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Photo: THE OREGONIAN/Bruce Ely!Climate Change and Heavy Precipitation in the Western US from Regional Climate ModelsYongxin Zhang: CIG, PCICValérie Dulière: CIGCliff Mass, Rick Steed, Mike Warner:Atmos SciRuby Leung & Qian Fu: PNNL


Why are we concerned about!heavy precipitation and climate change?!Observations!Theory!


The Centralia station!


The Centralia station!Return period of annual maximum daily precipitation!5.04.5Annual Peak Precip (in)4.03.53.02.52.01.52.5 yr!3.3 in!1.00.5--1948-1976!--1977-2006!0.01.00 10.00 100.00Return Period, Tr (1/p)


The thermodynamic control on atmospheric moisture:!Claussius-Clapeyron!dlnedT = L = α(T) ≈ 0.07 K-12RT€Atmospheric moisture increases 7% !per degree Celsius of warming!Held and Soden, J Climate, 2006 !


Total global precipitation does not increase !according to Claussius-Clapeyron!


Horizontal moisture transport increasesaccording to Claussius-Clapeyron!


Moisture convergence drives !Precipitation minus Evaporation !Δ(P - E) = α ⋅ ΔT ⋅ (P - E)which also scales like!€Claussius-Clapeyron!Dry gets drier!Wet gets wetter!


Future Storm Track ChangesStronger N PacificStorm trackChange from 1960-2000 to2080-2100Composite of 16 Global Climate ModelsNorth AmericaNPAsiaEuropeStronger N AtlanticStorm trackULBRICH ET AL. 2008


North America Climate Change


Going to ExtremesTebaldi et al 2006!


Regional Climate Models (aka dynamic downscaling) WRF (NOAH LSM) ECHAM5 forcing CCSM3 forcing HadRM (PRECIS) – HadCM3 forcing


WRF CCSM3CCSM3-WRF simulation 2030-2060 minus 1970-2000Regional average precipitation changes !are comparable to global forcing!Big contrasts around topography inregional model!Less than globalmodelComparable toglobal modelRegional average temperature changegenerally follow global model!Amplified warming over high terrain!


Value Added by Regional ModelPercent Change Fall Precipitation along 48°N!CascadesOlympics


Trends in Extreme Precipitation (1970-2000)


Trends in Extreme Precipitation (1970-2000)Trend in Annual Maximum One-dayPrecipitation mm/day per year!


Future ChangesPercent change from 1970-1999 and 2030 -2059 !Avg precip onrainy days!Avg precip onall days!


Future ChangesAnnual max !1-day precip!Fraction ofprecip over 95percentile!


Photo: THE OREGONIAN/Bruce Ely!• Global-scale thermodynamic and dynamic changes pointtoward increases in precipitation over the region!• The pattern and distribution is quite uncertain due tomesoscale weather and terrain effects!• Attribution of historical changes is doubtful!• Increases in extreme precipitation are more consistentthan increases in total precipitation!

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