Comparing Methods for Estimating Crop Consumptive Water Use in the Delta: Background and Preliminary Results

Eric Kent, Kyaw Tha Paw U, Jenae’ Clay, Michelle M. Leinfelder-Miles, Josué Medellín-Azuara, Yufang Jin, Quinn Hart, Andy Wong, Nadya Alexander,

Andrew Bell, Martha Anderson, Daniel Howes, Forrest Melton, Tariq Kadir, Morteza Orang, Jay R. Lund

SJC and Delta Field Crops Meeting

January 6th, 2017

Background

• SB 88: measurement of diversions

• Challenges to this: Measurements difficult because of hydrology—shallow ground water, channel waters higher than land levels, so seepage important

• ET/consumptive water use measurements can be more accurate way to get at agricultural water use

Background: Measuring and Estimating Consumptive

Water Use Field Measurements 7 Model-Based ET Estimates

https://watershed.ucdavis.edu/project/delta-et

Background: Estimating Consumptive Water Use

• CalSIMETAW (DWR) • DETAW (DWR) • SIMS (NASA)

Crop coefficient methods

𝐸𝑇𝑎 = 𝐸𝑇𝑜 ∗ 𝐾𝑐

Snyder, R.L. 2014

Crop coefficient

Reference ET Accounts for weather

Background: Estimating Consumptive Water Use

Satellite Remote Sensing

Advantages • Complete spatial coverage • Less expensive than field measurements (for large

numbers of fields) Disadvantages • Satellite overpasses only about every two weeks –

ET must be interpolated in between • Additional uncertainties

Background: Estimating Consumptive Water Use

Direct measurement of water vapor flux with Eddy Covariance

Energy Balance Residual with Eddy Covariance

Energy Balance Residual with Surface renewal

Field Measurements

Field Measurements Energy Balance Residual Method-for Consumptive Water Use = actual Evapotranspiration

𝐸𝑇𝑎 =𝐿𝐸

𝐿

Water Evaporated and Transpired (mm)

=

Total amount of energy used to change water from liquid to gas

L=the amount of energy needed to convert 1 mm of water from liquid to gas

Field Measurements

Energy Balance Residual Method

𝐸𝑇𝑎 =𝐿𝐸

𝐿

Water Evaporated and Transpired (mm)

=

Total amount of energy used to change water from liquid to gas

the amount of energy needed to convert 1 mm of water from liquid to gas

𝑅𝑛 = 𝐻 + 𝐺 + 𝐿𝐸

So we will obtain ETa by measuring LE

Field Measurements

Energy Balance Residual Method

𝐸𝑇𝑎 =𝐿𝐸

𝐿

Water Evaporated and Transpired (mm)

=

Total amount of energy used to change water from liquid to gas

the amount of energy needed to convert 1 mm of water from liquid to gas

𝑅𝑛 = 𝐻 + 𝐺 + 𝐿𝐸

LE = 𝑅𝑛 −𝐺 − 𝐻

Rearranging to solve for LE

So we will obtain ETa by measuring LE

Field Measurements

Net Radiation

LE = 𝑅𝑛 −𝐺 − 𝐻

• Shortwave radiation from the sun + thermal radiation from Earth

• The main source of energy at the crop surface

Field Measurements

Ground Heat Flux

Assumed negligible at the daily scale where measurements are not available

LE = 𝑅𝑛 −𝐺 − 𝐻

Field Measurements

Sensible Heat Flux

Energy from the surface used to heat the air (or vice versa)

Eddy Covariance Surface Renewal

LE = 𝑅𝑛 −𝐺 − 𝐻

2016: Alfalfa Surface Renewal

LE = 𝑅𝑛 −𝐺 − 𝐻

Energy Balance Components

12:00 00:00 06:00 18:00 00:00

July 28 July 29

(W/m2)

0

200

400

600

Preliminary Results: 2015 • One month of field measurements in fallow fields (4 fallow fields-all above

sea level)

Reference Evapotranspiration CIMIS

Bare Soil Measured Evapotranspiration

Preliminary Results: 2015 • One month of field measurements in fallow fields (4 fallow fields-all above

sea level)

• Comparison of 7 models for all Delta Crops in 2015

• 2015 preliminary report: https://watershed.ucdavis.edu/project/delta-et

Reference Evapotranspiration CIMIS

Bare Soil Measured Evapotranspiration

2016 Field Measurements

• 14 Fields; 20 ETa stations

• Alfalfa, Corn, Pasture

• Different Irrigation System Types

• Different Groundwater Table Depths

Before Alfalfa Cutting

(W/m2)

(W/m2)

Daily Total ET = 0.16 in (4.15 mm)

Daily Total ET = 0.05 in (1.25mm) After Alfalfa Cutting

Ongoing Work

• Processing and analysis of 2016 field data

• Comparison with modeled ET from 7 different methods

• Final peer-reviewed report Spring 2017

• Additional fallow field measurements

Acknowledgments

Delta Growers and Land Owners, State Water Resources Control Board, California Department of Water Resources, Delta Protection Commission, Delta Stewardship Council, North Delta Water Agency, Central Delta Water Agency, and South Delta Water Agency

Michael George, John Collins, Christine Rico, Juan Mercado, Jean-Jacques Lambert, David Edgar, Sebastian Häusler, Shirley Alvarez, Megan McAuliffe, Berline Francis, Nicolas Bambach, Nadia Vendrame, Yujiu Xiong, Phumudzo Tharaga, Rodrigo Monteiro, Matthew Gilbert, Hananeh Jafary, and Matthew Read, J. Andrés Morandé, Barbara Bellieu, and Cathryn Lawrence

This work would not have been possible without the collaboration and support from the following: