oasification in iran

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December 2010


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Integrated modelling of the SoilWater-Atmosphere-Plant System {Processes}

Impact on surface water (+/-) and direction of flows (< >).

Precipitation /irrigation

Interception

Transpiration

Soil evaporation

Surface runoff/on Drainage / infiltration

Deep percolation / Seepage

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Integrated modelling of the SoilWater-Atmosphere-Plant System

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www.swap.alterra.nl


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Integrated modelling of the SoilWater-Atmosphere-Plant System{Equations}

Soil water flow : Richards equation based on Darcys Law.

Soil hydraulic function: Van Genuchten and Mualem.

Hysteresis: Scott et al.

Precipitation : Rain gauges or tipping buckets

Interception: Von Hoyningen-Hune and Braden

Transpiration: Penman-Monteith Soil evaporation: Penman-Monteith

Surface runoff: Horton / Dunne - {Surface runoff is defined as a function of theponding height}

Deep percolation/seepage: {Soil water f low/soil hydraulic function}

Drainage/infiltration: Hooghoudt and Ernst8


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Shortcomings of the SWAP model

Temporal restrictions as it was developed for calculations withdaily meteorological input data.

Horizontal and vertical space of application are limited. It is a one dimensional model designed for processes in the

unsaturated zone. In the saturated zone a pseudo two dimensional approach allows

interaction with a surface water system but this is very sensitiveto the scale of the application.

No simulation of regional groundwater Hydrology.

No interaction of between crop growth and nutrient availability. No non equilibrium sorption of pesticides and no simulation of

metabolites. Not compatible with all versions of Windows operating system.

(Kroes, J.G., 2004)

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The Borkhar irrigation district, Iran {Introduction}

SWAP team contacted concerning data for an oasification/(semi-)arid casestudy. Dr. Jos van Dam of Wageningen UR/SWAP team suggested:

Vazifedoust, M., J.C. van Dam, R.A. Feddes and M. Feizi, 2008. Increasing water productivity

of irrigated crops under limited water supply at field scale. Agricultural Water Management,95, 89-102.

Borkhar irrigation district is located north of the ancient town of Esfahan, Iran.

The region regularly faces widespread drought.

The district has a predominantly arid to semi-arid desert climate.

Water scarcity means that limited available water should be used efficiently. In order to avoid desertification increasing water productivity (WP) of irrigated

crops under limited water supply is of vital importance.

SWAP was used to evaluate irrigation strategies.

(Vazifedoust, M., J.C. van Dam, R.A. Feddes and M. Feizi, 2008)

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The field (M2) in the Borkhar irrigation district were planted with maize during 2004-2005. SWAP was calibrated using data from the two sites to simulate increasing water productivity

of irrigated crops in the Borkhar region under conditions of water scarcity.

Photosynthesis and Transpiration related through diffusion processes of CO2 and H2O.

Water Use Efficiency= Dry Matter Growth Rate Transpiration Rate.

In irrigation practices Water Productivity (WP) is a proxy for Water Use Efficiency. Integrating Dry Matter Yield and Transpiration over time (growing season) gives > Efficiency

of water used by crop = WPT (Water Productivity with respect to Transpiration).

At field scale it is difficult to distinguish Transpiration T (mm) from Soil Evaporation E (mm)hence instead of WPT we use WPET (Water Productivity with respect to Evapotranspiration).

Total Dry Matter Yield (Y) is converted into Marketable Yield (YM).

WP values for the crop were simulated using Transpiration (T), Evapotranspiration (ET),

Irrigation (I) and Marketable Yield (YM). If Irrigation + Precipitation is considered water use of the crop then WPI+P may be used

which under arid conditions tends towards WPI and WP$ as an expression in terms of money.


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WP indicators express the benefit derived from the consumption of waterand assess strategies for scarce water usage.

WP indicators provide a vision of where and when water could be saved. WP indicators are useful for looking at the potential increase in crop yield

that may result from increased water availability. WP indicators are necessary to plan for efficient irrigation and water

management under water scarcity . SWAP helps simulate the water balance components and therefore

increase our ability to improve water productivity (WP) under watershortage.

SWAP/ WP - Which irrigation strategies help us achieve more crop perdrop?


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The Borkhar irrigation district, Iran {Data collection}

Data collected from the maize field:

Meteorological data. Irrigation data. Soil layers, texture and bulk density. Crop parameters for the detailed crop growth module. Soil layers and derived soil hydraulic parameters.

Root mean square error RMSE and number of observationsfor soil moisture content. SWAP water balance components for maize.


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The Borkhar irrigation district, Iran {SWAP simulation}

Recorded data input into SWAP and simulation results used to calculate:

Simulated total dry matter yield (Y), simulated dry matter of storage organ(YSO), simulated marketable yields (YM), root mean square error RMSEand number of observations for the maize crop.

Prices ($ kg-1) and costs ($ kg-1) for the maize crop in the Borkhar irrigationdistrict in 2005 applied to calculate net return and water productivity.

Water productivity indicators (WPT), (WPET) and (WPI) in (kg m3) and ($m3) for the field.

Water productivity indicators (WPT), (WPET) and (WPI) in (kg m3

) and ($m3) for the maize crop.


Oasification - Simulating irrigationstrategies using SWAP

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(Vazifedoust, M., J.C. van Dam, R.A. Feddes and M. Feizi, 2008) 28


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Oasification - Simulating irrigation

strategies using SWAP

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The Borkhar irrigation district, Iran {Results}


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Oasification - Simulating irrigation

strategies using SWAP

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Conculsion

- Borkhar - High irrigation requirement, high transpirationrates and negligible rainfall

- The maize field (M2) suffers from water deficit and requiresoptimised irrigation

- Over irrigation can lead to nutrient leaching and thereforedecreased yield

- The semi-arid climate of the region is not conducive toachieving high crop yields

- Fodder maize provides the highest economic benefit in theBorkhar irrigation district relative to other crops


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Conclusion (2)

Soil characteristics of the region have surprisingly

high clay content. By reducing cultivated land we can actually

increase economic gains

Water balance can tell us a lot about soil profileand soil moisture content

Relatively successful oasification strategy

More crop per drop

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Further research into Oasification and SWAP :

Oasification blog {Group website with links}www.oasification.org/

United Nations Convention to Combat Desertificationwww.unccd.int/

Food and Agriculture Organisation (UN)

www.fao.org/desertification/

SWAPwww.swap.alterra.nl/

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Thank you

oasification in iran

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