discussion on using evapotranspiration for water rights management rick allen -- university of...
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Discussion on using Evapotranspiration for Water Rights Management Rick Allen -- University of Idaho, Kimberly, Idaho
Partners and Collaborators:Jeppe Kjaersgaard, Magali Garcia, R. Trezza – University of IdahoTony Morse, W. Kramber – Idaho Dept. Water ResourcesWim Bastiaanssen – WaterWatch, M. Tasumi --Univ. Miyazaki, JapanJames Wright -- USDA-ARS
ET is calculated as a “residual” of the energy balance
ET = R - G - Hn
Rn
G (heat to ground)
H (heat to air) ET
The energy balance includes all major sources (Rn) and consumers (ET, G, H) of energy
Basic Truth: Evaporation consumes Energy
METRIC Energy balance
(radiation from sun and sky)
Therefore, we can account for impacts on ET caused by:
water shortage disease crop variety planting density cropping dates salinity management
(these effects can be converted into a crop coefficient)
Energy balance gives us “actual” ET
Interpolation of ETrF (i.e., Kc) for Monthly or Seasonal ET
n
miirirperiod ETxFETET 24
n
miir
n
miirir
periodr
ET
ETxFETFET
24
24
0
0.2
0.4
0.6
0.8
1
1.2
3/1
4/1
5/1
6/1
7/1
8/1
9/1
10/1
11/1
ET
rFSplined Satellite Date
Corn 2000
12/17/01
Comparison with Lysimeter Measurements:
Lysimeter at Kimberly (Wright)
1968-1991
Kimberly, Idaho – Periods between Satellites
Lysimeter data by Dr. J.L. Wright, USDA-ARS
Sugar Beets, 1989
Kimberly, Idaho
0
50
100
150
200
250
300
ET
d
urin
g p
erio
d, m
m
18-Apr
04-May20-May05-Jun
21-Jun07-Jul23-Jul
25-Sep
Lys. Kc on Sat. date x sum ETrSum. all lysimeter meas. (Truth)
SEBAL ET for period
Impact of using Kc from a single dayto represent a period: Kimberly 1989
METRIC ET for period
Perio
d of P
artia
l Cov
er
Sugar Beets
Seasonal ET - 1989
Cumulative ET in 1989 for Sugar Beets
0
100
200
300
400
500
600
700
800
4/1
/89
4/1
5/8
9
4/2
9/8
9
5/1
3/8
9
5/2
7/8
9
6/1
0/8
9
6/2
4/8
9
7/8
/89
7/2
2/8
9
8/5
/89
8/1
9/8
9
9/2
/89
9/1
6/8
9
9/3
0/8
9Cu
mu
lati
ve E
T (
mm
) fr
om
4/1
/89
SEBAL-ID Estimation Lysimeter Measurement
Error = 2.5%
0100200300400500600700800
Total
Lysimeter SEBALMETRIC
Lysimeter
718 mm
METRIC
714 mm
Sugar Beets
Comparison of Seasonal ET by METRICtm with Lysimeter
ET (mm) - April-Sept., Kimberly, 1989
0
100
200
300
400
500
Total
Lysimeter SEBAL
ET (mm) - July-Oct., Montpelier, ID 1985
SEBAL
405 mmLysimeter
388 mm
Comparison of Seasonal ET by SEBAL2000 with Lysimeter
Sharpening of Landsat 5 Thermal Band to 30 m
original (120 m thermal)sharpened (30 m thermal)
ETrF
Temp.
July2006
Sharpening of Landsat 5 Thermal Band to 30 m
Growing Season, 2006 – ET aggregated inside CLU’s
Comparison to Kc Curves
potato kc
60 100 140 180 220 260 3000.0
0.2
0.4
0.6
0.8
1.0
1.2
PotatoK
c
100 140 180 220 260 300 0.0
0.2
0.4
0.6
0.8
1.0
1.2
60 Day of Year
potato ndvi
60 100 140 180 220 260 3000.0
0.2
0.4
0.6
0.8
1.0
Potato
0.2
0.4
0.6
0.8
1.0
60 100 140 180 220 260 300 0.0
Day of Year
ND
VI
Vegetation Index
METRIC applied to year 2000
Average “curve”
717 fields in the Twin Falls area
0 25 50 km
TwinFalls weather station42.66oN/114.45oW (Elev.1195m)
beet kc
60 100 140 180 220 260 3000.0
0.2
0.4
0.6
0.8
1.0
1.2
S.BeetK
c
100 140 180 220 260 300 0.0
0.2
0.4
0.6
0.8
1.0
1.2
60 Day of Year
516 fields
Kc near 1.0 indicating high production agriculture
wgrain kc
60 100 140 180 220 260 3000.0
0.2
0.4
0.6
0.8
1.0
1.2
W.GrainK
c
100 140 180 220 260 300 0.0
0.2
0.4
0.6
0.8
1.0
1.2
60 Day of Year
564 fields
alfalfa kc
60 100 140 180 220 260 3000.0
0.2
0.4
0.6
0.8
1.0
1.2
AlfalfaK
c
100 140 180 220 260 300 0.0
0.2
0.4
0.6
0.8
1.0
1.2
60 Day of Year
325 fields
Approaches – 1 (METRIC)Base ET estimates on METRIC --7 to 10 day lag time, high expense --can apply an ‘attainable’ efficiency to derive Diversion
requirement
Can normalize to NDVI to estimate stressCan compare with actual Diversions, ET/NDVI from a few other years (2000, 2003, 2006)Advantage – gives ‘actual’ ETDisadvantage Expensive and with time delay One ‘look’ each 16 days only, at best Some native uncertainty in ET estimates (+/-10%?)
“in-season injury assessment”
Approaches – 2 (Satellite NDVI)
Base ET estimates on NDVI --quick, one day lag time, low expense --apply an ‘attainable’ efficiency to derive Diversion
requirement
Compare with actual DiversionsAdvantage quick, low cost can use SPOT, IRS, etc. if the current LS fails
Disadvantage May not see ET reductions caused by stress (water
shortage) “Injury” based on act. vs. required diversions
“in-season injury assessment”
Approaches – 3 (no satellite)
Calculate ratio of running average Diversion to running average reference ET (from weather data) Compare to other years (> 20)Advantage quick, inexpensive longer time series for context (>20 years for
Agrimet)
Disadvantage May need to normalize for cropping patterns May need to normalize for shift to sprinklers
“in-season injury assessment”
“basal” Kc
“mean” Kc
0.0
0.2
0.4
0.6
0.8
1.0C
rop C
oeffic
ient (E
TrF
)
0.0 0.2 0.4 0.6 0.8 1.0NDVI
3 June 19 June 21 July
717 Potato Fields,
2000
“basal” Kc
“mean” Kc
0 25 50 km
TwinFalls weather station42.66oN/114.45oW (Elev.1195m)
34
34
refref
refrefNDVI
“basal” Kc
“mean” Kc
0
0.2
0.4
0.6
0.8
1
1.2
0 0.2 0.4 0.6 0.8 1
NDVI
Kc
6/3 6/19 7/5 multi-field average (for 12 images Mar-Oct)
Potato“mean” Kc
0
0.2
0.4
0.6
0.8
1
1.2
0 0.2 0.4 0.6 0.8 1 NDVI as
K cr
Alfalfa Beans Beet Corn Potato-S Potato-L Sgrain Wgrain
K cr = 1.17 NDVI as + 0.05 R 2 = 0.94
Kcm
“mean” Kc vs. NDVI Well-watered fieldsMagic Valley, 2000
“mean” Kc vs. NDVI
0
0.2
0.4
0.6
0.8
1
1.2
0 0.2 0.4 0.6 0.8 1
NDVI (toa)
Kc (
ET
rF)
Alfalfa Sugar Beet CornPotato S.Grain W.GrainETrF = 1.25 NDVI
May to September 2000Magic Valley, IdahoAverages of 100's of fieldseach satellite date
Well-watered fields
Development of a seasonal Kc curve from NDVI – Comparison against 1989 Lysimeter data at Kimberly for Landsat Overpass Dates (Kc and NDVI were then splined between dates to obtain daily ET estimates)
0
0.2
0.4
0.6
0.8
1
1.2
4/1
/89
5/1
/89
6/1
/89
7/1
/89
8/1
/89
9/1
/89
10
/1/8
9
ND
VI,
Kc
Sugar Beets
0
0.2
0.4
0.6
0.8
1
1.24
/1/8
9
5/1
/89
6/1
/89
7/1
/89
8/1
/89
9/1
/89
10
/1/8
9
ND
VI,
Kc
NDVIas
Kcr
Grass
0
200
400
600
800
1000
Grass Sugar Beet
ET
(m
m/6
mo
.)
VI based est.
Lysimeter meas.
Comparisons between daily ET determined by METRIC for specific crops and ET determined from the general Kcm vs. NDVIsurf relationship, year 2000, Magic Valley, averaged over 100’s of sampled fields
Comparisons between 5-day ET determined by METRIC for specific crops and ET determined from the general Kcm vs. NDVIsurf relationship, , year 2000, Magic Valley, averaged over 100’s of sampled fields
Alfalfa 1001 5.0 5.4Beans 479 8.5 8.5Beet 904 -1.7 -2.2Corn 846 -6.3 -4.4
Potato-S 733 2.0 1.6Potato-L 846 -1.5 -1.8S.Grain 720 -0.9 -1.0W.Grain 837 -1.4 -0.3
Standard Error - 4.6 4.3
CropsMETRIC ET
(mm)
Kc from NDVI at
satellite (%)
Kc from NDVI corrected to surface (%)
Error (%) in seasonal ET estimated using Kc estimated using the NDVI (normalized difference vegetation index) relative to seasonal ET calculated by METRIC – positive values indicate overestimation.
0
200
400
600
800
1000
1200
Se
as
on
al E
T (
mm
)
Alfa
lfa
Bea
ns
Bee
t
Cor
n
Pot
ato-
S
Pot
ato-
L
Sgr
ain
Wgr
ain
ET (METRIC)
ET (NDVIas)
“Performance” of Irrigation Projects
Mar Apr May Jun Jul Aug Sep Oct
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Project wide Crop Coefficient -- METRIC Twin Falls Tract -- 220,000 acres -- Alfalfa Reference Basis
2000
2003Kc
March, Sept., and Oct. unavailable for 2003 due to clouds
Irrigation Project Performance -- Idaho
Apr May Jun Jul Aug Apr-Aug
0.0
0.2
0.4
0.6
0.8
1.0
Evapotranspiration as a Ratio of Diversion plus Precipitation
2000
2003
Rat
io
Twin Falls Canal Company, Idaho
Irrigation Project Performance -- Idaho
“basal” Kc
“mean” Kc
0.0
0.2
0.4
0.6
0.8
1.0C
rop C
oeffic
ient (E
TrF
)
0.0 0.2 0.4 0.6 0.8 1.0NDVI
3 June 19 June 21 July
717 Potato Fields,
2000
“basal” Kc
“mean” Kc
34
34
refref
refrefNDVI
Can the NDVI-based Kc pick up ‘stress’ caused by water shortage?
Stress? orRandom errorin Kc estimate?
Year 2000: Mean 24-h Evapotranspiration from METRIC
0
1
2
3
4
5
6
7
8
9
6/3 6/19 7/5 7/21 8/14 8/22
Landsat Overpass Date
Me
an
ET
24
mm
A&B GW
A&B GW (Item -G)
A&B SW
N of A&B GW
S of A&B SW
W of A&B GW
W of A&B SW
NW of A&B Mixed
Year 2000: M ean ETrF (i.e ., Kc) from M ETRIC
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
6/3 6/19 7/5 7/21 8/14 8/22
Landsat Overpass Date
Me
an
ET
rF
A&B GW
A&B GW (Item -G)
A&B SW
N of A&B GW
S of A&B SW
W of A&B GW
W of A&B SW
NW of A&B Mixed
Year 2000: M ean NDVI from M ETRIC
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
6/3 6/19 7/5 7/21 8/14 8/22
Landsat Overpass Date
Me
an
ND
VI
A&B GW
A&B GW (Item -G)
A&B SW
N of A&B GW
S of A&B SW
W of A&B GW
W of A&B SW
NW of A&B Mixed
Year 2000: Ratio of M ean ETrF to M ean NDVI
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
6/3 6/19 7/5 7/21 8/14 8/22
Landsat Overpass Date
Me
an
ET
rF/
me
an
ND
VI
A&B GW
A&B GW (Item -G)
A&B SW
N of A&B GW
S of A&B SW
W of A&B GW
W of A&B SW
NW of A&B Mixed
High because of evaporation from surface floodingor high because of no stress??
Issues
If NDVI (and thus ET) is ‘low’ is it because: shift in crop types due to market shift in crop types because of perceived
water shortage (i.e., internal mitigation) chronic shortage of water during
development cool spring – late/retarded development warm summer – accelerated ripening
Approaches – 1 (METRIC)Base ET estimates on METRIC --7 to 10 day lag time, high expense --can apply an ‘attainable’ efficiency to derive Diversion
requirement
Can normalize to NDVI to estimate stressCan compare with actual Diversions, ET/NDVI from a few other years (2000, 2003, 2006)Advantage – gives ‘actual’ ETDisadvantage Expensive and with time delay One ‘look’ each 16 days only, at best Some native uncertainty in ET estimates (+/-10%?)
“in-season injury assessment”
Approaches – 2 (Satellite NDVI)
Base ET estimates on NDVI --quick, one day lag time, low expense --apply an ‘attainable’ efficiency to derive Diversion
requirement
Compare with actual DiversionsAdvantage quick, low cost can use SPOT, IRS, etc. if the current LS fails
Disadvantage May not see ET reductions caused by stress (water
shortage) “Injury” based on act. vs. required diversions
“in-season injury assessment”
Approaches – 3 (no satellite)
Calculate ratio of running average Diversion to running average reference ET (from weather data) Compare to other years (> 20)Advantage quick, inexpensive longer time series for context (>20 years for
Agrimet)
Disadvantage May need to normalize for cropping patterns May need to normalize for shift to sprinklers
“in-season injury assessment”
Impact of Irrigation System Type on ET-- south-central Idaho -- 2003
METRIC Analyses by Lorite, Allen and Robison
Impact of Irrigation System Type on ET-- south-central Idaho -- 2003
METRIC Analyses by Lorite, Allen and Robison
Impact of Irrigation System Type on ET-- south-central Idaho -- 2003
METRIC Analyses by Lorite, Allen and Robison