Climate Change in the Tahoe Basin:
Trends, Impacts & Drivers
Robert Coats
UC Davis Tahoe Environmental Research Center
&
Hydroikos Ltd.
Google Earth
Coop weather stations used to examine regional temperature trends
25
(a) Reno
P<0.0007
20
(b) Boca
20
15
15
10
10
5
5
0
0
P<0.12
-5
P<0.0003
P<0.074
-5
-10
1880 1900 1920 1940 1960 1980 2000 2020
1880 1900 1920 1940 1960 1980 2000 2020
20
20
(c) Truckee RS
o
Ave. Temp., C
15
P<0.02
(d) Tahoe City
15
10
10
5
5
0
P<0.03
0
P<0.12
P<0.01
-5
1880 1900 1920 1940 1960 1980 2000 2020
-5
1880 1900 1920 1940 1960 1980 2000 2020
20
20
P<0.3
15
15
P<0.03
(f) Sierra Average
(e) Lake Spaulding
10
10
5
5
0
0
P<0.23
-5
1880 1900 1920 1940 1960 1980 2000 2020
P<0.0001
(From WRCC)
-5
1880 1900 1920 1940 1960 1980 2000 2020
Annual Average of Tmax, Tave & Tmin
0.14
(a) Reno
0.12
***
***
0.10
0.08
0.06
*
0.04
0.02
0.00
***
Tmin
Tmax
***
***
***
***
*
***
*
*
o
C yr-1
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
(c) Truckee RS
Tmin
Tmax
***
**
***
**
**
*
**
***
**
***
* ** *
**
*
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0.06
0.04
0.02
*
* ***
**
*
**
*
0.00
-0.02
-0.04
-0.06
*
Tmin
Tmax
(e) Lake Spaulding
**
**
JanFebMarAprMayJun Jul AugSepOctNovDec
0.14
(b) Boca
0.12
0.10
0.08
***
* ***
0.06
0.04
*
*
0.02
0.00
Tmin
Tmax
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
(d) Tahoe City
Tmin
Tmax
* * ** * *
***
***
* * * ** *
***
***
*
***
***
*
*** ***
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Tmin
Tmax
(f) Sierra Average
***
**
*
**
***
**
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Thiel slope of trend in monthly averages of Tmax and Tmin,1956-2005.
*** indicates P< 0.01; ** P=0.01-0.05; * P =0.05-0.10; no asterisk indicates P =
0.15-0.1
Why does the Glenbrook Station
show an apparent cooling trend in
summer?
Location of old Glenbrook weather station. Coop ID No. 263205
Glenbrook Fire Station, Coop ID No. 263205
Glenbrook Fire Station, Coop ID No. 263205
80.0
2
R = 0.1344
P < 0.0004
Percent
60.0
40.0
20.0
0.0
1900
1920
1940
1960
1980
2000
Water Year
Percent of total annual precipitation as snow, based on
Tahoe City precipitation and temperature data
2020
Num ber of Days
120
y = -0.2923x + 637.12
R 2 = 0.2649
100
80
60
40
20
0
1910
1920
1930
1940
1950
1960
1970
1980
1990
Water Year
Number of days with average temperature
below freezing at Tahoe City, Dec.-March
2000
2010
35
30
Number of Days
P < 0.045
25
20
15
10
5
0
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
Beginning Year of Semi-decade
Number of days per semi-decade that daily rainfall at Tahoe
City exceeded 3.9 cm, the 95th percentile value for days
with rain .
D a te
4-Jul
24-Jun
14-Jun
4-Jun
25-May
15-May
5-May
25-Apr
15-Apr
1960
y = -0.4249x + 986.23
2
1970
1980
R = 0.142
P < 0.011
1990
2000
Water Year
Average date of snowmelt peak discharge for 5 streams in
the Tahoe Basin, (Ward, Blackwood, UTR, Trout & Third
Cr.) after removal of total annual snowfall effect
2010
Shift in the Date of Peak
Snowmelt Discharge for
Streams in and Near the
Tahoe Basin
1961-05
1949-94
*
1972-05
1973-05
1971-05
1961-05
1972-05
1960-04
1961-04
Trend Slope (days yr-1)
and Significance
(corrected for
autocorrelation) from
Kendall Trend Test
Effect of Total Annual
Snowfall removed by
LOWESS smoothing
Map by Janet Brewster, CTC
The air temperature and
streamflow data suggest that the
Tahoe Basin is warming faster than
the surrounding region.
Why?
The Lake Enhancement
Hypothesis
(a)
(b)
MODIS satellite images of Lake Tahoe, day and night, at
mid-summer. (a) Reflected Near-IR radiation, 0.84-0.85
µm , at 10:50 AM PST, 7/31/2007. (b) Outward Long wave
radiation, 10.8-11.3 µm, at 10:10 PM PST, 8/5/2007.
Source: Todd Steissberg, Univ. California at Davis.
The snow albedo perturbation
hypothesis
Modeled effect of soot deposition on March mean snow water
equivalent (Fig. 12 from Qian et al. 2009. Jour. Geophys. Res.)
Airborne Soot
10
µg m -3
n = 267; Ave.= 2.02
1
South Lake Tahoe
Bliss State Park
Lassen Volcanic NP
n = 388; Ave. = 0.16
0.1
n = 439; Ave. = 0.076
0.01
1990 1992 1994 1996 1998 2000 2002 2004
Water Year
Annual averages of near-surface atmospheric fine total
elemental carbon concentration (< 2.5 µm), Dec., Jan and
Feb. (Source: http://vista.cira.colostate.edu/IMPROVE)
Facts about Lake Tahoe
¾
¾
¾
¾
¾
¾
¾
¾
¾
¾
Volume =
156 km3
Surface Area =
498 km2
Average Depth =
313 m
Max. Depth =
505 m
Basin Area =
1310 km2
Elevation =
1898 m
Mean Res. Time =
650 yr
Mixes below 450 m about 1 yr in 4
Well-oxygenated to bottom
Decline in clarity related to both fine sediment
and increasing PP
6.5
2
o
C
R = 0.4327
T e m p e ra tu re ,
6.0
5.5
5.0
4.5
Jan-70 Jan-74 Jan-78 Jan-82 Jan-86 Jan-90 Jan-94 Jan-98 Jan-02 Jan-06
Volume-averaged daily temperature of Lake Tahoe, deseasonalized
Transparency Standard
Lake Tahoe Secchi Depth—A measure of lake clarity
Warm Phase (+)
Cool Phase (-)
The Pacific Decadal Oscillation
(http://www.jisao.washington.edu/pdo/).
Snowmelt Peak Day
200
190
180
170
160
150
140
130
120
110
100
y = -6.1833x + 145.03
2
R = 0.1765
P < 0.004
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
Average PDO, Apr-June
Snowmelt peak Julian day vs. average April-June PDO.
Snowmelt peak is average of 5 streams in the Tahoe Basin, after
removal of total annual snowfall effect
3.0
2
R = 0.3191
2.0
R e s id u a l,
o
C
P< 10
1.0
-8
0.0
-1.0
-2.0
-3.0
1910
1920
1930
1940
1950
1960
1970
1980
1990
Year
Average April-June Tmin Residuals at Tahoe City,
after removal of the PDO Effect
2000
2010
D e a s e a s o na lize d La k e
T e m pe ra ture , o C
6.5
6.3
6.1
5.9
5.7
5.5
5.3
5.1
4.9
4.7
4.5
R 2 = 0.1225
-3
-2
-1
0
1
2
Monthly PDO
Figure 11. Monthly average of deseasonalized lake
temperature vs. PDO in previous month, 1970-2007.
3
4
20
20
15
15
Ave. Ann. Temp., deg. C
10
5
5
0
0
-5
2000
2020
2040
2060
2080
2100
-5
2000
20
20
15
15
10
2020
10
PCM A2
5
5
0
0
-5
2000
GFDL B1
10
GFDL A2
2040
2060
2080
2100
2080
2100
PCM B1
-5
2020
2040
2060
2080
2100 2000
2020
2040
2060
Year
Modeled 21st Century Temperature Trends for the Tahoe Basin
Annual Averages of Daily Tmax and Tmin
Average of 12 Downscaled 7.5’ Cells
Source: USGS/SIO
Is This the Future Tahoe Forest??
Or this?
http://www.flheritage.com
Largemouth Black Bass: Alien Invaders at Lake Tahoe
Fuel Load Reduction, near Incline
Photo by Steve DeVries
The Angora Fire, 2007
Changes in the Watershed
Earlier Onset of Spring
Stressed Vegetation
Larger, More Frequent Fire
More Rain, Less Snow
More frequent floods
Lower summer streamflow
More Soil and Channel Erosion
Acknowledgements
¾
Patty Arneson, UCD
¾ Michelle Breckner, WRCC
¾ Janet Brewster, CTC
¾ Charles Goldman, UCD
¾
¾
¾
¾
Scott Hackley, UCD
John Reuter, UCD
Geoff Schladow, UCD
Iris Stewart-Frey, U.Santa Clara
Some Useful Resources
Hydroikos ftp site:
Host = ftp-dom.earthlink.net
(ftp://ftp-dom.earthlink.net )
User ID = ftp@hydroikos.com
password = spartina
path = /Public/Climate Change
realclimate.org
climatechoices.org
climatecrisiscoalition.org
ipcc.ch
climatechange.ca.gov/index.php