Water productivity analysis from field to regional scale
Keywords: distributed modelling, inverse modelling, data assimilation, irrigation water management, salinization, Bhakra Irrigation System,India.In agricultural production systems, a profound water productivity analysis requires quantification of different hydrological variables such as transpiration, evapotranspiration and percolation, and biophysical variables such as dry matter and grain (or seed) production in relation to different irrigation and agricultural management practices.Sirsa district, located in the Bhakra Irrigation System in Haryana (India), has been selected for a case study. The study area, covering 0.42 million ha, is characterized by typical problems of canal water scarcity, poor groundwater quality, rising and declining groundwater levels, waterlogging and secondary salinization, and less than optimal crop production.The field scale ecohydrological Soil-Water-Atmosphere-Plant (SWAP) model when coupled with field experiments, remote sensing and GIS as used in this study, increases the capabilities of reliable simulation of water productivity from field to regional scale.SWAP was calibrated and validated using the observations at different farmer fields representing various combinations of soil, crop, and irrigation amount and its quality. Inverse modelling was used to determine indirectly the soil hydraulic parameters at fieldscale,and the observed soil moisture and salinity profiles were used as system response. The calibrated and validated SWAPincluding detailed crop growth simulations was extended in a distributed mode to quantify the required hydrological and biophysical variables at regional scale. Field experiments, satellite images and existing geographical data were used to derive and aggregate the input parameters and boundary conditions at the appropriate scales. The accuracy and reliability of spatial aggregation of representative input parameters was determined by comparingthe evapotranspiration simulated by distributed SWAP modelling withindependent satellite remote sensing basedevapotranspirationdata at different spatial and temporal scales.The water productivity WP was computed for different scales and in different forms viz., crop yield per unit amount of water used in transpiration T , evapotranspiration ET , or ET plus percolation from field irrigations and seepage losses from the conveyance system. Considerable spatial variation in WP values was observed not only for different crops but also for the same crop. For instance, the WPET , expressed in the terms of grain yield per unit amount of ET , for wheat varied from 1.22 to 1.56 kg m -3 among different farmer fields monitored in Sirsa district during the agricultural year 2001-02. At field scale, the average WPET (kg m -3 ) was 1.39 for wheat, 0.94 for rice and 0.23 for cotton, and represents its average values for the climatic and growing conditions in Northwest India. Factors responsible for low values of WP include a high share (20 to 40%) of soil evaporation into ET for rice, percolation from fields and seepage losses (34 to 43% of the total canal inflow) from the conveyance system. The simulated water and salt limited crop yields were higher than the recorded crop yields, and indicate substantial nutritional, pest and disease stresses. Also, the study revealed a considerable fluctuation of the estimated net groundwater recharge and salt build-up over the main canal commands in Sirsa district. Better crop management, reduction in seepage losses and canal water reallocation (15%) from the northern to the central canal commands are recommended to improve the WP , and to halt the rising and declining groundwater levels.Although ecohydrological models offer predictions for the future, they may become inaccurate due to over- or underparameterisation, especially in case of distributed modelling at regional scale. Therefore,a sequential ' updating ' algorithm has been developed to improve the simulated total dry matter production in SWAP, whenever an observation of total dry matter production is available.
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| Format: | Doctoral thesis biblioteca |
| Language: | English |
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Wageningen University
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| Subjects: | crops, geographical information systems, integration, mathematical models, productivity, remote sensing, soil, water management, bodem, geografische informatiesystemen, gewassen, integratie, productiviteit, waterbeheer, wiskundige modellen, |
| Online Access: | https://research.wur.nl/en/publications/water-productivity-analysis-from-field-to-regional-scale |
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