1. University of Washington
Land Cover Change and Climate Change Effects on Streamflow in Puget Sound Basin, Washington
Lan Cuo1, Dennis Lettenmaier1, Marina Alberti2, Jeffrey Richey3
1: Department of Civil and Environmental Engineering, University of Washington
2: Department of Urban Design and Planning, University of Washington
3: Department of Chemical Oceanography, University of Washington
February 21, 2007
University of Washington
Good afternoon. Today, I am going to talk about land cover change and climate change effects on streamflow. There is a lot of information. I hope that you can bear with me.

2. Background Objectives
Early settlement started in the mid 1800s in the Puget Sound Basin.
Population has increased by 17 times since 1900.
70% of Washington state population lives in the Puget Sound Basin.
Land cover change is mainly caused by logging and urbanization.
Temperature is changing in the Puget Sound.
Objectives
How does land cover change affect streamflow in the Puget Sound Basin?
How does temperature change affect streamflow in the Puget Sound Basin?
I will talk about background, objectives, methodology and results. In the end, I will try to draw some conclusions. In the mean time, like the other part of the world, puget sound is experiencing climate change, mainly seeing from temperature change. These raise questions of how land cover and climate change affects streamflow. Those questions are also the objectives of the current study.

3. Methodology Study Area - Puget Sound Basin Area: 30,807 sqr.km
Bounded by the Cascade
and Olympic Mountains
Maritime climate, annual precipitation 600 mm mm, October – April
Land cover: 82% vegetation
7% urban
11% other

4. Methodology
Generate forcing data and land cover maps for the study area.
Calibrate hydrology model.
Study land cover change effects by removing the long term trend in temperature.
Study climate change effects using temperature regime detrended to 1915, temperature regime detrended to 2002, and historical temperature regime.

5. Methodology Model: Distributed Hydrology Soil Vegetation Model
Interception
Evapotranspiration
Snow accumulation and melt
Energy and radiation balance
Saturation excess and infiltration excess runoff
Unsaturated soil water movement
Ground water recharge and discharge

6. Forcing Data –Basin Averaged Historical Annual Precipitation
Eastern Puget
Sound Basins

7. Forcing Data –Basin Averaged Historical Annual Precipitation
Western Puget
Sound Basins

8. Forcing Data –Basin Averaged Historical Annual Tmin
Eastern Puget
Sound Basins

9. Forcing Data –Basin Averaged Historical Annual Tmin
Western Puget
Sound Basins

10. Forcing Data – Basin Averaged Historical Annual Tmax
Eastern Puget
Sound Basins

11. Forcing Data – Basin Average Historical Annual Tmax
Western Puget
Sound Basins

12. Data: 2002 Land Cover Map (Alberti et al., 2004)
Land Cover Types
Proportion (%)
Dense urban (>75% impervious area)
2.41
Light-mediu urban (<75% impervious area)
3.97
Bare ground
0.42
Dry ground
1.30
Native grass
0.05
Grass/crop/shrub
5.36
Mixed/deciduous forest
32.19
Coniferous forest
36.41
Regrowth vegetation
0.61
Clear cuts
0.50
Snow/rock/ice
7.85
Wetlands
0.34
Shoreline
0.13
Water
8.46

13. Data: Reconstructed 1883 land cover
Land Cover Types
Proportion (%)
Light-mediu urban (<75% impervious area)
0.40
Grass/crop/shrub
7.43
Mixed/deciduous forest
29.61
Coniferous forest
48.23
Snow/rock/ice
6.38
Water
7.96
Source:
Department of Interior, Density of Forests-Washington Territory, 1883
2. Historical records of Puget Sound county population development

14. Results: Calibration

15. Results: Calibration

16. Results: Monthly Statistics of Calibrated and Measured Streamflow
Basin (gage)
Observation Mean (cms)
Simulation Mean (cms)
Correlation Coefficient
RMSE (cms)
Model Efficiency
Cedar ( )
7.93
8.22
0.88
2.78
0.77
Deschutes ( )
0.97
0.99
0.89
0.41
0.80
Green ( )
12.03
12.42
0.86
4.96
0.67
Nisqually ( )
10.31
9.96
0.87
3.99
0.73
Puyallup ( )
12.12
12.36
0.78
4.33
0.54
Snohomish ( )
35.05
33.74
10.48
0.75
Stillaguamish ( )
32.48
32.91
0.81
11.74
0.58
Duckabush ( )
11.72
9.94
4.19
0.69
Quilcene ( )
4.34
4.03
2.17
0.64
Hamma Hamma ( )
10.40
10.27
0.82
3.91
0.65
Skokomish ( )
14.84
14.93
5.04

17. Results: Land Cover Change Effects: Seasonal Flow
Eastern Puget
Sound Basins

18. Results: Land Cover Change Effects: Seasonal Flow
Western Puget Sound Basins

19. Results: Land Cover Change Effects: Seasonal Flow
71% urbanization
Urbanization Affected Gages
64% urbanization
31% urbanization

20. Results: Mean Annual Streamflow
Basin (gage)
1883 Land Cover (cms)
2002 Land Cover (cms)
2002 vs. 1883
Change (%)
Cedar ( )
6.66
7.06 6
Deschutes ( )
0.98
1.06 8
Green ( )
10.61
11.70 10
Nisqually ( )
10.26
11.58 13
Puyallup ( )
11.54
12.40 7
Snohomish ( )
29.46
31.85
Stillaguamish ( )
30.77
31.44 2
Quilcene ( )
2.29
2.75 20
Duckabush ( )
9.01
10.18
Hamma Hamma ( )
8.90
9.86 11
Skokomish ( )
13.24
14.87 12
Springbrook Creek ( )
0.27
0.33 22
Upper Mill Creek ( )
0.37
0.46 24

21. Results: Daily Peak Flow
Eastern Puget
Sound Basins

22. Results: Daily Peak Flow
Western Puget Sound Basins

23. Results: Daily Peak Flow
71% urbanization
Urbanization Affected Gages
64% urbanization
31% urbanization

24. Annual Maximum Daily Peak Flow (AMDPF)
Mann-Kendall Trend Analysis on Measurement and Model Residuals for Upland Gages
Annual Maximum Daily Peak Flow (AMDPF)
Gage Location
Gage
Start Period
End Period
Confidence level
Slope
Cedar river near Cedar
falls -
0.03
Duckabush river near
Brinnon
0.9
0.40
NF Skokomish at
Hoodsport
0.02
SF Skykomish at Index
0.14
SF Stillaguamish at
Granite Falls
0.6
1.20
To found out if we can see the increase in peak flow and annual flow, “paired catchment”, i.e., model basin and real basin residuals were studied. The trend of the residual was examined using the Mann-Kendal analysis.
No significant trend was found in monthly and annual streamflow at the above gages.
Although model simulation shows increase trend in AMDPF and annual streamflow for upland basins, the trend might not be statistically significant.

25. Climate Change Effects: Seasonal Flow
Eastern Puget Sound Basins

26. Climate Change Effects: Seasonal Flow
Western Puget Sound Basins

27. Climate Change Effects: Seasonal Flow
71% urbanization
Urbanization Affected Gages
64% urbanization
31% urbanization

28. DJF: winter months, JJA: summer months
Basin (gage)
Detrended 1915 vs. Historical
Detrended 2002 vs. Historical
DJF
JJA
Cedar ( )
-25%
18%
33%
-21%
Green ( )
-10% 7%
10%
-7%
Nisqually ( )
-9%
14%
Puyallup ( )
-8% 9%
-6%
Snohomish ( )
-3% 6% 3%
Stillaguamish ( )
Quilcene ( )
11% 2%
Duckabush ( ) 1%
-5%
-1% 5%
Hamma Hamma ( )
-2%
Skokomish ( )
-15%
Deschutes ( )
-4% 4%
Springbrook Creek ( )
-0.3%
-0.5%
0.3%
Upper Mill Creek ( )
-0.2%
-0.8%
0.4%

29. Climate Change Effects: Daily Peak Flow
Eastern Puget Sound Basins

30. Climate Change Effects: Daily Peak Flow
Western Puget Sound Basins

31. Climate Change Effects: Daily Peak Flow
71% urbanization
Urbanization Affected Gages
64% urbanization
31% urbanization

32. Climate Change Effects: Mean Annual Flow Change
Basin (gage)
Detrended 1915 vs. Historical
Detrended 2002 vs. Historical
Cedar ( )
-3% 3%
Deschutes ( )
-0.2%
0.2%
Green ( )
-0.4%
0.5%
Nisqually ( )
-0.9%
0.9%
Puyallup ( )
-0.7%
0.7%
Snohomish ( )
0.8%
Stillaguamish ( )
-0.3%
0.3%
Quilcene ( )
Duckabush ( )
-0.5%
Hamma Hamma ( )
0.4%
Skokomish ( )
Springbrook Creek ( )
0.6%
Upper Mill Creek ( )

33. Mann-Kendall Trends of Raw Measurement: Combination of Climate Change Effects and Land Cover Change Effects
Gages
Maximum Daily Peaks
Monthly Q
Annual Q
Confidence level
Slope -
-0.06
0.95
-0.02
-0.03
0.60
0.27
0.003
0.01
0.90
0.52
0.02
0.80
0.89
0.10
0.06
1.17
0.04
Now, let’s look at the gages that we looked before. This time, we don’t compare them with model basin, but just look at the data themselves. These data would tell the effects of both natural and anthropogenic induced changes, predominantly, climate change and land cover change effects. We examine the trend in instantaneous peaks, monthly Q and annual Q.
For upland basins, land cover is not a dominant effect in changing streamflow.

34. Pacific Decadal Oscillation (PDO)
Positive phase (+): warmer and dryer climate
Negative phase (-): colder and wetter climate
In upland basins, PDO perhaps play a more important role than land cover change effects.

35. Conclusions
In upland basins, fall, winter and spring streamflows are higher under current land cover condition because of lower ET. Summer streamflow is lower in 2002 scenario because of less water storage in the basin.
On average, mean annual streamflows are slightly higher under current land cover condition which might not be statistically significant.
Peak flows are affected by the combination of ET and infiltration excess runoff. Peak flows tend to be higher under current land cover condition for most basins.
Chances of getting peak flows are higher under current land cover condition.

36. Conclusions
Climate change mainly affects upland basins where snow occurs. Temperature change mainly affects seasonal distribution of streamflow. Warmer temperature regime tends to generate higher winter flow but lower summer flow due to less snow occurrence, early snow melt and less basin snow storage.
Simulation shows that land cover change might be more important than climate change in affecting the streamflow in lowland urbanizing basins.
Trend study in upland gauged stations shows that land cover change is not the dominant factor that influences peak flows, monthly and annual flows in the upland basins.
Regional climate system such as PDO perhaps plays a more important role in affecting streamflow in the upland basins.

37. Thank You !