View
215
Download
0
Tags:
Embed Size (px)
Citation preview
Two-Step Calibration Method for SWAT
Francisco Olivera, Ph.D.Assistant ProfessorHuidae ChoGraduate Student
Department of Civil EngineeringTexas A&M UniversityCollege Station - Texas
SWAT 2005Zurich, Switzerland
July 14th, 2005
Can we extract spatial information from
temporal data?
Francisco Olivera, Ph.D.Assistant ProfessorHuidae ChoGraduate Student
Department of Civil EngineeringTexas A&M UniversityCollege Station - Texas
SWAT 2005Zurich, Switzerland
July 14th, 2005
Objective
Given: A calibration routine that adjusts the terrain parameters independently for each sub-basin and HRU (i.e., extracts spatial information).
Hypothesis: A model that can reproduce the system’s responses for a “long” period of time has the correct parameter spatial distribution.
Lake Lewisville Watershed
Period of record: 1987 – 1999
• Four temperature stations: one inside the watershed and three outside.
• Six precipitation stations: two inside the watershed and four outside.
Area: 2500 km2
• Four flow gauging stations: one is an inlet, one is used for calibration, and two are used for (spatial) validation.
Calibration and validation
Three-year warm-up period. Calibration periods:
One year: [1992-1994] + [1995] … Six years: [1987-1989] + [1990-1995]
Validation period: Four years: [1993-1995] + [1996-1999]
Calibration location Validation location
Calibration parameters
Parameter Description
CN2 SCS runoff curve number
SOL_AWC Soil available water capacity (mm H2O/mm soil)
ESCOSoil evaporation compensation factor. Whenever the upper layer cannot meet the evaporative demand, SWAT extracts more soil water from the lower layer.
GWQMN Threshold depth of water in the shallow aquifer required for return flow to occur (mm H2O)
GW_REVAPGroundwater “revap” coefficient. Revap is the process by which water moves into the overlying unsaturated zone from the shallow aquifer by the capillary fringe or deep-rooted plants.
REVAPMNThreshold depth of water in the shallow aquifer for “revap” or percolation to the deep aquifer to occur (mm H2O)
CH_K2 Effective hydraulic conductivity in main channel alluvium (mm/hr)
ALPHA_BFBaseflow alpha factor (days) is a direct index of groundwater flow response to changes in recharge.
OV_N Manning’s “n” value for overland flow
SLOPE Average slope steepness (m/m)
SLSUBBSN Average slope length (m)
Calibration levels
Watershed: All sub-basin and HRU parameters are adjusted by applying one single parameter-change rule over the entire watershed.
Sub-basin: All sub-basin and HRU parameters are adjusted by applying a different parameter-change rule in each subbasin. Follows watershed calibration.
HRU: Each HRU parameter is adjusted differently. Follows sub-basin calibration.
Method A (plus/minus): -0.05 < α < 0.05
Method B (factor): 0.9 < α < 1.1
Method C (alpha): -0.5 < α < 0.5
Parameter-change rules
i 1 i max minP P (P P )
i 1 i i minP P (P P )
i 1 i max iP P (P P )
Initial conditions
Initial conditions for the iterative calibration process: Non-uniform: parameter values based on land-
use and soil-type data. Uniform: average parameter values throughout
the watershed … let the calibration process extract the spatial information.
Objective functions
Sum of the square of the residuals (SSR)
Sum of the absolute value of the residuals (SAR)
No logQ or Q in the denominator was used because some flows were zero.
2simulated observedSSR (Q Q )
simulated observedSSR Q Q
Model efficiency
Model efficiency was evaluated with the Nash-Sutcliffe coefficient:
where is the long-term flow average (i.e., the predicted flows with “no model”).
2simulated observed
2 2observed observed
(Q Q ) SSRNS 1 1
(Q Q ) (Q Q )
Q
Hydrologic unitC
alib
ratio
n //
SS
R /
/ D
istr
ibut
ed
// P
lus-
min
us /
/ 4
2
The increase in NS between subbasin and watershed is small, and between HRU and subbasin is negligible.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liffe
co
effi
cien
t
SGPHGPWGPWGP
Hydrologic unitV
alid
atio
n //
SS
R /
/ D
istr
ibut
ed /
/ P
lus-
min
us /
/ 42
The decrease in NS between subbasin and watershed is small, and between HRU and subbasin is negligible.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liffe
co
effi
cien
t
SGPHGPWGPWGP
Objective functionC
alib
ratio
n //
Dis
trib
uted
//
Plu
s-m
inus
//
42
The increase in NS between subbasin and watershed is small, and between HRU and subbasin is negligible.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liff
e c
oe
ffic
ien
t
SGPHGPWGPWGP
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 2 3 4 5 6
Number of years used in calibration
Nas
h-S
utc
liffe
co
effi
cien
t
SGP
HGP
WGP
SSR
SAR
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6
Number of years used in calibration
Nas
h-S
utc
liffe
co
effi
cien
t
SGP
HGP
WGP
WGP
Objective functionV
alid
atio
n //
Dis
trib
uted
//
Plu
s-m
inu
s //
42
The increase in NS between subbasin and watershed is small, and between HRU and subbasin is negligible.
SSR
SAR0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 2 3 4 5 6
Number of years used in calibration
Nas
h-S
utc
liffe
co
effi
cien
tSGP
HGP
WGP
Parameter change functionC
alib
ratio
n //
SS
R /
/ D
istr
ibut
ed
// 4
2
The NS values for the factor parameter-change-function are slightly lower than for the other functions.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 2 3 4 5 6
Number of years used in calibration
Nas
h-S
utc
liffe
co
effi
cien
t
HGAWGAWGFSGFSGPHGFHGPSGAWGP
Parameter change functionV
alid
atio
n //
SS
R /
/ D
istr
ibut
ed /
/ 42
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 2 3 4 5 6
Number of years used in calibration
Nas
h-S
utc
liffe
co
effi
cien
t
HGAWGAWGFSGFSGPHGFHGPSGAWGP
Spatial variabilityC
alib
ratio
n //
SS
R /
/ P
lus-
min
us /
/ 42
The NS values are not significantly affected by the initial assumed spatial variability.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liffe
co
effi
cie
nt
WAPSGPSAPHGPHAPWGP
Hydrographs - CalibrationC
alib
ratio
n //
SS
R /
/ P
lus-
min
us /
/ 42
The simulated hydrographs are fundamentally equal even though the initial conditions before
the calibration were very different.
0
50
100
150
200
250
1/1/1990 1/1/1991 1/1/1992 12/31/1992 12/31/1993 12/31/1994
Flo
w (
m3/s
) HGP
WAP
WGP
Observed
Parameter valuesS
SR
//
Ave
rage
//
Plu
s-m
inus
//
HR
U
Same results were obtained from significantly different sets of initial parameters.
70
75
80
85
90
95
100
70 75 80 85 90 95 100
Curve number (base)
Cu
rve
nu
mb
er
SSR // Distributed // Plus-minus // Watershed
Spatial variabilityV
alid
atio
n //
SS
R /
/ P
lus-
min
us /
/ 4
2
The NS values are not significantly affected by the initial assumed spatial variability.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liffe
co
effi
cie
nt
WAPSGPSAPHGPHAPWGP
Hydrographs - ValidationV
alid
atio
n //
SS
R /
/ P
lus-
min
us /
/ 4
2
The simulated hydrographs are fundamentally equal even though the assumptions during
calibration were very different.
0
20
40
60
80
100
120
140
160
1/1/1996 12/31/1996 12/31/1997 12/31/1998
Flo
w (
m3/s
) HGP
WAP
WGP
Series1
Spatial validationC
alib
ratio
n //
SS
R /
/ P
lus-
min
us /
/ 38
The initial assumed spatial variability does not make a significant difference; however, the watershed-based calibration is more accurate.
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liffe
co
effi
cien
t
WAPSGPSAPHGPHAPWGP
0
2
4
6
8
10
12
14
16
1/1/1990 1/1/1991 1/1/1992 12/31/1992 12/31/1993 12/31/1994
Flo
w (
m3/s
) HGP
WAP
WGP
Observed
Spatial and temporal validationV
alid
atio
n //
SS
R /
/ P
lus-
min
us /
/ 3
8
In validation over space and time, the watershed-based calibration with an average initial spatial variability has the highest NS values.
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liffe
co
effi
cien
t
WAPSGPSAPHGPHAPWGP
0
2
4
6
8
10
12
14
16
1/1/1996 12/31/1996 12/31/1997 12/31/1998
Flo
w (
m3/s
) HGP
WAP
WGP
Observed
Spatial validationC
alib
ratio
n //
SS
R /
/ P
lus-
min
us /
/ 37
Not even the watershed-based calibration using the spatial variability defined by the soil and land use data produces a good NS value.
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liffe
co
effi
cien
t
WAPSGPSAPHGPHAPWGP
0
10
20
30
40
50
60
70
80
1/1/1990 1/1/1991 1/1/1992 12/31/1992 12/31/1993 12/31/1994
Flo
w (
m3/s
) HGP
WAP
WGP
Observed
Spatial and temporal validationV
alid
atio
n //
SS
R /
/ P
lus-
min
us /
/ 3
7
-1.5
-1.0
-0.5
0.0
0.5
1.0
1 2 3 4 5 6
Number of years used in calibration
Na
sh-S
utc
liffe
co
effi
cien
t
WAPSGPSAPHGPHAPWGP
Not even the watershed-based calibration using the spatial variability defined by the soil and land use data produces a good NS value.
0
5
10
15
20
25
30
35
40
1/1/1996 12/31/1996 12/31/1997 12/31/1998
Flo
w (
m3/s
) HGP
WAP
WGP
Observed
Discussions
Dispersion is the hydrodynamic process by which some water particles flow faster than others.
Because of dispersion, it is difficult to know exactly when and where a particle entered the system.
The effect of dispersion (i.e., response width) increases proportionally to the square root of the flow time; while the effect of advection (i.e., location of the response centroid) increases linearly with the flow time.
In small watersheds, dispersion “mixes” all responses (i.e., unit hydrograph); while in large watersheds, advection keeps responses “separate” (i.e., flow-time area diagrams).
t
Q
dispersion
advection
Conclusions
It was not possible to “extract hydrologic information from temporal data” for the 2,500-km2 Lake Lewisville watershed.
The effect of the spatial variability was small compared to the effect of hydrodynamic dispersive processes in the system.
The number of years used for calibrating the model was fundamental for determining the parameter values.
The parameter-change rule and the selected objective function did not significantly affect the calibration process.