Cover picture: Irrawaddy Delta, Myanmar - September 2008 (© Swiatek Wojtkowiak) Copies of FAO publications can be requested from: SALES AND MARKETING GROUP Information Division Food and Agriculture Organization of the United Nations Viale delle Terme di Caracalla 00100 Rome, Italy E-mail: [email protected] Fax: (+39) 06 57053360 Web site: http://www.fao.org FAO WATER Climate change, water REPORTS and food security 36 by Hugh Turral FAO consultant Jacob Burke and Jean-Marc Faurès FAO Land and Water Division FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 2011 The designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations (FAO) concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or products of manufacturers, whether or not these have been patented, does not imply that these have been endorsed or recommended by FAO in preference to others of a similar nature that are not mentioned. ISBN 978-92-5- All rights reserved. FAO encourages reproduction and dissemination of material in this information product. Non-commercial uses will be authorized free of charge, upon request. Reproduction for resale or other commercial purposes, including educational purposes, may incur fees. Applications for permission to reproduce or disseminate FAO copyright materials, and all queries concerning rights and licences, should be addressed by e-mail to [email protected] or to the Chief, Publishing Policy and Support Branch, Office of Knowledge Exchange, Research and Extension, FAO, Viale delle Terme di Caracalla, 00153 Rome, Italy. © FAO 201 iii Preface Under the IPCC emissions scenarios, higher temperatures are projected to affect all aspects of the hydrological cycle. More frequent and severe droughts and floods are already apparent, and their impact increases as a growing population becomes more dependent upon a set of atmospheric and hydrological circulations. Climate change will impact the extent and productivity of both irrigated and rainfed agriculture across the globe. Reductions in river runoff and aquifer recharge are expected in the Mediterranean basin and in the semi-arid areas of the Americas, Australia and southern Africa, affecting water availability in regions that are already water-stressed. In Asia, the large contiguous areas of irrigated land that rely on snowmelt and high mountain glaciers for water will be affected by changes in runoff patterns, while highly populated deltas are at risk from a combination of reduced inflows, increased salinity and rising sea levels. Everywhere, rising temperatures will translate into increased crop water demand. Both the livelihoods of rural communities and the food security of a predominantly urban population are therefore at risk from water-related impacts linked primarily to climate variability. The rural poor, who are the most vulnerable, are likely to be disproportionately affected. Various adaptation measures that deal with climate variability and build upon improved land and water management practices have the potential to create resilience to climate change and to enhance water security. They imply a good understanding of the impact of climate change on available water resources and on agricultural systems, and a set of policy choices, and investments and managerial changes to address them. This report summarizes current knowledge of the anticipated impacts of climate change on water availability for agriculture. The implications for local and national food security are examined; and the methods and approaches to assess climate change impacts on water and agriculture are discussed. The report emphasizes the need for a closer alignment between water and agricultural policies and makes the case for immediate implementation of ‘no-regrets’ strategies which have both positive development outcomes and make agricultural systems resilient to future impacts. It is hoped that policy makers and planners will find in this report the elements of information and guidance that are needed to assess and respond to the challenge that climate change is expected to impose on agricultural water management and food security. Alexander Müller Assistant Director-General Natural Resources Management and Environment Department iv Acknowledgements This report was prepared by Hugh Turral, FAO consultant, in collaboration with Jacob Burke and Jean-Marc Faurès, from the FAO Land and Water Division. It has benefited substantially from inputs obtained during the Expert Consultation on Climate Change, Water and Food Security organized by FAO in February 2008, in preparation for the High-Level Conference on World Food Security: the Challenges of Climate Change and Bioenergy, held in Rome, Italy, in June 2008. Participants in the Expert Consultation were: Petra Döll (University of Frankfurt-Main), Rachid Doukkali (Morocco), Ashley Halls (Mekong River Commission), Bertjan Heij (The Netherlands), Erda Lin (China), Festus Luboyera (UN-FCCC), David Molden (IWMI), Claudia Ringler (IFPRI), Mahendra Shah (IIASA), Mark Svendsen (USA), Marja-Liisa Tapio-Biström (Finland), Francesco Tubiello (Columbia University), and Avinash Tyagi (WMO). FAO participants in the Expert Consultation were Abdelkader Allali, Rosalud Delarosa, Thierry Facon, Karen Frenken, Theodor Friedrich, Aruna Gujral, Thomas Hofer, Jippe Hoogeveen, John Jorgensen, Marketta Juppi, Amir Kassam, Sasha Koo-Oshima, Parviz Koohafkan, Johan Kuylenstierna, Nadia Scialabba, Reuben Sessa and Pasquale Steduto. v Contents Preface iii Acknowledgements iv List of figures ix List of tables x List of boxes x List of acronyms and abbreviations xi Executive summary xv 1. Introduction 1 1.1. Overview 1 1.2. Trends versus predictions 3 2. Setting the scene 5 2.1. Water, food security and environment 5 2.2. IPCC 4th Assessment and the Stern Review 6 2.2.1. The IPCC 4th Assessment and associated analysis 6 2.2.2. Climate versus weather – the downscaling problem 10 2.2.3. The agricultural implications of the IPCC Working Group I report (Physical Science) 12 2.2.4. Broad regional impacts – food security and climate change 16 2.2.5. The agricultural implications of the IPCC Working Group II report (Adaptation) 18 2.2.6. The agricultural implications of the IPCC Working Group III report (Mitigation) 19 2.2.7. The Stern Review 19 2.3. Agricultural systems dependent on water management 20 2.3.1. Rainfed agriculture 20 2.3.2. Irrigated agriculture 23 2.3.3. Inland fisheries and aquaculture 25 2.3.4. Livestock grazing and fodder production 26 2.3.5. Forested land 27 2.4. Economic competition for water, climate change and the challenge for water allocation 28 vi 2.5. The pace of agricultural change and climate change projections 29 3. The baseline and trends in agricultural water demand 31 3.1. Agricultural projections to 2030 and the associated demand for water 31 3.1.1. Global analysis 31 3.1.2. Regional analysis 32 3.2. Emerging trends in agricultural water management 36 3.3. Anticipated trends in agricultural water management 40 3.3.1 Trends without climate change 40 3.3.2 Analysis of economic drivers and future investments 41 4. Specific climate change impacts related to agricultural water management 45 4.1. Introduction 45 4.1.1. Predictive modeling and its limitations in determining agricultural impact 45 4.1.2. Impacts on nations or river basins? 46 4.2. Principal climate change drivers in agriculture 47 4.3. Overall impacts on crop production 47 4.3.1. Direct effects of temperature and changes in precipitation 47 4.3.2. Carbon dioxide ‘fertilization’ of crops 50 4.3.3. Pests and diseases 54 4.4. Impacts on water supply and demand – a global picture 54 4.4.1. Overall water supply impacts 54 4.4.2. Groundwater 55 4.4.3. Implications for water institutions 57 4.5. Regional impacts 58 4.6. Impacts at river basin level: systemic considerations 61 4.6.1. Introduction 61 4.6.2. Glaciers and runoff 63 4.6.3. Arid basins 65 4.6.4. Recycling water 68 4.6.5. Land-use change in river basins – afforestation and sediment management 68 4.6.6. Basins with increasing runoff – managing deltas 69 4.6.7. The susceptibility of wetlands to climate change 70 4.6.8. A basin example 70 4.7. Food security and environment linkages 70 4.8. Climate change impact typology 72 4.9. Summary: the combined impacts – positive and negative 75 5. Prospects for adaptation 77 5.1. Introduction 77 vii 5.2. On-farm adaptation 83 5.2.1. Crop selection and crop calendar 85 5.2.2. Farm and crop management – fertilizer management 90 5.2.3. Water management on farm 91 5.2.4. Irrigation technologies on farm 93 5.2.5. Depletion accounting 94 5.2.6. Flood protection and erosion 96 5.2.7. Commercial agriculture 97 5.3. Adaptation at irrigation system level 98 5.3.1. Introduction 98 5.3.2. Water allocation 99 5.3.3. System performance 99 5.3.4. Cropping patterns and calendars 100 5.3.5. Conjunctive use of surface water and groundwater 101 5.3.6. Irrigation policy measures 102 5.4. Adaptation at river basin and national levels 105 5.4.1. Irrigation sector policy 105 5.4.2. Coping with droughts 106 5.4.3. Coping with flooding; structural and non-structural interventions 107 5.4.4. Managing aquifer recharge 109 5.4.5. Assessment of adaptation options to ensure irrigation supply security 111 5.5. Adaptive capacity in agricultural water management – policies, institutions and the structure of the sub-sector 112 5.5.1. Mechanisms for allocation 112 5.5.2. National food policy issues 113 5.6. Institutions 114 5.7. Long-term investment implications for agricultural water management 115 6.