1. A dvanced Water Education Workshop July 18, 2006 Tempe AZ Dr. Katie Hirschboeck The Laboratory of Tree-Ring Research The University of Arizona The Laboratory of Tree-Ring Research The University of Arizona katie@ltrr.arizona.edu What Tree Rings can Teach Us about the History of Drought DROUGHT INDICATORS:

2. Trees and stones will teach you that which You can never learn from masters. -- St. Bernard of Clairvaux

3. Overview of Drought Indicators Tree Rings -- How they work -- What they tell us -- Why it’s important Applying the Indicators: -- Using tree rings in water resource management DROUGHT INDICATORS

4. Source: NOAA PALEOCLIMATOLOGY SITE http://www.ncdc.noaa.gov/paleo/ http://www.ncdc.noaa.gov/paleo/ Overview: Drought Indicators (aka “PROXIES) “Natural archives” -- Storage of important climatic and hydrologic information recorded by natural processes -- Ideally, can be dated to build chronologies

5. Source: http://www.ncdc.noaa.gov/paleo/drought/drght_data.html http://www.ncdc.noaa.gov/paleo/drought/drght_data.html THE DATA: RECONSTRUCTING DROUGHT Long periods (back 10,000 yrs) pollen, charcoal, lake sediments, paleo-lake levels Last 2000 years lake salinity changes, archaeological records, millennial-length tree-ring records Last 500 years historical documents, tree-ring records Instrumental Record

6. How they work What they tell us Why it’s important Tree Rings:

7. environmentally beneficial years environmentally stressful years TREE RINGS: For a tutorial from the Univ of Arizona’s Laboratory of Tree Ring Research (LTRR) using some of these images, see: http://www.ltrr.arizona.edu/dendrochronology.html

8. pith bark tree ring photo © Government Printing Office, Washington, D.C.

9. REPLICATION – “noise” minimized by sampling many trees at a site + more than one core per tree Images from Henri Grissino-Mayer’s Ultimate Tree-Ring Web Pages http://web.utk.edu/~grissino/default.html http://web.utk.edu/~grissino/default.html

10. CROSSDATING – matching patterns in rings of several tree-ring series allow precise dating to exact year Images from Henri Grissino-Mayer’s Ultimate Tree-Ring Web Pages http://web.utk.edu/~grissino/default.htmlhttp://web.utk.edu/~grissino/default.html

11. B B 19001910 A A 19201930 C C 18901880187018601850 Crossdating: allows a chronological record to be constructed back in time “Bridging” back in time Image from Henri Grissino-Mayer’s Ultimate Tree-Ring Web Pages http://web.utk.edu/~grissino/default.htmlhttp://web.utk.edu/~grissino/default.html

12. Tree-ring width chronologies from DRY sites are highly correlated with PRECIPITATION patterns. Statistical models are used to “calibrate” the tree-ring chronologies in terms of PRECIPITATION units... DENDROCLIMATOLOGY TREE RINGS CLIMATE Tree Rings and Climate by H.C. Fritts, 1976

13. ComplacentSensitive (photo © A.C. Caprio). Source: Tree Rings and Climate by H.C. Fritts, 1976 Example of classic “sensitive tree”

14. New Mexico Average Statewide Precipitation (Sep – May) SOURCE: Swetnam & Betancourt, 1998 Journal of Climate TREE-RING WIDTHS  PRECIPITATION TREE-RING RECONSTRUCTIONS OF CLIMATE:

15. 1660s Drought SOURCE: Swetnam & Betancourt, 1998 Journal of Climate LONGTERM RECONSTRUCTION OF PRECIPITATION (Sep - May) Average of six 1000-year chronologies from AZ & NM New Mexico Average Statewide Precipitation (Sep – May)

16. Reconstructed drought indices from many tree- ring sites extrapolated to a grid: Palmer Drought Severity Index (PDSI) DRYWET Source: http://www.ncdc.noaa.gov/paleo/pdsiyear.html http://www.ncdc.noaa.gov/paleo/pdsiyear.html Edward Cook, David Meko, David Stahle & Malcolm Cleaveland

17. Dry PDSI wet INDIVIDUAL YEAR Reconstructed PDSI Maps HH LL Individual years obtained from: http://www.ncdc.noaa.gov/paleo/pdsiyear.html http://www.ncdc.noaa.gov/paleo/pdsiyear.html

18. Statistical models are used to “calibrate” the tree-ring chronologies in terms of STREAMFLOW units... DENDROHYDROLOGY TREE RINGSSTREAMFLOW Stockton, C.W., 1975, Long term streamflow records reconstructed from tree rings, University of Arizona Press, Tucson, Arizona, 111 pp.

19. WHY TREE-RING RECONSTRUCTIONS ARE IMPORTANT: --The observed (gaged) record is a fairly good indicator of past extremes -- but it does not reflect the highest or lowest flows possible, nor the longest persistence of extremes -- for this longterm perspective we need tree-rings

20. PHYSICAL BASIS FOR DENDROHYDROLOGY PRECIPITATION  SOIL MOISTURE SURFACE & SUB- SURFACE INFLOW OUTFLOW EVAPO- TRANSPIRATION Based on: Meko, D.M., Stockton, C.W., and Boggess, W.R., 1995, : Water Resources Bulletin, v. 31, no. 5, p. 789-801.

21. UPPER COLORADO RIVER BASIN Stockton, C.W., 1975, Long term streamflow records reconstructed from tree rings, University of Arizona Press, Tucson, Arizona, 111 pp. Stockton, C.W., and Jacoby, G.C., 1976, Long-term surface-water supply and streamflow trends in the Upper Colorado River Basin, Lake Powell Research Project Bulletin No. 18: National Science Foundation, 70 pp.

22. Colorado River at Lees Ferry Reconstructed Runoff Stockton, 1975 Stockton & Jacoby, 1976 Anomalously wet period

23. Applying Tree-Ring Using tree rings in water resource management Indicators:

24. A TREE-RING-BASED ASSESSMENT OF SYNCHRONOUS EXTREME STREAMFLOW EPISODES in The Upper Colorado & Salt-Verde River Basins K.K. Hirschboeck & David M. Meko Project web site: http://www.ltrr.arizona.edu/srp.htm http://www.ltrr.arizona.edu/srp.htm THE CURRENT DROUGHT IN CONTEXT: A Tree-Ring Based Evaluation Of Water Supply Variability For The Salt-Verde River Basin

25. Salt-Verde River Basin Streamflow Reconstruction Tree Rings Statistical Calibration: Regression Reconstruction Model Time Series of Reconstructed Streamflow Observed Streamflow

26. 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 Years of High & Low Streamflow in the Salt-Verde-Tonto River Basin Even in a single tree, the record of extreme wet and dry streamflow episodes is evident.

27. 1950s DROUGHT

28. Long-Term Context of Salt-Verde-Tonto’s Current Drought – IS IT UNPRECEDENTED? Severity of current drought in terms of single years is worst in observed record Current drought is about as severe as 1950s in terms of flows averaged over 11 years... Even during 1950s drought, occasional 1-year “breaks” of above normal flow were not unusual 8 other droughts in the long-term tree-ring record were as severe as the current drought Late 1500s mega-drought was much more severe than the current drought

29. PURPOSE: use long-term records from tree rings... to reconstruct annual streamflow in the two basins & analyze variations of extreme low flow & high flow over the past several hundred years Upper Colorado River Basin Salt-Verde-Tonto River Basin SYNCHRONOUS EXTREME STREAMFLOW EPISODES

30. What’s at stake: Reliability of the Colorado River system as a water-supply buffer for the Salt River system during times of extreme drought The central question guiding the research was: How frequently have extreme droughts or high flows occurred in both basins simultaneously in the past?

31. Reconstructed Flows in Each Basin Reconstruction not as robust in this period Common Period for both basins = 1521-1964 R 2 =0.77 RE=0.74 R 2 =0.70 RE=0.68

32. 1. Thresholds were used to identify extreme streamflow episodes: Low Flow, L (drought) and High Flow, H in each basin 2. Existing tree-ring data were used to refine previous tree-ring reconstructions of streamflow and produce new reconstructions 3. Extreme synchronous streamflow scenarios: LL, HH, LH, HL were defined in observed & reconstructed records Comparing Extremes in the Two Basins:

33. Defining Joint Drought * Colorado (north) / Salt-Verde-Tonto (south) * Thresholds for L, H defined by 25 th and 75 th percentiles of annual flows LH = Dry Colo, Wet Salt-Verde HL = Wet Colo, Dry Salt-Verde HH = Wet in both basins LL = Dry in both basins

34. Observed Flows & Thresholds Thresholds from observed flows Thresholds from reconstructed flows

35. 1660166116621663166416651666166716681669 1670 = missing ring 16711672 wide rings shift to narrower rings SALT RIVER BASIN TREE-RING CORE (site near Show Low) Extreme High & Low Flow Years in BOTH Basins Together Salt-Verde-Tonto (SVT) & Upper Colorado River Basins (UCRB) The 1660s Drought:

36. Probability (HL) = 0 / 444 = 0 Probability (LH) = 67 / 444 = 0.004 Reconstructed Flows: HL and LH Events A rare occurrence!!

37. Probability (HH) = 57 / 444 = 0.128 Probability (LL) = 66 / 444 = 0.149 Reconstructed Flows: LL and HH Events The more typical behavior for extreme years!

39. Key Conclusions & Implications Synchronous extreme events in the same direction (LL and HH events) were much more frequent than LH or HL events Extreme synchronous low flow (LL) and high flow (HH) events tended to cluster in time Because of clustering tendency, it's more probable that episodes of sustained drought or sustained high flow will persist  more of a burden on water systems management Reservoir storage can buffer water supplies during these persistent episodes, but supplies will be increasingly strained as droughts extend over multi- year periods BOTTOM LINE: Severe droughts and low flow conditions in one basin are unlikely to be offset by abundant streamflow in the other basin

40. The bottom core shows a very narrow micro-ring for 2002 Top core missing the year 2002 (27 of 30 trees at this site had no 2002 ring!) UPDATING THE TREE-RING RECORD TO BETTER ASSESS THE CURRENT DROUGHT... SALT –VERDE BASIN

41. ... And what about the Colorado River at Lees Ferry... ? Stockton, 1975 Stocketon & Jacoby, 1976 Anomalously wet period

42. Cores from ~1,200 trees in 60 locations throughout the Colorado River Basin Woodhouse, Gray & Meko (2006) Updated streamflow reconstructions for the Upper Colorado River Basin Water Resources Research, Vol. 42, No. 5, W05415 The main points of the 1976 research hold up. Droughts more severe and intense than we've seen in the gauged record occurred in the past. The long-term mean flow is lower than the gauged mean flow.... A new tree-ring- based reconstruction of 508 years of Colorado River streamflow:

43. “.. as many as 8 droughts similar in severity (in terms of average flow) to the 5-year 2000- 2004 drought have occurred since 1500." Plot of probable extremely low flow (> 10% chance of being exceeded) "The long-term perspective provided by tree- ring reconstructions points to a looming conflict between water demand and supply in the upper Colorado River basin" Woodhouse, Gray & Meko (2006)

44. A final reflection on TREES as TEACHERS....

45. “Life must be lived forward, but understood backward” - Kierkegaard