The Future is Not The Past: Megadroughts and Climate Change in Western North America

The Future is Not The Past:Megadroughts and Climate Changein Western North America

10/15/15, 2:03 PMMegadrought may plague parts of USA

Page 1 of 4http://www.usatoday.com/story/weather/2015/02/12/western-plains-drought-climate-change/23298093/

Megadrought may plague parts of USA Doyle Rice, USA TODAY 5:52 p.m. EST February 12, 2015

We ain't seen nothing yet: The intense drought in California is only an appetizer compared with what's comingthis century across much of the western and central USA, according to a study out Thursday.

During the years 2050 to 2100, the Southwest and Great Plains will face a persistent "megadrought" worsethan anything seen in the past 1,000 years, and the dry conditions will be "driven primarily" by human-inducedglobal warming, scientists said.

There's at least an 80% chance of a megadrought in these regions if climate change continues unabated, TobyAult, an atmospheric scientist at Cornell University and co-author of the research, said at a news conference

Thursday in San Jose.

A megadrought is defined as a drought that lasts for decades or longer, such as those that scorched portions of the West in the 12th and 13th centuries.Ault said megadroughts should be considered a natural hazard on par with earthquakes and hurricanes.

USA TODAY

California's 100-year drought

(http://www.usatoday.com/story/weather/2014/09/02/california-megadrought/14446195/)

To identify past droughts, scientists studied tree rings to find out how much or little rain fell hundreds or even thousands of years ago. Scientistsused that historical data in combination with 17 different computer model simulations to predict what changes we may see this century.

The computers showed robust and consistent drying in the Southwest and Plains, due to a combination of reduced precipitation and warmertemperatures that dried out the soils.

"Natural droughts like the 1930s Dust Bowl and the current drought in the Southwest have historically lasted maybe a decade or a little less," Ben Cook,climate scientist at NASA's Goddard Institute for Space Studies and lead author of the study, said in a statement.

(Photo: Rich Pedroncelli, AP)

10/15/15, 2:03 PMNASA: Megadroughts to scorch American West for decades - CNN.com

Page 1 of 4http://www.cnn.com/2015/02/14/us/nasa-study-western-megadrought/

Risk of American

'megadroughts' for

decades, NASA warns

Updated 2:47 PM ET, Wed March 4, 2015 | VideoSource: CNN/NASA

By Ben Brumfield, CNN

Story highlights

The current drought is bad, but it's nomegadrought

NASA: If greenhouse gas emissions don'tdrastically drop, the nation's West facesdroughts that could last decades

(CNN)There is no precedent in contemporary weather recordsfor the kinds of droughts the country's West will face, if

greenhouse gas emissions stay on course, a NASA study said.

No precedent even in the past 1,000 years.

The feared droughts would cover most of the western half of the

United States -- the Central Plains and the Southwest.

Those regions have suffered severe drought in recent years. But it

doesn't compare in the slightest to the 'megadroughts' likely to hit

them before the century is over due to global warming.

These will be epochal, worthy of a chapter in Earth's natural

history.

Even if emissions drop moderately, droughts in those regions will

get much worse than they are now, NASA said.

The space agency's study conjures visions of the sun scorching

cracked earth that is baked dry of moisture for feet below the

surface, across vast landscapes, for decades. Great lake

reservoirs could dwindle to ponds, leaving cities to ration water

to residents who haven't fled east.

10/15/15, 2:04 PMUS 'at risk of mega-drought future' - BBC News

Page 1 of 7http://www.bbc.com/news/science-environment-31434030

Science & Environment

Home Video World US & Canada UK Business Tech Science Magazine

13 February 2015 Science & Environment

US 'at risk of mega-drought future'By Jonathan AmosBBC Science Correspondent, San Jose

American society would need to find strategies to cope with droughts that lasted decades

The American south-west and central plains could be on course for super-droughts the like of which they have not witnessed in over a 1,000 years.

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10/15/15, 2:07 PMCalifornia megadrought: It's already begun.

Page 1 of 8http://www.slate.com/blogs/future_tense/2015/03/20/california_megadrought_it_s_already_begun.html

Follow us on Twitter for more great Slate stories! Follow Follow @slate@slate

ASU | NEW AMERICA | SLATE Learn moreabout FutureTense

THE CITIZEN'S GUIDE TO THE FUTURE MARCH 20 2015 5:40 PM

Californias Next Megadrought Has Already

BegunBy Eric Holthaus

Expect more of this. Above, the Almaden Reservoir in January 2014 in San Jose, California.Photo by Justin Sullivan/Getty Images

As California limps through another nearly rain-free rainy season, the state is taking increasingly bold action to save water.

On Tuesday, the California state government imposed new mandatory restrictions on lawn watering and incentives to limit water use in hotels and

restaurants as part of its latest emergency drought regulations. On Thursday, California Gov. Jerry Brown announced a $1 billion plan to support water

projects statewide and speed aid to hard-hit communities already dealing with shortages. Last month federal water managers announced a zero

allocation of agricultural water to a key state canal system for the second year in a row, essentially transforming thousands of acres of California

farmland into dust.

This weeks moves come after the state has fallen behind targets to increase water efficiency in 2015 amid the states worst drought in 1,200 years.

Last year, voters passed a $7.5 billion water bond and the legislature approved its first-ever restrictions on groundwater pumping, which wont go into

full effect until 2025. Stricter, more immediate limits on water use are possible as summer approaches.

Collaborators:Richard Seager, Jason Smerdon, Park Williams, Sloan Coats, Ed Cook, Dave Stahle, Toby Ault

With Funding From:NSF, NOAA, NASA

What is a drought?

Williams et al, in review

GRACE Satellitehttp://photojournal.jpl.nasa.gov/catalog/pia18816

Lake Mead (July 6, 2000)

Lake Mead (July 24, 2015)

source: NOAA

Lake Mead

L

L

LSL

SL

S

LSS

S

S S

S S

S

S

S

L

L

SL

SL

L

SL

SL

SL

S L

S

SS

S

SS

SSS

S

L

L SL

SL

The Drought Monitor focuses on broad-

scale conditions. Local conditions may

vary. See accompanying text summary for

forecast statements.

http://droughtmonitor.unl.edu/

U.S. Drought Monitor October 13, 2015

Valid 8 a.m. EDT

(Released Thursday, Oct. 15, 2015)

Intensity:

D0 Abnormally DryD1 Moderate DroughtD2 Severe DroughtD3 Extreme DroughtD4 Exceptional Drought

Author:

David Miskus

Drought Impact Types:

S = Short-Term, typically less than 6 months (e.g. agriculture, grasslands)

L = Long-Term, typically greater than 6 months (e.g. hydrology, ecology)

Delineates dominant impacts

NOAA/NWS/NCEP/CPC

What is a megadrought?

Relict tree stumps(West Walker River)

http://www.sierranaturenotes.com/naturenotes/paleodrought2.htm

>100 years old;cannot survive in waterlogged

soils

Medieval Megadroughts

Woodhouse & Overpeck(1998), BAMS

2705Bulletin of the American Meteorological Society

(Lehmer 1970; Wendland 1978),

and in northwestern Iowa afterabout A.D. 1100 and intensify-ing by A.D. 1200 (Bryson and

Murray 1977). The next majordrought is characterized prima-rily by an onset of eolian activ-

ity in the western Great Plains.It is difficult to determine the ex-act date of onset, but activity be-

gan sometime after ~A.D. 950(Forman et al. 1992; Formanet al. 1995; Madole 1994, 1995;

Muhs et al. 1996). Other proxydata that help confirm this pe-riod of drought are those from North Dakota lake sedi-

ments (Laird et al. 1996; Laird et al. 1998) and alluvialsediment records from western Nebraska and Kansas(Brice 1966; May 1989; Martin 1992). Although there

is dendroclimatic and lake-level evidence of droughtin the Sierra Nevada and White Mountains between~A.D. 900 and 1100, (LaMarche 1974; Stine 1994;

Hughes and Graumlich 1996), there is no evidence ofan onset of drought conditions occurring in the South-west at this time.

The third major drought episode of the A.D. 11200period occurred roughly between A.D. 700 and 900. Inarchaeological evidence in the Four Corners area,A.D. 750 was the starting date for a drought that lasted

several centuries (Euler et al. 1979; Dean et al. 1985;Peterson 1994), and a tree-ring reconstruction ofdrought for New Mexico also reflects this drought

(Grissino-Mayer 1996). Drought is recorded in west-ern Minnesota lake varves at this time (Dean et al.1994; Dean 1997) while North

Dakota lake sediments indicatedrought conditions typified theperiod A.D. 700850 (Fig. 11;

Laird et al. 1996; Laird et al.1998). In another more coarselyresolved record of lake sedi-

ments in North Dakota, highsalinity conditions are indicatedto have begun about this time

and continued through the fif-teenth century, a period contain-ing the droughts of the tenth,

twelfth, and late thirteenthcenturies (Fritz et al. 1991). Inthe central California drought

record from giant sequoia, the

period A.D. 699823 had the highest drought frequency

in the past 2000 years (Hughes and Brown 1992).Drought appears to have occurred in the White Moun-tains about this time as well (Hughes and Graumlich

1996). The onset of the earliest of these four droughtsoccurred about the middle of the third century and ap-pears to have lasted up to three centuries. A dendro-

climatic reconstruction of precipitation for northernNew Mexico (Grissino-Mayer 1996) shows this to bea period of consistently average to below-average pre-

cipitation until about A.D. 500. Drought-sensitive gi-ant sequoia in central California suggest that theperiod A.D. 236377 was one of the three periods withthe highest frequency of drought within the past two

millennia (Hughes and Brown 1992). During theclosely corresponding period, A.D. 200370, more fre-quent drought conditions were indicated by high lake

salinity in North Dakota lake sediments (Laird et al.1996; Laird et al. 1998). Archaeological remains in

FIG. 10. Paleoclimatic records of Great Plains and western U.S. century-scale drought,

A.D. 1present, as recorded in a variety of paleoclimatic data. The pale gray horizontal bars

reflect the length of the series, and the dark gray indicate periods of drought. Orange verti-

cal bars represent multidecadal droughts that appear to have been widespread.

FIG. 11. North Dakota Moon Lake salinity record, here spanning A.D. 11980 (Laird et al.

1996). Deviations from the mean (based on past 2300 yr) log salinity values are shown with

negative values indicating low salinity and wet conditions and positive values indicating

high salinity and dry conditions. Note the shift in salinity values around A.D. 1200, likely

reflecting a change in drought regime from more frequent, intense droughts prior to A.D. 1200

to relatively wetter conditions in the last 750 yr. The average temporal resolution of the

chronology is about one sample per five years, with an estimated error in the absolute chro-

nology of 5060 yr. The 92-yr gap in the data from 1618 to 1710 is due to desiccation in

this section of the core.

Yellow = Widespread Droughts

Ancestral Puebloan(~1271-1297)

Cahokia(~1323-1350)

Late 16th Cent.(~1568-1591)

Cold Pacific, Warm Atlantic

Feng et al (2008), Journal of Climate

them calcite from Panama [Lachniet et al., 2004]. Lakesediment cores from Alaska show that salmon were consis-tently more abundant from 900 to 1200 AD [Finney et al.,2002]. Because the abundance of salmon is closely related towarm El Nino-like interdecadal variations [Mantua et al.,1997; Zhang et al., 1997], this indicates that the easterntropical Pacific may have been warmer during medieval times.[11] In summary, the proxy records in the Pacific Ocean are

not in agreement about the SST anomalies in the easterntropical Pacific Ocean during medieval times. Some show

strong cooling (i.e., strong La Nina-like pattern), while someshow weak cooling (i.e., weak La Nina-like pattern), andothers even show warming. These different SST interpreta-tions complicate our understanding of the role played by thePacific Ocean on the medieval drought in North America.

2.2. Medieval SST Anomalies in theNorth Atlantic Ocean

[12] In recent decades, numerous proxy temperatures forthe North Atlantic Ocean have been generated [Kim et al.,

Figure 1. Proxy-inferred sea surface temperature anomalies (!C) in medieval times for CAM 3.0experiments. Values are differences from modern averages. Square is for Palmyra Island, which wasfrequently referred to in the text. Dots show the location of high proxy temperature data in North AtlanticOcean. The temperature differences between medieval and the modern times revealed by those recordsare also shown (see Table 1 for detail).

Table 1. High-Resolution Proxy Temperature Data in North Atlantic Region Used in This Studya

Site LocationProxy Sources,Climate Indicator

SampleResolution

TemperatureAnomalies Reference

GISP (72.6!N, 37.6!W) Greenland Borehole temperature N/A 1.0!C Dahl-Jensen et al. [1998]M992275(66.55!N, 17.70!W)

North of Iceland Diatom 20 years 1.0!Cb Jiang et al. [2005]

Chesapeake Bay(38.90!N, 76.40!W)

Northeastern U.S. Mg/Ca of OstracodLoxoconcha

110 years 0.0!Cc Cronin et al. [2003]

Sargasso Sea(33.69!N, 57.61!W)

Bermuda d18O of G. ruber About 50 years 1.01.5!C Keiwign [1996]

GeoB60072(30.85!N, 10.27!W)

Northwest African Alkenone paleothermometry About 30 years 0.81.0!C Kim et al. [2007]

Pigmy Basin, PBBC-1(27.19!N, 91.41!W)

Gulf of Mexico Mg/Ca of G. ruber 10 years 1.0!C Richey et al. [2007]

ODP Hole 658C(20.75!N, 18.58!W)

Cap Blanc, Mauritania Planktonic foraminiferal About 50 years 0.8!Cb deMonocal et al. [2000]

Cariaco Basin(10.76!N, 64.70!W)

Southern margin of the Caribbean d18O of G. ruber Annual 1.0!Cd Black et al. [2004]

aThe temperature anomalies in the fifth column are the difference between medieval and the modern times.bAverages of warm and the cold season SSTs.cLarge temperature fluctuations in medieval time in Chesapeake Bay was documented. The temperature was about 6!C warmer than modern times at

around 900 AD but about 4!C cooler at around 950 AD and 1050 AD. Overall the temperature in Chesapeake Bay in medieval times is about the sameamplitude as the modern time.

dBlack et al. [2004] suggested that the cooling trend of temperature during the last 2000 years in Cariaco Basin was at least 2!C and hence indicate thatthe temperature in the medieval times was at least 1!C warmer than the modern times.

D11101 FENG ET AL.: SST INFLUENCES ON MEDIEVAL DROUGHT

3 of 14

D11101

~900-1200 CE

Drought in the future?

LETTERS NATURE CLIMATE CHANGE DOI: 10.1038/NCLIMATE1716

CMIP3 models, SRES scenarios CMIP5 models, RCP scenariosComparison with

emulated CMIP3 RCP

RCP 8.5

RCP 6.0

RCP 4.5

RCP 2.6

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Historical (24)SRES B1 (20)SRES A1B (24)SRES A2 (19)

Historical (42)RCP 2.6 (26)RCP 4.5 (32)RCP 6.0 (17)RCP 8.5 (30)

Figure 1 |Global temperature change and uncertainty. Global temperature change (mean and one standard deviation as shading) relative to 19862005for the SRES scenarios run by CMIP3 and the RCP scenarios run by CMIP5. The number of models is given in brackets. The box plots (mean, one standarddeviation, and minimum to maximum range) are given for 20802099 for CMIP5 (colours) and for the MAGICC model calibrated to 19 CMIP3 models(black), both running the RCP scenarios.

Surface temperature change (C)

DJFRCP85: 20162035

JJASRESA2: 20812100

DJFSRESA2: 20812100

DJFSRESA2: 20162035

JJARCP85: 20812100

DJFRCP85: 20812100

JJARCP85: 20162035 JJASRESA2: 20162035

2.0 1.5 1.00.5 0.0 0.5 1.0 2.0 3.0 4.0 5.0 7.0 11.01.5

Figure 2 | Patterns of surface warming. Multi-model mean surface warming for two seasons (DecemberFebruary, DJF, and JuneAugust, JJA) and two20-year time periods centred around 2025 and 2090, relative to 19862005, for CMIP5 (left) and CMIP3 (right). Stippling marks high robustness,hatching marks no significant change and white areas mark inconsistent model responses (see Methods and Supplementary Figs S2 and S3).

370 NATURE CLIMATE CHANGE | VOL 3 | APRIL 2013 | www.nature.com/natureclimatechange

2013 Macmillan Publishers Limited. All rights reserved

Precipitation

Heterogeneous precipitation response

Knutti & Sedlacek (2013), Nature

Low confidencein some regions

NATURE CLIMATE CHANGE DOI: 10.1038/NCLIMATE1716 LETTERS

Precipitation change (%)

DJFRCP85: 20162035

JJASRES-A2: 20812100

DJFSRES-A2: 20812100


JJARCP85: 20812100

DJFRCP85: 20812100

JJARCP85: 20162035 JJASRES-A2: 20162035

80 40 20 10 5 2.5 0 5 10 20 40 802.5

Figure 3 | Patterns of precipitation change. Multi-model mean relative precipitation change for two seasons (DecemberFebruary, DJF, and JuneAugust,JJA) and two 20-year time periods centred around 2025 and 2090, relative to 19862005, for CMIP5 (left) and CMIP3 (right). Stippling marks highrobustness, hatching marks no significant change and white areas mark inconsistent model responses (see Methods and Supplementary Figs S2 and S3).

score used in weather prediction (seeMethods). In contrast to othercriteria1921, it considers the magnitude of change, the sign, naturalvariability and inter-model spread. The main conclusions aresimilar if other methods are used to measure model agreement20,21.Small and large dots indicate good and very good agreementbetween models, respectively (see Methods). Hatching marks areaswhere at least 80% of the models show no significant change,information that is often not highlighted yet clearly relevant forimpacts and adaptations. A significant warming with high modelagreement is evident already for a projection centred around2025. Regions where most models show significant changes butdo not agree well (robustness R< 0.5) are masked as white. Evenfor precipitation, the extent of those is limited, as pointed outrecently20,22. The area of the Earth where the robustness R exceeds0.8 (fine stippling) for precipitation change is depicted in Fig. 4a(black lines). The area fraction with robust projections is increasingwith global temperature as the precipitation signal emerges, butlevels off at about 3 C, where the signal further strengthens, butmodel differences also become pronounced. There are also large

areas with no significant precipitation change (that is, 50% of theglobe in boreal winter for 2 Cwarming)20,23.

Whereas the similarity of the projected precipitation change inCMIP3 and CMIP5 is reassuring, the similarity of the measureof robustness is more troublesome. The stippled area in CMIP3and CMIP5 is nearly identical, implying little increase in modelagreement in CMIP5 for precipitation changes. The correspondingresults for RCP4.5 and SRES B1 are similar. Robustness over landis slightly higher but also similar in CMIP3 and CMIP5 (Fig. 4c).There are several hypotheses that potentially explain the lack ofconvergence and associated reduction of uncertainty. There couldbe (1) inherent limitations in the way models are built givenlimited computational resources and spatial resolution, (2) lack ofprocess understanding, (3) lack of accurate long term observationsto constrainmodels, (4) lack of consensus onmetrics of present-daymodel performance that clearly separate better from worse modelsin terms of projection quality, (5) inherent limitation of climatechange not being predictable owing to internal variability, (6)addition of dissimilar models from institutions new in CMIP5

NATURE CLIMATE CHANGE | ADVANCE ONLINE PUBLICATION | www.nature.com/natureclimatechange 3

NATURE CLIMATE CHANGE DOI: 10.1038/NCLIMATE1716 LETTERS

Precipitation change (%)

DJFRCP85: 20162035

JJASRES-A2: 20812100



JJARCP85: 20812100

DJFRCP85: 20812100

JJARCP85: 20162035 JJASRES-A2: 20162035

80 40 20 10 5 2.5 0 5 10 20 40 802.5

Figure 3 | Patterns of precipitation change. Multi-model mean relative precipitation change for two seasons (DecemberFebruary, DJF, and JuneAugust,JJA) and two 20-year time periods centred around 2025 and 2090, relative to 19862005, for CMIP5 (left) and CMIP3 (right). Stippling marks highrobustness, hatching marks no significant change and white areas mark inconsistent model responses (see Methods and Supplementary Figs S2 and S3).

score used in weather prediction (seeMethods). In contrast to othercriteria1921, it considers the magnitude of change, the sign, naturalvariability and inter-model spread. The main conclusions aresimilar if other methods are used to measure model agreement20,21.Small and large dots indicate good and very good agreementbetween models, respectively (see Methods). Hatching marks areaswhere at least 80% of the models show no significant change,information that is often not highlighted yet clearly relevant forimpacts and adaptations. A significant warming with high modelagreement is evident already for a projection centred around2025. Regions where most models show significant changes butdo not agree well (robustness R< 0.5) are masked as white. Evenfor precipitation, the extent of those is limited, as pointed outrecently20,22. The area of the Earth where the robustness R exceeds0.8 (fine stippling) for precipitation change is depicted in Fig. 4a(black lines). The area fraction with robust projections is increasingwith global temperature as the precipitation signal emerges, butlevels off at about 3 C, where the signal further strengthens, butmodel differences also become pronounced. There are also large

areas with no significant precipitation change (that is, 50% of theglobe in boreal winter for 2 Cwarming)20,23.

Whereas the similarity of the projected precipitation change inCMIP3 and CMIP5 is reassuring, the similarity of the measureof robustness is more troublesome. The stippled area in CMIP3and CMIP5 is nearly identical, implying little increase in modelagreement in CMIP5 for precipitation changes. The correspondingresults for RCP4.5 and SRES B1 are similar. Robustness over landis slightly higher but also similar in CMIP3 and CMIP5 (Fig. 4c).There are several hypotheses that potentially explain the lack ofconvergence and associated reduction of uncertainty. There couldbe (1) inherent limitations in the way models are built givenlimited computational resources and spatial resolution, (2) lack ofprocess understanding, (3) lack of accurate long term observationsto constrainmodels, (4) lack of consensus onmetrics of present-daymodel performance that clearly separate better from worse modelsin terms of projection quality, (5) inherent limitation of climatechange not being predictable owing to internal variability, (6)addition of dissimilar models from institutions new in CMIP5

NATURE CLIMATE CHANGE | ADVANCE ONLINE PUBLICATION | www.nature.com/natureclimatechange 3

Soil moisture changesmuch more widespread

Dai (2013), Nature Climate Change

LETTERS

NATURE CLIMATE CHANGE DOI: 10.1038/NCLIMATE1633

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(%)

Figure 2 | Future changes in soil moisture and sc_PDSI_pm. a, Percentage changes from 19801999 to 20802099 in the multimodel ensemble meansoil-moisture content in the top 10 cm layer (broadly similar for the whole soil layer) simulated by 11 CMIP5 models under the RCP4.5 emissions scenario.Stippling indicates at least 82% (9 out of 11) of the models agree on the sign of change. b, Mean sc_PDSI_pm averaged over 20902099 computed usingthe 14-model ensemble mean climate (including surface air temperature, precipitation, wind speed, specific humidity and net radiation) from the CMIP5simulations under the RCP4.5 scenario. A sc_PDSI_pm value of 3.0 or below indicates severe to extreme droughts for the present climate, but itsquantitative interpretation for future values in b may require modification.

layer during the twenty-first century over most of the Americas,Europe, southern Africa, most of the Middle East, southeast Asiaand Australia. The multimodel mean suggests decreases rangingfrom 5 to 15% by 20802099. The drying in the soil-moisturefield is largely reproduced by the sc_PDSI_pm calculated usingthe same multimodel mean climate, although the sc_PDSI_pmsuggests larger increases in wetness over central and eastern Asiaand northern North America (Fig. 2b). Similar changes (but withsome regional differences) are also seen in CMIP3 models3,4 (Sup-plementary Fig. S1) and in all seasons (Supplementary Fig. S2).

As SSTs have large influences on land precipitation and drought,here I carried out amaximumcovariance analysis18 (MCA) of globalfields of SSTs (40 S60 N) and sc_PDSI_pm (60 S75 N) fromboth observations and the CMIP models (also done for SST versussoil moisture for the model data). The goal is to examine whetherthe models can reproduce the observed relationship revealed by theleading MCA modes between SST and sc_PDSI_pm and whetherthe models can simulate the recent drying trend. By focusing onthe leading MCA modes, many (but not all) of the unforced,irreproducible natural variations are excluded in such comparison.

Figure 3 shows that the second MCA modes (MCA2) fromobservations and the models are remarkably similar in spatial

patterns. They both represent the variations induced by the ElNio-Southern Oscillation (ENSO), as the SST patterns (Fig. 3b,d)resemble the typical ENSO-induced SST anomaly patterns12 andthe temporal coefficient is highly correlated (r = 0.87) with anENSO index (Fig. 3a). There are substantial decadal tomultidecadalvariations in this ENSO mode from observations as noticedpreviously19, with the recent period since about 1999 becomingcooler in the central and eastern Pacific than the previous periodfrom 1977 to 1998 (Fig. 3a,b). For the MCA2, we focus on thesimilarity in the spatial patterns between the observations andmodels, as the temporal coefficient for the multimodel ensemblemean (not shown) should bear little resemblance to the observedtemporal evolution, which is realization dependent. The impact ofENSO on drought is reflected by the MCA2 for the sc_PDSI_pm,whose patterns (Fig. 3c,e) largely resemble those of ENSO-inducedprecipitation20, with drier conditions over Australia, south Asia,northern South America, the Sahel and southern Africa and wetterconditions over the continental USA, Argentina, southern Europeand southwestern Asia in El Nio years.

Figure 4 shows that the first leading MCA modes (MCA1)from observations and the models represent the global warming,as the temporal coefficient is correlated strongly (r = 0.97) with

54 NATURE CLIMATE CHANGE | VOL 3 | JANUARY 2013 | www.nature.com/natureclimatechange

2013 Macmillan Publishers Limited. All rights reserved

Why?

Temperature

Widespread androbust warming

Knutti & Sedlacek (2013), Nature



emulated CMIP3 RCP

RCP 8.5

RCP 6.0

RCP 4.5

RCP 2.6

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DJFRCP85: 20162035

JJASRESA2: 20812100

DJFSRESA2: 20812100

DJFSRESA2: 20162035

JJARCP85: 20812100

DJFRCP85: 20812100

JJARCP85: 20162035 JJASRESA2: 20162035

2.0 1.5 1.00.5 0.0 0.5 1.0 2.0 3.0 4.0 5.0 7.0 11.01.5


2 NATURE CLIMATE CHANGE | ADVANCE ONLINE PUBLICATION | www.nature.com/natureclimatechange



emulated CMIP3 RCP

RCP 8.5

RCP 6.0

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DJFRCP85: 20162035

JJASRESA2: 20812100

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DJFRCP85: 20812100

JJARCP85: 20162035 JJASRESA2: 20162035

2.0 1.5 1.00.5 0.0 0.5 1.0 2.0 3.0 4.0 5.0 7.0 11.01.5


2 NATURE CLIMATE CHANGE | ADVANCE ONLINE PUBLICATION | www.nature.com/natureclimatechange

Warming increases atmospheric demand for water

The Water Budget

site dominated by grasses and a 15-year-oldaspen (Populus tremuloides) forest comparedwith an 80-year-old black spruce (Picea mariana)forest, primarily in spring and summer. Annualsensible heat flux decreased by more than 50%compared with the 80-year site, mostly in springand summer. During summer, the aspen foresthad the highest latent heat flux, lowest sensibleheat flux, and lowest midday Bowen ratio(defined as the ratio of sensible heat flux tolatent heat flux).

Boreal ecosystems store a large amount ofcarbon in soil, permafrost, and wetland (2) andcontribute to the Northern Hemisphere terrestrialcarbon sink (3), althoughmature forests have lowannual carbon gain (Fig. 1C). The climate forcingfrom increased albedo may offset the forcingfrom carbon emission so that boreal deforestationcools climate (8). Similar conclusions are drawnfrom comprehensive analysis of the climate forc-ing of boreal fires (25). The long-term forcing is abalance between postfire increase in surface

albedo and the radiative forcing from greenhousegases emitted during combustion. Averaged overan 80-year fire cycle, the negative forcing fromsurface albedo exceeds the smaller positive bio-geochemical forcing. Yet in the first year afterfire, positive annual biogeochemical forcing fromgreenhouse gas emission, ozone, black carbondeposited on snow and ice, and aerosols exceedsthe negative albedo forcing.

Boreal forests are vulnerable to global warming(5). Trees may expand into tundra, but die back

Momentum flux wind speed 0 ua

Dep

th Tsoil

Dep

th Soil water

Surface energy fluxesA HydrologyB Carbon CycleC

Reflected solar radiation Absorbed

solar radiation

Diffuse solar radiation

Em

itted

long

wav

e ra

diat

ion

Long

wav

e ra

diat

ion

Late

nt h

eat f

lux

Sen

sibl

e he

at fl

ux

Soil heat flux

Precipitation

Interception Evaporation

Sublimation

Infiltration Melt Snow

Transpiration

Evaporation

Throughfall stemflow

Surface runoff

Drainage

Photosynthesis

Fire

Autotrophic respiration

Foliage

Stem

Root Soil carbon

Nutrient uptake

Litterfall

Direct solar radiation

r s

r a

r a

Transpiration

Heterotrophic respiration

Mineralization

Urbanization

F

Vegetationdynamics

D

Landuse

E

Competition

Disturbance

Growth Establishment

Deforestation

Farm abandonment

Fig. 2. The current generation of climate models treats the biosphere andatmosphere as a coupled system. Land surface parameterizations representthe biogeophysics, biogeochemistry, and biogeography of terrestrialecosystems. (A) Surface energy fluxes and (B) the hydrologic cycle. These

are the core biogeophysical processes. Many models also include (C) thecarbon cycle and (D) vegetation dynamics so that plant ecosystems respond toclimate change. Somemodels also include (E) land use and (F) urbanization torepresent human alteration of the biosphere.

CRE

DIT:C

ARIN

CAIN

13 JUNE 2008 VOL 320 SCIENCE www.sciencemag.org1446

Forests in Flux

on

Augu

st 2

0, 2

013

ww

w.s

cien

cem

ag.o

rgD

ownl

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warming means more of this

and less of this

PrecipONLY

Precip+Warming

PDSI:2080-2099

Warming intensifies and spreads the area of soil moisture drying

Soil Moisture(2050-2099)

How will future droughts compare to the past?

Central Plains

10 8 6 4 2 0 2 4

SM2m

10 8 6 4 2 0 2 4

SM30cm

10 8 6 4 2 0 2 4NORESM1ME

NORESM1M

MIROCESMCHEM

MIROCESM

INMCM4

GISSE2R

GFDLESM2M

GFDLESM2G

GFDLCM3

CNRMCM5

CESM1CAM5

CESM1BGC

CCSM4

CANESM2

BCCCSM11

ACCESS13

ACCESS10

NADA

PDSI

NADA (11001300) NADA (15011849) NADA (18502005)Model (18502005) Model (20502099)

Southwest10 8 6 4 2 0 2 4

SM2m

10 8 6 4 2 0 2 4

SM30cm

10 8 6 4 2 0 2 4NORESM1ME

NORESM1M

MIROCESMCHEM

MIROCESM

INMCM4

GISSE2R

GFDLESM2M

GFDLESM2G

GFDLCM3

CNRMCM5

CESM1CAM5

CESM1BGC

CCSM4

CANESM2

BCCCSM11

ACCESS13

ACCESS10

NADA

PDSI

NADA (11001300) NADA (15011849) NADA (18502005)Model (18502005) Model (20502099)

21st Century Risk of a multidecadal

(>35 years) drought increases from

10-15%

to

>80%

source: Ed Hawkins, twitter

Year-to-Date (January-September)Global Temperatures

Is temperature already beginning to play a role?

L

L

LSL

SL

S

LSS

S

S S

S S

S

S

S

L

L

SL

SL

L

SL

SL

SL

S L

S

SS

S

SS

SSS

S

L

L SL

SL

The Drought Monitor focuses on broad-

scale conditions. Local conditions may

vary. See accompanying text summary for

forecast statements.

http://droughtmonitor.unl.edu/

U.S. Drought Monitor October 13, 2015

Valid 8 a.m. EDT

(Released Thursday, Oct. 15, 2015)

Intensity:

D0 Abnormally DryD1 Moderate DroughtD2 Severe DroughtD3 Extreme DroughtD4 Exceptional Drought

Author:

David Miskus

Drought Impact Types:

S = Short-Term, typically less than 6 months (e.g. agriculture, grasslands)

L = Long-Term, typically greater than 6 months (e.g. hydrology, ecology)

Delineates dominant impacts

NOAA/NWS/NCEP/CPC

Credit: Yosemite Conservatory, http://www.yosemiteconservancy.org/webcams

http://www.yosemiteconservancy.org/webcams

Warmer temperatures mean:

LESS SNOW,

EARLIER SNOW MELT and RUNOFF,

LESS WATER GOING TO SURFACE RESERVOIRS

California:Worst single (2014) and 3-year

(2012-2014) drought for much of state

Williams et al, 2015: GRL

! 25!

668!Figure 2. Maps of JJA PDSIsc and ranking for 2014 and 20122014. Rankings are based on all 669!years between 19012014 and a ranking of 1 indicates record-breaking drought. PDSIsc in this 670!figure is based on VOSE precipitation and temperature, PRISM humidity, and LDAS wind 671!velocity and insolation. Polygons bound the seven NOAA climate divisions (division numbers 672!shown in (a)). 673! 674! 675! 676! 677! 678! 679! 680! 681! 682! 683! 684! 685! 686! 687! 688! 689! 690! 691! 692! 693! 694! 695! 696! 697! 698! 699! 700!

Williams et al, 2015: GRL8-27%

How much worse did human-caused warming trends make the California Drought?

! 11!

Figure S7. (a) Contribution of each of the four anthropogenic warming scenarios to PDSIsc. In 2014, the anthropogenic effect was approximately -0.3 to -0.7. In (b and c), it is assumed that the anthropogenic warming effect in 2014 was the effect illustrated by the 50-year low-pass filter when applied to the VOSE temperature data (-0.46). The grey histogram in (b) and grey empirical cumulative distribution function in (c) represent the distribution of 19012014 PDSIsc values when the warming effect is removed. Blue curves are estimates of the distribution function from the kernal density function, meant to represent the hypothetical probability distribution of PDSIsc values in 2014 in the absence of anthropogenic warming. The orange curves are recalculations of this hypothetical PDSIsc distribution shifted uniformly by -0.46, mean to represent the true probability distribution of PDSIsc values in 2014 when anthropogenic warming is included.

Human Contribution ONLY

Drier

Wetter

July 6, 2000 July 24, 2015

Yuma, AZ: wheat field

Thank You.

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