SIERRA NEVADA SNOWPACK
MARCH 2016
Snowpack Resources in CA and NV
S nowpack in California and Nevada supplies water, ecosystem
services, and recreation. Snowpack serves as a natural reservoir as
well as a key source of surface water and groundwater. In
California, the spring snowpack on average stores about 70% as much
as the water stored in the State’s reservoirs, shown in figure 1.
The snowpack plays a vital role in water management in accumulating
water during the cool stormy season and then releasing water as
snowmelt during the drier, warmer spring and summer period. In the
Colorado River Basin, which supplies almost all of Southern Nevada
and approximately 55% of Southern California water, runoff from
snowmelt contributes about 70% of total water supplies. In
addition, melted snowpack recharges ground water, often more
effectively than run-off. For example, in the Spring Mountains,
west of Las Vegas, approximately 50-90% of groundwater recharge
comes from snow.
Snowpack varies considerably from year to year in response to
precipitation delivered by North Pacific storms and temperature
fluctuations. Snowpack is often reported as snow water equivalent
(SWE), or the amount of water stored in the snow. To accumulate
snow, temperatures must be cold enough to cause the precipitation
to fall as snow and to prevent the snow from melting. In the past
two years, 2014 and 2015, Sierra Nevada snowpack was
disproportionately depleted because of record high temperatures
(figure 2). Results from hydrologic model runs in which 2014
temperatures were replaced with temperatures from 1917-2013
suggests that temperatures caused the 2014 snowpack in California
to be lower by 60% on average. The results ranged between 2014
snowpack decreasing by as much as 160% and increasing by 20%, with
92% of the scenarios showing that snowpack was lower in 2014. The
low snowpack in the last two years provides a scenario of future
water supply conditions under climate change.
Figure 1: The total water stored in the 12 major reservoirs
defined by CA Department of Water Resources, and the other 161
reservoirs, and in the monthly snowpack. The solid red line is the
average reservoir storage from 2000-2015 and the dashed red line is
the average snowpack plus reservoir storage. Updated from Dettinger
and Anderson, 2015.
STRONG EL NIÑO E VENTSStrong El Niño events tend to result in
colder winter temperatures and increased precipitation throughout
much of California and Nevada. This combination of cooler than
average temperatures and increase precipitation typically leads to
increased SWE during most strong El Niño events, with exceptions in
1965-66 and 1991-92.
CONTACTS: David Pierce – [email protected] Kalansky–
[email protected]
— A N O A A R I S A —
Snow Water EquivalentTuolumne BasinMar 23 2014
SWE (meters)
Figure 3: SWE has traditionally been measured by manual snow
samples and by fixed pillows. Recently these surface measure-ments
have been supplemented by airborne lidar. Mapped here over the
Tuolumne Basin. Image courtesy of NASA Airborne Snow
Observatory.
Temp Precip
Figure 4: Temperature and precipitation Oct-Mar departure from
average during strong El Nño events (1957/58,
1965/66,1972/73,1982/83,1991/92,1997/98). Courtesy of NOAA
2005 20
0620
07 2008
2009
2010
2011
2012
2013
2014
2015 20
160
102030405060
Calendar Years
Mill
ions
of A
cre-
Feet
Water Stored in California Reservoirs and Snowpack
161 other reservoirs
Total Snowpack
12 major reservoirs
2000-15Normals (snow & total reservoirs)
Milli
on o
f Acr
e Fe
et
Calendar Years200
6200
7200
8200
9201
0 2011
2012
2013
2014
2015
2016200
5
20
30
10
40
50
60
0
WATER STORED IN CALIFORNIA RESERVOIRS AND SNOWPACK
4848
50
52
54
56
0
50%
100%
150%
200%
1970 1980 1990 2000 2010
2014
2015
April
1st
Sno
wpa
ck (p
erce
nt o
f nor
mal
) Ave Winter Tem
p (˚F)
Figure 2: April 1st percent of normal SWE (blue bars and 2014
-2015 yellow bars ) and winter (DJF) temperatures (red line) for
California. Data courtesy of the CA DWR and WRCC.
0%1970
2014
48
50
52
54
56
Average Winter Tem
p (˚F)
April
1st
SW
E (p
erce
nt o
f nor
mal
)
100%
2015
1980 1990 2000 2010
50%
150%
200%
0 -10 100Inches˚F NCEI NCEI
5.0 -5.0
CALIFORNIA APRIL 1ST SWE AND WINTER TEMPERATURES
0
40 km0.500.450.390.320.260.190.130.06
0 10 20 30
Snowpack and Climate Change
Historical observations, combined with climate models, indicate
that climate change is already affecting spring snow accumulation
in the western U.S. Historical snow measurements reveal that April
1st SWE values have declined in the northern Sierra, though less so
in the southern Sierra. The difference is because the high
elevation of the southern Sierra makes the region less susceptible
to changes in temperature thus far. Observations across the West
indicate that the proportion of precipitation as snow has declined
also. Figure 5 shows the fraction of snow that falls between -2 and
0˚C; snow that falls in this temperature range is more likely to
fall as rain as the climate warms. Besides water supply
implications, snow instead of rain is an important deterrent for
flooding, and has obvious impacts on recreation. Snowfall, snow
accumulation, snowmelt and other aspects of snowpack are predicted
to change at different rates in the future depending on their
sensitivity to temperature as compared to precipitation. The table
below shows the projected year when different variables related to
snowpack are predicted to change beyond natural climate variability
in different regions in the West.
n CNAP, the California Nevada Applications Program, is a NOAA
RISA team conducting applied climate research that is inspired by
and useful to decision makers in the region cnap.ucsd.edu.
n NIDIS, National Integrated Drought Information System, works
with the federal, state, tribal and local partners to improve
drought early warning, preparedness, and response to impacts,
drought.gov.
n WRCC, the Western Regional Climate Center, develops products,
provides services, and improves capabilities that enhance the
delivery of climate information to the public in collaboration with
NOAA partners, www.wrcc.dri.edu.
n SWCSC, the Southwest Climate Science Center, sponsored by the
US Depart. of the Interior, provides scientific information, tools,
and techniques to anticipate, monitor, and adapt to climate change,
www.doi.gov/csc/southwest.
In mountain regions across the West as climate continues to warm
over the 21st century, more precipitation will fall as rain rather
than snow and the more snow will melt prior to April 1st.
Projections of climate change in the Sierra Nevada find rain
accounting for 50.6% (145 mm) more of precipitation and 62.3%
(63mm) more of snow melt prior to April 1st than in historical
norms (figure 6).
RCP 8.5 (Business as usual emission scenario)
RCP 4.5
(Emission reduction)
Sierra
Nevada Great Basin
Wasatch CO River
Basin
Sierra Nevada
Great Basin
Wasatch CO River
Basin
SWE 2055 2045 2055 2070 2075 2075
Precip Falling as Snow 2060 2055 2080 2090 2070 2100
Last day of snow season 2035 2028 2025 2045 2030 2033
For more information see Pierce and Cayan, 2013
Dettinger, M. D., et al., 2015, Ecological Applications, 25 (8),
2069-2093.Dettinger, M.D. and M. Anderson, 2015, San Francisco
Estuary and Watershed Science, 13(2).Pierce, D. W. and D. R. Cayan,
J. of Climate, 26,4184-4167.
0.28
0.20
0.15
0.10
0.05
0
Fraction Figure 5. Fraction of snow that falls between -2 and
0˚C. The snow that falls in this temperature range is most
susceptible to fall as rain in a warming climate. From Dettinger et
al. 2015
PROJECTED YEAR WHEN SNOW VARIABLE CHANGES BEYOND NATURAL CLIMATE
VARIABILITY
2055 2055
2055
2045
2060 2080
20302035 2025
2070
20702090
2075 2075
2100
2045 2030 2035
(a) FRACTION OF ANNUAL PRECIPITATION FALLINGIN THE DAILY
TEMPERATURE RANGE: -2C < Tavg < 0C
FRAC
TIO
N
0.00
0.05
0.10
0.15
0.20
0.28
0 1 2 3 4 5 6Warming, in degrees C
0
0.1
0.2
0.3
0.4
0.5
Frac
tion
of T
otal
Pre
cipi
tatio
nas
Sno
w v
s Rai
n
(b) Fraction of Western Precipitation Falling on Dayswith Tmin
< 0C under Various Imposed Warmings
0 2 4 6 8Warming, in degrees C
0
0.2
0.4
0.6
0.8
1
Frac
tion
of W
est w
ith >
this
Prec
ip-F
orm
Cha
nge
10% increase in rain fraction20% change30% change40% change50%
change
(c) Areas in the Western US subject to Rain-Snow Conversions of
Various Percentages
Sierra Nevada
Tota
l pre
cip.
(mm
)
Rain+145 (50.6%)
Melts+63 (62.3%)
SWE−169 (−30.3%)Snow
2020 2060
020
060
010
00
Figure 6. Projected changes in snow variables in the Sierra
Nevada throughout the 21st century relative to historical norms.
From Pierce and Cayan, 2013
