Difficulties in the Measurement and
Interpretation of High Elevation Climate Data
Because things change… and so does perspective!
What you see here….
Isn’t what you get here…
Up Front Information…
1.The Snow Survey Data Collection System was installed,
operated and maintained to be a relational system – NOT a
representative system.
The Congressional charge is: Measure snow
to predict seasonal water supply !
If a site does not correlate well with streamflow – its gone!
2. Because it is a relational data collection system, it has all
kinds of systematic bias in addition to random bias.
3. This presentation has a very narrow geographic domain,
Utah. This is my area of expertise, my data collection
system.
4. It does cast doubt on some analyses, results and
conclusions from other studies – and dang well it should!
Lets start with physical change…
Burts Miller Ranch
8
7
SWE - Inches
6
5
30 yr Avg
15 yr Avg
4
5 yr Avg
3
2
1
3
0
97
94
91
88
85
82
79
76
73
70
67
64
61
58
55
52
49
46
43
40
37
34
0
Significant decline starting in the early 1980’s, then
stabilization at a much lower level – why? – irrigation ponds,
ditches and a stream change in the mid 70’s…
Burts Miller Ranch - 1936
Note the open meadow and the height of the trees
Burts Miller Ranch – 2005 – note a subtle change… not
vegetation – topography! On the order of inches…
Possible impact from sub-surface irrigation –
late 70’s – 80’s started getting notes that
stated ‘water dripping from tube sample’…
“Cooperative
system –
many
partners”
Site moved
due to…
whatever –
like
“plowing”
1948 – first swe measurements taken
1957 – snow course moved
1964 – snow course moved again
1987 – snow course plowed
1988 – snow course moved once again
1988 – snow course transferred to NRCS from USGS
In the Utah
DCO, these
moves are
identified by
independent
station
names!
Yankee Meadows Snow
course – with the
stream re-routed
through the course…
Snow, perhaps more than other climate variables, is highly
susceptible to even small changes in vegetation: height,
width, density, composition, species, location, etc.
Imagine a forest ‘crown surface’ 80 years ago and how that
surface has changed – and how that change impacts snow.
Harris Flat – wind patterns thru the trees…. Pillow moved.
Trial Lake - Steel and Hypalon Pillows April 1 SWE
Hypalon
Steel
25
Inches of SWE
20
15
10
5
0
1997
1998
1999
2000
2001
2002
2003
2004
2005
Sensor Changes – Steel to Hypalon: 5% to
25% reduction of SWE!
1. All SNOTEL sites had Steel on original installation
2. Idaho, Montana and Wyoming went carte blanc to hypalon
in the early to mid 90’s, others as steel pillows fail. About
75% of the pillows on the San Juan are Hypalon.
3. There is a systematic SWE decrease in the SNOTEL data
due to sensor change – ranging from 5% to 25%. Changes
are more predominant at lower elevations.
Why is this important – hypalon pillows have decreased
SWE, later accumulation and earlier melt vs steel pillows! All
sensor related, not global temperature related!
Are snowpacks IN UTAH melting out earlier? 6 of the 10 early
melters have changes from steel to hypalon pillows…
Difference between meltout dates: the 80's minus the 90's
Above the 0 line, early melt, below 0 Line, later meltout
8
Avg difference in Days
6
4
2
0
-2
-4
-6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
SNOTEL melt out dates - 90's minus 2001-2007
Above the 0 line = earlier Melt
12
10
8
Days
6
4
2
0
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71
-2
-4
How much of this is drought related vs temperature
related? Lower snowpacks, less mass, less energy
required for melt – can we/should we distinguish between?
Transducer errors…
0.1 to 5.0 inches of
SWE
Hysteresis – same value going up as coming down? Do
sensors come back to zero? Physical phenomena? This
impacts melt out dates…
Offset Adjustments at Various SNOTEL Sites
6.0
5.0
4.0
Inches of SWE
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
Lets move to VEGETATION
CHANGE…
A “GROWING” concern… pun
intended! This issue is big and
is generally a SYSTEMATIC
downward driver…
Vegetation factors such as:
Height, density, type, distance, canopy, branching patterns,
etc can have a tremendous impact on snow accumulation.
Up to 40% less snow under a conifer forest than an open
meadow.
Up to 25% less under a conifer forest than an aspen forest.
Changing from brush to grass can decrease accumulations.
Redden Mine
30
SWE - Inches
25
20
30 yr Avg
15 yr Avg
5 yr Avg
15
10
5
3
0
97
94
91
88
85
82
79
76
73
70
67
64
61
58
55
52
49
46
43
40
37
34
0
Why do we think vegetation influences snow accumulation/ablation
besides the volumes of research quantifying it? – we can show specific
sample points impacted… at numerous sites.
Note this clearing – the 2 sample points here are statistically
different in current data than when it looked like this…
Garden City Summmit
30
SWE - Inches
25
20
30 yr Avg
15 yr Avg
5 yr Avg
15
10
5
No statistical difference between 90-05 and 39-48
3
0
97
94
91
88
85
82
79
76
73
70
67
64
61
58
55
52
49
46
43
40
37
34
0
Garden City Summit
Garden City Summit
Garden City Summit
Snow Course plotted against the SNOTEL site – clearly
observed is a decrease in SWE accumulation on the pillow
beginning in the early 90’s - due to ???
Brighton Snotel vs. Brighton Cabin
40
35
30
25
pillow swe
20
sc swe
15
10
5
0
1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
March 1 reading
Here is context – we got new neighbors,
they cut trees, cleared brush and
changed the snow accumulation
patterns.
Buckboard Flat
20
18
16
SWE - Inches
14
12
30 yr Avg
15 yr Avg
5 yr Avg
10
8
6
4
2
3
0
97
94
91
88
85
82
79
76
73
70
67
64
61
58
55
52
49
46
43
40
37
34
0
Buckboard Flat influenced by Vegetation change. Low latitude, 9000 ft. we
can compare this one to another site with less vegetation change…
Lasal Mountain Lower
16
14
SWE - Inches
12
10
30 yr Avg
15 yr Avg
5 yr Avg
8
6
4
2
3
0
94
97
88
91
82
85
76
79
70
73
64
67
58
61
52
55
46
49
40
43
34
37
0
Lasal Mountain Lower – low latitude, 8800 ft – why is this one not
decreasing since it is close to Buckboard Flat, more exposed and Lower?
So – no decrease in snow here – no tree type vegetation
change, nearby Buckboard flat has lost 25% of snowpack
and has massive vegetation change…
Here I would like to inferentially cast doubt on snowpack data
from other areas…
Utah is the second driest state (maybe the driest is some
sense) in the Union. Among many other things we can’t do –
we don’t grow trees and vegetation like other states!
Fish Lake
16
14
SWE - Inches
12
10
30 yr Avg
15 yr Avg
5 yr Avg
8
6
4
2
3
0
97
94
91
88
85
82
79
76
73
70
67
64
61
58
55
52
49
46
43
40
37
34
0
Fish Lake – Possible Vegetation Change – low elevation, high exposure, Cloud Seeding?
Lily Lake
Parleys Summit
30
SWE - Inches
25
20
30 yr Avg
15 yr Avg
5 yr Avg
15
10
5
Parleys Summit – no decline in snowpack…
3
0
97
94
91
88
85
82
79
76
73
70
67
64
61
58
55
52
49
46
43
40
37
34
0
Why is Mill D South declining… But Parleys, only 3 miles
distant and the same aspect and elevation is not?
Mill D South
30
20
30 yr Avg
15
15 yr Avg
5 yr Avg
10
5
3
0
94
97
88
91
85
79
82
73
76
67
70
61
64
55
58
49
52
46
40
43
0
34
37
SWE - Inches
25
Possibly because Parleys is right down this power-line with
very active vegetation management…
Someone built a 2 story house right on the northwest end
of the snow course – new trees growing.
Bryce Canyon
9
8
SWE - Inches
7
6
5
4
3
2
1
3
0
97
94
91
88
85
82
79
76
73
70
67
64
61
58
55
52
49
46
43
40
37
34
0
Why is Bryce Canyon, low elevation, low latitude not
declining in SWE – yet Trial Lake, high elevation, high
latitude is declining?
No change in vegetation…
3
0
97
94
91
88
85
82
79
76
73
70
67
64
61
58
55
52
49
46
43
40
37
34
SWE - Inches
Trial Lake
35
30
25
20
30 yr Avg
15 yr Avg
5 yr Avg
15
10
5
0
^ End
Marker
Pole
Trial Lake, 1936
Percent SWE Difference due to Conifer Encroachment
at Trail Lake
120%
100%
Percent
80%
60%
40%
20%
0%
-10
-5
0
5
10
15
20
25
30
35
Distance from Course
40
45
50
55
60
Conclusions on vegetation on 16 long term
snow courses in Utah –
1. If the site had significant vegetation
change – SWE is Declining
2. If the site has not had vegetation change,
SWE is Stable
SNOTEL sites will likely
be MORE vulnerable to
vegetation changes than
many snow course’s –
due to site location….
Many snow courses were
open and exposed and
vegetation changes took
many years – SNOTEL’s are
located to protect the $30K
instrumentation – often in
the trees out of sight…
Weather Modification
impacts on snow
measurement sites in
Utah – 50 and 100
mile radius from
generator sites.
A general 14%
increase for the
specific years of
operation in any
given area.
If you are looking for a 10% decline in SWE – that is within
measurement error at some sites… particularly low elevation.
Measurement Error (0.5 Inch/1.27 Cm) - as a
Percent of April 1 Average
14
12
Percent
10
8
6
4
2
B
ur
ts
m
ill
er
B
ra
uc
nc
kb
h
oa
rd
Fl
at
Fi
s
G
h
B
La
R
C
ke
M
ea
do
w
G
s
oo
se
be
H
rr
ob
y
bl
e
C
re
H
un
G
ek
ar
tin
de
gt
n
on
C
ity
H
or
se
sh
oe
M
ill
D
so
ut
La
h
sa
lL
ow
er
Pa
rle
R
ed
ys
de
n
M
in
e
Tr
i
a
Pa
lL
ng
ak
e
ui
tc
h
La
B
ry
ke
ce
C
an
yo
n
0
The total percent
change to the 19712000 average for
each site in Utah to
NORMALIZE the data.
Are we getting less snow? More Snow? –
statistically speaking No.
No detectable change in snow at this time.
Percent Deviation From Long Term Average of the Total
of 15 Snow Courses in Utah
120%
100%
80%
Percent
60%
40%
20%
20
05
20
02
19
99
19
96
19
93
19
90
19
87
19
84
19
81
19
78
19
75
19
72
19
69
19
66
19
63
19
60
19
57
19
54
19
51
19
48
19
45
19
42
19
39
19
36
-20%
19
33
19
30
0%
-40%
-60%
Studies that start in the early 1950’s and end in 2000 are prebiased to a declining snowpack conclusion….
Statistical comparison of observed April 1 SWE data
Station
Burts Miller Ranch
Buckboard Flat
Fish Lake
GBRC Meadows
Gooseberry RS
Hobble Creek
Garden City Summit
Huntington Horseshoe
Mill D South
Lasal Mountain Lower
Parleys Summit
Redden Mine
Trial Lake
Panguitch Lake
Bryce Canyon
Period
37-50
56-70
59-70
61-72
30-40
59-72
39-48
54-77
35-50
31-47
54-77
60-81
58-77
57-81
53-72
T-Stat
1.82
0.3
-0.74
0.6
-0.77
0.63
0.77
0.65
2.09
-0.04
0.28
1.21
0.64
-0.28
-0.82
T-Critical
1.71
1.7
1.71
1.71
1.71
1.7
1.71
1.69
1.7
1.7
1.69
1.69
1.69
1.69
1.69
Mean Change Significant
-1.5
yes
-0.6
no
0.9
no
-1.1
no
0.7
no
-1.1
no
-1.5
no
-1.2
no
-3.5
yes
0
no
-0.4
no
-1.8
no
-1.4
no
0.4
no
1.1
no
Statistical comparison of ADJUSTED April SWE data
Station
Burts Miller Ranch
Buckboard Flat
Fish Lake
GBRC Meadows
Gooseberry RS
Hobble Creek
Garden City Summit
Huntington Horseshoe
Mill D South
Lasal Mountain Lower
Parleys Summit
Redden Mine
Trial Lake
Panguitch Lake
Bryce Canyon
Period
T-Stat
T-Critical
Mean Change
Significant
37-50
1.00
1.70
-0.74
no
56-70
-1.07
1.70
2.47
no
59-70
0.71
1.69
-0.93
no
61-72
2.61
1.70
-4.52
yes
30-40
0.87
1.71
-0.74
no
59-72
0.67
1.70
-1.13
no
34-47
0.49
1.70
-1.09
no
54-77
2.59
1.68
-4.52
yes
35-50
1.38
1.70
-2.41
no
31-47
-1.07
1.70
1.47
no
54-70
-1.31
1.70
2.20
no
60-78
-1.75
1.68
2.91
yes
58-77
-0.68
1.68
1.47
no
55-62
-0.26
1.70
0.32
no
53-72
-0.52
1.69
0.67
no
Temperature Data:
Initial system could not
transmit temperature data
Added later:
Sometimes on the shelter
Sometimes on a tower
Various aspirators
Various thermistors
Mid 90’s standardization to
tower installation, 7, 17 or 27
feet, white aspirator and
extended range thermistor.
Mounted near top and offset on shelter, silver aspirator
Current installation – 5 to 6 feet from tower, white
aspirator, extended range thermistor
Why the switch to the extended range thermistor?
Because -30 was regularly exceeded which means that
for much of the historical record, minimums are not
accurate
Shelter Maximums are warmer…. Shelter minimums are
colder
Hewinta Average Minimum Temperature 85-99
on Shelter, 99-06 on Tower
Sensor on Shelter
Sensor on Tower
15
10
Degrees C
5
0
1
-5
-10
-15
-20
-25
16 31 46 61 76 91 106 121 136 151 166 181 196 211 226 241 256 271 286 301 316 331 346 361
Sensor change – YSI standard to YSI extended range: system
wide +1 degree C – mid 90’s- 2005.
The offending site…
among many, many such
sites…
Current temperature data collection status:
1. All sensors currently are mounted on meteorological tower
at 7, 17 or 27 feet and about 5 feet from the tower.
2. All sensors are currently extended range thermistors.
3. About 50% have white aspirators, the rest have the older
aluminum aspirators. We still have a ways to go to
completely standardize temperature data collection.
4. Almost all temperature data pre 2000 could have
significant bias due to mounting location – some would be
reasonably good if mounted on the tower.
5. Meteorological towers were installed starting in the mid
1990’s – standardizing all data collection at the snow
pillow.
6. SUMMARY – I WOULDN’T GIVE A TINKERS DAMN FOR
MOST OF THE DATA SET AT THIS POINT!
Growing vegetation will systematically bias this temperature
data set in future years. Big Flat is 1650 feet higher than MV.
Big Flat and Merchant Valley SNOTEL
Minimum Average Monthly Temperature
94 Big Flat 10,350 ft
94 Merchant Valley 8700 ft
10
Degrees C
5
0
Oct
-5
-10
-15
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Prior to the Trial Lake analysis - 64
sites in Utah – 48% of the total –
have had either significant
vegetative, physical or other impacts
that could negatively change snow
accumulation / ablation patterns.
This Figure is likely much too low
given the impacts quantified at Trial
Lake.
SWE to PCP ratios –
1.Since SWE is a driver, these little
“indicators” have ALL the systematic
problems associated with SWE Data!
2. And they have more! – lots more!
Perfect World… SWE=PCP, only the initial offset varies…
SWE/PCP Ratio - Initial Offset and SWE/PCP = 1
Offset 4
Offset 3
Offset 2
Offset 1
1
0.9
0.8
Ratio
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1
3
5
7
9
11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Time
-1
-2
-3
-4
-5
Date
92707
1E+05
21806
50105
71204
92303
1E+05
21402
42701
70800
91999
1E+05
21098
42397
70496
91595
1E+05
20694
41993
63092
91191
1E+05
20290
41589
62688
90787
1E+05
12986
41185
62284
90383
1E+05
12582
40781
61880
83079
1E+05
Ratio
Ben Lomond Peak Swe/Pcp Ratio - Individual Events
10
9
8
7
6
5
4
3
2
1
0
Ben Lomond Peak Daily SWE/PCP Ratios Above Average to
Below Average Accumulation Years
1997 SWE/PCP Ratios
2007 SWE/PCP Ratios
1.2
SWE/PCP Ratios
1
0.8
0.6
0.4
0.2
0
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Ben Lomond Peak Monthly SWE/PCP Ratios - High
Years VS Low Years
Low Snowpack Years
High Snowpack Years
1.2
Ratio - SWE/PCP
1
0.8
0.6
0.4
0.2
0
Nov
Dec
Jan
Feb
Mar
Apr
May
Ben Lomond Trail SWE/PCP Ratios - High SWE Years
and Low SWE Years
High Years
Low Years
0.9
0.8
SWE/PCP Ratio
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
nov
dec
jan
feb
mar
apr
may
Dills Camp SNOTEL SWE/PCP Ratio - High and Low
SWE Years
Low SWE Year
High SWE Year
1.2
1
Ratio
0.8
0.6
0.4
0.2
0
nov
dec
jan
feb
mar
apr
may
Little Grassy SNOTEL - SWE/PCP Ratio - High SWE
Years vs Low SWE Years
Low Years
High Years
1.20
1.00
Ratio
0.80
0.60
0.40
0.20
0.00
nov
dec
jan
feb
mar
apr
may
/2
00
8
/2
00
8
/2
00
8
/2
00
8
3/
4/
20
08
2/
26
/2
00
8
/2
00
8
3.5
3
2.5
2
8
1.5
6
1
4
0.5
2
Wind Dir 181
0
0
Wind
SWE/PCP Ratio
2/
19
2/
12
2/
5/
20
08
1/
29
1/
22
1/
15
1/
8/
20
08
1/
1/
20
08
SWE/PCP Ratio
SWE/PCP Ratio and Wind
Wind
14
Wind Dir 356
12
10
East Fork of Blacks Fork Precipitation Gage
East Fork of Blacks Fork Snow Course
19
61
19
63
19
65
19
67
19
69
19
71
19
73
19
75
19
77
19
79
19
81
19
83
19
85
19
87
19
89
19
91
19
93
19
95
19
97
19
99
20
01
20
03
20
05
20
07
SWE/PCP Ratio
East Fork of Blacks Fork SWE/PCP Ratio
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
SWE to PCP ratios
1. Insensitive to shortened SWE seasons
2. Very sensitive to drought
3. Sensitive to the number and magnitude of
events
4. Sensitive to wind and storm direction
General Observations:
1. No pattern of statistically significant
decreased SWE in the long term snow
courses using these statistical methods.
2. A presumed signature of Global Warming
(decreased snowpack at lower elevations
and southern latitudes) is not statistically
detectable from other influences in Utah’s
snowpack data at this time using these
techniques. Other researchers have found
decreased SWE.
3. Attributing a change (decrease/increase)
in snowpack accumulation/ablation
characteristics to a single specific cause is
difficult to statistically prove given the
natural variability of climate parameters
and the multiplicity of other influences
impacting snowpack in Utah.
4. This is precisely why we use 30 year
averages – to reflect CURRENT
conditions.
If you cant tell how fast your snowpack
is changing – or if it is changing due to a
specific influence…
How can you predict an outcome with
any degree of certainty?
Our Recommendation for Long Term Snow
Study in Utah
Station
Fish Lake
GBRC Meadows
Gooseberry RS
Hobble Creek
Huntington Horseshoe
Trial Lake
Panguitch Lake
Bryce Canyon
Elevation - Meters Latitude Longitude
2652
3049
2561
2262
2988
3037
2500
2440
38.50
39.30
38.78
40.18
39.61
40.68
37.70
37.63
111.77
111.45
111.45
111.38
111.30
110.95
112.65
112.17