SURFACE AND SUBSURFACE
HYDROLOGICAL PROCESSES IN THE
MOUNTAINS
Dennis P. Lettenmaier
Department of Civil and Environmental Engineering
University of Washington
Mountain hydroclimate and water resources workshop
National Center for Atmospheric Research
Boulder, CO
October 17, 2007
Processes and variables considered
• Surface Characteristics
– Topography
– Soils
– Vegetation
• Surface meteorological drivers
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Precipitation
Temperature
Solar Radiation
Wind
• Land surface hydrological processes
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Snow
Subsurface hydrology
Runoff generation
Evapotranspiration
• Hydrologic observations in mountain environments
• Implications at the large scale – Colorado River climate
sensitivity
1. Surface Characteristics
Where are the mountains?
Topography and vegetation, Puget Sound
drainage basin, Washington
Reynolds Creek Experimental Watershed vegetation, from
field observations (left) and classified imagery (right)
from Seyfried et al, WRR 2001
Topography
and soil depth,
Upper
Billabong
Creek
Catchment,
NWS, Australia
visual courtesy CSIRO
2. Surface meteorological drivers
PRISM annual
precipitation
climatology,
western U.S.
(visual from
NOAA/NWS)
PRISM monthly maximum temperature map, Sep, 2007
Source: www.prism.orgegonstate.edu
Annual mean beam radiation (MJ/m2/day,
Mt. Jumbong region, Korea
from Kang et al, Can. J. For. Res., 2002
Downward solar radiation as a function of spatial
averaging scale, Green Lakes Basin, Niwot Ridge,
CO (2 PM, Apr 1)
Visual courtesy Danny Marks
Wind and snow accumulation factor, Reynolds
Mountain East, for wind direction 230 degrees
from Winstral and Marks, HP, 2002
3. Land surface hydrological processes
Snow processes in a forest environment
Partial snow coverage – Reynolds Creek Experimental
Watershed (photo courtesy Danny Marks)
Niwot Ridge Weather Station
Visual courtesy John Pomeroy
Visual courtesy John Pomeroy
Visual courtesy John Pomeroy
Visual courtesy John Pomeroy
Energy balance over mountain snowpack, San Juan Mountains, CO, Spring 2005
from Bales et al, WRR, 2006
visual courtesy Danny Marks
Runoff generation – the saturation excess mechanism
Saturated area (source: Dunne and Leopold)
Expansion of saturated area during a storm (source:
Dunne and Leopold)
Simulated
depth to water
table, Green
River basin,
Washington,
Jan – July,
1996
Saturation excess
isn’t always the
mechanism!
The importance of
seasonal changes in
surface energy fluxes -Distributed model
spatial average (ADM)
latent heat flux,, as
compared with
macroscale equivalent
model (MSE)
ADM
MSE - ADM
From Arola and Lettenmaier, J Clim, 1996
4. Hydrologic observations in mountain
environments
RCEW Ridge Site (visual courtesy Danny Marks)
RCEW Grove Site (visual courtesy Danny Marks)
Snow Water Equivalent
(SWE) measurement –
old and new
Mt. Bigelow flux tower, AZ
Stream gauge, Lower Stringer Creek, MT
Concluding comments – why small scale
hydrologic processes matter at the large scale
Colorado River basin climate sensitivities as a case
study: Why don’t GCM projections match those of
hydrologic models?
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RUNOFF(mm/yr)
P-E (from Seager et al 2007)
A2_EMISSIONS SCENARIO
140
120
Co River discharge (from C&L, 2007)
100
80
60
40
20
0
Visual courtesy Danny Marks
Visual courtesy John Pomeroy