ESTIMATION OF EVAPOTRANSPIRATION IN SARDAR SAROVAR COMMAND AREA USING WEAP

BY : RINA . CHOKSI, GOPAL H. BHATTI AND PROF. H. M. PATEL

CIVIL ENGINEERING DEPARTMENT,

FACULTY OF TECHNOLOGY AND ENGINEERING, THE M.S. UNIVERSITY OF BARODA, VADODARA

0

1000

2000

3000

4000

5000

6000

7000

8000

1911

1921

1931

1941

1951

1961

1971

1981

1991

2001

252

251

279

319

361

439

548 683 84

6 1027

7743

7771

7001

6129

5409

4446

3563

2858

2308

1902

Population(Million)

Per capita wateravailability(Cubic meters)

Source : Tata Energy Research Institute, (TERI), 1998 and Census India, 2001.

Per capita availability of fresh water estimated in 2001 in Gujarat was 1137 m3 per annum. As against national renewable fresh water standing of 2000m3. In view of this Gujarat can be identified as “Water Scarce State”.

India’s Population and Per-capita Water Availability

Available Water Resources in Gujarat State

• Total geographical area of state is 19.6 M ha.

• Cultivable area is 12.5 M ha. • Population of about 60.38 million (as per

2011 census). • States decade growth rate 19.17 %. • The state’s water resources are just 2.28%

of India’s total water resources. • Indicating the low availability per-capita

water. • Source : Gujarat State Water Policy, 2004

& GWSSB, 2005

River basins in Gujarat State

17

71 97

North & South Gujarat Saurashtra Kutch

Total 185 river basins in the state of Gujarat 17 basins are in the North and South Gujarat; 71 and 97 basins are in Saurashtra and Kutch region.

82%

15.80%

2.20%

Availability of quantum of water resources in Gujarat State

The availability of quantum of water resources in the north and south Gujarat is 82% . Total water available in Saurashtra and Kutch region is 15.80% and 2.20% respectively.

Sardar Sarovar Project Command Area

• The Sardar Sarovar Project is one of the largest irrigation projects of India.

• The GCA is 3.43 M ha, while CCA is

2.12 M ha. • Around 8215 villages and 135

towns/cities of Gujarat shall be covered under Narmada Project.

• Soil distribution ranges from loamy to

clayey. • Crops grown in the area are maize,

cotton, pulses, paddy, bajra, castor, tobacco and pulses in Kharif and wheat, maize, gram, jowar, pulses, vegetables in Rabi season

Objectives

• To estimate the actual crop evapotranspiration of maize and wheat crops in the study area.

• To carry out daily soil moisture balance in root zone.

• To evaluate two different irrigation scheduling

strategies, conventional and model based.

Methodology • Data collection related to irrigation

and crop water requirements from various agencies.

• Estimation of Reference evapotranspiration by using daily meteorological data of the year 2008-09 .

• Computing crop evapotranspiration for selected major crops.

• Estimating irrigation requirements.

• Working out strategies for irrigation. • Software usage

• Using MABIA Method in WEAP It includes modules for estimating

reference evapotranspiration and soil water capacity. For a daily simulation of transpiration, evaporation, irrigation requirements and scheduling

• The method uses dual crop coefficient where crop coefficient value is divided into a ‘basal’ crop coefficient, kcb and a separate, Ke, representing evaporation from the soil surface.

• The method is an improvement over CROPWAT, which uses single crop coefficient and hence, does not separate evaporation and transpiration.

CROP WATER REQUIREMENT

• Crop water requirement = Evaporation +Transpiration +Seepage below the Ground + Drainage.

• Major component is evaporation and transpiration combined to gather named Evapotranspiration.

Reference ETo • The rate of evapotranspiration from a

reference surface is called reference evapotranspiration.

• ETo can be computed from meteorological

data and crop data. It depends on: • Weather parameters such as radiation,

maximum and minimum temperature, humidity and wind speed;

• Crop factors such as crop type, development

stage, crop height, type of irrigation and Management and environmental conditions

• Different climatological methods are used for

estimating reference crop evapotranspiration (ETo).

• The FAO Penman-Monteith method is

recommended as the sole standard method for the definition and computation of the ETo.

Potential Evapotranspiration under Standard conditions (ETc)

• Amount of water that would be consumed by evapotranspiration if no water restrictions exists.

• The soil has extensive moisture and it is covered by fully developed vegetation.

• Crop evapotranspiration (ETc) can be calculated by multiplying the reference ETo by crop coefficient Kc (Allen et al., 1998).

Crop Coefficient • Crop coefficient (Kc) can be calculated by two

approaches. • Single crop coefficient and dual crop coefficient. • In single crop coefficient, difference in

Evaporation and transpiration between field crops and reference grass surface can be integrated in a single crop coefficient (Kc).

• Dual crop coefficient is separated into two

coefficients :– • A basal crop coefficient (Kcb). Actual

evapotranspiration conditions when the soil surface is dry but sufficient root zone moisture is present to support full transpiration.

• A soil evaporation coefficient (Ke). Soil

evaporation coefficient (Ke) calculated when the topsoil dries out, and evaporation is less and evaporation reduces in proportion to the amount of water available in surface soil layer .

• Source : (Allen et al., 1998; Allen R. G. 2002; Allen et al., 2005

Actual Evapotranspiration under non standard conditions (ETc act)

• It is the amount of water that would be consumed by evapotranspiration in the catchment, including water supplied by irrigation also. It is also known as ET adj.

• The crop is under stress in the dry

soil when the potential energy of soil water drops below the threshold value.

• The effect of soil water stress can

be estimated by water stress coefficient (Ks) multiplied with basal crop coefficient (Kcb).

Computing crop evapotranspiration

• For Estimating irrigation requirements. • Estimating crop water requirements by calculating the

soil water balance of the root zone on daily basis. • Planning the depth and timing of irrigation • A daily water balance, expressed in terms of depletion

at the end of the day, is:

• Where = root zone depletion at the end of day i [mm] = depletion in the root zone at the end of the previous

day, i-1 [mm] = precipitation on day i [mm], limited by maximum

daily infiltration rate [mm] = surface runoff from the soil surface on day i [mm] = net irrigation depth on day i that infiltrates the soil

[mm] = capillary rise from the groundwater table on day i

[mm] = actual crop evapotranspiration on day i [mm] = water flux out of the root zone by deep percolation

on day i [mm]

Daily water balance

Reduced evaporation or transpiration due to limited moisture availability resulting from increasing soil moisture deficits:

• When soil is wet, stress coefficient (Ks) value is maximum and evapotranspiration occurs at potential rate.

• If there is precipitation or irrigation, Ks = 1. • As the soil surface dries, Ks<1 and when no

water is available for evapotranspiration in the top soil, Ks=0.

• To avoid crop water stress, irrigation needs to be applied. Ks can be calculated as follows (Allen et al., 1998; Allen R. G. 2002).

• • Where, TAW= Total Available Water (mm) RAW= Readily Available water (mm) Dr, i = root zone depletion at end of

day i (mm) p = depletion factor

Source:- Rushton et al., 2005.

Working out strategies for irrigation

ASE NO. CROP PLANTING DATE

HARVESTING DATE

IRRIGATION STRATEGY

IRRIGATION SCHEDULING

IRRIGATION AMOUNT

I raditional practices

Maize 5th July 22nd September

18th ,47th, 60th day 25 mm

Wheat 1st November

28th February

1st, 6th, 11th, 34th, 46th, 58th, 60th, 72nd, 84th day

60 mm

II Model

specified

Maize 5th July 22nd September

100% RAW

100% Depletion

Wheat 1st November

28th February

100% RAW

100% Depletion

• Irrigation to be applied before or at the moment when readily available water (RAW) is equal or greater than soil moisture depletion (SMD) to avoid crop water stress. i.e. (SMD <= RAW).

• Irrigation applied at fixed interval and fixed amount as per practices followed by localities.

• Irrigation to be applied when crop reaches at a fixed % of soil moisture depletion.

• The irrigation amount can also be determined according to fixed depth, % of deletion, % of RAW and % of TAW.

Reference PET Scenario : All Days (366)

Reference PETScenario: Reference, All Days (366)

2008

-03-

0120

08-0

3-07

2008

-03-

1320

08-0

3-19

2008

-03-

2520

08-0

3-31

2008

-04-

0720

08-0

4-13

2008

-04-

1920

08-0

4-25

2008

-05-

0120

08-0

5-07

2008

-05-

1320

08-0

5-20

2008

-05-

2620

08-0

6-01

2008

-06-

0720

08-0

6-13

2008

-06-

1920

08-0

6-25

2008

-07-

0220

08-0

7-08

2008

-07-

1420

08-0

7-20

2008

-07-

2620

08-0

8-01

2008

-08-

0720

08-0

8-14

2008

-08-

2020

08-0

8-26

2008

-09-

0120

08-0

9-07

2008

-09-

1320

08-0

9-19

2008

-09-

2620

08-1

0-02

2008

-10-

0820

08-1

0-14

2008

-10-

2020

08-1

0-26

2008

-11-

0120

08-1

1-08

2008

-11-

1420

08-1

1-20

2008

-11-

2620

08-1

2-02

2008

-12-

0820

08-1

2-14

2008

-12-

2120

08-1

2-27

2009

-01-

0220

09-0

1-08

2009

-01-

1420

09-0

1-20

2009

-01-

2620

09-0

2-02

2009

-02-

0820

09-0

2-14

2009

-02-

2020

09-0

2-26

Milli

met

er

12.512.011.511.010.510.09.59.08.58.07.57.06.56.05.55.04.54.03.53.02.52.01.51.00.50.0

Comparison of potential and actual crop coefficient for case 1

agriculture catchment

Kc PotentialScenario: Reference, All Days (366)

3/1/20

083/7

/2008

3/13/2

008

3/19/2

008

3/25/2

008

3/31/2

008

4/6/20

084/1

2/200

84/1

8/200

84/2

4/200

84/3

0/200

85/6

/2008

5/12/2

008

5/18/2

008

5/24/2

008

5/30/2

008

6/5/20

086/1

1/200

86/1

7/200

86/2

3/200

86/2

9/200

87/5

/2008

7/11/2

008

7/17/2

008

7/23/2

008

7/29/2

008

8/4/20

088/1

0/200

88/1

6/200

88/2

2/200

88/2

8/200

89/3

/2008

9/9/20

089/1

5/200

89/2

1/200

89/2

7/200

810

/3/20

0810

/9/20

0810

/15/20

0810

/21/20

0810

/27/20

0811

/2/20

0811

/8/20

0811

/14/20

0811

/20/20

0811

/26/20

0812

/2/20

0812

/8/20

0812

/14/20

0812

/20/20

0812

/26/20

081/1

/2009

1/7/20

091/1

3/200

91/1

9/200

91/2

5/200

91/3

1/200

92/6

/2009

2/12/2

009

2/18/2

009

2/24/2

009

1.351.301.251.201.151.101.051.000.950.900.850.800.750.700.650.600.550.500.450.400.350.300.250.200.150.100.050.00

Case 1 Traditional practices Kc Potential .

agriculture catchment

Kc ActualScenario: Reference, All Days (366)

3/1/20

083/7

/2008

3/13/2

008

3/19/2

008

3/25/2

008

3/31/2

008

4/6/20

084/1

2/200

84/1

8/200

84/2

4/200

84/3

0/200

85/6

/2008

5/12/2

008

5/18/2

008

5/24/2

008

5/30/2

008

6/5/20

086/1

1/200

86/1

7/200

86/2

3/200

86/2

9/200

87/5

/2008

7/11/2

008

7/17/2

008

7/23/2

008

7/29/2

008

8/4/20

088/1

0/200

88/1

6/200

88/2

2/200

88/2

8/200

89/3

/2008

9/9/20

089/1

5/200

89/2

1/200

89/2

7/200

810

/3/20

0810

/9/20

0810

/15/20

0810

/21/20

0810

/27/20

0811

/2/20

0811

/8/20

0811

/14/20

0811

/20/20

0811

/26/20

0812

/2/20

0812

/8/20

0812

/14/20

0812

/20/20

0812

/26/20

081/1

/2009

1/7/20

091/1

3/200

91/1

9/200

91/2

5/200

91/3

1/200

92/6

/2009

2/12/2

009

2/18/2

009

2/24/2

009

1.351.301.251.201.151.101.051.000.950.900.850.800.750.700.650.600.550.500.450.400.350.300.250.200.150.100.050.00

Case 1 Traditional practices Kc Actual. It is marginally lesser in initial period of wheat

Comparison of actual Crop Coefficient of both cases

agriculture catchment

Kc ActualScenario: Reference, All Days (366)

3/1/20

083/7

/2008

3/13/2

008

3/19/2

008

3/25/2

008

3/31/2

008

4/6/20

084/1

2/200

84/1

8/200

84/2

4/200

84/3

0/200

85/6

/2008

5/12/2

008

5/18/2

008

5/24/2

008

5/30/2

008

6/5/20

086/1

1/200

86/1

7/200

86/2

3/200

86/2

9/200

87/5

/2008

7/11/2

008

7/17/2

008

7/23/2

008

7/29/2

008

8/4/20

088/1

0/200

88/1

6/200

88/2

2/200

88/2

8/200

89/3

/2008

9/9/20

089/1

5/200

89/2

1/200

89/2

7/200

810

/3/20

0810

/9/20

0810

/15/20

0810

/21/20

0810

/27/20

0811

/2/20

0811

/8/20

0811

/14/20

0811

/20/20

0811

/26/20

0812

/2/20

0812

/8/20

0812

/14/20

0812

/20/20

0812

/26/20

081/1

/2009

1/7/20

091/1

3/200

91/1

9/200

91/2

5/200

91/3

1/200

92/6

/2009

2/12/2

009

2/18/2

009

2/24/2

009

1.351.301.251.201.151.101.051.000.950.900.850.800.750.700.650.600.550.500.450.400.350.300.250.200.150.100.050.00

Case 1 Traditional practices Kc actual

Case 2 Model

specified Kc actual

are marginally higher in

initial period

agriculture catchment

Kc ActualScenario: Reference, All Days (366)

3/1/20

083/7

/2008

3/13/2

008

3/19/2

008

3/25/2

008

3/31/2

008

4/6/20

084/1

2/200

84/1

8/200

84/2

4/200

84/3

0/200

85/6

/2008

5/12/2

008

5/18/2

008

5/24/2

008

5/30/2

008

6/5/20

086/1

1/200

86/1

7/200

86/2

3/200

86/2

9/200

87/5

/2008

7/11/2

008

7/17/2

008

7/23/2

008

7/29/2

008

8/4/20

088/1

0/200

88/1

6/200

88/2

2/200

88/2

8/200

89/3

/2008

9/9/20

089/1

5/200

89/2

1/200

89/2

7/200

810

/3/20

0810

/9/20

0810

/15/20

0810

/21/20

0810

/27/20

0811

/2/20

0811

/8/20

0811

/14/20

0811

/20/20

0811

/26/20

0812

/2/20

0812

/8/20

0812

/14/20

0812

/20/20

0812

/26/20

081/1

/2009

1/7/20

091/1

3/200

91/1

9/200

91/2

5/200

91/3

1/200

92/6

/2009

2/12/2

009

2/18/2

009

2/24/2

009

1.351.301.251.201.151.101.051.000.950.900.850.800.750.700.650.600.550.500.450.400.350.300.250.200.150.100.050.00

Comparison of ET actual and ET potential of both cases

CASE NO. CROP TOTAL ET actual (mm)

TOTAL ET pot

1 Maize 251.12 251.12

Wheat 478.13 479.82

2 Maize 251.39 251.39

Wheat 506.01 506.13

ET Actual ET Potential

ET Actual and PotentialScenario: Reference, All Days (366)

3/1/

2008

3/7/

2008

3/13

/200

83/

19/2

008

3/25

/200

83/

31/2

008

4/6/

2008

4/12

/200

84/

18/2

008

4/24

/200

84/

30/2

008

5/6/

2008

5/12

/200

85/

18/2

008

5/24

/200

85/

30/2

008

6/5/

2008

6/11

/200

86/

17/2

008

6/23

/200

86/

29/2

008

7/5/

2008

7/11

/200

87/

17/2

008

7/23

/200

87/

29/2

008

8/4/

2008

8/10

/200

88/

16/2

008

8/22

/200

88/

28/2

008

9/3/

2008

9/9/

2008

9/15

/200

89/

21/2

008

9/27

/200

810

/3/2

008

10/9

/200

810

/15/

2008

10/2

1/20

0810

/27/

2008

11/2

/200

811

/8/2

008

11/1

4/20

0811

/20/

2008

11/2

6/20

0812

/2/2

008

12/8

/200

812

/14/

2008

12/2

0/20

0812

/26/

2008

1/1/

2009

1/7/

2009

1/13

/200

91/

19/2

009

1/25

/200

91/

31/2

009

2/6/

2009

2/12

/200

92/

18/2

009

2/24

/200

9

Met

er

0.0080

0.0075

0.0070

0.0065

0.0060

0.0055

0.0050

0.0045

0.0040

0.0035

0.0030

0.0025

0.0020

0.0015

0.0010

0.0005

0.0000

Case 1: Traditional practices

Case 2: Model specified

ET Actual ET Potential

ET Actual and PotentialScenario: Reference, All Days (366)

2008

-03-

0120

08-0

3-07

2008

-03-

1320

08-0

3-19

2008

-03-

2520

08-0

3-31

2008

-04-

0620

08-0

4-12

2008

-04-

1820

08-0

4-24

2008

-04-

3020

08-0

5-06

2008

-05-

1220

08-0

5-18

2008

-05-

2420

08-0

5-30

2008

-06-

0520

08-0

6-11

2008

-06-

1720

08-0

6-23

2008

-06-

2920

08-0

7-05

2008

-07-

1120

08-0

7-17

2008

-07-

2320

08-0

7-29

2008

-08-

0420

08-0

8-10

2008

-08-

1620

08-0

8-22

2008

-08-

2820

08-0

9-03

2008

-09-

0920

08-0

9-15

2008

-09-

2120

08-0

9-27

2008

-10-

0320

08-1

0-09

2008

-10-

1520

08-1

0-21

2008

-10-

2720

08-1

1-02

2008

-11-

0820

08-1

1-14

2008

-11-

2020

08-1

1-26

2008

-12-

0220

08-1

2-08

2008

-12-

1420

08-1

2-20

2008

-12-

2620

09-0

1-01

2009

-01-

0720

09-0

1-13

2009

-01-

1920

09-0

1-25

2009

-01-

3120

09-0

2-06

2009

-02-

1220

09-0

2-18

2009

-02-

24

Milli

met

er

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

In maize crop, actual evapotranspiration is found same in Case-I and Case-II as this crop is not under water stress in both the cases. But, in case of wheat crop; the water stress condition has resulted lower value of actual evapotranspiration in Case-I

Soil Moisture Balance

CASE NO. CROP

DECREASE IN SOIL MOISTURE (mm)

TOTAL PRECIPITATION (mm)

TOTAL IRRIGATION* (mm)

TOTAL RUNOF F (mm)

TOTAL FLOW TO GROUND WATER (mm)

INCREASE IN SOIL MOISTURE (mm)

1 Maize 109.74 883 75 211.78 508.42 96.404

Wheat 446.27 0 540 101.05 108.31 452.91

2 Maize 113.78 883 21.69 178.17 484.23 104.68

Wheat 470.85 0 349.13 0 0 313.97

Surface Runoff Precipitation Irrigation Increase in Soil MoistureFlow to Groundwater Decrease in Soil Moisture

Land Class Inflow s and Outflow sScenario: Reference, All Days (366)

3/1/20

083/7

/2008

3/14/2

008

3/21/2

008

3/28/2

008

4/4/20

084/1

1/200

84/1

7/200

84/2

4/200

85/1

/2008

5/8/20

085/1

5/200

85/2

2/200

85/2

9/200

86/4

/2008

6/11/2

008

6/18/2

008

6/25/2

008

7/2/20

087/9

/2008

7/15/2

008

7/22/2

008

7/29/2

008

8/5/20

088/1

2/200

88/1

9/200

88/2

5/200

89/1

/2008

9/8/20

089/1

5/200

89/2

2/200

89/2

9/200

810

/5/20

0810

/12/20

0810

/19/20

0810

/26/20

0811

/2/20

0811

/9/20

0811

/15/20

0811

/22/20

0811

/29/20

0812

/6/20

0812

/13/20

0812

/20/20

0812

/26/20

081/2

/2009

1/9/20

091/1

6/200

91/2

3/200

91/3

0/200

92/5

/2009

2/12/2

009

2/19/2

009

2/26/2

009

Cubic

Met

er

9.0

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

-9.0

Decrease in Soil MoistureFlow to Groundwater Increase in Soil MoistureIrrigation Precipitation Surface Runoff

Land Class Inflow s and Outflow sScenario: Reference

3/1/20

083/7

/2008

3/13/2

008

3/20/2

008

3/27/2

008

4/2/20

084/9

/2008

4/16/2

008

4/23/2

008

4/29/2

008

5/6/20

085/1

3/200

85/2

0/200

85/2

6/200

86/2

/2008

6/9/20

086/1

5/200

86/2

2/200

86/2

9/200

87/6

/2008

7/12/2

008

7/19/2

008

7/26/2

008

8/2/20

088/8

/2008

8/15/2

008

8/22/2

008

8/29/2

008

9/4/20

089/1

1/200

89/1

8/200

89/2

5/200

810

/1/20

0810

/8/20

0810

/15/20

0810

/22/20

0810

/28/20

0811

/4/20

0811

/11/20

0811

/18/20

0811

/24/20

0812

/1/20

0812

/8/20

0812

/14/20

0812

/21/20

0812

/28/20

081/4

/2009

1/10/2

009

1/17/2

009

1/24/2

009

1/31/2

009

2/6/20

092/1

3/200

92/2

0/200

92/2

7/200

9

Milli

met

er

160

140

120

100

80

60

40

20

0

-20

-40

-60

-80

-100

Case 1: Traditional practices

Case 2: Model specified

The model specified irrigation strategy prevents runoff and deep percolation

Soil Moisture Depletion, RAW And TAW

Case-I Traditional Practices

Case-II Triggering Irrigation when Soil Moisture Depletion reaches 100% of RAW

Readily Available WaterSoil Moisture DepletionTotal Available Water

Depletion and Available WaterScenario: Reference, All Days (366)

2008

-03-01

2008

-03-07

2008

-03-13

2008

-03-19

2008

-03-25

2008

-03-31

2008

-04-07

2008

-04-13

2008

-04-19

2008

-04-25

2008

-05-01

2008

-05-07

2008

-05-13

2008

-05-20

2008

-05-26

2008

-06-01

2008

-06-07

2008

-06-13

2008

-06-19

2008

-06-25

2008

-07-02

2008

-07-08

2008

-07-14

2008

-07-20

2008

-07-26

2008

-08-01

2008

-08-07

2008

-08-14

2008

-08-20

2008

-08-26

2008

-09-01

2008

-09-07

2008

-09-13

2008

-09-19

2008

-09-26

2008

-10-02

2008

-10-08

2008

-10-14

2008

-10-20

2008

-10-26

2008

-11-01

2008

-11-08

2008

-11-14

2008

-11-20

2008

-11-26

2008

-12-02

2008

-12-08

2008

-12-14

2008

-12-21

2008

-12-27

2009

-01-02

2009

-01-08

2009

-01-14

2009

-01-20

2009

-01-26

2009

-02-02

2009

-02-08

2009

-02-14

2009

-02-20

2009

-02-26

Millim

eter

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

Readily Available WaterSoil Moisture DepletionTotal Available Water

Depletion and Available WaterScenario: Reference, All Days (366)

2008

-03-

0120

08-0

3-07

2008

-03-

1320

08-0

3-19

2008

-03-

2520

08-0

3-31

2008

-04-

0720

08-0

4-13

2008

-04-

1920

08-0

4-25

2008

-05-

0120

08-0

5-07

2008

-05-

1320

08-0

5-20

2008

-05-

2620

08-0

6-01

2008

-06-

0720

08-0

6-13

2008

-06-

1920

08-0

6-25

2008

-07-

0220

08-0

7-08

2008

-07-

1420

08-0

7-20

2008

-07-

2620

08-0

8-01

2008

-08-

0720

08-0

8-14

2008

-08-

2020

08-0

8-26

2008

-09-

0120

08-0

9-07

2008

-09-

1320

08-0

9-19

2008

-09-

2620

08-1

0-02

2008

-10-

0820

08-1

0-14

2008

-10-

2020

08-1

0-26

2008

-11-

0120

08-1

1-08

2008

-11-

1420

08-1

1-20

2008

-11-

2620

08-1

2-02

2008

-12-

0820

08-1

2-14

2008

-12-

2120

08-1

2-27

2009

-01-

0220

09-0

1-08

2009

-01-

1420

09-0

1-20

2009

-01-

2620

09-0

2-02

2009

-02-

0820

09-0

2-14

2009

-02-

2020

09-0

2-26

Milli

met

er

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

Concluding Remarks • In maize crop, actual

evapotranspiration is found same in Case-I and Case-II as this crop is not under water stress in both the cases.

• But, in case of wheat crop;

the water stress condition has resulted lower value of actual evapotranspiration in Case-I.

• The model specified irrigation

strategy also prevents runoff and deep percolation.

• Thus saving of water can be achieved by application of WEAP in determining irrigation requirements in real time condition.

• The prevention of water

stress condition by model application also improves yield of crop

References • Allen R. G., Pereira L.S., Raes D. and Smith M. 1998. Crop evapotranspiration - Guidelines for

computing crop water requirements –United Nations Food and Agriculture Organization, Irrigation and drainage paper 56 Produced by: Natural Resources Management and Environment Department

• Allen R. G. 2002. Evapotranspiration : The FAO-56 Dual Crop Coefficient Method and Accuracy of predictions for Project-wide Evapotranspiration, International meeting on Advances in Drip/Micro Irrigation

• Allen R. G. 2005. FAO-56 Dual crop coefficient Method for estimating Evaporation from soil and application Extensions. Journal of Irrigation and Drainage Engineering ASCE/January/February 2005.

• Kumar R., Vijay Shankar and Mahesh Kumar. Modeling of Crop Reference Evapotranspiration : A Review. Universal journal of Environment Research and Technology, 1(3):239-246

• Rossa R. D., Paredesa P., Rdriguesa G. C., Alvesa I. , Fernandoa R. M., Pereirra L. S. 2012. Implementing the Dual Crop Coefficient approach in interactive software. Agricultural Water Management, 103 : 8-24

• Rushton K. R., Eilers V.H.M., Carter R. C. 2005. Improved soil moisture balance methodology for recharge estimation, Journal of Hydrology 318 (2006): 379-399.

• WEAP 2011. Tutorial modules & and user guide, Sieber J., Purkey D., Stockholm Environment Institute (SEI)

Thank you

Irrigation Strategy for Maize and Wheat Crop

CASE NO. CROP PLANTING DATE

HARVESTING DATE

IRRIGATION STRATEGY

IRRIGATION SCHEDULING

IRRIGATION AMOUNT

I Maize 5th July 22nd September

18th ,47th, 60th day 25 mm

Wheat 1st November 28th February

1st, 6th, 11th, 34th, 46th, 58th, 60th, 72nd, 84th day

60 mm

II Maize 5th July 22nd September 100% RAW 100%

Depletion

Wheat 1st November 28th February 100% RAW 100% Depletion

Motivation of the study • Complexities involved in

estimation of Crop water requirement with different parameters. (Weather, Crop, Soil)

• The intricacy involved in measurement of rainfall and/or irrigation losses by surface run off, percolation beyond root zone and soil moisture use of crops.

• Uncertainties arise in estimating the moisture availability.

• Development in recording meteorological data using automated instruments on daily as well as hourly basis.

• Using this data it is also possible to precisely estimate reference evapotranspiration.

• Using advance model such as Penman Monteith it is possible to integrate all this technology related to data and model to precisely monitor the irrigation process (soil moisture balance).

• The applying the water to the

crops when it is not essential; while not applying when it is desirable.

Basal Crop and Soil Evaporation Coefficients

• Kcb represents actual evapotranspiration conditions when the soil surface is dry but sufficient root zone moisture is present to support full transpiration.

• Soil evaporation coefficient (Ke) calculated when the topsoil dries out, and evaporation is less and evaporation reduces in proportion to the amount of water available in surface soil layer (Allen et al., 1998; Allen R. G. 2002; Allen et al., 2005).

Runoff and Flow to Groundwater

during Irrigation of Maize and Wheat Crop

CASE NO. CROP TOTAL ETactual (mm)

TOTAL PRECIPITATION (mm)

TOTAL IRRIGATION* (mm)

TOTAL RUNOFF (mm)

TOTAL FLOW TO GROUND WATER (mm)

1 Maize 251.12 883 75 211.78 508.42

Wheat 478.13 0 540 101.05 108.31

2 Maize 251.39 883 21.69 178.17 484.23

Wheat 506.01 0 349.13 0 0

Land Class Inflows and Outflows Surface Runoff Precipitation Irrigation Increase in Soil MoistureFlow to Groundwater Decrease in Soil Moisture

Land Class Inflow s and Outflow sScenario: Reference, All Days (366)

3/1/20

083/7

/2008

3/14/2

008

3/21/2

008

3/28/2

008

4/4/20

084/1

1/200

84/1

7/200

84/2

4/200

85/1

/2008

5/8/20

085/1

5/200

85/2

2/200

85/2

9/200

86/4

/2008

6/11/2

008

6/18/2

008

6/25/2

008

7/2/20

087/9

/2008

7/15/2

008

7/22/2

008

7/29/2

008

8/5/20

088/1

2/200

88/1

9/200

88/2

5/200

89/1

/2008

9/8/20

089/1

5/200

89/2

2/200

89/2

9/200

810

/5/20

0810

/12/20

0810

/19/20

0810

/26/20

0811

/2/20

0811

/9/20

0811

/15/20

0811

/22/20

0811

/29/20

0812

/6/20

0812

/13/20

0812

/20/20

0812

/26/20

081/2

/2009

1/9/20

091/1

6/200

91/2

3/200

91/3

0/200

92/5

/2009

2/12/2

009

2/19/2

009

2/26/2

009

Cubic

Met

er

9.0

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

-9.0

Case 1

Case 2 Decrease in Soil MoistureFlow to Groundwater Increase in Soil MoistureIrrigation Precipitation Surface Runoff

Land Class Inflow s and Outflow sScenario: Reference

3/1/20

083/7

/2008

3/13/2

008

3/20/2

008

3/27/2

008

4/2/20

084/9

/2008

4/16/2

008

4/23/2

008

4/29/2

008

5/6/20

085/1

3/200

85/2

0/200

85/2

6/200

86/2

/2008

6/9/20

086/1

5/200

86/2

2/200

86/2

9/200

87/6

/2008

7/12/2

008

7/19/2

008

7/26/2

008

8/2/20

088/8

/2008

8/15/2

008

8/22/2

008

8/29/2

008

9/4/20

089/1

1/200

89/1

8/200

89/2

5/200

810

/1/20

0810

/8/20

0810

/15/20

0810

/22/20

0810

/28/20

0811

/4/20

0811

/11/20

0811

/18/20

0811

/24/20

0812

/1/20

0812

/8/20

0812

/14/20

0812

/21/20

0812

/28/20

081/4

/2009

1/10/2

009

1/17/2

009

1/24/2

009

1/31/2

009

2/6/20

092/1

3/200

92/2

0/200

92/2

7/200

9

Millim

eter

160

140

120

100

80

60

40

20

0

-20

-40

-60

-80

-100

• Penman- Monteith Equation: • (1)

• Where, ETo =reference evapotranspiration [mm day-1],

Rn =net radiation at the crop surface [MJ m-2 day-1], G=soil heat flux density [MJ m-2 day-1], T= mean daily air temperature at 2 m height [°C], u2=wind speed at 2 m height [m s-1], es=saturation vapour pressure [kPa], ea=actual vapour pressure [kPa], es-ea=saturation vapour pressure deficit [kPa], ∆=slope vapour pressure curve [kPa °C-1], γ=psychrometric constant [kPa °C-1].

Working out strategies for irrigation

• Irrigation to be applied before or at the moment when readily available water (RAW) is equal or greater than soil moisture depletion (SMD) to avoid crop water stress. i.e. (SMD <= RAW).

• Irrigation applied at fixed interval and fixed amount as per practices followed by localities.

• Irrigation to be applied when crop reaches at a fixed % of soil moisture depletion.

• The irrigation amount can also be determined according to fixed depth, % of deletion, % of RAW and % of TAW.