The elevation-dependence of warming
in high-resolution regional climate simulations
over the Rocky Mountains
Justin Minder & Ted Letcher
Thanks to:
Roy Rasmussen, Changhai Liu, Kyoko Ikeda
University at Albany
NCAR/RAL
What is elevation-dependence of ΔT in a high-resolution RCM?
Why?
Headwaters
Domain
Regional climate model (RCM)
• Weather Research & Forecast (WRF) model
• Horiz. grid spacing: 4km
Control simulation
• 8 yrs: 2000-2008
• Boundary conditions (BC’s) from reanalysis
“Pseudo-global warming” experiment
• Same BC’s with monthly perturbations
(wind, humidity, temperature)
• BC perturbations from GCM experiment of midRasmussen et al. (2011)
century climate (AR4-SRES A2)
• …also add CO2
Focus on the regional response • Same weather but shifted climate
to large-scale warming
Spatial pattern of warming
April (2003)
April (7-yr average)
Wyoming
(oC)
Colorado
New Mexico
contours of elev.:
2.7km, 4km
• Up to 3oC extra warming at
certain locations
• Apparent elevation dependence
Spatial pattern of warming
June (2003)
June (7-yr average)
Wyoming
(oC)
Colorado
New Mexico
contours of elev.:
2.7km, 4km
• Up to 3oC extra warming at
certain elevations
• Apparent elevation dependence
• Structure varies with season
Elevation dependence of warming (by season)
Nov
Dec
ΔT [oC]
ΔT [oC]
Ma
r
Apr
ΔT [oC]
ΔT [oC]
Jul
Aug
ΔT [oC]
ΔT [oC]
Feb
Jan
ΔT [oC]
ΔT [oC]
May
Jun
ΔT [oC]
ΔT [oC]
Oct
Sep
• Up to 1oC extra warming at
certain elevations
• Structure varies with season
ΔT [ C]
[ C]
interannual
variability
• ΔTLarge
o
o
Elevation dependence of warming (spring)
Ma
r
Apr
ΔT [oC]
ΔT [oC]
Jun
May
Elevation-dependence
most-pronounced in
March-June
ΔT [oC]
ΔT [oC]
elevation (km)
Elevation dependence of atmospheric warming
perturbations on boundaries
April
March
June
elevation (km)
May
ΔT [oC]
• Elevation-dependence is not inherited
from free-atmospheric warming
• Develops due to regional-scale
processes
ΔT [oC]
Spatial pattern of warming & snow loss
Snow cover change (April, 7-yr average)
Warming (April, 7-yr average)
(oC)
contours of elev.:
2.7km, 4km
contour of control
climate 25% snow cover
Spatial pattern of
warming closely tied to
snow cover change
Spatial pattern of warming & snow loss
Snow cover change (June, 7-yr average)
Warming (June, 7-yr average)
(oC)
contours of elev.:
2.7km, 4km
contour of control
climate 25% snow cover
Elevation dependence of warming & snow loss
(spring)
March
April
May
June
ΔT[oC]
ΔT[oC]
ΔT[oC]
ΔT[oC]
Δsnow cover
[frac.]
Δsnow cover
[frac.]
Δsnow cover
[frac.]
Δsnow cover
[frac.]
Elevation dependence of warming & snow loss
(summer)
Aug
July
ΔT[oC]
Δ snow cover [frac.]
ΔT[oC]
Δ snow cover [frac.]
Elevation dependence of warming &
soil moisture change (summer)
Aug
July
ΔT[oC]
Δ soil moisture [m3 m-3]
ΔT[oC]
Δ soil moisture [m3 m-3]
• Projection of complex spatial pattern, so caution warranted
• Some elevations receive up to 1oC extra warming
• Varies strongly with season and year
Mechanisms:
• Snow-albedo feedback is the dominant signal
• Changes in soil moisture, clouds, water vapor, and
vegetation may play secondary roles
ΔT[oC]
elev. (km)
Elevation-dependent warming is apparent in high-resolution
RCM experiments over the Rockies
elev. (km)
Concluding thoughts
Δsnow cover [frac.]
Thoughts for the future
• Focus on mechanisms. Use models as tools for
understanding, not just projection
• Model fidelity is still uncertain
• Need better techniques for diagnosing and
understanding differences between models