© 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 5 th IPCC GCMs project +4-6°F warming by 2060, under mid and high emissions 31 GCMs X 2 RCP Emissions Scenarios IPCC 5 th Assessment (CMIP5) models Which emissions pathway will we take?

Stewart et al., 2005 Recent trends: Observed: Warming** Observed: Less snowpack** Observed: Less snow/more rain**; changing snow thresholds Observed: Earlier greenup dates; more tree mortalities; enhanced wildfires Observed: Animals moving north** Observed: Earlier snowfed streamflow**

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 5 th IPCC GCMs project large precipitation volatility but modest avg change (maybe drier) 31 GCMs X 2 RCP Emissions Scenarios IPCC 5 th Assessment (CMIP5) models Are there other changes lurking below weak annual- avg trends?

All DrierAll 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. 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 10 th percentile or less SWE increase greatly 40% PROJECTED SNOW-WATER CHANGES During 21 st 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 21 st 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 21 st 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 CONTRIBUTION LARGE 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, models, A2 emissions Northern Sierra Nevada Median of A2 emissions Median of B1 emissions Center of sliding 50-yr window Percentage of historical 50-yr flood 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