The Impact of Orographic Precipitation on the Form of

Mountain Ranges

Alison Anders Earth and Space Sciences

Dale Durran Atmospheric Sciences

Gerard Roe Earth and Space Sciences

University of Washington, Seattle, WA, USA

Do mountains and mountain weather co-evolve?

Gyala Peri (7150 m) from the Po-TsangPo River, TibetThanks to Noah Finnegan

Erosion by Rivers Shapes Mountain Landscapes

Queets basin,Olympic Mountains

Washington, USA

• Channel network sets landscape relief

Elwha River, Olympic Mountains, Washington, USA

• Hills are at the critical slope and fail as rivers erode

Stream Power Model of River Incision

• Erosion balances uplift

Stream Power Model of River Incision

Typical River Channel Profile

0

100

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400

500

0 20 40 60 80 100Distance (km)

Ele

vati

on (

m)

Steep Upper SectionLow Discharge

Gentle Lower SectionHigh Discharge

Stream Power Model of River Incision

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0 20 40 60 80 100Distance (km)

Ele

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Q*S

Erosion Rate is Proportional to Discharge times Slope

Precipitation Patterns Can Influence Topography

• Patterns persist for the response time of the system; at the scale of ~10 km, this is ~100,000 years

Q/Q S/S

Range-Scale Impacts: Olympic Mountains, Washington, USA

Elevation ~ 0 – 2400m Precipitation ~850 – 5000 mm

Low S, High Q

Range-Scale Impacts: Olympic Mountains, Washington, USA

Elevation ~ 0 – 2400m Precipitation ~850 – 5000 mm

High S, Low Q

Sub-Range Scale Variability

• How do precipitation patterns and topography compare at small scales (~10 km)?

• MM5 run by UW researchers for forecasting precipitation at a 4km resolution

• 2 years of archived precipitation forecasts

• Simple Ice Scheme (Dudhia, 1989)

MM5 Annual Precipitation

MM5 Intense Storm Precipitation

Conclusions

• Storm Events

• Seasonal Totals

• Annual Totals

In the Olympics, MM5 precipitation is consistently modulated by topography

Conclusions

• Simulated Precipitation is Greater on Ridges than in Valleys

• Simple Model Predicts Ridges are Lower and More Gently Sloping than with Uniform Precipitation

Further Work

• Field validation of precipitation pattern

Further Work

• Landscape evolution modeling

CASCADE landscape evolution model, courtesy of Jean Braun

Tectonic Uplift

Atmospheric Issues

• High spatial resolution precipitation patterns

• Interactions between topography and precipitation

• Stability of precipitation patterns through glacial-interglacial climate cycles

Mountain Weather and Mountains Co-evolve

Further Work• Other Mountain Ranges

European Alps

Precipitation Gauge ClimatologyFrei and Schär, 1998

Further Work• Other Mountain Ranges

Himalaya

TRMM Satellite PR Climatology1998-2001