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1

Drought in a Changing Climate

“Insufficient water to meet needs” – K. Redmond

Look at any climate record…

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2

2004/05 “Lake” Death Valley

Wettest Year for Southern California

2006/07Squaw Valley “Ski” Resort, California

2006/07 Kindling in Waiting

Driest Year for Southern California

Ratio of Standard Deviation to Mean in Water Year Precipitation

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3

Impacts: Great Drought in India 1876-1878

• Multi-year monsoon failure in southern India• Widespread crop failure• Death toll of 5.5 million due to famine

Late Victorian Holocausts (2001) by Mike Davis

El Nino Famines and the Making of the Third World

0

20

40

60

80

100

% D

RO

UG

HT

AR

EA

1150 1253936 1034

1321 1829

YEAR

1915

LONG-TERM CHANGES IN DROUGHT AREA IN THE 'WEST'

THE CENTRAL DATES OF THESIGNIFICANT (p<0.05) EPOCHSARE INDICATED WITH ARROWS

DRIER

WETTER

1613

800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Cook et al., Science (2004)

Western US Drought Area

Southwestern US

Water is most precious, least abundant resource…

Agricultural society farming in a desert

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4

Collapse: Drought and the Anasazi

Populations expanded dramatically during wet years.

Population collapses related to megadroughts

See Collapse by Jared Diamond

Benson et al. (2006)

Num

ber o

f hab

itatio

n si

tes

Simple one-dimension balance

Source: http://azclimate.asu.edu/mbdi/about.php

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Evaporative Demand

• Amount of water that could be evaporated and transpired from plants if water is not limited

• Function of atmospheric conditions (and vegetation)• Warmer air leads to higher vapor pressure deficit and demand

Global Water Balance

Impacts are already here

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+1°C

Less spring snow means…

Less summer flow

Luce and Holden, 2009

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Drought

Drivers of California drought

Precipitation dataset

Palmer Drought Severity Index (PDSI)

DRY

WET

3-yr mean Precipitation 3-yr mean Atmospheric demand (Potential Evapotranspiration)

3-yr running mean

2012-2014

Into Soil Out of soil

20

Palmer Drought Severity Index

PDSI

Precipitation & EvaporationPrecipitation only

~70%

~30% ~22%

Roles of precipitation versus evaporation in causing California drought: 2012–2014

California’s current multi-year drought would have been 10-25% less severe in the absence of climate change

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2012-2014 Drought Severity Ranking (since 1901)

Actual

Worst on record

Without Warming Trend

Conclusion: Human-caused warming has increased severity of droughts. Natural

climate variability dominates

22

https://vimeo.com/89648161

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9

Syrian Drought

• Worst in region in at least 500 years• 85% livestock loss, 75% crops damaged• Demise of crop yields forced 1.5 million to flee farming and settle

in urban centers

The occurrence of a 3-year drought as severe as that of 2007-2010 was made 2-3 times more likely due to man-made climate change

Colin P. Kelley et al. PNAS 2015;112:3241-3246

• Misguided agricultural/water use policies (decline of groundwater)• Two-thirds of country in rain-fed agriculture• Influx of migration from Iraq• Forced to import wheat, livestock feed etc. • Large spikes in food prices• Refugees

http://publicradio1.wpengine.netdna-cdn.com/updraft/files/2015/03/CC-Syrian-timeline.png

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IdahoMagazine

NASA MODIS, 8/23/15

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Burned Area in Western US

2005

-201

5 av

erag

e

Littell et al., 2009; Dennison et al., 2014

−1.5 −1 −0.5 0 0.5 1 1.5 2

30

100

300

1000

Fuel aridity (σ)

Fore

st F

ire A

rea

(kha

)

1984−19992000−2015

R2 = 0.76P<0.0001

Abatzoglou andWilliams,inpress

ObservationsNo ACCBurned area

−2

−1

0

1

2

Fuel

arid

ity (σ

)

a)

1950 1960 1970 1980 1990 2000 2010

20

40

60

80

% a

rea

(+1 σ

)

250

500

750

1000Forest fire area (ha x 1000)

Fuel aridity Index (top) and percent of forests with high fuel aridity (>1 sigma)

Abatzoglou and Williams, in press

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Anthropogenic Climate Change doubled extent of forest fire in western US

Abatzoglou and Williams, in press

Extreme Events

Happen without climate change Climate changes alter the probability of extreme events

End