modelling of mountain precipitation andreas f. prein wegener center for climate and global change...

Modelling of Mountain Precipitation

Andreas F. Prein

Wegener Center for Climate and Global Change (WEGC) and Institute for Geophysics, Astrophysics, and Meteorology (IGAM), Institute of Physics, University of Graz, Graz, Austria

Workshop on Statistical Applications to Climate Extremes

30 October, 2012, Zurich, Switzerland

1.1. IntroductionIntroduction

◦ Orographic Precipitation & Extremes

◦ A Simple Concept of Heavy Precipitation

2.2. Modelling of Orographic Precipitation

Modelling of Orographic Precipitation

◦ A Scale Problem

◦ Model Performance

◦ Higher Resolution Higher Quality?

◦ Model Projections of Future Climate

3.3. Summary and OutlookSummary and Outlook

OvervieOvervieww

Prein, Workshop on Statistical Applications to Climate Extremes, 2012 2/15

1. Introduction1. IntroductionOrographic Precipitation & Orographic Precipitation & ExtremesExtremes

3/15

Precipitation generated/enhanced by a forced upward movement of air due to orography

Prein, Workshop on Statistical Applications to Climate Extremes, 2012

PRISM Group, Oregon Stade University

NOAA

1. Introduction1. IntroductionAA SimpleSimple Concept of Heavy Concept of Heavy PrecipitationPrecipitation

4/15

C. F. Chappell“the heaviest precipitation occurs where the rainfall rate is highest for the longest time”

Floods: associated with slow-moving precipitation

systemsPrecip. ofDuration Rate Precip.Precip.total

sources precip.

rate precip. extreme precipitation

events: related to deep

convection

[kg]Air Dry Mass

[g]Vapor Water Mass


Ratio MixingRateAscent Efficiency Precip. Rate Precip.

Relationship Precip.total and other factors is

multiplicative nonlinear

!






◦ A Scale Problem





OvervieOvervieww


2. Modelling of Orographic 2. Modelling of Orographic Precip.Precip.A Scale ProblemA Scale Problem

6/15

Extreme precipitation Processes on all scales

Time and Space Scale of Atmospheric Motion

Microscale2 m

Mesoscale20 km

Synoptic Scale200 km

Global Scale5000 km

Scale

Secondsto

minutes

Minutesto

hours

Hoursto

days

Days to aweek or more

Time

Glo

bal C

lim

ate

Mod

els

(GC

Ms)

Reg

ion

al C

lim

ate

Mod

els

(RC

Ms)

• Downscaling Methodso Dynamical Downscaling: Regional Climate Models (RCMs) [Giorgi and Mearns 1991]

o Statistical Downscaling [Wilby and Wigley 1997]

o Stretched Grid Models [Staniforth and Mitchell 1978]


Con

vecti

on

P

erm

itti

ng

Mod

ells

(CP

Ms)

Convection Permitting Scale

~<4 km grid spacing

2. Modelling of Orographic 2. Modelling of Orographic Precip.Precip.Model PerformanceModel Performance

7/15

• GCMs ◦ underestimate intensity of extreme precip. in mountain regions◦ Deficits in simulating quasi-stationary circulation patterns

• RCMs ◦ improve representation of hydrological cycle in mountainous regions [e.g., Jones et al. 1995,

Giorgi et al. 2001] but can only partly correct systematic errors in large-scale forcing

• Convection Permitting Simulations major improvements on mesoscale:◦ Location and Intensity of extreme precipitation [Hohenegger et al. 2009, Prein et al. 2012]

◦ Timing of the summertime precipitation diurnal cycle [Hohenegger et al. 2008, Prein et al. 2012]

◦ Orographic precipitation patterns [ Rassmussen et al. 2011, Prein et al. 2012]


Moisture Supply

2. Modelling of Orographic 2. Modelling of Orographic Precip.Precip.Higher Resolution Higher Resolution Higher Quality? Higher Quality?

8/15

WRF 4 km WRF 12 km WRF 36 km

Summertime Average Extreme


Prein et al. 2012


9/15

Winter Average Extreme

WRF 4 km WRF 12 km WRF 36 km


Prein et al. 2012

Spatial Correlation

Coefficients:

0.80 0.78 0.65


10/15

• Finer grids more precipitation (frontal systems)• 12 km necessary to get location of maxima• Finer grids more spatial variability

September 19th-21st 1999 event using the COSMO-CLM ModelObservation [2 km]

50 km Model 12 km Model 3 km Model 1 km Model


-9.9 mm/d -2.9 mm/d +3.3 mm/d +3.7 mm/dDifference:

-61 % -11 % 0 % +5 %STDDEV:

2. Modelling of Orographic 2. Modelling of Orographic Precip.Precip.Model Projections of Future ClimateModel Projections of Future Climate

• Models underestimate the observed increase in heavy precipitation with warming [Allan and Soden 2008].

• Most GCMs/RCMs show increase in frequency and intensity of heavy precipitation events [e.g., Kharin and Zwiers 2000, Hennessy et al. 1997, Giorgi et al. 2011].

• Changes in the Physics of Extreme Events[e.g. Mahoney et al. 2012]

◦ More Intense storms in Colorado Front Range and Rocky Mountain regions◦ Less hail reaching the surface

11/15

Maximum grid point event-total precipitation [mm/d] versus elevation Max hail/graupel by elevation [mm]


Current: Future:

2. Modelling of Orographic 2. Modelling of Orographic Precip.Precip.Model Projections of Future Model Projections of Future ClimateClimate

12/15

• Clausius-Clapeyron (CC)-Scalingo In a warmer climate moisture content increase by ~7 %/K [e.g., Emori &

Brown 2005; Held & Soden 2006; Allan & Soden 2008; Prein at al. 2011]

o Global Precipitation and Evaporation increase with ~1-3%/K [IPCC 2001, Allen & Ingram 2002; O’Gorman et al 2011]

due to energy budget of free atmosphereo Orographic Precipitation likely increase with ~7%/K [Schmidli et al. 2002; Schär

& Frei 2005; Shi and Durran 2012]


[10 mm]Precipitable Water [50 mm]

Precipitable Water [70 mm] [13 mm]

40 mm 57 mm

up t

o 9

9 %

condensa

tion

Up t

o 9

9 %

condensa

tion






◦ A Scale Problem





OvervieOvervieww


• Focus on more frequent moderate intensity• Usage of extreme value statistic

• Trends in Extremes are hard to detect• Detection probability of events decreases

with increasing rareness [Frei and Schär 2001]

• Can we trust our models? • How large are the model errors and how can we reduce them?(Problems: observations, resolved scales, physical understanding, uncertainties,…)

• How will the processes change?• Climate moistening, microphysics (hail, snow), soil-moisture-atmosphere, runoff…• Are changes dependent on region, season…

• How will the ingredients change?• Changes in global circulation• Will ingredients for extreme events occur more frequently?• Will a different set of ingredients lead to

extremes?

3. Summary and 3. Summary and OutlookOutlook

14/15Prein, Workshop on Statistical Applications to Climate Extremes, 2012

Major ChallengesMajor Challenges Possible SolutionsPossible Solutions

• Evaluation of models with observations• Model intercomparison studies (ensembles)• Model development• Finer grid spacings

• Pseudo climate warming simulations• Toy models, Idealized simulations• Coupling of RCMs with regional ocean models, runoff models…

• High resolution global simulations• Stretched grid models• Regionalization of GCM projections

Thank you for your attention


• Spatial Variability – Station Density; Radar Shadows

• Processes on different scales (synoptic – micro scale)

• Measurement Errors (especially in DJF)


18/15

Precipitation over the Alps feeds four major European rivers and plays a crucial role in supplying water to the continent, in shaping Alpine ecosystems and in providing hydropower for civilization. Heavy precipitation can also cause flash floods, land slides and avalanches. This map shows observed precipitation in August 2005, when more than 150 mm of rain fell within 3 days over Austria, Germany and Switzerland. Six casualties and more than 2 billion Euros in damage occurred within Switzerland alone. (Source: MeteoSwiss)

http://www.euro4m.eu/High_resolution_precipitation_data.html


19/15

Summertime ThunderstormsAn example: The Big Thompson River flood (Colorado 1976)

EastWest

GREAT PLAINSFRONT RANGE

Moisture Supply

1. An conditionally or potentially unstable airmass

2. Weak environmental shear3. Humid environment – weak

outflow4. Thermal induced upslope

winds




Winter precipitation [mm/d]T32-CGCM 45km-CRCM

1. Improvement in the intensity and location2. Shadow effect downstream of the Rocky Mountains

Obs. (Willmott and Matsuura)

[Laprise 2010]

modelling of mountain precipitation andreas f. prein wegener center for climate and global change...

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