07Snow

07Snow - 10/18/2007 Topics ESM 203: Snow in the hydrologic...

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Unformatted text preview: 10/18/2007 Topics ESM 203: Snow in the hydrologic cycle Jeff Dozier and Thomas Dunne Fall 2007 Snow accumulation and runoff Energy balance of the snowpack Water fl W t flow Snow metamorphism and melt Implications for nutrient cycling in watersheds Long-term trends 3 Worldwide importance of the mountain snowpack Example: Merced River, Happy Isle in Yosemite Valley Barnett et al., Nature, 17 Nov 2005 1/6 of Earth's population relies on glaciers or seasonal snow for their water supply Peterson et al., USGS 4 ESM 203: Snow in the hydrologic cycle 1 10/18/2007 SWE (snow water equivalence) and mass balance SWE = s d (snow density depth) [kg m -2 ] = s ( z ) dz s ,n d n (layers) 0 0 d n Measurement of SWE and Snowfall (Divide by density of water to express as a depth equivalent) SWE = d s [m or mm] w = 1000kg m -3 Mass balance: SWE = Snowfall - Sublimation - Runoff Water balance: Runoff = Melt Storage 5 7 Manual measurement of SWE Automated measurement with snow pillow Map of pillows in Bales et al. 2006 6 8 ESM 203: Snow in the hydrologic cycle 2 10/18/2007 SnowSnow-pillow data for Dana Meadows (DAN) and Tuolumne Meadows (TUM) 1800 1600 1400 1200 SWE, mm 1000 800 600 400 200 0 2003 2005 2005 2003 DAN 1983 Example forecast, May 2003 Kings River below Pine Flat Reservoir, April-July unimpaired runoff (units are 1,000 acre-ft) acre ft) 50-yr mean Max Min This year % of avg 80% prob range 880 880 1090 TUM 1983 1,234 3,113 274 980 79% 10/01 11/01 12/01 01/01 02/01 03/01 04/01 05/01 06/01 07/01 9 11 Accumulation and ablation inferred from snow pillow data, Tuolumne Meadows (TUM) and Dana Meadows (DAN) Mesoscale/regional distribution Synoptic scale storms El Elevation i Topographic configuration 10 12 ESM 203: Snow in the hydrologic cycle 3 10/18/2007 Molecular structures of water and ice Ih Electron microscope photo of snowflake water Ice Ih (New York University, The MathMol Hypermedia Textbook http://www.nyu.edu/pages/mathmol/textbook/info_water.html) 13 From USDA snow microscopy 15 New snow Saturation vapor pressure 45 40 satu uration vapor pressure, mb water ice 35 30 25 20 15 10 5 0 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 temperature, C 14 16 ESM 203: Snow in the hydrologic cycle 4 10/18/2007 Saturation vapor pressure 10 Rimed new snow sa aturation vapor pressure, mb water ice 1 0.1 -40 -35 -30 -25 -20 temperature, C -15 -10 -5 0 17 19 Saturation vapor pressure (waterice) (water 0.30 Rime on chairlift 0.25 vapor pressure, mb 0.20 0.15 0.10 0.05 0.00 -40 -35 -30 -25 -20 temperature, C -15 -10 -5 0 18 20 ESM 203: Snow in the hydrologic cycle 5 10/18/2007 Can't measure Sublimation or Melt, so calculate via energy balance RN Net radiation H Sensible heat exchange L Latent heat exchange (energy used in evaporation) G Heat flow into/out of pack, direction T M Energy used in melting E Sublimation = L/[w(v+f)] Qm Melt = M/(w f) Dry snow M=0 RN = H + L + G + M Snow is a collection of scattering grains i Wet snow G=0, because T is uniform 21 Measurement of snowpack energy exchange (Sierra Nevada) Snow spectral reflectance and absorption coefficient of ice 22 ESM 203: Snow in the hydrologic cycle 6 10/18/2007 Net solar radiation 27 Snowmelt Runoff? Energy balance methods calculate surface melt rate accurately Still have to get it to the bottom of the pack Melt leads to local convergence of water near surface River Stage, ft Rain-onRain-on-snow event, Independence Creek near Truckee 7 6 5 4 3 2 1 0 12/25 12/28 12/31 1/3 1/6 1/9 1/12 1/15 Date, 1996-97 Depressions form because of enhanced metamorphism and settling Additional water flows into these depressions Development of "flow fingers" Process re-occurs in snowpack where impediments to flow exist (e.g., crusts) t) 26 28 ESM 203: Snow in the hydrologic cycle 7 10/18/2007 Rain on snow Melt source is condensation on the snow surface, not the rain itself h i i lf Compare specific heat of water with latent heats of fusion and vaporization e.g., 1 kg water at 1C releases 4.2103 J, enough to melt just 0.013 kg ice but, 1 kg of condensate releases 2.5 106 J, enough to melt 7.5 kg ice 75 The storm, not the rain, melts the snow But the rain helps develop the flow fingers 29 31 Snow metamorphism on the ground Depth hoar Typical snow pit Wet snow 30 32 ESM 203: Snow in the hydrologic cycle 8 10/18/2007 Saturation vapor pressure 10 Electron microscope photo of a bond between snow grains sa aturation vapor pressure, mb water ice 1 0.1 -40 -35 -30 -25 -20 temperature, C -15 -10 -5 0 33 35 Growth of grains by vapor diffusion & growth of bonds by grain boundary diffusion cold Molecular structures of water and ice Ih early warm late 34 water Ice Ih (New York University, The MathMol Hypermedia Textbook http://www.nyu.edu/pages/mathmol/textbook/info_water.html) 36 ESM 203: Snow in the hydrologic cycle 9 10/18/2007 Ionic pulse in laboratory and field lysimeter cross-section through flow finger A changing western snowpack? Concentration is highest at initial melt, and is higher in background wetting front than in flow fingers background wetting front 37 (Harrington et al., Hydrol. Process., 1995) Less snow? Earlier melt? 39 Service, R. F., As the West goes dry, Science, 20 Feb 2004 ESEM photo of impurities in snow Dust and algae 38 ESM 203: Snow in the hydrologic cycle 10 10/18/2007 Spectral reflectance of dirty snow and snow with red algae (Chlamydomonas nivalis) (Chlamydomonas nivalis) ESM 236, spring break 43 Radiative forcing concept Web pages California Cooperative Snow Survey p y UCSB Snow Hydrology Research Group Mammoth Mountain research site (near real-time data) Mammoth Mountain Ski Patrol (data, pits, photos) California snowmelt runoff forecasts (Bulletin 120) ESM 236 The Mountain Snowpack Snow crystal photos Patty Rasmussen & Ken Libbrecht Libbrecht, Caltech National Snow and Ice Data Center University of Colorado 44 ESM 203: Snow in the hydrologic cycle 11 ...
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