{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture4 - Water Budget II Evapotranspiration P = Q ET G S...

Info icon This preview shows pages 1–14. Sign up to view the full content.

View Full Document Right Arrow Icon
Water Budget II: Evapotranspiration P = Q + ET + G + ΔS
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
Evaporation Transfer of H2O from liquid to vapor phase Diffusive process driven by Saturation (vapor density) gradient ~ ( ρ s – ρ a) Aerial resistance ~ f(wind speed, temperature) Energy to provide latent heat of vaporization (radiation) Transpiration is plant mediated evaporation Same result (water movement to atmosphere) Summative process = evapotranspiration (ET) Dominates the apportionment of rainfall ~ 95% in arid areas ~ 70% for all of North America
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Evapo-Transpiration ET is the sum of Evaporation: physical process from free water Soil Plant intercepted water Lakes, wetlands, streams, oceans Transpiration: biophysical process modulated by plants (and animals) Controlled flow through leaf stomata Species, temperature and moisture dependent
Image of page 4
Four Requirements for ET por Pressure Gradient Ener gy Wat er Win d NP TP
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
NASA 3850 zettajoules per year
Image of page 6
Energy Inputs Radiation Budget Rtotal = Total Solar Radiation Inputs on a horizontal plane at the Earth’s Surface Rnet = Rtotal – reflected radiation = Rtotal * (1 – albedo) Albedo (α) values Snow 0.9 Hardwoods 0.2 Water 0.05 Flatwoods pine plantation 0.15 Flatwoods clear cut ____ Burn ____ Asphalt 0.05
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Energy and Temperature The simplest conceptualization of the ET process focuses solely on temperature . Blaney-Criddle Method: ET = p * (0.46*Tmean+8) Where p is the mean daytime hours Tmean is the mean daily temp (Max+Min/2) ET (mm/day) is treated as a monthly variable
Image of page 8
Vapor Deficit – Drives the Process Distance between actual conditions and saturation line Greater distances = larger evaporative potential Slope of this line ( δ ) is an important term for ET prediction equations Usually measured in mbar/°C
Image of page 9

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Water Availability: PET vs. AET PET (potential ET) is the expected ET if water is not limiting Given conditions of: w ind, Temperature, Humidity AET (actual ET) is the amount that is actually abstracted (realizing that water may be limiting) AET = α * PET Where α is a function of soil moisture, species, climate In Florida, ~ α is unity for the summer, 0.75 otherwise ET:PET is low in arid areas due to water limitation ET ~ PET in humid areas due to energy limitation
Image of page 10
A Simple Catchment Water Balance Consider the net effects of the various water balance components (esp. ET) ET controlled by water availability and atmospheric demand The “Budyko” Curve Dry conditions: when Eo:P → ∞, ET:P → 1 and R:P → 0 Wet conditions: when Eo:P → 0 ET → Eo
Image of page 11

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Budyko Curve
Image of page 12
Wind With evaporation, boundary layer gets saturated This inhibits further evaporation UNLESS new air with a vapor deficit replaces Turbulence at boundary layer is therefore necessary to ensure a steady supply of undersaturated air
Image of page 13

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 14
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern