ANALYSIS OF CLIMATIC CHANGES IN THE SAN
JUAN MOUNTAIN (SJM) REGION DURING THE
20 TH CENTURY
Imtiaz Rangwala imtiazr@envsci.rutgers.edu
MTNCLIM 2008 1

¾ Nature of climate change in the SJM
¾ It’s relationship to changes in the stream flow in the region
¾
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¾ Historical climate records for the SJM region
¾ Analysis of these records for the 20 th century
- Temperature
- Elevation Dependent Warming?
(NWS vs SNOTEL)
- Precipitation, SWE, Snowdepth
¾ Role of the Pacific Climate
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Study Region
SJM
¾ 13 Counties
¾ 105.5-109 W and 37-38.5 N http://hprcc.unl.edu/
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Snow water equivalent (SWE): SNOTEL (26),
Since mid-1940s
Snow Course (26)
Snow-depth: Snow Course (26)
Since mid-1940s
… and refining (esp. SNOTEL data)
• discarding impossible values
• filling in missing values
JAN thru
JUN
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¾ Possible 2 o C warming between 1906-2005
¾ Rapid warming between 1995 and 2005
¾ Both NWS and SNOTEL sites confirm this trend
NWS anomalies – relative to 1960-1990
SNOTEL anomalies – relative to 1990-2005
NWS vs SNOTEL r = 0.68
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1950-2005 Æ r = 0.94
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D iv
. 2
CO division - 2
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?
1950-2005 Æ r = 0.84
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NASA/GISS
14 http://data.giss.nasa.gov/gistemp/

At SJM:
¾ Surface warming twice that of global average
¾ Mid century cooling occurred later
¾ Late century warming started later too but happened more rapidly
1906-2005 Æ r = 0.55
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1906-2005 Æ r = 0.56
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Trends based on the 5 o x 5 o gridded GHCN (Global
Historical Climatology Network) land surface dataset provided by NCDC, NOAA
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SJM: NWS vs SNOTEL
¾ SNOTEL sites 2500 ft higher than NWS sites
¾ Warming larger at SNOTEL than NWS except winter
¾ Spring and summer: Warming at least 2 times higher at SNOTEL
¾ Similar increases in T-max and T-min
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Warming rates for 3 decades (C/decade)
¾ Large warming in 1995-2005
¾ SNOTEL > NWS
¾ Similar increases in Max. T and Min. T during 1995-2005 particularly at SNOTEL sites
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Warming rates for 3 decades (C/decade): Seasons
1995-2005: The decade of highest warming?
¾ Warming in all seasons at both sites
¾ Higher at SNOTEL except winter
¾ Very large during spring and summer at SNOTEL
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Conclusions:Temperature
¾ The surface temperature in the SJM region may have increased by about 2 o C between 1906-2005
¾ Half of this warming happened between 1990-2005; which is confirmed at both NWS and SNOTEL sites
¾ Temperature trends correlate well between NWS and
SNOTEL sites
¾ More recent trends in warming in the San Juans appear to have started later than most other regions in the U.S. but has been more rapid
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¾ Broad temperature trend in the SJM is to similar to that of the contiguous US for the 20 th century
¾ Elevation dependency in local warming – higher rates at
SNOTEL sites
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(Nov-May)
¾ Anomalies are normalized
¾ 25% decrease during 1995-2005
NWS vs SNOTEL r = 0.80
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Snowfall And Snow-depth r = 0.87
¾ 25% decrease in snow-depth during 1995-2005
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Snowfall And SWE
¾ 40% decrease in SWE during 1995-2005
¾ Decrease in the total annual snow residence time
Snowfall vs SWE: r = 0.83
SWE (Snow Course vs SNOTEL): r = 0.96
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Snowfall And Snow-depth
Decadal Average
Snowdepth following snowfall trend
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Snow-depth: Snow Course Sites
Large snowdepth decreases in mid-late spring
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Increase in Spring Melt?
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I-80
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(+) ENSO and (+) PDO
More Snowfall and
Lower Winter Temperatures in the SJM
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¾ Pre-1975: Relationship exist but weak
¾ Post-1975: Breaks down; in fact becomes opposite?
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¾ Rapid decreases in Snowfall (25%), SWE (40%) and
Snowdepth (25%) at SNOTEL/Snow Course sites during the 1995-2005 period.
¾ These decreases in Snowfall cannot be explained by the traditional ENSO/PDO pattern.
¾ Large warming in spring and early summer can be related to the decreases in snow amount through the snow-albedo feedback mechanism
¾ Large decreases in SWE in spring may reflect in significant changes in the seasonal streamflow in the region.
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• MSI mini-grant program
– Koren Nydick
• Jim Miller and Dave Robinson – Rutgers
• Staff and Researchers at MSI
• People of Silverton
• DATA Sources
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Rapid temperature increases
And
A rapid snow loss
(In recent decades)
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1906-2005 Æ r = 0.52
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1906-2005 Æ r = 0.52
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Monsoon Precipitation
¾ No long term trends
NWS vs SNOTEL r = 0.91
¾ However, a sharp decrease between 1995-2005
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