Spring flood reconstruction from tree rings (continuous and discontinuous series)

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In this presentation, we use tree rings (continuous and discontinuous series) to reconstruct past spring floods in cold environments. Spring floods are short duration events that may not be visible in classical tree ring indicators such as ring widths. Ice scars are conspicuous evidences of past spring floods and can greatly augment the reconstruction’s reliability, but pose a certain number of statistical problems when they are used as proxies. Some of these problems are described and solved here, using a novel reconstruction procedure.

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Spring flood reconstruction from tree rings (continuous and discontinuous series)

  1. 1. É"enne  Boucher   Taha  B.M.  J.  Ouarda   Yves  Bégin     Antoine  Nicault   Ins<tut  Na<onal  de  la  Recherche  Scien<fique   Centre  Eau-­‐Terre-­‐Environnement   boucher@cerege.fr   Photo  credit:  S.  Popov   World  Dendro  2010,  Rovaniemi,  Finland  
  2. 2. Why  reconstruct  spring  floods?   Hudson  bay   LA  GRANDE  (LG)   hydroelectric  complex  
  3. 3. Why  reconstruct  spring  floods?  
  4. 4. Infilling  of   hydroelectric   reservoirs   Spring   Why  reconstruct  spring  floods?   boucher@cerege.fr  
  5. 5. Pros   Cons   A  mul<-­‐proxy  dendrohydrological  approach  to   reconstruct  spring  floods   Discon<nuous  series  /  uncertain<es  /  non-­‐lineari<es   Direct  rela<onship  with  streamflow  Con<nuous  series   Indirect   rela<onships  with   streamflow  
  6. 6. Discrete  event  series   e.g.  ice  scarred  trees  
  7. 7. Uncertain  discrete  series   [0.05,  0.5,  0.95]   Propor<on  of  ice-­‐scarred  trees  around  a  northern  lake   Propor<ons    N  trees  sampled   boucher@cerege.fr  
  8. 8. Model  uncertain"es  of  discrete  event  series   Uncertain<es  around  observed  propor<ons  are  binomialy   distributed  1)     Model  verifica"on   Jackknife  resampling  3)     Calibra"on  /  Reconstruc"ons     Performed  using  Generalized  Addi<ve  Models  (GAMs)   2)     € g(E(Q)) = B0 + f1TR1 + f2TR2 + ... boucher@cerege.fr  
  9. 9. Reconstruc<on  of  May  water  supplies  to  the   Caniapiscau  reservoir  (northern  Québec,  Canada)   boucher@cerege.fr  
  10. 10. Hudson  bay   La  Grande  HE  complex  
  11. 11. Dendrochronological  data   =  Earlywood  density   =  Ice  scar  chronology  at  lake  Montausier   boucher@cerege.fr  
  12. 12. Water  supplies  to  the  Caniapiscau  reservoir,     &  hydrological  variables  to  reconstruct   boucher@cerege.fr  
  13. 13. Discrete  and  con<nuous  dendroseries   Propor<on  of  ice  scoured  trees  around  lake  Montausier   Earlywood  density,  PC1   Earlywood  density,  PC2   boucher@cerege.fr  
  14. 14. The  Montausier  lake  ice  scar  chronology   (an  other  look  at  it…)   Propor<ons   N=300   boucher@cerege.fr   For  each  year,  N=300  possible  propor<ons  were  randomly  generated     from  a  binomial  distribu<on.       Colors  indicate  «  the  number  of  "mes  a  simulated  propor<on  value  falls  in  each  class  »  
  15. 15. Rela<onships  between  TR  series  &    water  supplies  (QMay)  to  the  Caniapiscau  Reservoir   Propor<ons   of  ice  scarred  trees,   Montausier  lake   PC1     Index   (wet  sites)   PC2    index   (mesic  xeric  sites)  
  16. 16. Calibra<on  /  verifica<on  sta<s<cs     &  comparison  with  a  tradi<onal  MLR  approach   € g(E(QMay )) = B0 + f1X1 + f2X2 + ... € E(QMay ) = B0 + B1X1 + B2X2 + ... +   boucher@cerege.fr  
  17. 17. Historical  May  water  supplies  to  the     Caniapiscau  Reservoir   boucher@cerege.fr  
  18. 18. Discussion  and  Conclusion   -­‐  A  new  approach  to  reconstruct  paleofloods  from  tree  rings  in   northern  environment.  It  allows:     1)  to  take  advantage  of  both  discrete  and  con"nuous  tree  ring  proxys   2)  to  model  and  include  the  uncertainty  of  discrete  TR  series  within  the   calibra<on  /  reconstruc<on  process   3)  to  account  for  non-­‐linear  rela"onships  that  occur  in  natural   environments   -­‐      Our  approach  can  be  used  in  other  environments  /  situa<ons   where  discrete  and  con<nuous  tree  ring  series  are  available  
  19. 19. BIENVILLE   MONTAUSIER   CORVETTE   LEC   NECOPASTIC   HERVÉ   POLARIS  
  20. 20. Many  thanks  to   +  field  assistants  throughout  the  years  boucher@cerege.fr  

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