Lecture 9 -...

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http://www.ccrs.nrcan.gc.ca/ccrs/rd/apps/landcov/cchange/evapo_e.html Prepared by T. Wagener & P. Reed S t t U ii t Penn State University Water esources Resources ngineering Engineering ecture 9 - Lecture 9 1
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ydrologic Processes Hydrologic Processes 2
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ontent Content . arth’s Energy Balance 1. Earth s Energy Balance 2. Evapotranspiration . ater Balance Approach 1. Water Balance Approach 3. Measuring Evaporation vaporation 4. Evaporation 1. Evaporation Pan 2. Energy Balance Method 3. Aerodynamic Method 4. Combined Aerodynamic and Energy Balance 3 Method
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CLOUD FORMATION PRECIPITATION * * * * * * * * EVAPORATION WT SNOWMELT RUNOFF FROM FALLING RAIN FROM WET INFILTRATION IL OVERLAND FLOW SPRING INTERCEPTION DEPRESSION VEGETATION AND PUDDLES TRANSPIRATION ROM FROM STREAMS ND WT SS O STORAGE SOIL MOISTURE WATER TABLE (WT) FROM SOIL AND OPEN WATER WT GROUNDWATER BASE FLOW STREAM FLOW LAKE OR 4 Modified from Brutsaert, 2005. Hydrology . Cambridge University Press IMPERMEABLE LAYER (IL) SEA
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hy do we care? Why do we care? 5
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hy do we care? Why do we care? 6
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hy do we care? Why do we care? • Calculating water losses to the 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 the hydrologic cycle. 7
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arth’s Energy Balance: Radiation 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. et radiation t the earth’s surface is the major energy input for evaporation of water 8 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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arth’s Energy Balance: Emission Earth s Energy Balance Emission Radiation emission is governed by the Stefan-Boltzman w here the missivity f the surface igma) is law where e is the emissivity of the surface, σ (sigma) is the Stefan-Boltzman constant [5.67 x 10 -8 W/m 2 *K 4 ), and T p is the absolute temperature of the surface in degrees Kelvin (degrees C plus 273).
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This note was uploaded on 04/11/2008 for the course C E 361 taught by Professor Reed,patrickmichwalters,geoffrey during the Spring '07 term at Pennsylvania State University, University Park.

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Lecture 9 -...

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