21st Century Climate Change Effects on Streamflow in the Puget Sound, WA.

Lan Cuo, Eric P. Salathé Jr. and Dennis P. Lettenmaier

Nov. 7, 2007Hydro Group Seminar

Seattle, WA

• Background• “Warming of the climate system is unequivocal, as is now evident

from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level “ – IPCC AR4

• Mountain snowpack is the key to understanding Pacific Northwest (PNW) water resources. In upland Puget Sound river basins, snow is the dominant form of water storage, storing water from the winter (when most precipitation falls) and releasing it in spring and early summer. Climatic variations and changes that influence spring snowpack, therefore, can have a significant impact on water resource availability in the Puget Sound.

• Objectives• How does climate change affect streamflow in the Puget Sound

Basin?

Methodology

• Study Area - Puget Sound Basin

• Bounded by the Cascade

• and Olympic Mountains

• Area: 30,000 sqr.km

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

• Land cover: 82% vegetation

• 7% urban

• 11% other

The Emission Scenarios of the IPCC Special Report on Emission Scenarios (SRES)A1. The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and socialinteractions, with a substantial reduction in regional differences in per capita income.

Based on technological emphasis, A1 has 3 groups:A1F1: fossil intensiveA1T: non-fossil energy sourcesA1B: balance across all sources (where balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end use technologies).

Methodology – terminology explanation

Methodology

• Generate 1/16th degree climate forcing data using composite GCM results for 2010-2090.

• Test the reliability of GCM composite forcing by using composite GCM historical climate forcing in 1950 -1999.

• Use DHSVM to simulate streamflow for 2010-2090 for A1B scenario.

• Compare the A1B scenario (2010-2090) streamflow with the simulated historical (1950-1999) streamflow.

Models Institutions

BCCR Univ. of Bergen, Norway

CCSM3 NCAR, USA

CGCM 3.1_t47 CCCma, Canada

CGCM3.1_t63 CCCma, Canada

CNRM_CM3 CNRM, France

CSIRO_MK3 CSIRO, Australia

ECHAM5 MPI, Germany

ECHO_G Max Plank Institute for Mathematics, Germany

GFDL_CM2_1 Geophysical Fluid Dynamic Laboratory, USA

GISS_AOM NASA/GISS, (Goddard Institute for Space Studies) USA

HADCM Met Office, UK

HADGEM1 Hadley Center Global Environment Model, v 1., UK

INMCM3_0 Institute Numerical Mathematics, Russia

IPSL_CM4 IPSL (Institute Pierre Simon Laplace, Paris, France

MIROC_3.2 CCSR/NIES/FRCGC, Japan

PCM1 NCAR, USA

16 Models used to Simulate IPCC Emission Scenario A1B

Data: Eastern Puget Sound Annual Tmin2010 -2090 is the composite (average) of all 16 models.

Data: Western and Lowland Puget Sound Annual Tmin

Data: Eastern Puget Sound Annual Tmax

Data: Western and Lowland Puget Sound Annual Tmax

Data: Eastern Puget Sound Annual Precipitation

Data: Western and Lowland Puget Sound Annual Precipitation

Climate change in the Puget Sound Sub-basins, 2010-2090 average minus 1915-2002 average

Basins Mean annual Tmin (°C)

Mean annual Tmax (°C)

Mean annual Precip. (mm) ∆Tmax ∆Tmin ∆Prcp

Skagit -0.5 10 2400 2.2 2.5 196

Stillaguamish 2 12.5 2400 2.1 2.5 258

Snohomish 1 11 2400 2.1 2.4 239

Cedar 2.6 12.6 2100 2 2.4 114

Green 2.1 12 2000 2.2 2.5 91

Puyallup 1.5 11.6 1600 2.1 2.2 248

Nisqually 2.5 13 1600 2 2.3 222

Deschutes 4.3 15.4 1200 1.8 2.1 93

Skokomish 2.4 13 3000 1.7 1.9 443

Hammahamma 0.2 10.8 2500 1.8 2 333

Duckabush 0 10.7 2400 1.9 2 274

Dosewallips -1.6 9.4 2100 1.8 2 323

Quilcene -0.8 10.7 1600 1.9 2.1 375

Lowland_east 3.8 14.2 1500 2 2.2 190

Lowlnad_west 3.4 13.8 1500 1.9 2 244

Basin average 1.5 12 2020 2 2.2 243

Results: Model Calibration

Results: Model Calibration

Results: Model Calibration

Results: Model Calibration

Results: Model Calibration

Results: the Reliability of GCM Composite Forcing

Three data sets:1. Observed streamflow2. Simulation with observed forcing3. Simulation with GCM composite4. Period is 1950-1999

Results: Reliability of GCM Composite Forcing 1950 - 1999

Gages Period Mean Daily Streamflow (cms)

Mean Monthly Streamflow (cms)

Obs. Sim. (comp)

Sim. (hist)

Obs. Sim. (comp)

Sim (hist)

12115000 1950-1999

7.28 7.32 7.23 7.30 7.32 7.24

12115500 1950-1999

2.86 2.58 2.52 2.87 2.53 2.52

12117000 1956-1999

2.77 2.57 2.54 2.78 2.58 2.54

However, simulations with GCM composite forcing have very poor Nash-Sutcliff Number and RMSE.

Results: Reliability of GCM Composite Forcing

Results: Streamflow change in SRES A1B

Preliminary Conclusions

1. Statistically downscaled GCM composite forcing data are suitable for studying mean hydrological properties such as daily, monthly and seasonal mean, but not for detailed time series study.

2. In a future, warmer temperatures will result in more winter precipitation falling as rain rather than snow throughout much of the Puget Sound. This change will result in:

• less winter snow accumulation, • higher fall, winter, early spring streamflows, • earlier spring snowmelt, • earlier peak spring streamflow, and • lower summer streamflows

Acknowledgement:This work is supported by the University of Washington CIG and PRISM.