Two solitudes - how seasonality biases drought from tree rings

TWOSOLITUDES

how seasonality biases drought records from tree rings

TWOSOLITUDES

how seasonality biases drought records from tree rings

why are Canadian streamflow reconstructions so lousy?

0%

20%

40%

60%

80%

100%

Canada USA

explainedvariance

0%

20%

40%

60%

80%

100%

Canada USA

explainedvariance

Woodhouse et al., 2006Upper Colorado River

Woodhouse, 2007Middle Boulder Creek

Meko et al., 2001Sacramento River

Meko et al., 2007Colorado River

0%

20%

40%

60%

80%

100%

Canada USA

explainedvariance

Woodhouse et al., 2006Upper Colorado River

Woodhouse, 2007Middle Boulder Creek

Meko et al., 2001Sacramento River

Meko et al., 2007Colorado River

Beriault and Sauchyn, 2006Churchill River

Watson and Luckman, 2005Bow River

Case and MacDonald, 2003Saskatchewan River

Gedalof et al., 2007Columbia River

Bonin and Burn, 2005Athabasca River

why are Canadian tree rings not connected to climate modes?

Janice Lough and Hal Fritts

The Southern Oscillation and tree rings: 1600 - 1961Journal 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 OscillationThe Holocene 1, 1991

David Stahle and collaborators

Experimental dendroclimatic reconstruction of the Southern OscillationBulletin of the American Meteorological Society 79, 1998

Stahle et al., 1998

Prairie ringwidth records138

Significant correlation with ENSO4

Expected from random chance6.9

seasonality

Trees, seasonality and climate forcings

The southwestern US

Trees, seasonality and climate forcings

The Canadian Prairies

DROUGHT AND SEASONALITY

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

DROUGHT AND SEASONALITY

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

CLIMATE MODES AND TREE RINGS

2 In which regions are drought reconstructions most strongly 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

CORRELATIONCOMPOSITESCOHERENCE

PART ONEtree rings, drought and seasonality

significant (α=0.05)

instrumental tree rings

SUMMER PRECIPITATION

WINTER PRECIPITATION

do tree rings replicate these patterns?

+

summer

winter

mixed

DOMINANT

exclusive

not

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 regionInternational Journal of Climatology 21, 2001

...the regional summer precipitation signal is strong in Pseudotsuga menziesii latewood-width [in southeastern Arizona].

““

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

Medicine Hat, Alberta

45

Prairie ringwidth records

138Significant correlation with ENSO

4Expected from random chance

6.9

ENSO and winter precipitation

PART TWOdrought records and climate modes

PDSI PDOAMO

ENSO

from tree rings

are these signals present in reconstructed drought?

Julia Cole and Ed CookThe changing relationship between ENSO variability and moisture balance in the continental United StatesGeophysical Research Letters 25, 1998

PDSI PDOAMO

ENSO

from tree rings

COMPOSITESwhere is it wet or dry when ENSO is strong?

PDSI PDOAMO

ENSO

from tree rings

LOWfrequency

61

LOW FREQUENCIES (>7yr)TREE-RINGS and PDO

0

mean squared coherence

0.5

0.25

61

LOW FREQUENCIES (>7yr)TREE-RINGS and PDO

0

mean squared coherence

0.5

0.25

1900 1920 1940 1960 1980 2000-3

-2

-1

0

1

2

3

-10

-5

0

5

10

62

Mexican PDSI

631900 1920 1940 1960 1980 2000-3

-2

-1

0

1

2

3

-10

-5

0

5

10PDO index Mexican PDSI

PDSI PDOAMO

ENSO

from tree rings

SEASONALITY AND DROUGHT

summer

winter

mixed

IMPLICATIONS

1590s

what/where OK

IMPLICATIONS

what/where OK

what/where/why NOT OK

IMPLICATIONS

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 droughtThe Holocene 16, 2006

summer

winter

mixed

MANY THANKS

Dave Meko

Ed Cook

Hal Fritts

Toby Ault