Effects of Climate Change on LakeTahoe (CA-NV), USAand what this might mean for lakes andreservoirs in Asia
S. Geoffrey Schladow
Goloka B. SahooJohn E. Reuter
Robert Coats
2nd WEPA International Workshop, Tokyo, February 23 2011

Courtesy of NASA

LAKE TAHOE
11th deepest lake in the world
Maximum depth = 501 m
Mean depth = 330 m
Surface area = 500 km2
Watershed area = 800 km2
63 Inflowing streams
1 Outflowing stream
Residence time ~ 650 yrs

OUTLINE
1. Current Climate Change at Lake Tahoe
2.

Why Future Climate Change was Studied at Lake Tahoe

3. Case Study: Future Impacts of Climate Change at LakeTahoe
4. Conclusions for Lake Tahoe
5. Implications of Climate Change for WEPA Nations

1. Current Climate Change at Lake Tahoe

2. Why Future Climate Change was Studied

Total Phosphorus
Groundwater
15%

Shoreline
Erosion 4%
Urban Upland38%

AtmosphericDeposition
15%
StreamChannelErosion 2%

Non-urban
Upland26%

3. Case Study: Future Impactsof Climate Change at L. Tahoe

General Circulation Model – GFDL, PCM, …..

GHG Emission Scenarios– A2, B1, B2, A1Fi …….

Downscaling or Regionalization
12 km x 12 km grid for air
temperature & precipitation

10 km x 10 km grid for windand shortwave radiation

Hundred Years of “Data”
2
Shortwave
radiation(kJ/mLongwave/dPrecipitation(mm/year)o /d)Averagewindspeed(m/s)
Average air temperature ( C)

19000
1325000
2500
2.5(a)(a)(a)(a)

GFDLA2

GFDLA2
GFDLA21224500
18500
2000
2.4
24000
1118000

1500
2.3
23500
1017500

23000
9
1000
2.2

17000
22500
8500
2.1
16500
22000
716000
21500
60
2.0
2000
2000
2000

2020
2020
2020

2040
2040
2040

Year
Year

2060
20602060

2080
2080

2100
2100

Downscaled 100 years climate data

Climate Data

TotalUplandFlow &Load

Subwatershed
Boundaries andStream Network

Stream Processes

Landuse Distribution
Land Processes

AbsorptionLake Model
Meteorology
Tributaries

Land Use

Atmospheric Deposition

Groundwater

Shoreline Erosion

Total Pollutant Load to Lake Tahoe

MineralParticles
Loss(coagulationand settling)

DO

CDOM

Nutrients (N, P)

Light Scatteringand Absorption

Phytoplankton
GrowthZooplankton
GrowthDetritus

Death

Loss

Loss

Secchi
Depth

Sediment

Hydrodynamic ModelDissolved Oxygen Module
Streams

Reaeration

AtmospherePhotosynthesis

Chlorophyll a

Respiration

Dissolved
OxygenNH4DOC
COD

Nitrification

Respiration

ZOOP

Heterotrophic
Respiration

SOD

(b)

15

12

9

Measured at 10 m below surf ace

4

Simulated at 10 m below surf ace
12
9

6

30

2004/04/09

2003/12/11

2003/08/13

2003/04/15

2002/12/16

2002/08/18

2004/12/05

Simulated at 100 m below surf ace

2004/12/05

Measured at 100 m below surf ace

2004/08/07

21

2004/08/07

2004/04/09

2003/12/11

2003/08/13

2003/04/15

2002/12/16

2002/08/18

2002/04/20

2001/12/21

15

2002/04/20

15

2001/08/23

2001/04/252000/12/26(c)

2001/12/21(d)

2001/08/23

18

2001/04/25

21

2000/12/26

Simulated at surf ace

2000/08/28

Measured at surf ace

2000/08/28

6

2000/04/30

918

2000/04/30

12

2000/01/01

15

Water temperature (oC )(a)2000/01/01

2004/12/05

2004/08/07

2004/04/09

2003/12/11

2003/08/13

2003/04/15

2002/12/16

2002/08/18

21

Water temperature (oC )2004/12/05

2004/08/07

2004/04/09

2003/12/11

2003/08/13

2003/04/15

2002/12/16

2002/08/18

6

2002/04/20

2001/12/21

0

2002/04/20

0

2001/08/23

2001/04/25

2000/12/26

2000/08/28

3

2001/12/21

3

2001/08/23

2001/04/25

2000/12/26

2000/08/28

18

2000/04/30

2000/01/01

Water temperature (oC )182000/04/30

2000/01/01

Water temperature (oC )Temperature Calibration and Validation
21
Measured at 50 m below surf ace
Simulated at 50 m below surf ace

12
9

6

30

2004/12/05

2004/08/07

2004/04/09

2003/12/11

03

2003/08/13

Simulated at 10 m below surf ace

2003/04/15

Measured at 10 m below surf ace

2002/12/16

6

2002/08/18

9

2002/04/20

12

2004/12/05

2004/08/07

2004/04/09

2003/12/11

2003/08/13

2003/04/15

2002/12/16

2002/08/18

2002/04/20

2001/12/21

2001/08/232001/04/25

2000/12/26

2000/08/28

2000/04/30

2000/01/01

15

3

2001/12/21(b)

2001/08/23

0

2001/04/25

Simulated at surf ace

2000/12/26

Measured at surf ace

2000/08/28

6

2000/04/30

9

Dissolved oxygen (g m-3)

12
15

Dissolved oxygen (g m-3)

2004/12/05

2004/08/07

2004/04/09

2003/12/11

2003/08/13

2003/04/15

2002/12/16

2002/08/18

2002/04/20(a)

2000/01/01

2004/12/05

2004/08/07

2004/04/09

2003/12/11

2003/08/13

2003/04/15

2002/12/16

2002/08/18

2002/04/20

2001/12/21

2001/08/23

2001/04/25

2000/12/26

2000/08/28

2000/04/30

3

2001/12/21

2001/08/23

32001/04/25

2000/12/26

2000/08/28

2000/04/30

2000/01/01

15

2000/01/01

Dissolved oxygen (g m-3)
15

Dissolved oxygen (g m-3)

DO Calibration and Validation
12(c)

96
Measured at 50 m below surf ace
Simulated at 50 m below surf ace

0(d)

12
96
Measured at 100 m below surf ace

Simulated at 100 m below surf ace

0Maximum mixing depth (m)

(a)

400

500
0

100

200

300

GFDL A2

2097

2093

2089

2085

2081

2077

2073

2069

2065

2061

2057

2053

2049

2045

2041

2037

2033

2029

2025

2021

2017

2013

2009

2005

2001

Maximum Mixing Depth in a Year

Water Temperature2097/01/05

2089/01/05

2081/01/05

2073/01/05

2065/01/05

2057/01/05

2049/01/05

2041/01/05

2033/01/05

2025/01/05

0

2017/01/05

2009/01/05(a)

2001/01/05

Depth from surface (m)Dissolved Oxygen

Simulated DO (mg/L) GFDLA2-case
1250

100
10150
8200

250
6300

350
4400
24500

Under Anoxic Conditions
Nutrients
release

Oxic Phase
Anoxic Phase(DO > 0.01mg/L) (DO < 0.01mg/L)

SOD

0.04 g-O2 m-2 d-1

0.0 g-O2 m-2 d-1

SRP

0.0 mg-P m-2 d-10.22 mg-P m-2 d-1

NO30.18 mg-N m-2 d-10.0 mg-N m-2 d-1

NH40.0 mg-P m-2 d-10.49 mg-N m-2 d-1

SOD: Sediment Oxygen Demand
SRP: Soluble Reactive Phosphorus
NO3: Nitrate
NH4: Ammonium

Source: Marc W. Beutel (2000) Ph. D Dissertation, UC Berkeley

Sediment Released Soluble Reactive Phosphorus

Comparison of “Internal” Load with External Loads
30

Annual SRP load (MT)

(a)
25
20
15
1050U

NU

SCE*ADGWSE*SRU : Stream loading from urban area
NU : Stream loading from nonurban area
SCE: Stream channel erosion
AD : Atmospheric deposition
GW : Ground water
SE : Shoreline erosion
SR : Sediment release4. Conclusions for Lake Tahoe♦ Lake temperature and stratification will continue to increase♦ Continued shift from snow to rain -> more extreme flows(present 1000 year flow event will be the 100 year flow by 2100)♦ Earlier snowmelt, lower summer streamflow, longer fire season♦ Prolonged stratification of the lake, with higher evaporation rate
♦ Reduced deep mixing -> reduced oxygen transport to deep water♦ Release of nitrogen and phosphorus from sediment♦ Changed nutrients and mixing alter phytoplankton community♦ Prolonged drought (> 20 yrs) by end of 2100

5. Implications for WEPA Nations♦ Lake temperatures will rise (increased microbial, viral threat)(Schneider and Hook 2010, Space observations of inland water bodies show rapid surface
warming since 1985. Geophysical Research Letters, Vol. 37, L22405, 5 pp.)

♦ Lake stratification will increase -> prolong or initiate anoxia ->release of N, P, Fe, Mn, Hg, H2S….. from sediments♦ Changed nutrients and mixing alter algal community -> water
quality (cyanobacteria, taste and odor, fish kills, nuisance algae)♦ More extreme flows – flushing of nutrients and sediments,
damage to infrastructure (e.g. Pakistan 2010), inundation ofWWTP♦ Prolonged drought -> how to allocate water? overdrawing
groundwater, elevated wildfire incidence♦ Need for new reservoirs – will have above impacts plus elevatedCH4 emissions

THANK YOU