Two solitudes - how seasonality biases drought from tree rings

TWO SOLITUDES how seasonality biases drought records from tree rings

why are Canadian streamﬂow reconstructions so lousy?

100% 80% 60% explained variance 40% 20% 0% Canada USA

100% Woodhouse et al., 2006 Meko et al., 2001 80% Sacramento River Upper Colorado River Meko et al., 2007 Colorado River Woodhouse, 2007 Middle Boulder Creek 60% explained variance 40% 20% 0% Canada USA

100% Woodhouse et al., 2006 Meko et al., 2001 80% Sacramento River Upper Colorado River Meko et al., 2007 Colorado River Woodhouse, 2007 Middle Boulder Creek 60% Case and MacDonald, 2003 explained Saskatchewan River Beriault and Sauchyn, 2006 Churchill River variance Bonin and Burn, 2005 Athabasca River 40% Watson and Luckman, 2005 Gedalof et al., 2007 Bow River Columbia River 20% 0% Canada USA

why are Canadian tree rings not connected to climate modes?

Janice Lough and Hal Fritts The Southern Oscillation and tree rings: 1600 - 1961 Journal of Applied Meteorology 24, 1985 Roseanne D’Arrigo and Gordon Jacoby A thousand year record of northwestern New Mexico winter precipitation reconstructed from tree rings and its relation to El Niño and the Southern Oscillation The Holocene 1, 1991 David Stahle and collaborators Experimental dendroclimatic reconstruction of the Southern Oscillation Stahle et al., 1998 Bulletin of the American Meteorological Society 79, 1998

Prairie ringwidth records 138 Signiﬁcant correlation with ENSO 4 Expected from random chance 6.9

seasonality

Trees, seasonality and climate forcings The southwestern US

Trees, seasonality and climate forcings The Canadian Prairies

DROUGHT AND SEASONALITY How does the connection between reconstructed drought 1 and seasonal precipitation vary across North America?

DROUGHT AND SEASONALITY How does the connection between reconstructed drought 1 and seasonal precipitation vary across North America? CLIMATE MODES AND TREE RINGS In which regions are drought reconstructions most strongly 2 connected to remote climate forcings (ENSO, PDO, AMO)?

The North American Drought Atlas Cook et al., 2007, Earth Science Reviews

Cook et al., 2007, Earth Science Reviews

CORRELATION COMPOSITES COHERENCE

PART ONE tree rings, drought and seasonality

signiﬁcant (α=0.05)

instrumental tree rings

SUMM ER PRECIP ITAT ION

WINTER PRECIPITAT ION

do tree rings replicate these patterns?

+

summer mixed winter

DOMINANT not exclusive

“ ...the regional summer precipitation signal is strong in Pseudotsuga menziesii latewood-width [in southeastern Arizona]. David Meko and Chris Baisan Pilot study of latewood-width of conifers as an indicator of variability of summer rainfall in the North American monsoon region International Journal of Climatology 21, 2001

Medicine Hat, Alberta Source: Environment Canada, Adjusted Historical Canadian Climate Data, 1895 – 2006

Prairie ringwidth records 138 Signiﬁcant correlation with ENSO 4 Expected from random chance 6.9 45

ENSO and winter precipitation

PART TWO drought records and climate modes

ENSO PDSI from tree rings PDO AMO

are these signals present in reconstructed drought?

Julia Cole and Ed Cook The changing relationship between ENSO variability and moisture balance in the continental United States Geophysical Research Letters 25, 1998

COMPOSITES where is it wet or dry when ENSO is strong?

LOW frequency

LOW FREQUENCIES (>7yr) TREE-RINGS and PDO 0.5 0.25 mean squared 61 0 coherence

3 Mexican PDSI 10 2 5 1 0 0 -1 -5 -2 -3 62 -10 1900 1920 1940 1960 1980 2000

3 PDO index Mexican PDSI 10 2 5 1 0 0 -1 -5 -2 -3 63 -10 1900 1920 1940 1960 1980 2000

SEAS ONALITY AND D ROUGHT

summer mixed winter

IMPLICATIONS 1590s

IMPLICATIONS what/where OK

IMPLICATIONS what/where OK what/where/why NOT OK

IMPLICATIONS tree ring model output Celine Herwiejer, Richard Seager and Ed Cook North American droughts of the mid to late nineteenth century: a history, simulation and implication for Mediaeval drought The Holocene 16, 2006

summer mixed winter

M A N Y TH AN KS Dave Meko Ed Cook Hal Fritts Toby Ault

Two solitudes - how seasonality biases drought from tree rings

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