Bibliography: page [9].OWRR Project A-002-COLO; grant nos. 14-01-0001-553, 726, 900, 1074, 1625

Dils, Robert E.

Froehlich, Henry A.

Meiman, James R. (James Richard)

English

OWRR Project A-002-COLO; grant nos. 14-01-0001-553, 726, 900, 1074, 1625

Meiman, James R. (James Richard), author

Froehlich, Henry A., author

Dils, Robert E., author

Natural Resources Center, Colorado State University, publisher

Mountain Scholar (Digital Collections of Colorado and Wyoming)

     SNOW ACCUMULATION IN  RELATION TO FOREST CANOPY  by  J. Meiman, H. Froelich and R. E. Dils      Completion Report No. 3      Gf3 6 <:Ctt,n i) .3) ('CJlorR,.q;J •(;011ins.St8te VniVArsity, FortNatural ?esources('e: .I-,er.~o~:leti~n Report series. no. 3SNOW ACCUMULATION INRELATION TO FOREST CANOPYPartial Completion ReportOWRR Project A-OD2-COLOTITLE: SURFACE WATERJune 30, 1969byJ. Meiman, H. Froehlich and R.E. Di1sDepartment of Recreation and Watershed ManagementColorado State Universitysubmitted toOffice of Water Resources ResearchU. S. Department of InteriorWashington, D. C.Covering research under Agreements14-01-0001-553, 726, 900, 1074, 1625authorized by PL 88-379, Title I, Sec.lOOduring FY 1965 through FY 1969LIBRARIESCO;~:_A~n ~"'\TE UN'VF:R~,nNATURAL RESOURCES CENTERColorado State UniversityFort Collins, Colorado'Norman A. Evans, DirectorABSTRACTSNOW ACCUMULATION IN RELATION TO FOREST CANOPYMaxtmum snowpack water equivalent is measured at 123 points in thespring of 1966, 1967, and 1968. These points are distributed overthree transects within a 4 square mile area in the Colorado Front Range.The north-facing slope ranges in elevation from 2900 to 3300 meters coveredby Picea engeZmanni and Abies Zasiocarpa at the upper elevations andPinus contorta at the lower. Water equivalent increases an average of42 rom/IOO m although only 28% of the total variance in water equivalentis associated with elevation. Forest cover measured by a Lemmon sphericaldensiometer within a cone of 1140 is significant in only one of the threeyears. Neither crown cover by compass quadrants, crown cover within acone of 21°, nor timber stand size classifications improve on the 1140Cone canopy measurement in explaining snow accumulation variability.Individual points vary widely in their relative accumulation from yearto year; the coefficient of determination for 1966 versus 1968 waterequivalent is only 25%. Snow water equivalent versus snow depth gives rvalues of 0.86, 0.90, and 0.73 for the three years respectively.Meiman, J., H. Froehlick, and R. E. OilsSNOW ACCUMULATION IN RELATION TO FOREST CANOPYPartial Completion Report to Office of Water Resources Research,Department of Interior, June 3D, 1969, 8 p.KEYWORDS -- snowl snowfall! *snow managementl *snow pack/SNOW ACCUMULATIO~ IN RELATIO~ TO EL~~ATION AND FOREST CANOPYJ. Meiman, H. Froehlich, and R. E. Di1sl/IntroductionThe weakest link in understanding the snow hydrologic cycle inmountainous terrain is probably the lack of knowledge of the arealdistribution of the snowpack. The objective of this study is toassess the association of maximum snowpack water equivalent withelevation and forest canopy in a Colorado Front Range watershed.There have been a number of similar studies in various geographicregions of the United States and Canada and many of these have beensummarized in a separate paper (Meiman, 1968)l/. These studiesgenerally have shown an increase in the water equivalent of the snow-pack at the time of maximum accumulation with increases in elevationand canopy opening. Results from these studies suggest great varia-bility in the factors influencing snow accumulation between and withingiven physiographic-climatic boundary conditions. Thus the effectsof elevation and forest canopy must be considered as components of acomplex of factors including air mass characteristics, large scalephysiography, and local relief.Study Area and ProcedureDuring the summer of 1965 three transects compriped of a total of123 observation points were established on a 10.4 km2 area in the UpperLittle Beaver watershed in the Colorado Front Range (Figure 1). Theseare not random samples but rather the transects were positioned to samplethe timbered portion of a generally north facing slope on which timberharvest was under consideration. The study area is about 24 km east ofthe Continental Divide. Elevation of the observation points ranges from2,900 to 3,300 meters. The area often is subject to very strong windsduring and after snowfalls. There is very little opportunity for snow-melt during the accumulation season.The alpine zone is located upwind from the timbered study area andconstitutes a snow contributing area. There are other smaller openareas resulting from fire within the timbered study area and the largerof these are designated on Figure 1. The timber is a combination ofspruce (Picea engelmanii) and fir (Abies lasiocarpaJ at the upperelevations and lodgepole pine (Pinus contortaJ with some intermixedaspen (Populus tremuloidesJ at the lower elevations. The forest coveris very heterogenious relative to age, stand density, and spatialdistribution. This situation is fairly typical of Colorado Front Rangeconditions.17~/Associate Professor, research assistant, and Associate Dean, Colo.State Univ., College of Forestry and Natural Resources. Researchsponsored by USDI-OWRR.Paper presented at National Workshop Seminar on Snow Hydrology atFredericton, New Brunswick, February, 1968.-2-T~e average height of the trees in the spruce-fir type is about15 meters and the avera~L' crown cover 44%. Averages for the lodgepolepine are 11 meters and 44% respectively .. Basal area for bach foresttypes is approximately 30.8m2/ ha (134 ft. 2/Ac.).Snow depth and water eq~ivalent w~re taken each spring, 1966through 1968, at a time judged to be near the maximum snowpack waterequivalent. Actual dates of sampling were 4/16/66, 4/8/67, and 3/27/68.Federal snow samplers were used. All samples were taken approximately30 em down hill from the marker pole. If a fallen limb or obstructionwas encountered sampling was repeated until the ground surface was reached.The stations were approximately 60 meters apart along the transects andwere designated by poles extending 2 to 2~ meters above ground.Timber stand measurements included species identification, basalarea, and crown cover. The forest stand about each point was classifiedinto U. S. Forest Service timber stand categories. Crown cover estimateswere made with a Lemmon Type A spherical densiometer; the crown covermeasured was6(1) that portion of the canopy appearing within a conehaving a 114 arc with measurements recorded for each quadrant centeredabout one of the four cardinal directions, and (2) within a cone of 21 0arc.ResultsThe results of the regression analyses are tabulated in Table 1.Figure 2 illustrates the large variability in water equivalent existingwithin 60-meter elevation zones and Figure 3 is a plot by years of thegeneral increase in maximum snowpack water equivalent with elevation.The lack of any relationship between stand size classification and waterequivalent is illustrated in Figure 4. A summarization of the datapresented in the tables and graphs and from the statistical analysisindicates the following relative to maximum snowpack water equivalenton the study area:1. A very large year-to-year variation in the relative values ofindividual points.2. A highly significant increase with elevation in all yearsaveraging 42 mm/10Om (5.04 in/lOOO ft).3. Elevation is associated with only 28% of th~ total variance.4. Crown cover as measured in a 1140 arc is significant in oneyear only.5. Crown cover by qu~rants corresponding to the four cardinaldirections does not improve the correlation.6. Crown cover as measured in a 210 arc does not improve thecorrelation.7. Timber stand size classifications as delineated by standardU. S. Forest Service procedures are not significant.8. Snow depth is very highly correlated.DiscussionPerhaps the most striking finding of the study is the low R2values associated with both '21evation and crown cover relative tomaximum snowpack water equivalent. Still more discouraging is thefailure of given points to reflect a consistent year-to-year accumu-lation relative to other points. It is not uncommon for a given point-3-to be 20 to 30% below the average far its 60-meter elevntion zone inone year and as much above the next yeuT; ma.ny points nave even greatervariation. This ~ould suggest a 13rge influence of the interaction ofwind patt~rn and snO\J aVdilability on ac~umulation at any given location.Snow availability here might mean not only the total initial snowfallbut also the opportunity for redistribution from tree crO~l and openareas exposed to ~ind action.Because of the ?oQr correlation oetween a standard 114 0 anglemeasurement of Qrown cover and maximum water equivale.nt it washypothesized that either a larger area or a smaller area of measurementmight be better. A larger-area-look was gained by using a timber standclassification as illustrated in Figure 4. There is no apparentconsistent relation between stand classification and water equivalent.A sroal1er-area-look was made by reducing the viewing angle with thedensiometer to 21°. Again as illustrated by the R2 values in Table 1there was no improvement. This was true even when eight of the obviouslypoor measurements were dropped from the analysis. It must thus beconclude~ that crQ~n ~ov~r is either not v~ry important for the conditionsstudied or that we are not measuring it correctly, i.e. as the snow"sees" it.An encourag~ng finding of this study is the relatively highcorrelation between snow depth and ~ater equivalent. This is especiallyimportant relative to the possibility of aerial observation of snow depthand then relating depth to water eqUivalent. The relatively low R2 valuefor 1963 can be explained by the fact that the 1968 measurements were theearliest of the three years with respect to snowpack-ripeness f hence thelarge variation in snowpack density.There are three areas of investigation that seem to have promise asindicated by these results. One approach is to charactetize the forestcanopy from above rather than from below. A second approach wouldinvolve a systematic analysis of local snow source areas~ Both of thesepossibilities are currently being explored utilizing large scale (1:6000)photographic analyses on a Kelsh plotter. A third effort currentlyunderway is an examination of 700 rob wind velocities during and aftermajDr snowfalls. Perhaps an even more fruitful study of ~ind effectscould b~ made on a physical model of the watershed ~n the wind tunnel.ConclusionsAlthough elevation and crown cover are significantly related tomaximum snDwpack water equivalent on the study area th~se two factorscombined can be associated with only 32% of the variance in waterequivalent averaged for the three years. It would appear that a betterway of describing the forest canoPY3 an evaluation of the role of localsnow contributing areas, and an analysis of wind conditions are needed topredict snow accumulation more accurately.Table 1. Results of Regression Analyses.Independent Variables Dependent Number of R2 Standard ErrorVariable Observations of Estimate1966 wFl./ 1967 WE 123 .48** 70mm1966 WE 1968 WE 123 .25** 1051967 WE 1968 WE 123 .44** 91Elevation 1966 WE 123 .18** 86" 1967 WE 123 .16** 90" 1968 WE 123 .28** 103" Avg. WE 123 .28** 77Crown Cover (1140 ) 1966 WE 123 NS" 1967 WE 123 .06* 95" 1968 WE 123 NSElevation) Crown Cover(1140 ) 1966 WE 123 ·fO** 8711 1967 WE 123 .21** 87" 1968 WE 123 .30** 102Avg. WE 123 .32** 75Elevation) Crown Cover(21 0 ) 1966 WE 115 .16** 84" 1967 WE 115 .19** 87" 1968 WE 115 .26** 104Snow Depth 1966 1966 WE 123 .74** 44It 1967 1967 WE 123 .80** 43" 1968 1968 WE 123 .54** 83Basal Area Crown Cover(114°) 123 .58** 9%Crown Cover (114 0 ) Crown Cover(21 0 ) 115 .52** 12%l/ WE = Water Equivalent of snowpack near time of maximum* Significant at 0.05 level** Significant at 0.01 levelIT8N~ --- .T TNLEGEND11/~ GOQ,nQ StO',on.0F1, Sprue. F,r Ar.o,<,.l P '.I Ladll.pof. P,n, Ar"_. _." Wellr,h'd Boundary~~-:: OrOln09'<,-._.,---.--....-I .... """<;10,460-....~ /co~LP-'--.~-.-I /;/9{~"'O\i //%/~\J:t<') .rl'--,I'-crla/"II10,466' /'·-x- r --... . __ ·"-..,. .>.--/--?~, Ir L p ~ SF 1)Sf . U'J LP~~.) I """ '-./j ._---~~/Alp,ne/\Wal.ralledNII[--~ -· ·-0]-_D.ny"COLORADO- ,,---_. ---_._'--.I /1'/..f ~»>:/./ 1;-'• Alp,n, I-A/ /',,,, ///.:;J CROWN (//:-,. IPOINT / f\,,463 /./~ II\\ \)_.-......1Figure I. Upper portion of little Beaver Watershedin Roosevelt Notional Forest, Colorado.o 1/4 1/2 3/4 , •• '.~ E"""?"+"?'3:=.=J3300 meter.10800 fit'3250106003150.,.I:~r10200 10400Elevation31003050'0000300098002950960010029005:IE Figure 2. Range of Water Equivalents I9 1966'5 e.~Within Elevatian Zones I 196725~600 • ~ 1968_ 20 1-500c•0>~0'llJ .- 400~15•0~30010200Figure 3. Snow Pack Accumulation Variation by Elevation Zones and YearII'•~..J eg I E300,Pr: 0 529 **Y :-43.72 +5.04 {IOOOff.el • ..,}(Inch.s)Y : - I I 10 + 42 ( 100 meter$)(mm)I/(alb/·~//'Z--A'!Jri.;/o;, " ....""...... .....;';' .....f'(/ ...... - _..L:.r: 'fr----////////:i,.. /--- /--lJ.10...C4U 1- 2000>:)trW'-..-0~5I100mtterl9500 9700 9900 10tOO 10300Elevati on Zones10500 10700 10900 ftetFigure 4 Distribution of Snow Pock by Tree Size Class and Elevation1967 Maximum Snow Pock127- 2 18 mm~ 9A:. SmoH Sawhmber~ 219-5311T11'l",• 8: Pol.Stand Size Cion Tree S'I@o 7: S••dllnQ, SOPl,nQ < 127 m/TI3002o , 1° .. 'h'III•1:1£~ E1210-c:CD'0>:; 8-1- 200CTw~CD-0~ 6c:0CD~4 -J-,OO2930to29902990to30503050to3"03110to31103110to32303230to meter,3290PUBLICATIONSMeiman, James R., Snow accumulation related to elevation, aspect, andforest canopy, National Workshop Seminar on Snow Hydrology, CanadianNational Committee on Snow Hydrology, Fredericton, New Brunswick,Feb. 1968, 8 p.Froehlich, H., Snow accumulation in relation to elevation and forest canopy,Ph.D. dissertation, Colorado State University, 1969, 50 p.

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