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 Washington2: Department of Urban Design and Planning, University of Washington3: Department of Chemical Oceanography, University of Washington

March 1, 2007

Climate Impact Group

University of Washington

• Background 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?

Methodology

• Study Area - Puget Sound Basin

• Bounded by the Cascade and Olympic Mountains

• Area: 30,807 sqr.km

• Maritime climate, annual precipitation 600 mm - 3000 mm, October – April

• Land cover: 82% vegetation 7% urban 11% other

Methodology• Generate 1/16th degree gridded 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 temperature change effects using

temperature regime detrended 1915, temperature regime detrended 2002, and historical temperature regime.

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

Forcing Data –Basin Averaged Historical Annual Precipitation

Eastern Puget Sound Basins

Mean annual Prcp:1200 mm – 2500 mm

Forcing Data –Basin Averaged Historical Annual Precipitation

Western Puget Sound Basins Mean annual prcp:

1600 mm – 3000 mm

Forcing Data –Basin Averaged Historical Annual Tmin

Eastern Puget Sound Basins

Mean annual Tmin:-0.5 – 4.5 C

Forcing Data –Basin Averaged Historical Annual Tmin

Western Puget Sound Basins

Mean annual Tmin:-1.8 – 2.5 C

Forcing Data – Basin Averaged Historical Annual Tmax

Eastern Puget Sound Basins

Mean annual Tmax:10 – 15 C

Forcing Data – Basin Average Historical Annual Tmax

Western Puget Sound Basins Mean annual Tmax:

9 – 13 C

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

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: 1. Department of Interior, Density of

Forests-Washington Territory, 1883

2. Historical records of Puget Sound county population development

Results: Model Calibration

Results: Model Calibration

Results: Monthly Statistics of Calibrated and Measured Streamflow

Basin (gage) Observation Mean (cms)

Simulation Mean (cms)

Correlation Coefficient

RMSE (cms)

Model Efficiency

Cedar (12115000) 7.93 8.22 0.88 2.78 0.77

Deschutes (12078720) 0.97 0.99 0.89 0.41 0.80

Green (12104500) 12.03 12.42 0.86 4.96 0.67

Nisqually (12083000) 10.31 9.96 0.87 3.99 0.73

Puyallup (12094000) 12.12 12.36 0.78 4.33 0.54

Snohomish (12141300) 35.05 33.74 0.88 10.48 0.75

Stillaguamish (12161000) 32.48 32.91 0.81 11.74 0.58

Duckabush (12054000) 11.72 9.94 0.87 4.19 0.69

Quilcene (12052210) 4.34 4.03 0.81 2.17 0.64

Hamma Hamma (12054500)

10.40 10.27 0.82 3.91 0.65

Skokomish (12056500) 14.84 14.93 0.88 5.04 0.77

Results: Land Cover Change Effects: Seasonal Flow

Eastern Puget Sound Basins

Results: Land Cover Change Effects: Seasonal FlowWestern Puget Sound Basins

Results: Land Cover Change Effects: Seasonal Flow

Urbanization Affected Gages

71% urbanization

64% urbanization

31% urbanization

Results: Mean Annual StreamflowBasin (gage) 1883 Land Cover

(cms)2002 Land Cover

(cms)2002 vs. 1883Change (%)

Cedar (12115000) 6.66 7.06 6

Deschutes (12078720) 0.98 1.06 8

Green (12104500) 10.61 11.70 10

Nisqually (12083000) 10.26 11.58 13

Puyallup (12094000) 11.54 12.40 7

Snohomish (12141300) 29.46 31.85 8

Stillaguamish (12161000) 30.77 31.44 2

Quilcene (12052210) 2.29 2.75 20

Duckabush (12054000) 9.01 10.18 13

Hamma Hamma (12054500) 8.90 9.86 11

Skokomish (12056500) 13.24 14.87 12

Springbrook Creek (12113346) 0.27 0.33 22

Upper Mill Creek (12113349) 0.37 0.46 24

Results: Daily Peak Flow Eastern Puget Sound Basins

Controlled Basin

Results: Daily Peak FlowWestern Puget Sound Basins

Results: Daily Peak Flow

Urbanization Affected Gages

71% urbanization

64% urbanization

31% urbanization

Mann-Kendall Trend Analysis on Measurement and Model Residuals for Upland Gages

Gage Location Gage Start Period End Period Confidence level

Slope

Cedar river near Cedar falls

12115000 1945-10-1 2002-9-30 - 0.03

Duckabush river nearBrinnon

12054000 1938-7-1 2002-9-30 0.9 0.40

NF Skokomish atHoodsport

12056500 1925-10-1 2002-9-30 - 0.02

SF Skykomish at Index 12133000 1922-2-1 1982-9-30 - 0.14

SF Stillaguamish atGranite Falls

12161000 1928-8-1 1980-11-30 0.6 1.20

• 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.

Annual Maximum Daily Peak Flow (AMDPF)

Temperature Change Effects: Seasonal Flow

Eastern Puget Sound Basins

Temperature Change Effects: Seasonal FlowWestern Puget Sound Basins

Warmer T regimeDetrended 1915

Colder T regimeDetrended 2002

Temperature Change Effects: Seasonal Flow

Urbanization Affected Gages

71% urbanization

64% urbanization

31% urbanization

Basin (gage) Detrended 1915 vs. Historical

Detrended 2002 vs. Historical

DJF JJA DJF JJA

Cedar (12115000) -25% 18% 33% -21%

Green (12104500) -10% 7% 10% -7%

Nisqually (12083000) -9% 14% 7% -9%

Puyallup (12094000) -8% 7% 9% -6%

Snohomish (12141300) -6% -3% 6% 3%

Stillaguamish (12161000) -10% 9% 10% -8%

Quilcene (12052210) -3% 11% 2% -7%

Duckabush (12054000) 1% -5% -1% 5%

Hamma Hamma (12054500) 2% -9% -2% 9%

Skokomish (12056500) 2% -15% -2% 14%

Deschutes (12078720) 0 -4% 0 4%

Springbrook Creek (12113346) -0.3% -0.5% 0.3% 1%

Upper Mill Creek (12113349) -0.2% -0.8% 0.4% 1%

DJF: winter months, JJA: summer months Potential problems in summer

Temperature Change Effects: Mean Annual Flow Change

Basin (gage) Detrended 1915 vs. Historical

Detrended 2002 vs. Historical

Cedar (12115000) -3% 3%

Deschutes (12078720) -0.2% 0.2%

Green (12104500) -0.4% 0.5%

Nisqually (12083000) -0.9% 0.9%

Puyallup (12094000) -0.7% 0.7%

Snohomish (12141300) -0.7% 0.8%

Stillaguamish (12161000) -0.3% 0.3%

Quilcene (12052210) -0.2% 0.2%

Duckabush (12054000) -0.5% 0.5%

Hamma Hamma (12054500) -0.5% 0.4%

Skokomish (12056500) -0.7% 0.7%

Springbrook Creek (12113346) -0.4% 0.6%

Upper Mill Creek (12113349) -0.3% 0.5%

Temperature Change Effects: Daily Peak Flow

Eastern Puget Sound Basins

Temperature Change Effects: Daily Peak FlowWestern Puget Sound Basins

Temperature Change Effects: Daily Peak Flow

Urbanization Affected Gages

71% urbanization

64% urbanization

31% urbanization

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 Confidence level

Slope Confidence level

Slope

12115000 - -0.06 0.95 -0.02 0.95 -0.03

12054000 0.60 0.27 - 0.003 - 0.01

12056500 0.90 0.52 0.90 0.02 0.80 0.02

12133000 - 0.89 0.80 0.10 - 0.06

12161000 0.60 1.17 0.60 0.04 0.60 0.06

For upland basins, land cover is not a dominant effect in changing streamflow.

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.

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 in upland basins.

• 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.

Conclusions• Temperature 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 streamflows in the upland basins.

• Regional climate system such as PDO perhaps plays a more important role in affecting streamflow in the upland basins.

Thank You !