Taking Measure: Determining the Representativeness of NRCS SNOTEL at a Basin-Wide Scale
Anne Nolin and Aimee Brown
Department of Geosciences, Oregon State University
Introduction
Continued population growth and development in the Pacific
Northwest of the United States and southwest British Columbia place
increasing pressure on already limited water resources in the
Columbia River Basin. In addition, uncertainties surrounding the
impact of global climate change on regional weather patterns and
conditions place further stresses on an already over allocated system.
In order to accurately plan for, and deliver, adequate supplies of fresh
water to the region, water managers must have access to
precise measurements of winter snowpacks in the river’s headwaters.
Historically managers in the Columbia River system have relied on the
USDA Natural Resources Conservation Service SNOTEL system to determine average snow water equivalence within the Columbia Basin. In
light of a changing climate, however, the efficacy and representativeness
of these measurements comes into question.
Objectives
t%FUFSNJOFUIFSFMJBCJMJUZPG4/05&-TJUFTJOSFQSFTFOUJOHTOPX
covered areas at a basin wide level
t"OBMZ[FTOPXBDDVNVMBUJPO[POFTJODPNQBSJTPOUP4/05&-TJUF
locations under an increasing temperature regime
t"DDPVOUGPSUIFSFQSFTFOUBUJWFOFTTPGDVSSFOUTJUFMPDBUJPOTBTUIFZ
relate to mean basin characteristics
Description of Data and Methods
t"NFUFSEJHJUBMFMFWBUJPONPEFM%&.
PGUIF64QPSUJPOPGUIF
Columbia Basin was constructed using elevation data from the
National Hydrography Dataset and a hydrologic unit code from the
U.S. Geologic Survey.
t#BTJOXJEFBSFBXBTDBMDVMBUFEBUFMFWBUJPOJOUFSWBMTPGNFUFST
and hypsometries derived from the total area within each elevation
band.
t4/05&-MPDBUJPOTXFSFNBQQFEVTJOH/3$4QSPWJEFEDPPSEJOBUFT
t4OPXDPWFSFEBSFBXBTEFSJWFEGSPNUIF1BSBNFUFSFMFWBUJPO
3FHSFTTJPOTPO*OEFQFOEFOU4MPQFT.PEFM13*4.
'PVSVOJRVF
snow classifications were determined using a binary tree developed by
/PMJOBOE%BMZ
t"UFNQFSBUVSFUISFTIPMEPG$XBTVTFEUPEFUFSNJOFTOPX
covered areas at risk of turning to rain given projected temperature
increases for the Pacific Northwest.
Results
Elevation within the U.S. portion of the Columbia River Basin ranges
GSPNKVTUBCPWFTFBMFWFMUPNPSFUIBONFUFSTBCPWFTFBMFWFMćF
Figure 1. U.S. Columbia River Basin Snow Covered Area. The use of PRISM data to classify
snow cover type allows for testing of the impact
projected temperature change may have on snow
packs in the U.S. portion of the Columbia River
Basin. Here, a 2.0º C temperature threshold was
used to determine areas of snow at risk of turning to rain, should projected ranges of temperature change occur. This threshold was determined
using snow climatology data from the National
Climatic Data Center Snow Climatology for the
region and the National Water and Climate
Center Snowpack Reports.
Figure 2. Hypsometric graph of
U.S. Columbia Basin. Plotting the
percent of the basin that is represented at different elevations helps
to create an image of the overall
shape and characteristics of the
basin. In the case of Columbia
River Basin, the elevation ranges
from about 10 meters above sea
level to over 4000 meters.
However, 93% of the land rests
below 2200 meters.
Figures 3. Graphics depicting snow
covered area within 200 meter elevation intervals, and the SNOTEL sites
at the given elevation. Climate
projections in the Pacific Northwest
indicate a warmer wetter region.
Implications may include an increased importance on higher elevation snow packs. Increasing the
ability of water managers to forecast
for water availabilty will require
increasing the ability of measurement
tools to accurately represent basin
wide conditions.
Discussion and Conclusions
4/05&-TJUFTJOUIFCBTJOBSFQSJNBSJMZMPDBUFEJOUIFMPXUPNJE
SBOHFFMFWBUJPOTXJUIBOBWFSBHFFMFWBUJPOPGNFUFST4OPXDPWFST
BCPVUPGUIFCBTJOJO%FDFNCFS+BOVBSZ'FCSVBSZ0GUIJTBNPVOU
JTBUSJTLPGUVSOJOHUPSBJOHJWFOB$UFNQFSBUVSFUISFTIPME
ćFNJEEMFBOEMPXFSFMFWBUJPOTPGUIFCBTJOBSFNPTUIFBWJMZSFQSFTFOUFECZ
SNOTEL. Average site elevation appears to rise traveling west to east across the
CBTJO"SFBTBCPWFNFUFSDPNQSJTFMFTTUIBOPGUIFUPUBMCBTJOBSFBBOE
receive no representation. As climate regimes change the placement of SNOTEL
locations will increase in importance.