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Iraq Project September 10, 2019 Sioux Falls, South Dakota

SSEBop ET Training Workshop. Welcome and Introductions. Iraq Project September 10, 2019 Sioux Falls, South Dakota. Outline. Why ET? Potential/Reference vs actual ET Review of in-situ measurement of ET PET Parameters. ET = Crop Water Use. Evapotranspiration =

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Iraq Project September 10, 2019 Sioux Falls, South Dakota

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  1. SSEBop ET Training Workshop Welcome and Introductions Iraq Project September 10, 2019 Sioux Falls, South Dakota

  2. Outline • Why ET? • Potential/Reference vs actual ET • Review of in-situ measurement of ET • PET Parameters

  3. ET = Crop Water Use Evapotranspiration = transpiration + evaporation Field Flux Tower Photo: Suat Irmak, UNL-Department of Biological Systems Engineering Landsat 8 Image: http://blogs.oregonstate.edu/inspire/2011/07/21/evapotranspiration/

  4. http://www.motherjones.com/environment/2014/02/wheres-californias-water-goinghttp://www.motherjones.com/environment/2014/02/wheres-californias-water-going Photos Credit: Almond Board of California

  5. Hydrologic cycle • Challenge with ET: • Gaseous state • Invisible • Only indirect measurement

  6. Why ET? • An important component of the hydrologic budget • ET = 62% of terrestrial rainfall • Involves the exchange of both mass and energy between soil/vegetation and atmosphere • Rn = ET + H + G • Directly related to plant biomass • Carbon budget • crop production monitoring • Irrigation water use and groundwater withdrawal • Land cover change monitoring

  7. Significance of ET • Depth, volume and rate (depth/time) important for designing: • Irrigation projects • Managing water quality • Predict snowmelt water yields • Flood control • Determine safe extraction from aquifers etc

  8. ET Facts Heating Curve for 1kg of water • ET requires a lot of energy More energy to change state (liquid to gas at 1000c, 2.45 MJ/kg) than to warm water from 00c to 1000c (0.45 MJ/kg) • ET involves a large amount of water movement in the landscape • 1 kg grain = 1000 kg of water http://www.physchem.co.za/Heat/Latent.htm#vaporization The diagram on the left shows the uptake of heat by 1 kg of water, as it passes from ice at -50 ºC to steam at temperatures above 100 ºC, affects the temperature of the sample. A: Rise in temperature as ice absorbs heat.B: Absorption of latent heat of fusion.C: Rise in temperature as liquid water absorbs heat.D: Water boils and absorbs latent heat of vaporization.E: Steam absorbs heat and thus increases its temperature.

  9. Global Water Budget… Ocean: E > P Land: P > ET ET = 63% of P Peixoto and Kettani, 1973 The Control of the Water CycleScientific American - Vol. 228 - pp. 46-61 Water Balance: Precipitation – Runoff – ET = 0 (annually) DS (daily, weekly, etc)

  10. ET is an Important Part of the Water Budget! (users ?) (users ?) (point/satellite) (gauge) Precipitation (P) – ET = River Flow (Q) + X +Recharge / -Withdrawal Climate Climate + Mang’t (LULC) ET P Important questions! Solutions require Knowledge of ET Q R/W

  11. ET Q Water Use Effort: For irrigation water use to estimate consumptive use. Water Budget Effort: Total ET as a component of the water budget. 12 digit HUC Watershed 460 (I) = 380 (ET) + 80 (G) But, P = 670 Recharge = 670 – 460-Q? = 210 - Q?

  12. ET components • Evaporation (from water and soil) • Water • energy and vapor press difference • Soil • Soil moisture and hydraulic conductivity • Transpiration (root-leaf-atmosphere)

  13. ET fractions during the growing season

  14. ET Processes • 1) A source of energy to supply the latent heat of vaporization: energy • 2) A concentration gradient in the water vapor: aerodynamics/advection • Provided by wind removal

  15. Evaporation vs boiling • Note that evaporation takes place at any temperature, and only at the surface of the liquid. • Boiling, on the other hand, only takes place at a definite temperature, and occurs within the liquid, as shown by the appearance of bubbles. http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/vappre.html#c3

  16. Depth vs Energy lET = Rn – H - G lET = Energy unit = (MJ/Kg)*(depth m) = MJ/m2 = MJ/m3 * m = MJ/m2 Latent heat of vaporization = 2.45 MJ/kg 1 kg of water = 0.001 m3 = 1 m x 1 m x 1 mm i.e, 2.45 MJ per m2 will vaporize 1 kg or (0.001 m, i.e., 1 mm) of water per m2 • 1 mm of water = 10 m3/ha •  0.001 m * 10,000 m2/ha 1m 1m

  17. ET measurement • Potential ET • Pan • Actual ET (direct and indirect) • Water balance (watershed scale): P - Q • Lysimeters (expensive but accurate) • Eddy covariance, Bowen Ratio • RS using energy balance methods, instantaneous

  18. Lysimeter Left and center, construction of the two large weighing lysimeters at KREC began in 1986. Each lysimeter consists of an underground chamber that houses a balancebeam weighing system with a rectangular “flower pot” measuring 6.5 feet wide by 13 feet long by 6.5 feet deep. Right, researchers enter the completed lysimeter. ET is determined by solving the water budget ET = P – Q – dS P = precipitation Q = discharge (runoff) dS = change in storage (weight change) http://californiaagriculture.ucop.edu/0502AMJ/pdfs/Lysimeters.pdf#search=%22lysimeters%22

  19. The Kearney lysimeters have been in constant use since 1987. One lysimeter measures water use in peaches, top, the other ‘Thompson Seedless’ grapes, bottom. The lysimeters have provided more accurate evapotranspiration values for peach trees and grape vines, information necessary in irrigation management decisions that ultimately affect plant health and fruit quality.

  20. ET estimation from climatological data • Seasonal • Blanney-Criddle • Temperature and sunshine hours • Hourly, daily • Potential/Reference ET • Penman (1948- combined energy and transport) • Penman-Monteith (included parameters for surface resistance) • Jasen-Haise (Radiation method, 5-day) • Thornthwaite (Temperature, monthly)

  21. The reference evapotranspiration, ETo, provides a standard to which: • evapotranspiration at different periods of the year or in other regions can be compared • evapotranspiration of other crops can be related.

  22. FAO 56: Crop ET

  23. FAO 56

  24. FAO 56: Crop ET

  25. Reference ET with Penman-Monteith

  26. FAO 56: Crop ET Characteristics of the hypothetical reference crop For the standardized reference ET Reference ET (ETo): (grass reference) http://www.kimberly.uidaho.edu/water/fao56/fao56.pdf Rns = Rs (1-0.23) (net shortwave) Rn = Rns – Rnl Rnl = DLWRF – ULRF; net longwave radiation is a function surface temp and back-emission from atmosphere

  27. Radiation Budget for ETo calculation Noah Molotch, 2010

  28. Surface Energy Balance Equation Rn - G - lET - H = 0 where Rn is the net radiation, H the sensible heat, G the soil heat flux and lET the latent heat flux. The various terms can be either positive or negative. Positive Rn supplies energy to the surface and positive G, lET and H remove energy from the surface. FAO 56: http://www.kimberly.uidaho.edu/water/fao56/fao56.pdf

  29. The Penman-Monteith form of the combination equation is: where Rn is the net radiation, G is the soil heat flux, (es - ea) represents the vapour pressure deficit of the air, ra is the mean air density at constant pressure, cp is the specific heat of the air, D represents the slope of the saturation vapour pressure temperature relationship, gis the psychrometric constant, and rs and ra are the (bulk) surface and aerodynamic resistances.

  30. Saturated Vapor Pressure for Water Saturated Vapor Density for Water Saturation vapour pressure shown as a function of temperature: e°(T) curve Saturation vapor pressure, es Slope of es w.r.t. to T

  31. Variation of the relative humidity over 24 hours for a constant actual vapour pressure of 2.4 kPa http://www.kimberly.uidaho.edu/water/fao56/fao56.pdf FAO 56

  32. Actual vapour pressure (ea) derived from relative humidity data • Relative humidity • The relative humidity (RH) expresses the degree of saturation of the air as a ratio of the actual (ea) to the saturation (e°(T)) vapour pressure at the same temperature (T):

  33. Standardized Reference ET, FAO 56 ETo reference evapotranspiration [mm day-1],Rn net radiation at the crop surface [MJ m-2 day-1],G soil heat flux density [MJ m-2 day-1],T mean daily air temperature at 2 m height [°C],u2 wind speed at 2 m height [m s-1],es saturation vapour pressure [kPa],ea actual vapour pressure [kPa],es - ea saturation vapour pressure deficit [kPa],D slope vapour pressure curve [kPa °C-1],g psychrometric constant [kPa °C-1], f(P). 900 = f(1/ra (1/208), gas constant (0.287 kJ.Kg-1. K-1), ratio of molecular weight of vapor to dry air (0.622), wind speed per day (86,400 s/day) g = ratio of air heat capacity to latent heat of vaporization (it varies little with T and P, so is considered a constant for a location). It relates vapor pressure to air temperature.

  34. Daily Global Product produced at EROS • https://earlywarning.usgs.gov/fews/datadownloads/Global/PET

  35. Senay et al., 2008. JAWRA

  36. GDAS: Generic Weather Forecast Process Observations Background (model) Information Gridded Analysis Every National Weather Service (NWS) forecast of more than six hours requires using environmental obs through Data Assimilation and Modeling (DAAM) Forecast Model Output GDAS for ETo Forecast Postprocessed Information Forecaster (NWS, commercial) Save Lives & Property Weather-Sensitive Commerce ($2+ T) Communications, Dissemination

  37. Observed data comes from various sources:

  38. Weather Ships: background • A typical weather patrol was 21 days on-station plus enroute time and about 10-days in port.  Four or five U.S. Weather Bureau observers joined the Coast Guard crews during each voyage.  A “station” was a 210-mile grid of 10-mile squares each with alphabet designations.  The center square, which the ship usually occupied, was “OS” (for “on-station”).  A radio beacon transmitted the call sign of the station and the square in which the ship was located.  Overflying aircraft would check in with the ship and receive its position, course and speed by radar tracking, and weather data.  Surface weather observations were made and transmitted every three hours; and upper winds every six hours by radar tracked balloons with a known ascension rate.  Using radiosonde transmitters and radar tracking, air temperature, humidity, pressure, wind direction and speed were obtained every twelve hours to elevations up to 50,000 ft. • http://www.uscg.mil/History/webcutters/rpdinsmore_oceanstations.html

  39. Close up of a hydrogen filled balloon at Cambridge Bay Upper Air station, Nunavut, Canada Rawinsonde weather balloon just after launch. Notice a parachute in the center of the string and a small instrument box at the end. After release it measures many parameters. These include temperature, relative humidity, pressure, and wind speed and wind direction. This information is transmitted back to surface observers. http://en.wikipedia.org/wiki/Weather_balloon

  40. GDAS parameters

  41. Challenges with Global ETo • Coarse resolution is limiting on complex topography (~100 km) • Proposed soln: apply site specific correction or use locally available ETo data for correction.

  42. Daily Global GDAS ETo for July 2004 6-hr weather forecast data from NOAA: Radiation, temp, wind, RH and pressure to solve the standardized P-M Equation • https://earlywarning.usgs.gov/fews/datadownloads/Global/PET

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