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10/10/16
1
Drought in a Changing Climate
“Insufficient water to meet needs” – K. Redmond
Look at any climate record…
10/10/16
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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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
10/10/16
6
+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
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