The Science Behind Measuring Depletions

Transcription

1 The Science Behind Measuring Depletions 1 The Science Behind Measuring Depletions Salim Bawazir, New Mexico State University Salim Bawazir is Associate Professor in the Civil Engineering (CE) Department at NMSU. He joined NMSU s CE Department as Assistant Professor in 3. He holds BS, MS and doctorate in CE () from New Mexico State University, with a minor in environmental management. He also holds a BS in agricultural engineering from NMSU. He teaches undergraduate and graduate courses in water resources engineering related fields. Salim s research is primarily in the area of water resources (hydrometeorology). He has authored and co-authored several peer-reviewed journal articles, proceedings, book chapters, technical reports, monographs, and over poster and oral presentations. He has more than 15 years of field experience in instrumentation and measurement of evapotranspiration from agricultural crops, riparian vegetation, and evaporation from reservoirs. Major component of hydrologic cycle Considered as a loss in Hydrologic Budget ET information is used for: Hydrologic and water resources planning Water management and allocation especially in water-scarce regions (e.g. NM) Water resources operation models Weather and climate change forecasting models Negotiating compacts and treaties involving water etc. Slide 1. Measuring Depletions Slide 3. Why Evapotranspiration (ET)? Evapotranspiration Evaporation Open water such as lakes, reservoirs, rivers, vegetation, ground surfaces, etc. Transpiration Removal of water from the soil by plant for building tissues and released from the leaf s interior into the atmosphere by evaporation. Time of year From day to day Daily Flux Totals (MJ/m^) RA Rso Rs Q H LE G DOY (1999) Equivalent Depth (mm) Slide. Evaporation and Transpiration Slide 4. Daily Fluxes Varies Widely 61 st Annual NM Water Conf., Where Does All the Water Go? History, Hydrology & Management of NM s Scarce Waters

2 Salim Bawazir Measured crop Climate Station Reference Crop Kc = ET/ETr 9.48 ( Q G) + γ U( es ea) ETr = T γ ( U ) ASCE Standardized Equation Slide 5. Traditional Method of Estimating Evapotranspiration (ET) Slide 8. LiDAR (Raman Water-Vapor Lidar) on a Trailer (in the back) LIght Detection And Ranging - LIDAR (Raman Water-Vapor Lidar) Error % - 6% Heat Pulse Technique (Transpiration) Lysimetry Lysimeters (extensively used to provide baseline information for other ET methods) Error 5 to 4% Measure the change in soil water over a period of time Slide 6. Alternative ET Methods Slide 9. Transpiration Measurement Using Heat Pulse Technique Micrometeorological methods (Bowen Ratio Energy Balance, Eddy Covariance..) LE = (Rn-G)/(1+β); H/LE Scintillometers Measures small fluctuations in the refractive index of air caused by temperature, humidity, and pressure induced variations in density (Optical Transmitter and receiver) Measures sensible heat flux only; Error 1 to 5% Remote Sensing Gas Exchange Stomata Conductance Class A Pan ET is determined by measuring change in soil water over a period of time (gravimetric, electromagnetic devices based on dielectric and capacitance, time domain reflectometry, etc.) Needs Calibration Works well in course soil ERROR 1% 3% for person working outside their specialty area can be as high as 7% Slide 7. Alternative ET Methods - Continue Slide 1. Evapotranspiration Based on Measurement of Soil Moisture November 5-7, 16

3 The Science Behind Measuring Depletions The Energy Budget: Q G = H + λe Net Radiation Sensible Heat Q Soil Heat Latent Heat H λ E ( ET ) Land Surface G Slide 11. The Energy Budget Equation Slide 14. Vertical Wind Speed Measured at High Frequency Satellite-based ET data are best estimates of radiative and aerodynamic processes viewed from space. Not Measurement Methods: inverse calibration modeling at extreme conditions (dry wet) Lag time (e.g. Landsat every 16 days) precipitation effects, irrigation; bias in seasonal estimates combination of satellite and ground measured values Potential bias in albedo and surface temperature- calibration is needed vegetation indices (use crop coefficient as a function of NDVI) Satellite have a view angle that is directly overhead (nearly nadir) other Aerodynamic exchanges in narrow vegetation systems; etc. ERROR 1% 4% Slide 1. Satellite-based ET Energy budget :- Slide 15. Ambient Temperature Measured at High Frequency Rn - G = H + LE w (m/s) Where: Rn = Net radiation (MJ/m²) G = Soil heat flux (MJ/m²) H = Sensible heat flux (MJ/m²) LE = Latent heat flux (MJ/m²) u (m/s) sensible heat flux, H = ρ cp Cov. [ w,t ] latent heat flux, LE = λ Cov. [ w,q ] Where: ρ = density of moist air in (g/m³) cp = heat capacity of air at constant pressure (J/g/ C) Cov. = covariance between w and T or q w = vertical air velocity in m/s T = air temperature ( C) q = density of water vapor (g/m³) λ = Latent heat of vaporization of water (J/g) Slide 13. Energy budget and Eddy Covariance Flux = mean (ρws) 16 Decomposition: W = mean (W) + W 14 1 Fluctuation has zero mean Osborne Reynolds (1895): Virtual Temp. (deg.c) Eddy Covariance :- 7 count Count Flux = mean (ρ) x Cov. (W,S) count Caballo Mowed Site Slide 16. Basic Derivation and Formulas 61st Annual NM Water Conf., Where Does All the Water Go? History, Hydrology & Management of NM s Scarce Waters 3

4 4 Salim Bawazir Evapotranspiration Studies I nstrumentation Setup OPEC Yaggi Antenna Lightning Rod { Net Radiometer Wind Speed/Direction Solar Pannel Relative Humidity/Air Temperature { 3D-SEC/Krypton Data Logger Enclosure Piezometer Grounding Rod Soil Heat Flux Plate Soil Temperature Data Logger Moisture Sensor Slide 19. One Propeller Eddy Covariance (OPEC) System Soil Heat Flux Plate Slide 17. Instrumentation Setup for Evapotranspiration Studies Slide. LI-75 and Krypton Hygrometers with 3-D Sonic Anemometer Slide D Sonic Anemometer and Krypton Hygrometer Slide 1. Daily Cycle of Measured Sensible Heat November 5-7, 16

5 The Science Behind Measuring Depletions 5 Slide. 3-min Means Sensible Heat Flux Slide 3. 3-minute Means of Sensible Heat Flux-3D Sonic vs. OPEC 61 st Annual NM Water Conf., Where Does All the Water Go? History, Hydrology & Management of NM s Scarce Waters

6 6 Salim Bawazir Slide 4. Evaporation Flux Tower at Elephant Butte Reservoir Slide 5. Net Radiation Measurement above Dense Saltcedar November 5-7, 16