Engineering Class 5: Rainfall Abstractions Evaporation

1 Objectives Rainfall Evaporation: ET Overview and Outline Abstractions Mass Balance

Objectives Be able to: . Define “abstractions” . Distinguish between different types of abstractions . Use a mass-balance approach to quantify an abstraction

2 Objectives Rainfall Evaporation: ET Overview and Outline Abstractions Mass Balance

What are “abstractions”?

3 Objectives Rainfall Evaporation: ET Overview and Outline Abstractions Mass Balance

Pidwirny, M. (2006). "Intercepon, Stemflow, Drip, and Throughfall". Fundamentals of Physical Geography, 2nd Edion. Aug. 25, 2009. hp://www.physicalgeography.net/fundamentals/8k.html Objectives Rainfall Evaporation: ET Overview and Outline Abstractions Mass Balance • Interception: Rainfall which is intercepted by and evaporated from canopies or plant residue

• Depression Storage

• Evaporation

• Transpiration Objectives Rainfall Evaporation: ET Overview and Outline Abstractions Mass Balance

Thurow, T.L., W.H. Blackburn, S.D. Warren, and C.A. Taylor, Jr. 1987. Rainfall intercepon by midgrass, shortgrass, and live moes. Journal of Range Management 40:455-460. Objectives Rainfall Evaporation: ET Overview and Outline Abstractions Mass Balance ET Types . Free . Lake . Bare . Transpiration . Interception Loss . Potential ET --- This is one of our major goals! . Actual ET

Estimating ET from Lakes . Water Balance . Mass Transfer (covered in textbook nicely) . Direct Measurement (Pan, Eddy Correlation) . Energy Balance (covered in textbook nicely) . Combination – Energy and Mass Transfer (Penman)

7 Objectives Rainfall Evaporation: ET Overview and Outline Abstractions Mass Balance

Example Problem: Mass Balance Approach

Given a watershed with area =3000 mi2 with average annual (P)=44 in and average annual dischage = 2000 ft3/s, what is the annual evaporation?

Hint: consider all mass fluxes in and out, including evaporation (E), inflow (I), precipitation (P), outflow (O), seepage to groundwater (GW), and change in water stored in the watershed (storage, or ∆S). Now, simply balance these components: E=I+P-O- Gw-∆S. Given what information is provided, what assumptions must you make?

8 Rainfall Abstractions

. Interception . Depression Storage . Infiltration . Evaporation . Transpiration

Interception Demo

Materials: Two separate – preferably broadleaf and non-broadleaf Water spray bottle (fan may help!) Interception • Portion of precipitation that wets above-ground objects • function of: storm size, species age and density, season

Depression Storage • Portion of precipitation that is captured in surface depressions • function of: surface slope and other characteristics

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