Examining climate change between the late 20th and mid
21st century in Colorado’s San Juan Mountains from
[relatively] high resolution climate models
Imtiaz Rangwala and Joe Barsugli
NOAA ESRL, Physical Science Division, Boulder, CO
UCAR PACE Postdoctoral Fellowship
Imtiaz.Rangwala@noaa.gov
MTNCLIM 2010
Outline
 Updated Historical Trends
- Rangwala and Miller, 2010 (1895-2005)
- PRISM (extended to 2009)
 Mean climate change from high resolution
models (NARCCAP – 50 km2)
- Mid 21st century MINUS Late 20th century
 Analyzing these models forced by NCEP B.C.
- Attributing changes observed between 1981-2005
Observation Stations: San Juans
• NWS – 25 (1950-2005)
• SNOTEL – 23 (1981-2005)
• 6 NWS stations – 1910-2005
(Homogenized USHCN v2)
• PRISM data (25 NWS
stations) – 1910-2009
Rangwala and Miller, 2010 (AAAR)
 Rapid warming between 1993-2005
 2003, 1934 warmest years at NWS; 2005 warmest at SNOTEL
 Only 2008 below normal since 1993
Rangwala and Miller, 2010
Comparison with Inter-mountain West
1900-2005
GHCN v2 Upper Basin: 34N-44N; 105W-120W
(63 stations)
3
Tmean (oC) - Annual
Upper CO Basin (34-44N, 105-112W): Data GHCN v2
Anomalies (oC)
2
1
0
-1
-2
R2 = 0.77
Upper Colorado Basin (63)
San Juan Mountains
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Tmax and Tmin:
- Actually observed variable
Tmax – daytime
Tmin – nighttime
- Affected differently by different
physical variables
Increases in Tmax – decreases in snow cover, soil
moisture, cloud cover
Increases in Tmin – increases in cloud cover,
water vapor, other greenhouse gases, aerosols
Trends
 Gradual long-term warming in Tmin
 Greater inter-annual variabilities in Tmax
 Unlike Tmax, Tmin anomalies remain
above normal since 1993
 1934 warming mostly in Tmax
Rangwala and Miller, 2010
 Spring and Summer – large daytime warming since 1994
 Positive extremes esp. in Summer are unprecedented since 1994 -> 1994, 2000, 2002,
2003. 2002 remains by far the warmest summer in the daytime on record
 1934 – highest Spring Tmax
Rangwala and Miller, 2010
 Unlike Tmax, Tmin increases in all seasons since 1994
Rangwala and Miller, 2010
Climate Change – Mid 21st Century
Story from “available” NARCCAP output
High Resolution (50km x 50km; 1/2o) Climate Models
 Only the A2 Scenario
Late 20th (1971-2000) and Mid 21st
(2041-2070) century simulations with
GCM boundary forcing
Late 20th century (1979-2005)
simulations with observed (NCEP)
boundary forcing
Value Added From NARCCAP
 Increase resolution by >16X relative to the GCMs
 Better representation of mountainous terrain
 Highest elevation raised to 11,000 ft from 8,000 ft
NARCCAP Analysis: Current Research Goals
 Future seasonal warming (Tmax and
Tmin) in the Upper Colorado Basin and their
causes
- With a pilot focus on the San Juans
 Models inter-comparison to verify the
prevalence of a signal and the process
 Elevation based analysis
 Analysis of NCEP forced runs to
understand late 20th century climate change
 Compare these results with statistically
downscaled data
Collaborations:
WWA – Joe Barsugli
Reclamation – James Prairie, Levi Brekke
CU – Jason Neff, Karen Cozzetto
BLM – San Juan Public Land Center
Mountain Studies Institute
Maximum Temperature Change
Mid-21st Century MINUS Late 20th Century
Minimum Temperature Change
Mid-21st Century MINUS Late 20th Century
Tmax Anomalies: Elevation Based Changes – 4 models
Low
5000-7000 ft
Middle
7000-9000 ft
High
9000-11000 ft
Tmin Anomalies: Elevation Based Changes – 4 models
Low
5000-7000 ft
Middle
7000-9000 ft
High
9000-11000 ft
Precipitation Analysis
Mid-21st Century MINUS Late 20th Century
Historic projections: San Juans
Total annual precipitation
Historic
Observations
(Source: Karen Cozzetto)
Historic projections
Total seasonal precip., all elevations
Historic
Observations
Historic
Observations
Historic
Observations
Historic
Observations
(Source: Karen Cozzetto)
Future Projections – All Seasons
(Source: Karen Cozzetto)
Summary 2041-70 minus 1971-00: Tmax, Tmin, Precip
Tmax: Largest increases in summer (> 3.5oC) and lowest in winter (2.5
oC).
Summer warming greater at higher elevation, primarily associated
with decreases in soil moisture
Tmin: About 3oC in all seasons. Winter shows a large divergence
among models. One model shows very large warming during winter (45oC)
Precip: Wetter winters (10%), Marginally drier spring, Marginally to
substantially (20%) drier summers, Mixed signal for fall
HRM3+HADCM3
CRCM+CGCM3
9000-11000 ft : Changes in Surface Temperature and Energy Balance
(2041-70 minus 1971-2000)
NDLR-net downwelling longwave
ASR-absorbed solar radiation
LAT & SEN- latent and sensible heat fluxes
HRM3+HADCM3
CRCM+CGCM3
5000-7000 ft : Changes in Surface Temperature and Energy Balance
(2041-70 minus 1971-2000)
NDLR-net downwelling longwave
ASR-absorbed solar radiation
LAT & SEN- latent and sensible heat fluxes
NCEP forced runs
 Summer of 2002 doesn’t stand out in the models
Thanks!!!