Water Policy for Food Security, a global conference

1. key points
•Drought and Flood are a common occurrence in California,
2012-2015 Drought is intense and warm as well as dry
•The absence of very large storms drives California dry (and wet) spells
• Climate change will likely exacerbate stresses on water resources
Climate Change Will Stress California’s
Already Volatile Water Supply
Dan Cayan
with Mike Dettinger, Mary Tyree, Sam Iacobellis
Scripps Institution of Oceanography and USGS
Climate Change Will Stress California’s
Already Volatile Water Supply
Dan Cayan
with Mike Dettinger, Mary Tyree, Sam Iacobellis
Scripps Institution of Oceanography and USGS
UC Davis Oct 2015

2. Sierra discharge highly variable
stddev/mean = 0.44
lowest 1977 highest 1983
Sierra discharge highly variable
stddev/mean = 0.44
lowest 1977 highest 1983
But ,Columbia discharge
is quite steady,
stddev/mean = 0.19
But ,Columbia discharge
is quite steady,
stddev/mean = 0.19
Annual discharge varies considerably in the
Sierra Nevada
Annual discharge varies considerably in the
Sierra Nevada
and Colorado discharge
is intermediately variable,
stddev/mean = 0.33
Cayan et al 2003
and Colorado discharge
is intermediately variable,
stddev/mean = 0.33
Cayan et al 2003

3. California and much of western region has been more-or-less dry since 1999
observed precipitation departure (% of average), 1998-99 thru 2013-14
California and much of western region has been more-or-less dry since 1999
observed precipitation departure (% of average), 1998-99 thru 2013-14
% departure from
1981-2010 average

4. U.S. Drought Monitor/National Weather Service Hanford

5. Dettinger and Cayan Drought and the Delta—A Matter of Extremes
accepted, San Francisco Estuary and Watershed Science, April 2014
a few large storms (or their absence)
account for a disproportionate amount of California’s precipitation variability
a few large storms (or their absence)
account for a disproportionate amount of California’s precipitation variability
5yr smoother
LARGE STORM
CONTRIBUTION
LARGE STORM
CONTRIBUTION
95%ile

6. Recent dry years have mostly been
warmer than normal.
2013-14 was exceptionally warm.
Recent dry years have mostly been
warmer than normal.
2013-14 was exceptionally warm.
Precipitation Departure
during dry years
Temperature Departure
during dry years
2013-14

7. Anomalous warmth during winter 2014-15Anomalous warmth during winter 2014-15

8. 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
+3°C
CMIP5 GCMs project +3°C
summer warming by 2060,
under mid and high RCPs
14 GCMs X 3 RCP Emissions
Scenarios IPCC 5th
Assessment
(CMIP5) models
July Temperature change Sacramento
Need to kmow
Which emissions pathway will we
take?
How much summer amplification
of warming?
How will temperature change in
Near term?
Need to kmow
Which emissions pathway will we
take?
How much summer amplification
of warming?
How will temperature change in
Near term?

9. Sierra Snowpack has been extremely low
2015 and 2014 spring snowpack disproportionately light
Sierra Snowpack has been extremely low
2015 and 2014 spring snowpack disproportionately light

10. Dettinger and Anderson SFEWS 2015

11. Loss of California Spring Snowpack
from 21st
Century warming
Loss of California Spring Snowpack
from 21st
Century warming
•Under this scenario, California loses half of its spring (April 1) snow pack due to
climate warming. Less snow, more rain, particularly at lower elevations. The result is earlier
run-off, more floods, Less stored water. This simulation by Noah Knowles is guided by
temperature changes from PCM’s Business-as-usual coupled climate simulation.
(this is a low-middle of the road emissions and warming scenario)
•Under this scenario, California loses half of its spring (April 1) snow pack due to
climate warming. Less snow, more rain, particularly at lower elevations. The result is earlier
run-off, more floods, Less stored water. This simulation by Noah Knowles is guided by
temperature changes from PCM’s Business-as-usual coupled climate simulation.
(this is a low-middle of the road emissions and warming scenario)
Knowles, N., and D.R. Cayan, 2002: Potential effects of global warming on the
Sacramento/San Joaquin watershed and the San Francisco estuary. Geophysical
Research Letters, 29(18), 1891.

12. Declining odds of median or higher snowpack
Source: Cayan et al. (2011)

13. Drier Summer Landscapes
increased warming and diminished snow
causes successively greater soil drying
throughout 21st
Century
(this picture could change somewhat under more
recent CMIP5 simulations)
Drier Summer Landscapes
increased warming and diminished snow
causes successively greater soil drying
throughout 21st
Century
(this picture could change somewhat under more
recent CMIP5 simulations)
early 21st
middle 21st
late 21st
Cayan et al. Ch 6 Southwest Climate Assessment

14. Projected patterns of precipitation changes
2090-2099 versus 1980-1999
Globally, dry regions become drier?

15. Although the number of
wet days is projected
to decrease with
climate change,
Although the number of
wet days is projected
to decrease with
climate change,
the intensity of the largest wet days
is projected to increase !
the intensity of the largest wet days
is projected to increase !
Suraj Polade Polade, S.D., Pierce, D.W., Cayan, D.R., Gershunov, A., and Dettinger, M.D., 2014, The key role of dry days in changing regional climate and precipitation regimes: Nature Scientific Reports,
4:4364, 8 p., doi:10.1038/srep04364.
28 CMIP5 RCP 8.5 GCMs
(2060–2089) vs. (1960-1989)

16. • California’s climate is prone to year-to-year and longer term variation in
precipitation—drought is an expected part of our climate..
• California’s current dry spell has built up over multiple years, a more/less dry
pattern has been in place since 1999.
• The absence of a few very large storms is often a key driver of dry years. And
large storms are frequently involved in “busting” drought.
.
• Continued, substantial climate warming is highly likely but changes in annual
precipitation is not well understood in California. However, climate change may
shift precipitation characteristics—fewer overall wet days but more intense
heavy events.
• In addition to the present ongoing dry spell, recurrent wet and dry events and
episodes, in the midst of warm temperatures will provide future learning
opportunities.
SummarySummary

19. Whole CONUS PDSI
CA/NV PDSI
California/Nevada drought
only moderately correlated w whole U.S.
PDSI from NCDC divisional dataset
California/Nevada drought
only moderately correlated w whole U.S.
PDSI from NCDC divisional dataset

20. ground water
withdrawl increases
greatly in
dry years
ground water
withdrawl increases
greatly in
dry years
Dry Year
Typical Year
Faunt et al 2009 USGS
pumping

21. How are droughts made?
>80%
Mike Dettinger

22. California’s large yearly variation in precipitation is
dictated by the presence or absence of storms during a
narrow seasonal window
California’s large yearly variation in precipitation is
dictated by the presence or absence of storms during a
narrow seasonal window
California has only about
120 days to accumulate
two thirds of its annual
precipitation. When
Pacific winter storms
Are diverted from
California (as last winter)
dry conditions result.
California year-to-year
variation in precipitation
is has the most volatile!
of the entire U.S.
Cayan et al.2003

23. Multi-year dry spells are quite common in California
Sacramento Drainage Divi standardized precip index 1900-2014 showing Intensity and Duration
Multi-year dry spells are quite common in California
Sacramento Drainage Divi standardized precip index 1900-2014 showing Intensity and Duration
Anne Steinemann et al. 2015 J. HydroMet. in press

24. Calif dought footprint is quite broad in western U.S.
Sierra flows often in same phase (wet or dry)
as the Columbia or the Colorado
Calif dought footprint is quite broad in western U.S.
Sierra flows often in same phase (wet or dry)
as the Columbia or the Colorado
Low Sierra flows
associated with large regional pattern
Cayan et al.2003

25. Sierra Nevada
Annual Precipitation
Coef of Variation ~31.5%
mean 39.1 inches
std dev 12.3 inches
Sierra Nevada
Annual Precipitation
Coef of Variation ~31.5%
mean 39.1 inches
std dev 12.3 inches
2012-2014 dry spell is characteristic of
California’s volatile precipitation climate
2012-2014 dry spell is characteristic of
California’s volatile precipitation climate
WY 2014 precip estimated
at 65% of LT mean
From California Climate Tracker
Western Regional Climate Center
California has a narrow
seasonal window to
generate its annual
water supply.
If atmospheric conditions are
unfavorable during that
period, a dry year results

26. prevalence of anomalously warm
daytime temperatures
during cool season months
of drought years
Sacramento Drainage Division
Dark bars are from 20% driest years
Pale bars are all years 1895-2014
prevalence of anomalously warm
daytime temperatures
during cool season months
of drought years
Sacramento Drainage Division
Dark bars are from 20% driest years
Pale bars are all years 1895-2014

29. CA1
ACCESS 1.0
CMCC CM
CMCC CMS
Climate Models
indicate occasional
drought for California
In 21st
Century
Climate Models
indicate occasional
drought for California
In 21st
Century

30. Recent Water Loss over Western U.S.
Surface displacements from GPS network show progressive uplift due to water mass loss in drought
Recent Water Loss over Western U.S.
Surface displacements from GPS network show progressive uplift due to water mass loss in drought
GPS estimate by Borsa et al showing deficit
of ~240km**3 water in March 2014 relative
to 2003-2014 baseline over western U.S.,
west of 109°W. This is in general agreement
with GRACE satellite observations, S. Castle
et al 2014 GRL found ~65km**3 water
water loss in Colorado Basin during 2004-
2013.
GPS estimate by Borsa et al showing deficit
of ~240km**3 water in March 2014 relative
to 2003-2014 baseline over western U.S.,
west of 109°W. This is in general agreement
with GRACE satellite observations, S. Castle
et al 2014 GRL found ~65km**3 water
water loss in Colorado Basin during 2004-
2013.
Borsa et al. 2014

31. Meko, D.M., Woodhouse, C.A., and Touchan, R., 2014, Klamath/San Joaquin/Sacramento hydroclimatic
reconstructions from tree rings: Report to California DWR 4600008850, 117 p.
1100 years of Sacramento River Discharge
little overall change but considerable variability and multi-year spells
reconstructed from tree ring records bu Dave Meko and colleagues, Univ Arizona
1100 years of Sacramento River Discharge
little overall change but considerable variability and multi-year spells
reconstructed from tree ring records bu Dave Meko and colleagues, Univ Arizona

32. prevalence of anomalously warm
daytime temperatures
during cool season months
of drought years
Sacramento Drainage Division
Dark bars are from 20% driest years
Pale bars are all years 1895-2014
prevalence of anomalously warm
daytime temperatures
during cool season months
of drought years
Sacramento Drainage Division
Dark bars are from 20% driest years
Pale bars are all years 1895-2014

33. Co- occurrences of high (h) and low (l) annual Columbia, Sierra, Colorado
discharge anomaly magnitudes > 0.7 1906-1999; anomalies +0.7 standard
deviations above long-term means are counted as high, more than –0.7
standard deviations below normal are counted as low.
Co- occurrences of high (h) and low (l) annual Columbia, Sierra, Colorado
discharge anomaly magnitudes > 0.7 1906-1999; anomalies +0.7 standard
deviations above long-term means are counted as high, more than –0.7
standard deviations below normal are counted as low.
Sierra
h l
Columbia
h 8 3
l 2 13
How often do extreme annual flows
co-occur in Sierra, Columbia, Colorado?
Sierra
h l
Colorado
h 13 4
l 2 16
Sierra and Columbia High
and especially low flows
co-occur. Relatively few
Years when they have
Opposing anomalies
Sierra and Columbia High
and especially low flows
co-occur. Relatively few
Years when they have
Opposing anomalies
Sierra and Colorado High and
especially low flows
co-occur. Relatively few
Years when they have
Opposing anomalies
Sierra and Colorado High and
especially low flows
co-occur. Relatively few
Years when they have
Opposing anomalies
Cayan et al.2003

34. 34
Atmospheric Rivers
West Coast flood generators
Atmospheric Rivers
West Coast flood generators

35. Summary
Drought Characteristics
•California’s climate is prone to year-to-year and longer term variation in
precipitation—drought is expected..
•California’s current dry spell has built up over multiple years, a more/less dry
pattern has been in place since 1999.
•Temperature during cool seasons of drought years—in recent decades, has
more often been warmer than cooler than average. As with precipitation,,
anomalous temperature strongly controlled by atmospheric circulation
Drought prediction is a challenge:
•The absence of a few very large storms is often a key driver of dry years. And
large storms are frequently involved in “busting” drought.
•there is not a unique atmospheric drought-circulation pattern.
.
•Anomalous Pacific SST patterns, tropical and extratropical appear in advance,
during and after strong drought circulation months, but signals are somewhat
weak.

36. 500mb height anomalies averaged, all months during Dry years500mb height anomalies averaged, all months during Dry years

37. ENSO vs. California Precipitation
Southern California
K. Redmond et al
Western Regional Climate Center

38. K. Redmond et al
Western Regional Climate Center

39. Nino 3.4 hatched regionNino 3.4 SST
Number dry yrs
Drought years occur during
All phases of ENSO
Drought years occur during
All phases of ENSO

40. PDO SST Anomaly Pattern
K. Redmond et al
Western Regional Climate Center
Number dry yrs
PDO Index
Drought years occur during
both phases of PDO
Drought years occur during
both phases of PDO

41. over 21st
Century occurs a marked decline of chances of reaching
or exceeding historical median
Snow Water Equivalent Sierra Nevada+
10%
….and, chances of historical 10th
percentile or less
SWE increases greatly
40%
Median Apr 1 SWE 11.9cm
10th
% Apr 1 SWE 3.6cm