Snow Cover in the Eastern Sierra Nevada: Year-To-Year
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North Palisade Peak SNOW COVER IN THE EASTERN SIERRA NEVADA: Big Pine Creek YEAR-TO-YEAR VARIATION AND POSSIBLE 1981-present EFFECTS ON INSECT POPULATIONS John Smiley University of California •Air temps recorded year round White Mountain Research Station •Cup shields radiation from above but not below ABSTRACT Using an 11-year temperature record from underneath the canopy of Sierra Willow bushes (Salix orestera) at multiple •21 “core” sites 11 years’ data sites in the Eastern Sierra Nevada, ranging from 2689-3544 meters above sea level in 8 different drainages, I determined the seasonal •Now over 40 sites timing of snow cover and snowmelt for each site. After fitting a linear regression model which factors out year to year variation in •Full data set on web ftp site Bishop Creek overall snow cover, the relationship to altitude became highly significant, with snow cover lasting approximately 13 days longerfor •Filtered and cleaned data set daily 1988-present each 100m elevation. I then used the year-to-year variation factor as an “relative snow cover index”. Plotting this index alongside max, min, and average the altitudinal range of the Willow Leaf Beetle Chrysomela aeneicollis revealed that years with reduced snow cover were often followed by extinction of low-altitude beetle populations. The most likely explanation for this is that reduced snow cover exposes the insects to more severe winter cold and/or desiccation. This suggests one mechanism by which these insect populations have been forced to move upward to higher elevations in the past decade. Days of 20 snow cover 10 0 Temp (°C) Rock Creek 3600 1988-present Combined plot of: 3400 -10 3200 •Annual altitudinal range of Willow 3000 Y 2800 -20 Leaf Beetle Chrysomela aeneicollis, Elevation color bands: 2600 Insect altitudinal range, 07/01/200809/01/2008 11/01/2008 01/01/2009 03/01/2009 05/01/2009 07/01/2009 09/01/2009 11/01/2009 4000-4250m light gray Date 3750-4000m light blue •Relative snow cover 2400 Big Pine Creek Temperature record inside willow 3500-3750m blue 2200 3250-3500m blue-green 1980 1985 1990 1995 2000 2005 Shrub – Saddlerock Lake, 3300m, 3000-3250m green •Percent average annual precipitation year 100 Bishop Creek drainage, 2008-09 2750-3000m yellow-green for Owens-Mono region Y lowestm hgihestm 2500-2750m tan 75 Relative snow cover 2250-2500m light tan 50 6-8 year drought 2000-2250m yellow Note that 2 out of 3 low snow cover years were followed by beetle range snowdays 25 contraction the following summer 0 -25 1980 1985 1990 1995 2000 2005 1999 2003 2007 200 year 250 250 250 Mono-Owens precipitation 150 200 200 200 150 150 150 100 #days #days #days 100 100 100 normal% of mono-owens index mono-owens 50 50 50 50 0 0 0 2600 2800 3000 3200 3400 3600 2600 2800 3000 3200 3400 3600 2600 2800 3000 3200 3400 3600 1980 1985 1990 1995 2000 2005 elevm elevm elevm Snow cover days as affected by year elevation, in 11 different years 220 2000 2004 2008 210 250 250 250 200 190 200 200 200 180 150 150 150 170 160 #days #days 100 100 #days 100 150 50 50 50 140 regional precipitation vs snow cover index 130 0 0 0 2600 2800 3000 3200 3400 3600 2600 2800 3000 3200 3400 3600 2600 2800 3000 3200 3400 3600 120 y = 0.4974x - 12.272 elevm elevm elevm 110 2 100 2006 R = 0.4429 90 80 120 days under snow 70 2005 60 100 2001 2005 2009 50 2008 40 250 250 250 1999, 2000, 2003,2009 30 80 200 200 200 20 2002 10 150 150 150 0 2004 60 #days #days 100 100 #days 100 -10 2001 -20 2007 50 50 50 40 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 0 0 0 2600 2800 3000 3200 3400 3600 2600 2800 3000 3200 3400 3600 2600 2800 3000 3200 3400 3600 altitude (m above sea level) elevm elevm elevm 20 snow cover idex Average slope ~ 13 days for each 100m elevation ~ 40 days for each 1000’ of 0 elevation. Y-intercept arbitrarily chosen at X = 2688m, used to create “relative snow cover” variable. For example, the “relative snow cover” -20 2002 2006 250 250 variable for 2006 is 101 while that for 2007 is -17 Days of snow cover varies from -40 200 200 year to year. Relationship between 0 50 100 150 200 150 150 days of snow cover and altitude is #days #days % of annual mean precipitation 100 100 relatively constant (about 0.13 50 50 days/m elevation) in later years 0 0 2600 2800 3000 3200 3400 3600 2600 2800 3000 3200 3400 3600 when a longer elevational transect Acknowledgements: I thank “team beetle” in all its The relationship between relative snow cover elevm elevm was included. manifestations over the years, particularly my colleagues variation and annual precipitation is significant Nathan Rank and Elizabeth Dahlhoff. (p<0.025) but variable (standard error ± 18 days)..