ET Comparison: ESPAM2 vs. METRIC Mike McVay ESHMC Meeting 12/12/2011
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Transcript of ET Comparison: ESPAM2 vs. METRIC Mike McVay ESHMC Meeting 12/12/2011
ET Comparison: ESPAM2 vs. METRICMike McVay ESHMC Meeting 12/12/2011
May-80 Oct-85 Apr-91 Oct-96 Mar-02 Sep-07 Mar-130
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•Could differences in modeled spring discharge (2006-2008) be the result of ESPAM2 underestimation of ET?
•Compare Bill Kramber’s METRIC ET analysis of western limb to ESPAM2 ET estimates.•Implicit assumption that METRIC is our best estimate of ET.
•Analysis investigated the Northside and AFRD2 irrigated lands.•Bill used irrigated land layers for 2002, 2006, and 2008 which have been developed from CLU data.•2000 irrigated land layer developed via refinement of 2002.•Irrigated land rasters “clipped” to AFRD2, Northside and Overlap shapefiles.•METRIC rasters for 2000, 2002, 2006 and 2008.•Calculated METRIC ET on the irrigated land.
The Kramber Analysis
•Analysis investigated the Northside and AFRD2 irrigated lands.•Model uses irrigated land layers for 2002 and 2006 which have been developed
from CLU data.•2000 irrigated land layer developed from crop classification of Landsat.•2008 is a repeat of 2006•Used irrigated land rasters “clipped” to Kramber’s AFRD2, Northside and Overlap shapefiles to construct .IAR file.•METRIC ET for 2000 and 2006 basis for adjustment factors.•Ran MKMOD8.
The ESPAM2 Analysis
•The Kramber ET estimate and the ESPAM2 ET estimate cannot be compared directly because ESPAM2 employs a global coefficient to incorporate edged effects from irrigation.•Edge effects can be due to advection of heat into the irrigated lands as well as overspray and runoff from the irrigated lands.•Development of the global coefficient employed the GIS analysis of ET on buffers extending 70 m and an additional 200 m beyond the irrigated land layers.
Edge-effect ET
•Analysis investigated the Northside and AFRD2 irrigated lands.•Performed Kramber METRIC analysis on ESPAM2 buffer.•Used the Kramber irrigated land layers for 2000, 2002, 2006, and 2008.•70 m and additional 200 m buffers created to calculate irrigation edge-effect ET.•Wetland areas removed from buffers as was done for ESPAM2.•Calculated ET volume on 70 Buffer (70_METRIC ET Depth x 70 m Buffer Area).•Calculated “background” ET volume using 200 m buffer (200_METRIC ET Depth
x 70 m Buffer Area).•Subtract background ET volume from 70 m Buffer ET volume to yield edge-effect ET volume.•Add edge-effect ET volume to irrigated land ET volume.
The Buffer Analysis
2000 2002 2006 20080
200,000
400,000
600,000
800,000
1,000,000
1,200,000
934,036
922,886
1,037,121
958,661
823,174
755,026
862,438888,976
872,105
774,751
892,301 938,646
Total ET Volume (AF) - Model Input vs METRIC Analysis
Model ET (AF)Kramber ET (AF)METRIC_Buff (AF)
ET V
olum
e (A
F)
2000 2002 2006 20080.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
2.86
3.00
3.27
3.03
2.78
2.41
2.69
2.932.94
2.47
2.78
3.09
ET per Acre (ft) - Model Input vs METRIC Analysis
Model ET (ft)Kramber ET (ft)METRIC_Buff (ft)
ET p
er A
cre
(FT)
2000 2002 2006 2008280,000
285,000
290,000
295,000
300,000
305,000
310,000
315,000
320,000
325,000322,726
313,023
319,743 319,743
296,636
313,806
320,400
303,346
Irrigated Acreage- Model Input vs METRIC Analysis
Model AcresKramber Acres
Irrig
ated
Are
a (a
cres
)
Kramber analysis employed irrigated land different from ESPAM2 input for 2000 and 2008.
2000 2002 2006 20080%
5%
10%
15%
20%
25%
Model ET Volume vs METRIC ET Volume (% METRIC)
Model - METRIC
ET V
olum
e Di
ffere
nce
(%)
2000 2002 2006 20080%
5%
10%
15%
20%
25%
Model ET Volume vs METRIC ET Volume (% METRIC)
Model - METRIC
ET V
olum
e Di
ffere
nce
(%)
-5%
0%
5%
10%
15%
20%
25%
Model ET Depth vs. METRIC ET Depth (% METRIC)
Model - METRIC
ET p
er A
cre
Diffe
renc
e (%
)
2000 2002 2006 2008
May-80 Oct-85 Apr-91 Oct-96 Mar-02 Sep-07 Mar-130
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MeasuredModelled
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•Could differences in modeled spring discharge (2006-2008) be the result of ESPAM2 misrepresentation of ET slope?
•ESPAM2 calibrated ET exhibits a +0.02% slope.•If the true slope of ET over time is steeper, the model may compensate by adjusting
spring discharge.
Could ET still be a factor in the spring discharge mismatch?
19801984
19881992
19962000
20042008
850,000
900,000
950,000
1,000,000
1,050,000
1,100,000
f(x) = 1028.03497536946 x − 1075123.49950739
f(x) = 1799.40049261084 x − 2603235.03054187
Total ET Volume (AF) AFRD2 & Northside
Calibrated ETLinear (Calibrated ET)Input ETLinear (Input ET)
The slope of ESPAM2 ET estimates over time is increased during calibration.
•Climate change.• Increase potential ET.• Increase growing season
•Crop mix changes.• More consumptive crops.
•Cultivar changes.• Higher yield per crop, higher consumptive use.
•Efficiency changes.• More efficient practices optimize yield, increase consumptive use.
•Practice changes.• Better technology, change in fertilizer, etc.
What can cause ET to increase over time?
1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 201030
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f(x) = 0.306604747162023 x − 574.039525283798
f(x) = 0.00877596631578937 x + 25.2869718315792f(x) = 0.135702442105263 x − 230.252292509474
Twin Falls Alfalfa - Frequent Cuttings
NWSLinear (NWS)AgriMetLinear (AgriMet)USBRLinear (USBR)In
ches
ET
Model Trend = 0.02 inches/year
Climate does not appear to add much trend to ET. Note: ETI NWS Trend is 0.16 in/yr for the model period.
•Difficult to quantify the remaining suspects.•Crop mix changes – voluntary reporting and adjusted to “hide” largest producers.•Cultivar changes – Even if ET differences between cultivars is determined,
changes over time may not be knowable.•Efficiency changes – The model incorporates sprinkler percentage,
but effects of efficiency not well constrained.•Practice changes – Likely unknowable.
If climate change is not adding significant slope to ET?
Discussion.