5 kaf MAE=248.0 kaf MAE=179.9 kaf MAE=280.6 kaf 32 32 32 32 32 32 -112 -110 -108 -112 -110 -108 -112 -110 -108 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 Sub-period reconstructions ultimately blended i d t ti lti t l bl d d 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 Reconstructed annual flows, SVT 5-yr dry spells 400 ) ow (pct of normal) 300 200 Flo Median 100 2002 baseline 1400 1500 1600 1700 1800 1900 2000 Year Year 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) 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: 2002 (missing in this core) 1999 2000 2001 2003 2004 2005 // = false ring bands This core is missing the year 2002 (27 of the 30 trees at this site trees at this site had no 2002 ring) Robinson Mt. AZ ROB 11B 1999 2000 2001 2002 2003 2004 2005 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? 80 Missing Rings 2002 ssing (%) 2002 60 40 40 Ring Mis 20 0 1400 1500 1600 1700 1800 1900 2000 800 Sample Size mber of Cores 600 400 Num 200 200 0 1400 1500 1600 1700 1800 1900 2000 Year 2002 was unprecedented for 2002 d t d f frequency of missing rings
Variations in Time-Averaged Flows Plotted as % of normal* *normal =median of all 6-year running means Reconstructed, SVT, 6-yr running mean Reconstructed SVT 6 yr running mean 200 80% CI t of normal) 150 Flow (pct 100 1999-2004 Baseline 50 1400 1400 1500 1500 1600 1600 1700 1700 1800 1800 1900 1900 2000 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 • Most severe conditions at ~1590 and ~1670 M t diti t 1590 d 1670
Variations in Length of Intervals Between High Flow / Wet Years Hi h Fl / W t Y High flows and large High flows and large floods can occur 1952 wide ring during periods of d drought and low ht d l flows 1950 &1951 1953-1956 narrow rings Wide rings can occur in otherwise narrow-ring sequences
Floods / High Flows & Reconstructed Flows High flow / flood “wet years” are tracked reasonably Hi h fl / fl d “ t ” t k d bl well by Verde River tree-ring reconstruction 5000 300 Note vertically exaggerated N t ti ll t d Verde River Basin Comparison: scale on this axis 4500 Observed, Reconstructed, 250 & Instantaneous Peak Flows 4000 Peak Flow Instantaneous Peak Discharge 3500 200 Observed Annual flow ual Flow Reconstructed Annual Flow 3000 s) Mean Annu (cms s) stantaneous (cms 2500 150 2000 100 1500 1500 Ins 1000 50 500 0 0 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 4000 Recent gap = 9 yr Widest gap = 13 yr 3500 3000 af) Flow (ka 2500 2500 “Wet Year” = 2000 flow above 1500 75 th percentile 1000 500 1920 1930 1940 1950 1960 1970 1980 1990 2000 Water Year • Interval longer in 1950s than during recent drought period • 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 Recent gap 4000 Widest gap = 22 yr 12 yr 3500 3500 3000 Flow (kaf) 2500 “Wet Year” = 2000 flow above 75 th 75 th 1500 percentile 1000 500 1400 1500 1600 1700 1800 1900 2000 Water Year Longest interval = 22 years (1382-1403) 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 for summer precipitation i it ti 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
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