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CE361 - Lecture 09

CE361 - Lecture 09 -...

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2/10/2009 1 http://www.ccrs.nrcan.gc.ca/ccrs/rd/apps/landcov/cchange/evapo_e.html Prepared by T. Wagener & P. Reed Penn State University Water Resources Engineering L 9 - Lecture 9 Hydrologic Processes 2
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2/10/2009 2 Content 1. Earth’s Energy Balance 2 E t i ti 2. Evapotranspiration 1. Water Balance Approach 3. Evaporation (incl. Measurement) 4. Evaporation Estimation 1. Evaporation Pan 3 2. Energy Balance Method 3. Aerodynamic Method 4. Combined Aerodynamic and Energy Balance Method CLOUD FORMATION PRECIPITATION * * * * * * * * SNOWMELT FROM EVAPORATION INFILTRATION IL OVERLAND FLOW SPRING INTERCEPTION WT RUNOFF WT DEPRESSION STORAGE FALLING RAIN FROM WET VEGETATION AND PUDDLES SOIL MOISTURE WATER TABLE (WT) TRANSPIRATION FROM SOIL FROM STREAMS AND OPEN WATER 4 Modified from Brutsaert, 2005. Hydrology . Cambridge University Press GROUNDWATER BASE FLOW IMPERMEABLE LAYER (IL) STREAM FLOW WT LAKE OR SEA
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2/10/2009 3 WHY DO WE CARE? 5 Why do we care? 6
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2/10/2009 4 Why do we care? 7 Why do we care? Calculating water losses to the atmosphere in hydrologic analysis and atmosphere in hydrologic analysis and design is important in water supply design , particularly reservoir design and operation . It is through the process of evaporation that the sun’s energy is introduced to drive th h d l i l 8 the hydrologic cycle.
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2/10/2009 5 http://earthobservatory.nasa.gov/Newsroom/MediaResources/Energy_Balance.pdf EARTH’S ENERGY BALANCE 9 http://upload.wikimedia.org/wikipedia/commons/0/0a/RHSGlasshouse.JPG Earth’s Energy Balance: Radiation R When radiation (e.g. emitted by the sun) strikes a surface, it is either reflected or absorbed. The fraction reflected is called the albedo α (0 α ≤ 1). The albedo of a deep water body is ~0.06, for fresh snow it is as high as 0.9. 10 Net radiation at the earth’s surface is the major energy input for evaporation of water. Feedback problem of climate change (ice melt)!
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2/10/2009 6 Earth’s Energy Balance: Emission Radiation emission is governed by the Stefan-Boltzman law where e is the emissivity of the surface, σ (sigma) is
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