North American Drought: Paleoclimatic and Historic

Contexts

Greg McCabeUSGS, WRD, Denver, CO

Drought occurs somewhere in the US almost every year Drought occurs somewhere in the US almost every year and can occur over a large portion of the country.and can occur over a large portion of the country.

Generally, the most spatially extensive Generally, the most spatially extensive droughts are the driest droughts.droughts are the driest droughts.

drierdrier

Courtesy of Stephen Gray

1954

1954

Instrumental

Tree-Ring

PDSI

Source: NOAA Paleoclimate web page

dry wet

Tree rings also capture the spatial variability of climate.

Uinta Basin Watershed: 50-yr Running Average

Why use climate reconstructions? The instrumental record may not include the full range of climate

variability.

Gray, Jackson,Betancourt(2004)

GreatDrought

Late 16th

CenturyMegadrought

20th

Cent.

Significant Cultural Events

Coronado’sCoronado’sEntrada 1541Entrada 1541

Persistent climate anomalies have had Persistent climate anomalies have had significant socio-economic impacts. significant socio-economic impacts.

PHDIPHDIMortality rate (Jamestown and Mortality rate (Jamestown and Roanoke colonies)Roanoke colonies)

Drought may Drought may have been the have been the cause of the lost cause of the lost Jamestown Jamestown Colony.Colony.

Stahle et al., Science, 1998Stahle et al., Science, 1998

wetwet

drydry

wetwet

drydry

Krusik & Cook (2004) North American Drought Atlas

800 900 1000 1100 1700 18001900

20001200 1300 140015001600

Western US Drought Area Index (-1 PDSI)

80 yr lowpass

Medieval Warm Period

Little Ice Age

Perc

en

t A

rea o

f D

rou

gh

t (<

-1 P

DS

I)Current drought occurrence in the western U.S. is Current drought occurrence in the western U.S. is approaching that of the Medieval Warm Period.approaching that of the Medieval Warm Period.

Schubert et al., Science, 2005

There is instrumental and model evidence that La Nina is a significant cause of persistent drought in

the U.S.

La Nina

Composite SSTs, 1930’s drought (1932-1938)

Schubert et al., Science, 2005

There is instrumental and model evidence that La Nina is a significant cause of persistent drought in the U.S. …but there also is a signal in the North

Atlantic.

La Nina

AMO

Composite SSTs, 1930’s drought (1932-1938)

Interaction of Pacific and Atlantic SSTs also may Interaction of Pacific and Atlantic SSTs also may govern centennial-scale trends in western U.S. govern centennial-scale trends in western U.S.

drought.drought.

Courtesy Julio Betancourt

Cool

Warm

Medieval Warm PeriodMedieval Warm PeriodAD 900-1300AD 900-1300

DRY

Cool

Warm

Little Ice AgeLittle Ice AgeAD 1400-1850AD 1400-1850

WET

Source: Steve Gray, U. Wyo.

UCRBThe 20th century included the wettest and 3rd wettest

periods in the UCRB during the past 500 years

using 1995 estimates of water useusing 1995 estimates of water useusing 1995 estimates of water use

Increasing water demand is stressing the Increasing water demand is stressing the UCRB water supply, even during one of the UCRB water supply, even during one of the

wettest centuries.wettest centuries.

Source: Glen Canyon Institute, March 2005

Mill

ion

Acr

e F

eet

Courtesy of Stephen Gray, U. Wyo.

Population growth and water demand have increased Population growth and water demand have increased dramatically in the UCRB during an anomalously wet dramatically in the UCRB during an anomalously wet period. What will happen when the climate is drier?period. What will happen when the climate is drier?

Severe-Sustained Drought (SSD) ExperimentsHarding et al., WRB, 1995

Harding et al., WRB, 1995

Effects of Severe-Sustained Drought (dry regime) on Lake Powell

Lake Powell ContentsSSD Drought vs. Current Conditions

0

5

10

15

20

25

1 4 7 10 13 16 19 22 25 28 31 34 37

Drought Year

Conte

nts

, m

af

SSD

Based on 1579-1616 reconstruction of flow at Lees Ferry (1579-1600 drought, 1601-1616 Based on 1579-1616 reconstruction of flow at Lees Ferry (1579-1600 drought, 1601-1616 recovery), 1992 water use.recovery), 1992 water use.

Harding et al., WRB, 1995

Effects of Severe-Sustained Drought (dry regime) on Lake Powell

Lake Powell ContentsSSD Drought vs. Current Conditions

0

5

10

15

20

25

1 4 7 10 13 16 19 22 25 28 31 34 37

Drought Year

Conte

nts

, m

af

SSD

CurrentRecent

Based on 1579-1616 reconstruction of flow at Lees Ferry (1579-1600 drought, 1601-1616 Based on 1579-1616 reconstruction of flow at Lees Ferry (1579-1600 drought, 1601-1616 recovery), 1992 water use.recovery), 1992 water use.

19951995

20042004

26-year moving average UCRB flow expressed as departures from the mean 26-year moving average UCRB flow expressed as departures from the mean flow for 1896-1921 (the period used for the Colorado Compact mean flow flow for 1896-1921 (the period used for the Colorado Compact mean flow

estimate)estimate)

The period used to estimate UCRB flows for the Colorado The period used to estimate UCRB flows for the Colorado Compact was wet relative to other periods in the 20Compact was wet relative to other periods in the 20thth

century, as well as to most other periods during the past century, as well as to most other periods during the past 500 years.500 years.

Tree ring reconstruction from Tree ring reconstruction from Woodhouse et al., WRR, 2006.Woodhouse et al., WRR, 2006.

Hydrologic Conditions May 2007Hydrologic Conditions May 2007

Map of below normal 14-day average streamflow compared to historical

streamflow for the day of year (United States)

Summary

- Droughts have significant climatic as well as socio-economic impacts.

- Since the end of the little Ice Age drought occurrence in the western US appears to have increased. Will this trend continue?

- Persistent US drought may be linked with persistently cool eastern tropical SSTs and warm North Atlantic SSTs.

- Climatic variability and change, as well as increased consumptive use of water resources may lead to future water supply problems in the UCRB.