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Diss. ETH No. 17069 Modelling Global Water and Food Relations – Development and Application of a GIS-based EPIC Model A dissertation submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH for the degree of Doctor of Sciences presented by Junguo Liu M.Sc. in Water and Environmental Resources Management UNESCO-IHE, Delft, the Netherlands born 19 February 1977 citizen of China accepted on the recommendation of Prof. Dr. Alexander J.B. Zehnder, examiner Dr. Hong Yang, co-examiner Prof. Dr. Peter Reichert, co-examiner Prof. Dr. Hubert H.G. Savenije, co-examiner 2007 i Contents Summary.......................................................................................................................I Zusammenfassung..................................................................................................... IV 1. Introduction............................................................................................................1 1.1. Background and motivation............................................................................1 1.2. Emerging issues in agricultural water management .......................................2 1.2.1.Irrigation efficiency and crop water productivity ..................................2 1.2.2.Real water and virtual water ..................................................................3 1.2.3.Green water and blue water ...................................................................3 1.3. Traditional models for food production studies on global and national scales. .........................................................................................................................4 1.4. A need for a flexible model for water-food studies ........................................8 1.5. Objectives and goals.......................................................................................8 1.6. Research contents of this thesis ......................................................................9 References................................................................................................................9 2. GEPIC – modelling wheat yield and crop water productivity with high resolution on a global scale..................................................................................15 2.1. Introduction...................................................................................................17 2.2. The EPIC model............................................................................................19 2.2.1.The selection of the EPIC model .........................................................19 2.2.2.Methods for estimating crop yield, ET, and CWP in EPIC.................20 2.3. Integration of EPIC with GIS – The GEPIC Model .....................................22 2.4. Simulation of yield and ET with the GEPIC model .....................................24 2.4.1.Data source, database development and simulation ............................24 2.4.2.Test of the GEPIC performance...........................................................28 2.5. Estimation of crop water productivity ..........................................................32 2.6. Discussion.....................................................................................................36 2.6.1.Yield and CWP ....................................................................................36 2.6.2.Virtual water flows embodied in the international wheat trade...........40 2.7. Conclusion ....................................................................................................41 Acknowledgements................................................................................................43 References..............................................................................................................43 ii 3. Modelling the role of irrigation in winter wheat yield, crop water productivity, and production in China ..............................................................50 3.1. Introduction...................................................................................................51 3.2. Material and methods....................................................................................53 3.2.1. The GEPIC model...............................................................................53 3.2.2.Input data .............................................................................................54 3.2.3.Regional delimitation...........................................................................57 3.2.4.Validation of the model .......................................................................59 3.3. Results and discussion ..................................................................................61 3.3.1.Irrigation depth and the role of irrigation for winter wheat yield in different regions...................................................................................61 3.3.2.CWP under rainfed and irrigated conditions .......................................63 3.3.3.Comparison of CWP in this study with others reported ......................67 3.3.4.Impacts of irrigation reduction on winter wheat production and policy implications..........................................................................................68 3.4. Conclusion ....................................................................................................71 Acknowledgements................................................................................................73 References..............................................................................................................74 4. Global consumptive water use for crop production: the importance of green water and virtual water.......................................................................................78 4.1. Introduction...................................................................................................79 4.2. Methods and data ..........................................................................................81 4.2.1. Calculation of crop water productivity (CWP)...................................81 4.2.2.Calculation of green water proportion in CWU...................................82 4.2.3.Calculation of CWU at the national and grid level..............................84 4.2.4.Calculation of net virtual water import (NVWI) and export (NVWE)85 4.2.5.Data 85 4.3. CWU and green water proportion.................................................................87 4.3.1.Spatial distribution of CWU ................................................................87 4.3.2.Spatial distribution of green water proportion in consumptive water use ..............................................................................................................91 4.4. Relation between CWU and virtual water trade ...........................................93 4.4.1.Net virtual water exporting countries ..................................................93 iii 4.4.2.Net virtual water importing countries..................................................95 4.5. Concluding remarks......................................................................................99 Acknowledgements..............................................................................................101 References............................................................................................................101 5. Concluding remarks and outlook.....................................................................105 5.1. Concluding remarks....................................................................................105 5.1.1.GEPIC for water-food studies............................................................105 5.1.2.GEPIC – beyond water-food studies..................................................107 5.1.3.Shortcomings of the GEPIC model....................................................110 5.2. Outlook .......................................................................................................110 References............................................................................................................111 Curriculum Vitae.....................................................................................................114 Acknowledgements ..................................................................................................116 iv Summary Water quality as a key to public and ecosystem health has been identified already for many decades. The question about the quantitative aspect of sufficient fresh water on a global scale has only recently found its way into scientific and policy discussions. Traditional studies of food production potential largely ignore water as a limiting factor. An increasing awareness of the importance of water in food production is of recent origin. Many attempts have been made to integrate water into the global and national food studies. Despite these efforts, a systematic tool that is capable of analyzing water-food relations with a high spatial resolution and covering the whole world has not yet been developed prior to the work descried in this thesis. The aim of this thesis is to develop a GIS-based EPIC model (GEPIC) to investigate water- food (crop) relations with a high spatial resolution on different geographical scales. The GEPIC model is applied for the analysis of crop water productivity (CWP), virtual water flows associated with food trade, and green and blue water contributions to food production.