© Hawkins

PROJECTED TEMPERATURE CHANGES

Virtually all climate simulations project warming, but with a wide envelope of temperature change Virtually all climate simulations project warming, but with a wide envelope of temperature change

5th IPCC GCMs project +4-6°F warming by 2060, under mid and high emissions

31 GCMs X 2 RCP Emissions Scenarios IPCC 5th Assessment (CMIP5) models

Which emissions pathway will we take?Which emissions pathway will we take?

Stewart et al., 2005

Recent Recent trends:trends:

Observed: Warming**

Observed: Less snowpack**

Observed: Less snow/more rain**; changing snow thresholds

Observed: Earliergreenup dates; more

tree mortalities; enhanced wildfires

Observed: Animals moving north**

Observed:Observed: Earlier Earlier snowfed snowfed streamflowstreamflow****

PROJECTED TEMPERATURE CHANGES

Median temperature trends from 14 GCMs under two emissions scenarios

Warming over California is moderated (somewhat) by its position in midlatitudes & on the coast.

Courtesy of Suraj Polade, SIO

Range of projections: +2.5 to 6C

PROJECTED PRECIPITATION CHANGES

Climate projections disagree as to wetter vs drier overall; projected changes stay within natural range of variability

Climate projections disagree as to wetter vs drier overall; projected changes stay within natural range of variability

5th IPCC GCMs project large precipitation volatility but modest avg change (maybe drier)

31 GCMs X 2 RCP Emissions Scenarios IPCC 5th Assessment (CMIP5) models

Are there other changes lurking below weak annual-avg trends?

Are there other changes lurking below weak annual-avg trends?

All Drier All Wetter

Among 12 projections with high-CO2 emissions, how many models yield increasing (decreasing) precipitation?

PROJECTED PRECIPITATION CHANGES

Northern California still on the edge between more-or-less precipitation.

Percentage Change from Historical Normals

Knowles and Cayan, 2002, Geophysical Research Letters.

Under recent scenarios, Sierra Nevada loses half of its spring (April 1) snow pack due to climate warming. This is an amount similar to the total free-board space set aside each winter for flood control in the Sierra Nevada.

Under recent scenarios, Sierra Nevada loses half of its spring (April 1) snow pack due to climate warming. This is an amount similar to the total free-board space set aside each winter for flood control in the Sierra Nevada.

LOSS OF SPRINGTIME SNOWPACK

How well do you even remember what a cool year is like?

Its been more than 35 yrs since the State of California experienced a year in its historical coolest quartile!

How well do you even remember what a cool year is like?

Its been more than 35 yrs since the State of California experienced a year in its historical coolest quartile!

OBSERVED LOSS OF COOL YEARS

….and, chances of historical 10th percentile or less SWE increase greatly

40%

PROJECTED SNOW-WATER CHANGES

During 21st Century, a marked decline of chances of reaching or exceeding historical median SWE

in Sierra Nevada is projected

10%

Drier Summer Landscapes

increased warming and diminished snow

causes successively greater soil drying during 21st Century

(this picture could change somewhat under more recent IPCC5 simulations)

Drier Summer Landscapes

increased warming and diminished snow

causes successively greater soil drying during 21st Century

(this picture could change somewhat under more recent IPCC5 simulations)

early 21st

middle 21st

late 21st

Cayan et al. 2013, Ch 6 Southwest Climate Assessment

PROJECTED SOIL MOISTURE (JUNE)

National Climate Assessment, 2013, Ch. 2

Projected changes in 99-percentile daily precipitation

Daily Extremes

PROJECTED CHANGES IN HEAVY PRECIPITATION

Dettinger and Cayan 2014, San Francisco Estuary and Watershed Science; Dettinger, in review, WRR

Historically, a few large storms (or their absence) account for most of Ca’s yr-to-yr precipitation variation.Historically, a few large storms (or their absence) account for most of Ca’s yr-to-yr precipitation variation.

5yr smoother

LARGE STORM CONTRIBUTIONLARGE STORM CONTRIBUTION

Light-to-mid storms

OBSERVED & PROJECTED ROLES OF LARGEST STORMS IN CALIFORNIA WET-DRY TRENDS

In some models, big storms get much bigger and total precipitation increases.

In all models, contributions from small-to-normal storms get smaller.

In models where big storms don’t change as much, precip stays the same or declines.

Cayan et al., Southwest Climate Assessment, 2013

16 models, A2 emissions

Northern Sierra Nevada

Median of A2 emissionsMedian of B1 emissions

Center of sliding 50-yr window

Per

cen

tag

e o

f hi

stor

ical

50-

yr f

lood

Das et al., ClimChg, 2012; JH, 2013

PROJECTED STREAMFLOW CHANGES

Distributions of 50-yr flood changes

Projected Changes in Colorado River Precip & Soil Moisture

Cayan et al., PNAS, 2010

Historical

Future

PROJECTED CHANGES IN DROUGHT RISKS

DROUGHTS > 11 yr

DROUGHTS > 35 yr

Ault et al., 2014, J. Climate

Increasing greenhouse gases

Based on projections from 27 CMIP5 GCMs

•Expect climate change; expect warming.

•Most of California may get more OR less precipitation overall (but expect southern California to get drier).

•Expect more dry days and more extreme large storms.

•Expect heat and precipitation change to produce wilder dry (and wet) spells in terms of runoff and recharge.

KEY POINTS