Using seasonal climate forecasts and the

CROPWAT model for irrigation planning and

management

Dr. Adriana-Cornelia Marica & Alexandru DanielDr. Adriana-Cornelia Marica & Alexandru Daniel

ROMANIAROMANIA

WMO & COST 718 Expert Meeting on Weather, Climate and WMO & COST 718 Expert Meeting on Weather, Climate and Farmers, Geneve, Farmers, Geneve, Switzerland,Switzerland, 15-18 November 2004 15-18 November 2004

Aim:Aim:

demonstrate how seasonal climate demonstrate how seasonal climate forecast combined with the CROPWAT model forecast combined with the CROPWAT model can estimate the soil water deficitscan estimate the soil water deficits during during maize growing season of 2003.maize growing season of 2003.

describe the experience of Romania as an describe the experience of Romania as an example of application of seasonal climate example of application of seasonal climate forecast in the agriculture sector;forecast in the agriculture sector;

Objectives:Objectives:

evaluate and predict a few months in advance evaluate and predict a few months in advance the daily and total soil moisture deficit during the daily and total soil moisture deficit during maize vegetation period in the rainfed and maize vegetation period in the rainfed and irrigated conditions;irrigated conditions;

compare various options for water supply and compare various options for water supply and irrigation management;irrigation management;

assess yield reduction due to crop stressassess yield reduction due to crop stress under under rainfed conditions or deficit irrigation;rainfed conditions or deficit irrigation;

compare the model results and analyze the compare the model results and analyze the skill level of seasonal forecast;skill level of seasonal forecast;

Sites in the southern region of Romania Sites in the southern region of Romania used for soil water deficits assessmentused for soil water deficits assessment

Seasonal Forecasts:Seasonal Forecasts:

predict major climate trends over a period of predict major climate trends over a period of several months to a few seasons;several months to a few seasons;

indicate areas where there is an increased indicate areas where there is an increased likelihood of some deviation from the climate mean likelihood of some deviation from the climate mean (dry or wet, warm or cold conditions);(dry or wet, warm or cold conditions);

Benefits for Agriculture:Benefits for Agriculture:

offer the potential for farmers to plan and take offer the potential for farmers to plan and take decisions on crop management (if to sow or not, to decisions on crop management (if to sow or not, to spray or not, to irrigate or not);spray or not, to irrigate or not);

modify decisions to decrease unwanted impacts or modify decisions to decrease unwanted impacts or take advantage of expected favorable conditions.take advantage of expected favorable conditions.

CALARASI 2003

0

20

40

60

80

100

120

VI VII VIII IX

mm

0

5

10

15

20

25

30

de

gre

e C

Normal Rainfall Forecast Rainfall

Normal Av.Temp. Forecast Av.Temp.

TARGU JIU 2003

0

20

40

60

80

100

120

VI VII VIII IX

mm

0

5

10

15

20

25

30

de

gre

e C

Normal Rainfall Forecast Rainfall

Normal Av.Temp. Forecast Av.Temp.

The monthly The monthly means values of means values of temperature and temperature and

rainfall rainfall estimated by estimated by

seasonal seasonal forecast for the forecast for the interval June-interval June-

September 2003September 2003, , as compared as compared

with the normalwith the normal

Functions ofFunctions of CROPWAT model:CROPWAT model:

• Is a method to support decision making for irrigation Is a method to support decision making for irrigation planning and management;planning and management;

• Calculates reference evapotranspiration, crop water Calculates reference evapotranspiration, crop water requirements and irrigation requirements;requirements and irrigation requirements;

• Develop irrigation schedules based on a daily soil-Develop irrigation schedules based on a daily soil-moisture balance;moisture balance;

• Allows the development of recommendations for Allows the development of recommendations for improved irrigation practices, the planning of irrigation improved irrigation practices, the planning of irrigation schedules and the assessment of production under schedules and the assessment of production under rainfed conditions or deficit irrigationrainfed conditions or deficit irrigation

Input data used:Input data used:

Monthly means climatic data:Monthly means climatic data:

• measured during April-May 2003 measured during April-May 2003 (min.& max. temp., (min.& max. temp., humidity, sunshine duration, wind speed and monthly rainfall)humidity, sunshine duration, wind speed and monthly rainfall)• estimated by seasonal forecasat for June-September estimated by seasonal forecasat for June-September 2003 2003 (air temperature and rainfall)(air temperature and rainfall)

Crop data:Crop data:

Soil data:Soil data: total available moisture: 227/191 mmtotal available moisture: 227/191 mm initial available soil moisture: 170 mm/163 mminitial available soil moisture: 170 mm/163 mm maximum root infiltration rate: 40 mm/daymaximum root infiltration rate: 40 mm/day maximum rooting depth: 1mmaximum rooting depth: 1m

real sowing date: 20 April real sowing date: 20 April (Calarasi)(Calarasi) / 5 May 2003 / 5 May 2003 (Tg.Jiu)(Tg.Jiu) standard crop coefficient (Kc), crop yield data (Ky)standard crop coefficient (Kc), crop yield data (Ky) and depletion fraction (P)and depletion fraction (P)

Model application:Model application:

• Running the CROPWAT model with rainfed maize iRunning the CROPWAT model with rainfed maize in n the forecasted and real weather conditions;the forecasted and real weather conditions;

• Running the model with application of irrigation using Running the model with application of irrigation using different scheduling criteria:different scheduling criteria:

irrigate at fixed intervals and depths;irrigate at fixed intervals and depths;

irrigate when 70% of total available soil moistureirrigate when 70% of total available soil moisture

depletion occursdepletion occurs;;

irrigate when 70 and 100% of readily soil moisture irrigate when 70 and 100% of readily soil moisture

depletion occursdepletion occurs..

ResultsResultsCALARASI 20030

50

100

150

200

250

mm

TAM RAM SMD

Daily soil moisture Daily soil moisture deficit simulated with deficit simulated with

CROPWAT model CROPWAT model during rainfed maize during rainfed maize growing season, in growing season, in

the weather forecast the weather forecast conditions for conditions for summer 2003summer 2003

TAM: total available TAM: total available moisture,moisture,

RAM: readily available RAM: readily available moisturemoisture

SMD: soil moisture deficitSMD: soil moisture deficit

TARGU-JIU 20030

50

100

150

200

250

mm

TAM RAM SMD

Cumulated values on the whole Cumulated values on the whole vegetation period of maize variables vegetation period of maize variables

simulated with CropWat in the simulated with CropWat in the estimated weather condition of 2003estimated weather condition of 2003

Sites Total Rain (mm)

Eff.Rain (mm)

SMD (mm)

Yield Red. (%)

Calarasi

Tg. Jiu

144

398

135

339

443

165

53%

4%

Soil Moisture Change When Scheduling Maize(Irrigate at fixed int.& depth)

0

50

100

150

200

250

mm

Net.Irr. TAM RAM SMD

Soil Moisture Change When Scheduling Maize(Irrigate when 70% of TAM depletion occurs)

0

50

100

150

200

250

mm

Net.Irr. TAM RAM SMD

Simulated results for irrigated maize at Simulated results for irrigated maize at Calarasi site in the forecast weather conditions Calarasi site in the forecast weather conditions

for summer 2003, using two scheduling for summer 2003, using two scheduling options:options:

4 irrigation of 60mm Irrigate 70% of TAM4 irrigation of 60mm Irrigate 70% of TAM

Soil Moisture Change When Scheduling Maize(Irrigate when 70% of RAM depletion occurs)

0

50

100

150

200

250

mm

Net.Irr. TAM RAM SMD

Soil Moisture Change When Scheduling Maize(Irrigate when 100% of RAM depletion occurs)

0

50

100

150

200

250

mm

Net.Irr. TAM RAM SMD

Simulated results for irrigated maize at Calarasi Simulated results for irrigated maize at Calarasi site in the forecast weather conditions for site in the forecast weather conditions for summer 2003, using summer 2003, using “optimal“optimal” scheduling ” scheduling

criteria:criteria:

Irrigate 70% of RAMIrrigate 70% of RAM Irrigate 100% of RAMIrrigate 100% of RAM

The effects of the rainfed and The effects of the rainfed and different irrigation scheduling different irrigation scheduling simulated with CROPWAT at simulated with CROPWAT at

Calarasi siteCalarasi site

OptionsOptions Net Net irrigationirrigation

(mm)(mm)

Yield Yield reductionreduction

(%)(%)

RainfedRainfed

Irr.fixed int&depthIrr.fixed int&depth

Irr. 70% of TAMIrr. 70% of TAM

Irr. 70% of RAMIrr. 70% of RAM

Irr. 100% of RAMIrr. 100% of RAM

--

240240

366366

405405

449449

53%53%

24%24%

10%10%

--

--

SOIL MOISTURE DEFICIT

0

100

200

300

400

500

600

CALARASI TARGU JIU

SM

D (

mm

)

Forecast

Real

Changes in Changes in growing season growing season rainfall and soil rainfall and soil moisture deficit moisture deficit in the seasonal in the seasonal weather forecast weather forecast as compared with as compared with the real weather the real weather conditionsconditions

Skill levelSkill levelTOTAL RAINFALL

0

100

200

300

400

500

CALARASI TARGU JIU

Rain

(m

m)

Forecast

Real

-35%

-60%

+11%

+91%

Effects of Effects of estimated and estimated and real weather real weather conditions on conditions on rainfed maize rainfed maize yield reduction yield reduction due to crop due to crop stressstress

ResultsResults

ESTIMATED MAIZE YIELD REDUCTION

0

10

20

30

40

50

60

70

CALARASI TG.JIU

%

Forecast

Real

CONCLUSIONSCONCLUSIONS

The application of seasonal weather forecast combined The application of seasonal weather forecast combined with CROPWAT model allows the estimation of soil water with CROPWAT model allows the estimation of soil water supply conditions with 3-4 months in advance and in case supply conditions with 3-4 months in advance and in case a skillful forecast can provides useful information for a skillful forecast can provides useful information for farmers to make decisions on irrigation planning and farmers to make decisions on irrigation planning and management in a dry season, avoiding yield reduction.management in a dry season, avoiding yield reduction.

According to the seasonal forecast for summer 2003 According to the seasonal forecast for summer 2003 and the first month of autumn, in Targu Jiu the maize crop and the first month of autumn, in Targu Jiu the maize crop was not affected by the soil water deficit, while in Calarasi was not affected by the soil water deficit, while in Calarasi the high soil moisture deficit led to yield reduction up to the high soil moisture deficit led to yield reduction up to 53% from the productive potential;53% from the productive potential;

In the real weather conditions, the maize crop was In the real weather conditions, the maize crop was affected by drought at both sites, the yield reduction affected by drought at both sites, the yield reduction percentage was 64% in Calarasi and 41% in Targu Jiu;percentage was 64% in Calarasi and 41% in Targu Jiu;

In the most sensitive areas to droughtIn the most sensitive areas to drought by application by application of irrigation the yield losses would be significantly of irrigation the yield losses would be significantly reduced;reduced;

The comparative analysis of the simulated results The comparative analysis of the simulated results has emphasized a higher skill level of seasonal forecast has emphasized a higher skill level of seasonal forecast for Calarasi site than for Targu Jiu site;for Calarasi site than for Targu Jiu site;

The precision level of forecast information for The precision level of forecast information for temperature was higher than for rainfall at both sites.temperature was higher than for rainfall at both sites.

CONCLUSIONSCONCLUSIONS

THANK YOU THANK YOU FOR YOUR FOR YOUR ATTENTIONATTENTION