Procedure of hydrological modeling in a semi-arid river basin with SWAT
By:
Ammar Rafiei
outline
• Objective
• Introduction
• Study area
• Preparation of data sets
• Model parameterization
• Uncertainty analysis
• Sensitivity analysis
• results
Objectives:
1- Building and calibrating a hydrological model in a semi arid river basin of Iran 2- Quantifying the water resources availability in the study area
Introduction
• Water scarcity in arid and semi arid area has negative impact on planning and management of this regions.
• Low precipitation , low water availability
• weakness of management
• Groundwater usage
• More than 90 % of water are using for agriculture with WUE less than 35 %
Study area
Razan-Ghavand watershed
• Watershed Area: 3100 Km2
• Max altitude 2842 m
• Min altitude: 1577 m
• Climate: semi arid
• Mean annual rainfall: 290 mm
• Mean annual temperature: 11⁰C
• Aquifer area: 1750 Km2
• Mean water level: 30 m
Study area: Razan-Ghavand
• Major river: Gharehchay river
with mean annual discharge at
the outlet: 6.68 m3s-1
Study area: Razan-Ghavand
• Major river: Gharehchay river with mean annual discharge at the outlet: 6.68 m3s-1
0.0010.0020.0030.0040.0050.0060.0070.0080.0090.00
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Q (
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River Discharge
Study area: Razan-Ghavand
• Major river: Gharehchay river
with mean annual discharge at
the outlet: 6.68 m3s-1
• Zehtaran river with mean annual
discharge at the outlet: 0.66 m3s-1
Study area: Razan-Ghavand
• Major river: Gharehchay river with mean annual discharge at the outlet: 6.68 m3s-1
• Zehtran river with mean annual discharge at the outlet: 0.66 m3s-1
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Q(m
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Discharge
Study area: Razan-Ghavand
• Major river: Gharehchay river
with mean annual discharge at
the outlet: 6.68 m3s-1
• Zehtaran river with mean annual
discharge at the outlet: 0.66 m3s-1
• Sirab-khomigan river with mean
annual discharge at the outlet:
0.33 m3s-1
Study area: Razan-Ghavand
• Major river: Gharehchay river with mean annual discharge at the outlet: 6.68 m3s-1
• Zehtaran river with mean annual discharge at the outlet: 0.66 m3s-1
• Sirab-khomigan river with mean annual discharge at the outlet: 0.33 m3s-1
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Q (
m3
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Discharge
Study area: Razan-Ghavand
• Major river: Gharehchay river with mean annual discharge at the outlet: 6.68 m3s-1
• Zehtaran river with mean annual discharge at the outlet: 0.66 m3s-1
• Sirab-khomigan river with mean annual discharge at the outlet: 0.33 m3s-1
• Koshabad river station, outside the watershed, with mean annual discharge at the outlet: 2.25 m3s-1
Land types
Material and method
SWAT input/output
Input:
• DEM
• Landuse
• Soil
• Climate data – Daily precipitation
– Daily temperature
• Agriculture management & practice data
Output:
• Hydrological component – Groundwater recharge
– Soil moisture
– Actual evapotranspiration
• Other Components: – Crop yield
– Water quality
– Sediment
Digital elevation model
Input:
• DEM • Landuse • Soil • Climate data
– Daily precipitation
– Daily temperature
• Agriculture management & practice data
Resolution : 25 m Source: topographical map 1:25000
Hydrological component Groundwater recharge Soil moisture Actual evapotranspiration
Other Components: Crop yield Water quality Sediment
Output:
Land use map
• Landsat 2009 • Supervised classification • Overall Accuracy = 71.4317% • Kappa Coefficient = 0.6604
Input:
• DEM • Landuse • Soil • Climate data
– Daily precipitation
– Daily temperature
• Agriculture management & practice data
Hydrological component Groundwater recharge Soil moisture Actual evapotranspiration
Other Components: Crop yield Water quality Sediment
Output:
Soil map
• Soil layers up to 5 layers
Input:
• DEM • Landuse • Soil • Climate data
– Daily precipitation
– Daily temperature
• Agriculture management & practice data
Hydrological component Groundwater recharge Soil moisture Actual evapotranspiration
Other Components: Crop yield Water quality Sediment
Output:
Climate data
No of rain gage stations= 21 No of Synoptic stations=4 No. of hydrometric stations =3
Input:
• DEM • Landuse • Soil • Climate data
– Daily precipitation
– Daily temperature
• Agriculture management & practice data
Hydrological component Groundwater recharge Soil moisture Actual evapotranspiration
Other Components: Crop yield Water quality Sediment
Output:
No of rain gage selected: 8 ( 2 outside + 6 inside)
Agriculture management & practice
Input:
• DEM • Landuse • Soil • Climate data
– Daily precipitation
– Daily temperature
• Agriculture management & practice data
Hydrological component Groundwater recharge Soil moisture Actual evapotranspiration
Other Components: Crop yield Water quality Sediment
Output: • Agricultural schedule both
for rainfed and irrigated lands
Model setup DEM
15 × 15 m Landsat Derived 2009 30 × 30 m
Soil Map 1:250000
HRU
No of sub basin with inlet: 138, No. of HRU with HRU: 831
Model set up
• Model was set up with inlet with non dominate HRU,
• Type of crop : winter wheat • Auto-irrigation and fertilization operation options
were used to simulate crop growth.
• evapotranspiration method : Hargreaves method • curve number (CN) was adjusted based on the
slop
• SUFI-2 was used to calibration and validation, uncertainty and sensitivity analysis,
Duration of calibration: 2003-2008 Duration of validation: 1998-2002 Warm up duration: 2 years • 28 Parameters was used for optimization
Uncertainty analysis
optimization Parameter Definition
CN2(.mgt) SCS runoff curve number for moisture condition II
GW_DELAY(.gw) Groundwater delay time (days)
ALPHA_BF(.gw) Baseflow alpha factor (days)
REVAPMN(.gw) Threshold water in shallow aquifer
GW_REVAP(.gw) Revap coefficient
RCHRG_DP(.gw) Aquifer percolation coefficient
GWQMN(.gw) Threshold water level in shallow aq. for baseflow
SOL_AWC(.sol) Available water capacity factor
SOL_K(.sol) Saturated hydraulic conductivity
SOL_BD(.sol) Soil bulk density
SOL_ALB(.sol) Moist soil albedo
EPCO(.hru) plant uptake compensation factor
SLSUBBSN(.hru) Average slope length (m)
OV_N(.hru) Manning's n value for overland flow
CH_N2(.rte) Manning's n value for main channel
CH_K2(.rte) Effective hydraulic conductivity in main channel alluvium
ALPHA_BNK(.rte) Base flow alpha factor for bank storage (days)
SFTMP(.bsn) Snowfall temperature
SMTMP(.bsn) Snow melt base temperature (ºC)
SMFMX(.bsn) Melt factor for snow on 21 Jun
SMFMN(.bsn) Melt factor for snow on 21 Dec
TIMP(.bsn) Snow pack temperature lag factor
SURLAG(.bsn) Surface runoff lag coefficient
ESCO(.hru) Soil evaporation compensation factor
HEAT_UNITS heat unit
HI_TARG harvest index
AUTO_WSTRS Water stress
BIO_TARG bio target
Results & Discussion
Results of SWAT output
Zehtaran
Omarabad
0.00020.00040.00060.00080.000
100.000120.000140.000160.000
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dis
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Time (monthly)
Observated data
simulated data
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Time (monthly)
observated data simulated data
NS: -0.76 , PBIAS:0.12, RMSE:14.20
NS: -15.9 , PBIAS:2.9, RMSE:1.5
Choose the duration for calibration and validation
- Sirab-khomigan discharge-shows different hydrological condition in I and II periods.
I
II
Sub basins affected to flow in each station
Stations Sub basins Area(km2)
14 (Sirab khomigan) 1,2,3,4,5,6,12,13,14 255
41(Zehtaran) 23,26, 27,28,29,32, 33, 34,
37,38,41
420
71(Omarabad) All subbasin 3100
Sensitivity analysis
• Global sensitivity
• One at a time method
Sensitivity analysis
• Global sensitivity
• One at a time method
Parameter Name t-Stat P-Value
r__CN2.mgt________23,26,27,28,29,32,33,34,37,38,41 -34.67 0.00
r__CN2.mgt________1,2,3,4,5,6,12,13,14 -15.06 0.00
v__SMFMN.bsn -11.31 0.00
v__ALPHA_BNK.rte________1,2,3,4,5,6,12,13,14 -9.39 0.00
v__ALPHA_BNK.rte________23,26,27,28,29,32,33,34,37,38,41
-9.27 0.00
r__SOL_AWC().sol________23,26,27,28,29,32,33,34,37,38,41
7.33 0.00
v__SMFMX.bsn -4.93 0.00
v__TIMP.bsn -4.89 0.00
v__GWQMN.gw________23,26,27,28,29,32,33,34,37,38,41
2.02 0.04
V__GW_DELAY.gw________1,2,3,4,5,6,12,13,14 2.34 0.02
v__CH_K2.rte________23,26,27,28,29,32,33,34,37,38,41
2.47 0.01
r__SOL_AWC().sol________1,2,3,4,5,6,12,13,14 1.97 0.05
v__GW_REVAP.gw________23,26,27,28,29,32,33,34,37,38,41
1.78 0.07
V__GW_DELAY.gw________7-11,15-22,24,25,30,31,35,36,39,40,42-138
1.64 0.10
Sensitivity analysis
• Global sensitivity
• One at a time method
Calibration and validation of outlet No.71
calibration
• P-factor=0.38
• R-factor=0.78
• R2 = 0.57
• NS= 0.56
validation
• P-factor= 0.45
• R-factor= 1.02
• R2 = 0.69
• NS= 0.66
Calibration and validation of outlet No.41
calibration validation
• P-factor= 0.51
• R-factor= 1.33
• R2 = 0.78
• NS= 0.42
• P-factor= 0.49
• R-factor= 1.76
• R2 = 0.71
• NS= 0.59
Calibration and validation of outlet No.14
calibration
• P-factor= 0.51
• R-factor= 1.26
• R2 = 0.48
• NS= 0.35
validation
• P-factor= 0.44
• R-factor= 0.36
• R2 = 0.91
• NS= 0.72
CROP calibration
Calibration winter wheat Validation winter wheat
Irrigated: p-factor= 0.67 r-factor= 0.70 MSE = 1.08 t/ha
Rainfed: p-factor= 0.83 r-factor= 0.77 MSE = 0.07 t/ha
Irrigated: p-factor= 0.92 r-factor= 1.25 MSE = 0.19 t/ha
Rainfed: p-factor= 0.70 r-factor= 0.54 MSE = 0.25 t/ha
-Average (2003-2008) monthly 95PPU ranges of a: actual evapotranspiration b: soil water
content c:perculation d:surface runoff
Water components spatial distribution
ET Percolation Precipitation
Surface runoff Soil water
Conclusion
• Low data availability , especially amount of water use , is one of the main problem to calibrate the model.
• In semi arid regions because of low river discharge, the calibration process is pretty difficult . hence, the crop calibration can increase the precision of model.