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LTRR-SRP II

LTRR-SRP II THE CURRENT DROUGHT IN CONTEXT: A TREE-RING BASED EVALUATION OF WATER SUPPLY VARIABILITY FOR THE SALT-VERDE RIVER BASIN. Dave Meko & Katie Hirschboeck University of Arizona - Laboratory of Tree-Ring Research. April 28, 2008 Salt River Project, Phoenix, AZ. MAIN OBJECTIVE.

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LTRR-SRP II

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  1. 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

  2. MAIN OBJECTIVE 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

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

  4. TREE-RING CHRONOLOGYUPDATING

  5. Tree-Ring Collections Douglas-fir at Wahl Knoll site, White Mountains , AZ

  6. Robinson Mt Site Black RiverPine Site Tree-RingCollections • Collections at 14 Sites in Fall 2005 • Species: • Douglas-fir • ponderosa pine • pinyon pine • Some re-collections, some new collections • Cores only

  7. 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 Site 2 - Black River Pine Core 13B Tree Ring Widths – the Basic Data Link to previous LTRR-SRP I study on joint drought (LLHH) in Salt-Verde and Upper Colorado Basins HH Years LL Year Narrow rings in dry years, wide rings in wet years

  8. STREAMFLOWRECONSTRUCTION PROCESS

  9. Overview of the Reconstruction Process Tree Ring Network Observed Streamflow Statistical Calibration: regression Reconstruction Models Time Series of Reconstructed Streamflow

  10. 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

  11. RESULTS OF THE NEW RECONSTRUCTION

  12. Annual Reconstructed Flows, 1330-2005 Plotted as % of normal* *normal = defined as 1914-2006 median of observed flows 5-yr dry spells Median2002 baseline • 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)

  13. “Missing” Rings (locally absent on tree where cored) Close up of cores from two different trees at Site 10, located near Flagstaff: // = false ring bands 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)

  14. Missing-Ring Percentage Through Time How unusual is such a high % of missing rings? 2002 2002 was unprecedented for frequency of missing rings

  15. Variations in Time-Averaged Flows Plotted as % of normal* *normal =median of all 6-year running means 1999-2004 Baseline • 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

  16. Variations in Length of Intervals Between High Flow / Wet Years 1952wide ring 1950 &1951 1953-1956narrow rings High flows and large floods can occur during periodsof drought and low flows Wide rings can occur within otherwise narrow-ring sequences

  17. Floods / High Flows & Reconstructed Flows High flow / flood “wet years” are tracked reasonably well by Verde River tree-ring reconstruction Verde River Basin Comparison: Observed, Reconstructed, & Instantaneous Peak Flows

  18. Length of Intervals Between Wet YearsBased on Observed Flows, 1914-2007 Recent gap = 9 yr “Wet Year” =flow above 75th percentile • 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

  19. Length of Intervals Between Wet YearsBased on Reconstructed Flows, 1330-2005 Recent gap 12 yr “Wet Year” = flow above 75th percentile 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

  20. EARLYWOOD-LATEWOOD EVALUATION

  21. 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

  22. Latewood Precipitation Signal – Wahl Knoll Example Signal Strength by Seasonal Grouping Prism Precipitation • Signal confined mainly to summer • Maximum of ~30% of variance of July or July+August precipitation explained by modeling Input-Output Model 1897-2005 Wahl Knoll Latewood Index

  23. 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

  24. THE CLIMATIC CONTEXT OF RECENT DROUGHTS& HIGH FLOW EPISODES

  25. The “Big Picture” Global Climate Context 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 • 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

  26. Link to LTRR-SRP- IProject Low Flow Years in Both SVT & UCRB 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 High Flow Years in Both SVT & UCRB

  27. Floods / High Flows & Reconstructed Flows High flow / flood “wet years” are tracked reasonably well by Verde River tree-ring reconstruction Verde River Basin Comparison: Observed, Reconstructed, & Instantaneous Peak Flows

  28. Jan 1993 Verde River Basin Instantaneous Peak Flows Classified by Synoptic Type Synoptic Convective Tropical Storm Feb 1995 Mar 1938 Winters of 1978-80 Dec /Jan 1952 Feb 1927 TS NormaSep 1970 Dec /Jan 2005 1950s convective dominance Water Year Analyzing the reconstruction synoptically:

  29. Synoptic Convective Tropical Storm Analyzing the reconstructionsynoptically: Both reconstructed & observed annual flows track the magnitude of the instantaneous peaks best during SYNOPTIC(winter) events

  30. Synoptic Circulation Patterns for SVT Verde Basin study: tree-ring record is a good indicator of winter storm track activity 1950s Drought Low flow years in SVT Dec – Feb 1950s pattern vs. “Recent Drought” pattern Recent High Flow Year pattern “Recent Drought” Low flow years in SVT Dec – Feb “Recent” High flow years in SVT Dec – Feb

  31. 1993 1978-1980 1996 & 2002 1953-1964 “Current” Drought 1950s+Drought Synoptic Atmospheric Circulation Patterns Linked to Dry and Wet Intervals Atmospheric Circulation Anomaly Patterns (700 mb)associated with Dry and Wet Intervalsin the Verde Basin Water Year

  32. drought / Importance of BLOCKING circulation anomaly patterns: Blocking leads to thePERSISTENCE of circulation features that produce EXTREMES

  33. Are streamflow variations cyclic? Spectrum, 1330-2005 Reconstruction ENSO footprint?

  34. SUMMARY & CONCLUSIONS

  35. 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

  36. 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!

  37. 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

  38. 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)

  39. Final Report will be posted at: http://fp.arizona.edu/kkh/srp2.htm

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