Recent Climate Change Modeling Results Climate Impacts Group University of Washington With: Patrick Zahn, Cliff Mass, Rick Steed Eric SlathéEric Salathé

IPCC Scenarios for Pacific Northwest Climate Change 2-10°F 1.5-4°F 0.5-2°F

Consensus of current Global Climate Models:  Intensification of Mid-latitude storms  Less frequent storms  Northward shift in storm track Changes in Pacific Storm Track

Shift in Pacific Storm Track J Yin, Geophys Res Lett, 2005 S Pole N Pole EQ Temperature Change to Change in Eddy Growth

Shift in Pacific Storm Track Salath é, Geophys Res Lett, 2006 Observed 20th Century Model Composite 21st Century Model Composite

Shift in Aleutian Low Salath é, Geophys Res Lett, 2006 Observed 20th Century Model Composite

Change in Orographic Enhancement Salath é, Geophys Res Lett, 2006 Precip Change: Downscaling without wind effect Precip Change: Downscaling with wind effect Difference

Downscaling

Empirical Downscaling Assumes climate model captures temperature and precipitation trends Quick: Can do many scenarios Shares uncertainties with global models Regional Climate Model Based on MM5 regional weather model Represents regional weather processes May produce local trends not depicted by global models Additional modeling layer adds bias and uncertainty Downscaling Methods Used in CIG Impacts studies

Mesoscale Climate Model  Based on MM5 Weather Model  Nested grids km  Nudging on outermost grid by forcing global model  Advanced land-surface model (NOAH) with interactive deep soil temperature

Potential Surprises How does loss of snowpack feed back on the climate? How do changes in the winds affect the local climate? Are their changes in cloudiness that can affect the local rate of warming?

MM5 Simulations ECHAM5 global model to force the mesoscale system to see how well the system is working , , Climate Change

ECHAM5 20th Century Validation 20th Century Temperature Trend Temperature Bias RMS Error Precipitation Seasonal Cycle

MM5-ECHAM 1990s Validation Obs Record High Obs Record Low Obs Mean Tmax MM5-ECHAM Temperature (°F) Max Temperature at SeaTac MM5-NNRP

1990s Validation Obs Record High Obs Record Low Obs Mean Tmin MM5-ECHAM Temperature (°F) Min Temperature at SeaTac MM5-NNRP

1990s Validation Gridded ObservationsMM5 - NCEP ReanalysisMM5 - ECHAM5 January July Mean Surface temperature

Winter Cold Bias Cold episodes occurred 1-2 times per winter with temperature getting unrealistically cold (below 10F) in Puget Sound: Also a general cold bias to minima, especially in Summer Performance varies with global forcing model: oECHAM5 better than PCM oNCEP Reanalysis performs quite well

Why Cold Outbreaks? Widespread surges of arctic air originate in Global Model, likely owing to poorly-resolved terrain (Cascades and Rockies). Extreme cold air inherited by MM5. Results from previous experiments with lower-resolution (T42) GCM indicate that higher resolution reduces frequency and severity of unrealistic cold events.

Issues in downscaling Example of cold bias in PCM control simulation Due to poor resolution, model generates intermittent spuriously cold events over the Western US Surf Temp (K)

Simulations of Future Climate Because there are some biases in the GCM runs, results for future decades (2020s, 2040s, and 2090s) will be evaluated against the ECHAM5-MM baseline

Simulations of Future Climate Because there are some biases in the GCM runs, results for future decades (2020s, 2040s, and 2090s) will be evaluated against the ECHAM5-MM baseline

Winter Warming 1990s to 2050s Temperature Change Difference between MM5 and ECHAM5 Change in Winter Temperature (degrees C)

Surface Radiation Balance Increased Absorption of Surface Solar Radiation

Loss of Snow cover and Warming Snow Cover ChangeTemperature Change Change in Winter Temperature (degrees C) Change in fraction of days with snow cover

Consistent trend over 21st Century 2020s2050s2090s Change in Winter Temperature (degrees C)

MM5 Compared to raw Climate model 2020s2050s2090s Change in Winter Temperature (degrees C)

Shift to Northerly Winds Change in Sea-level PressureChange in Surface Winds

Spring 1990s to 2050s Temperature Change Difference between MM5 and ECHAM5 Change in Spring Temperature (degrees C)

Radiative Balance Reduced Incident Surface Solar Radiation Increased Absorption of Solar Radiation

Pressure gradient and Cloud Pressure ChangeCloud Change Percent Change in Low Cloud Change in 850-mb Height (m)

Trend over 21st Century 2020s2050s2090s Change in Spring Temperature (degrees C)

2020s2050s2090s MM5 Compared to Raw Climate Model Change in Spring Temperature (degrees C)

Winter Trends at Various Stations MM5 - ECHAM5 Temperature Change (°C)

Winter Trends at Various Stations MM5 - ECHAM5 Temperature Change (°C) 10 IPCC Models

Applications: Air Quality

Applications: Hydrology

Summary  Projected Pacific Northwest Climate Change  warming: 1/4 to 1 ºF/decade  Probably more warming in Summer than Winter  Precipitation changes uncertain – Possibly wetter winters and drier summers  Challenges  Deficiencies in Global model propagate to regional model  Biases from regional model  Mesoscale model simulates different climate signal from global model  Loss of snow amplifies warming in Winter and Spring  Increased cloud cover in Spring -- reduces effect of snow loss