Tree rings have been used to reconstruct streamflow in the Colorado River basin over centuries. This revealed that severe multi-year droughts were more common than shown in the instrumental record. A 1,000-year drought reconstruction for western North America also indicated droughts could last decades. Tree rings have additionally helped develop the North American Drought Atlas which provides drought context for historical events and shows Asian monsoon variability over centuries.

1. November 20
Drought and dendrohydrology

2. WHAT IS
DROUGHT?

3. A drought refers to an extended period of time when a region
receives substantially less moisture than it does in most years.

4. METEOROLOGICAL DROUGHT
Source: Chazz Layne

5. HYDROLOGICAL DROUGHT
Source: David Sauchyn

6. AGRICULTURAL DROUGHT
Source: library_chic

8. This past summer, the central and western US
experienced the worst drought in two decades.

9. Corn stalk destroyed by severe drought near Round Rock, Texas.
Jay Janner

10. Despite the increase in productivity, you still can’t grow corn without water.
bushels of corn per acre
2002
1993
1980 (flood year)
1983 1988
Source: USDA

11. The Monticello Nuclear Generating Plant in Monticello, Minnesota
shekleton

12. The mighty Mississippi in 1988

14. In the 1940s, Tucson was a small city with less than 40,000 residents.

15. Nearly 1 million people now live in the Greater Tucson Metropolitan Area.

16. Photograph: Nevada Tourism Media Relations

19. The Central Arizona Project is a 336-mile canal that diverts water from the Colorado River
into central and southern Arizona.

20. Source: Chazz Lane

21. Water transfers in the American southwest
Courtesy Glen MacDonald

22. Photograph: Ben Amstutz

23. Photograph: Ben Amstutz

24. Photograph: Michael Koukoullis

25. THE COLORADO RIVER COMPACT
divides water from the Colorado River
among seven western states.

26. Observed discharge, Colorado River
Compact allocation (16.5 MAF)

27. Low reservoir
Photograph: Glen MacDonald

28. “ We’ve never had to worry about our water resources.
Our children will not enjoy that luxury.
Patricia Mulroy
Southern Nevada Water Authority
”

29. Observed discharge, Colorado River
Compact allocation (16.5 MAF)

30. READING
David Meko and Connie Woodhouse (2010), Application of
streamflow reconstruction to water resources management.
M.K. Hughes et al. (eds.), Dendroclimatology, Developments in
Paleoenvironmental Research.

31. 1
How have tree rings been used to understand
the hydrology of the Colorado River?
2 More generally, what do tree rings have to say
about drought across North America?

32. TRACING THE COLORADO

35. The history of precipitation and
runoff in the Colorado Basin as
indicated by tree-rings
Edmund Shulman
Ph.D. Thesis
Harvard University
1944

39. “
The growth of trees is undoubtably controlled more by
the movement of water than by the movement of any
other single substance.”
Hal Fri s
Tree Rings and Climate

40. water
stress
narrow ring reduced photosynthesis
less cell expansion
reduced cell division

42. INDIRECT
RELATION

43. READING
David Meko and Connie Woodhouse (2010), Application of
streamflow reconstruction to water resources management.
M.K. Hughes et al. (eds.), Dendroclimatology, Developments in
Paleoenvironmental Research.

46. Connie Woodhouse University of Arizona

47. Source: Woodhouse et al., 2006

48. stream gauge
tree-ring estimate
Source: Woodhouse et al., 2006

49. Source: Woodhouse et al., 2006

50. “ Average reconstructed annual flow for
the period 1844–1848 was lower than
the observed flow for 1999–2004.
”
Connie Woodhouse et al.
Water Resources Research, 2006

51. “ The long-term perspective provided by
tree ring reconstructions points to looming conflict
between water demand and supply in
”
the upper Colorado River basin.
Connie Woodhouse et al.
Water Resources Research, 2006

52. MEGADROUGHT
intensity at least equivalent to modern multiyear droughts
duration longer than the several years to decade thereof
Seager et al., Journal of Climate, 2008

53. Dave Meko University of Arizona

54. Relic tree, circa 323 BC Harmon Canyon, Utah

55. 1,200 years of Colorado River discharge Meko et al., GRL, 2007

56. THE COLORADO RIVER COMPACT
divides water from the Colorado River
among seven western states.

57. Tree rings provided the central evidence that caused municipal water agencies to
“RETHINK OLD
ASSUMPTIONS”
about worst-case scenarios for reservoir operations and re-evaluate the
potential duration and geographic scope of severe drought.

58. GLOBAL DROUGHT FROM TREES

59. Terry Hash planted 800 acres of co on, corn, wheat and sorghum. Almost all of it was destroyed by the 2011 Texas drought.
Jay Janner

61. Palmer Drought Severity Index
The PDSI incorporates historical records of precipitation
and temperature into a water-balance model to estimate
the amount of water available in the soil relative to
average conditions and is typically produced once a month.

62. +4 extreme wet
-4 extreme drought
(compared to ‘average’ for that place)

63. How much water is in this soil?

64. One hundred years of drought history around Minneapolis-St. Paul
Source: North American Drought Atlas

66. Ed Cook Lamont-Doherty Earth Observatory

67. Drought grid (blue dots) Cook et al., JQS, 2010

68. Average PDSI, AD 1580 to 1600

69. HOW DO WE KNOW
THIS WORKS?

70. Dalhart, TX, 1938

71. Tree ring
Source: David Stahle

72. June 1833
All-time record flooding on the Arkansas,
Canadian, and Verdigris Rivers in Oklahoma.
950 displaced Creek and Seminole drown
on floodplain farmsteads.
Source: David Stahle

73. Source: David Stahle

74. How has the extent of severe
drought changed through time?

75. Observed (blue) and tree-ring (red) PDSI in ‘The West’

76. A 1,000 years of drought in the West Cook et al., Science, 2004

77. Can the Drought Atlas help us place
historical events within a context of
long-term environmental change?

78. Square Tower House Great Pueblo Drought
Mesa Verde, Colorado A.E. Douglass (1929)
Source: David Stahle

79. North American Drought Atlas h p://www.ncdc.noaa.gov/cgi-bin/paleo/pd08plot.pl

80. Source: Ingmar Zahorsky

81. “ Much of the world’s population lives in monsoon Asia
and depends on monsoon rainfall for water and
agricultural fertility.
”
Wahl and Morrill
Science, 2010

82. Average spatial pa erns of precipitation and wind during summer
E R Wahl, C Morrill Science 2010;328:437-438

83. MONSOON ASIA
DROUGHT ATLAS
h p://www.ncdc.noaa.gov/paleo/pubs/cook2010/cook2010.html

85. Tree rings show extent of ‘Great Drought’, 1876-1878
E R Cook et al. Science 2010;328:486-489

86. “ The tree-ring record shows that droughts
lasting decades have routinely gripped
western North America.
”
Jonathan Overpeck and Bradley Udall

87. GEOG5839
XT C L AS S
NE