Climatic Inferences from Dendroecological Reconstructions - Dendroclimatology - page 269

Large Fire Years Small Fire Years

A. B.

1.0

1.0

0.5 0.5

0.0

0.0

-0.5 -0.5

-1.0 -1.0

-1.5 -1.5

-5-4-3-2-1 0 1 2 3 4 5 -5-4-3-2-1 0 1 2 3 4 5

0.50

0.50

C.

D.

0.25 0.25

0.00 0.00

-0.25 -0.25

-0.50 -0.50

-5 -4 -3 -2 -1 0 1 2 3 4 5 -5 -4 -3 -2 -1 0 1 2 3 4 5

1.5 1.5

1.0 1.0

0.5

E. 0.5

0.0 0.0

F.

-0.5

-0.5

-1.0 -1.0

-1.5 -1.5

-5-4-3-2-1 0 1 2 3 4 5 -5-4-3-2-1012345

Fire Year

Fire Year

Fig. 9.4 Superposed epoch analysis (SEA) of large and small regional fire years in relation to
summer Palmer Drought Severity Indices (PDSIs) in the southwestern United States and Niño-3
sea surface temperature (SST). Plots A and B show results for largest (38) and smallest (36) fire
years during the period 1600-1900, using tree-ring width reconstructions of southwestern PDSI
(Cook et al. 2004 ) . Plots C and D show results from SEA using the same sets of fire years against
a reconstruction of Niño-3, an index of the El Niño/Southern Oscillation (ENSO) (Cook 2000 ) .
Plots E and F show SEA results using modern PDSI based on instrumental data and the largest
(19) and smallest (23) fire years from area burned records from all federal, state, and private lands
in Arizona and New Mexico during the period 1905-2004. Lines in each plot represent the 0.05,
0.01, and 0.001 confidence intervals based on Monte Carlo simulations of random distributions of
annual climate conditions for PDSI and Niño-3

1-3 years of wet conditions. These fires were mainly surface fires, burning in grasses
and herbaceous fuels, and wet conditions would have resulted in more continuous
and denser fuels that would have burned more readily and have been widespread
during subsequent drought years (e.g., Brown and Wu 2005 ) .