Climate Change and Agricultural Water Management in Developing Countries

Climate Change and Agricultural Water Management in Developing Countries

Edited by

Chu Thai Hoanh

Robyn Johnston

Vladimir Smakhtin

International Water Management Institute (IWMI), Colombo, Sri Lanka

CABI is a trading name of CAB International

© CAB International 2016. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners.

A catalogue record for this book is available from the British Library, London, UK.

Library of Congress Cataloging-in-Publication Data

Names: Chu, Thai Hoanh, 1949– | Johnston, Robyn. | Smakhtin, Vladimir.

Title: Climate change and agricultural water management in developing countries / edited

by Chu Thai Hoanh, Robyn Johnston, and Vladimir Smakhtin, International Water

Management Institute (IWMI), Colombo, Sri Lanka.

Description: Boston, MA: CABI, 2015. | Series: CABI climate change series |

Includes bibliographical references and index.

Identifiers: LCCN 2015027427 | ISBN 9781780643663 (hbk : alk. paper)

Subjects: LCSH: Water-supply, Agricultural--Management--Developing countries. |

Crops and climate--Developing countries. | Climatic changes--Developing countries.

Classification: LCC S494.5.W3 C55 2015 | DDC 631.709172/4--dc23 LC record available at http://lccn.loc.gov/2015027427

ISBN-13: 978 1 78064 366 3

Commissioning editor: Nicki Dennis and Ward Cooper

Editorial assistant: Emma McCann

Production editor: Lauren Povey

Typeset by AMA DataSet Ltd, Preston, UK.

Printed and bound in the UK by CPI Group (UK) Ltd, Croydon, CR0 4YY.

Contents

Contributors

Preface

1   Climate Change and Agricultural Development: A Challenge for Water Management

Chu Thai Hoanh, Robyn Johnston and Vladimir Smakhtin

2   Adaptation to Climate Change Impacts on Agriculture and Agricultural Water Management – A Review

Shreedhar Maskey, Dinesh Bhatt, Stefan Uhlenbrook, Krishna C. Prasad and Mukand S. Babel

3   Global Water Requirements of Future Agriculture: Using WATERSIM

Aditya Sood

4   Impacts of Climate Change on Crop Water Requirements in Huang-HuaiHai Plain, China

Qin Liu, Changrong Yan, Jianying Yang, Xu-rong Mei, Weiping Hao and Hui Ju

5   Impacts of Climate Change and Adaptation in Agricultural Water Management in North China

Jun Xia, Xingguo Mo, Jinxia Wang and Xinping Luo

6 Climate Change Impacts and Adaptation in Agricultural Water Management in the Philippines

Felino P. Lansigan and Amparo C. Dela Cruz

7   Adaptation Strategies to Address the Climate Change Impacts in Three Major River Basins in India

Krishna Reddy Kakumanu, Kuppannan Palanisami, Pramod Kumar Aggarwal, Coimbatore Ramarao Ranganathan and Udaya Sekhar Nagothu

8   Water Management for Agricultural Production in a Coastal Province of the Mekong River Delta under Sea-level Rise

Ngo Dang Phong, Chu Thai Hoanh, Tran Quang Tho, Nguyen van Ngoc, Tran Duc Dong, To Phuc Tuong, Nguyen Huy Khoi, Nguyen Xuan Hien and Nguyen Trung Nam

9   Aquaculture Adaptation to Climate Change in Vietnam’s Mekong Delta

Suan Pheng Kam, Tran Nhuong, Chu Thai Hoanh and Nguyen Xuan Hien

10  Groundwater for Food Production and Livelihoods – The Nexus with Climate Change and Transboundary Water Management

Karen Villholth

11  Irrigated Crop Production in the Syr Darya Basin: Climate Change Rehearsal in the 1990s

Oxana Savoskul and Elena Shevnina

12  Mitigating Greenhouse Gas Emissions from Rice Production through Water-saving Techniques: Potential, Adoption and Empirical Evidence

Bjoern Ole Sander, Reiner Wassmann and Joel D.L.C. Siopongco

13  Linking Climate Change Discourse with Climate Change Policy in the Mekong: The Case of Lao PDR

Jana Prosinger, Diana Suhardiman and Mark Giordano

Index

Contributors

Pramod K. Aggarwal, International Water Management Institute, Hyderabad, India. E-mail: [email protected]

Mukand S. Babel, Asian Institute of Technology, Water Engineering and Management (WEM), PO Box 4, Klong Luang, Pathumthani 12120, Thailand. E-mail: [email protected]

Dinesh Bhatt, UNESCO-IHE Institute for Water Education, PO Box 3015, 2601 DA, Delft, the Netherlands and Ministry of Irrigation, Department of Irrigation, Jawalakhel, Lalitpur, Nepal. E-mail: [email protected]

Amparo C. Dela Cruz, University of the Philippines Los Baños, Los Baños, Laguna, Philippines. E-mail: [email protected]

Tran Duc Dong, Southern Institute for Water Resource Planning, Ho Chi Minh City, Vietnam. E-mail: [email protected]

Mark Giordano, Georgetown’s School of Foreign Service, Georgetown University, Washington, DC. E-mail: [email protected]

Weiping Hao, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081 and Key Laboratory of Dryland Agriculture, Ministry of Agriculture, Beijing 100081, China.

Nguyen Xuan Hien, Southern Institute for Water Resources Planning, Ho Chi Minh City, Vietnam. E-mail: [email protected]

Chu Thai Hoanh, International Water Management Institute, Colombo, Sri Lanka. E-mail: [email protected]

Robyn Johnston, International Water Management Institute, Colombo, Sri Lanka. E-mail: [email protected]

Hui Ju, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081 and Key Laboratory of Agricultural Environment, Ministry of Agriculture, Beijing 100081, China.

Krishna Reddy Kakumanu, International Water Management Institute, Hyderabad, India. E-mail: [email protected]

Suan Pheng Kam, The WorldFish Center, Penang, Malaysia. E-mail: [email protected]

Nguyen Huy Khoi, Southern Institute for Water Resource Planning, Ho Chi Minh City, Vietnam. E-mail: [email protected]

Felino P. Lansigan, University of the Philippines Los Baños, Los Baños, Laguna, Philippines. E-mail: [email protected]

Qin Liu, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081 and Key Laboratory of Dryland Agriculture, Ministry of Agriculture, Beijing 100081, China. E-mail: [email protected]

Xinping Luo, Key Laboratory of Water Cycle and Related Land Surface Processes, Chinese Academy of Sciences, Beijing 100101, China. E-mail: [email protected]

Shreedhar Maskey, UNESCO-IHE Institute for Water Education, PO Box 3015, 2601 DA, Delft, the Netherlands. E-mail: [email protected]

Xu-rong Mei, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081 and Key Laboratory of Dryland Agriculture, Ministry of Agriculture, Beijing 100081, China. E-mail: [email protected]

Xingguo Mo, Key Laboratory of Water Cycle and Related Land Surface Processes, Chinese Academy of Sciences, Beijing 100101, China. E-mail: [email protected]

Udaya Sekhar Nagothu, Norwegian Institute for Agricultural and Environmental Research-Biforsk, Ås, Norway. E-mail: [email protected]

Nguyen Trung Nam, Southern Institute for Water Resource Planning, Ho Chi Minh City, Vietnam. E-mail: [email protected]

Nguyen van Ngoc, Southern Institute for Water Resource Planning, Ho Chi Minh City, Vietnam. E-mail: [email protected]

Tran Nhuong, The WorldFish Center, Penang, Malaysia. E-mail: [email protected]

Kuppannan Palanisami, International Water Management Institute, Hyderabad, India. E-mail: [email protected]

Ngo Dang Phong, International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines and Nong Lam University, Ho Chi Minh City, Vietnam. E-mail: [email protected]

Krishna C. Prasad, Chandra Engineering Consultants, Mills Area, Janakpur-1, Post Code 45600, Nepal. E-mail: [email protected]

Jana Prosinger, School of Oriental and African Studies, London. E-mail: [email protected]

Coimbatore Ramarao Ranganathan, Tamil Nadu Agricultural University, Coimbatore, India.

Bjoern Ole Sander, Crop and Environmental Sciences Division, International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines. E-mail: [email protected]

Oxana Savoskul, International Water Management Institute (IWMI), PO Box 2075, Colombo, Sri Lanka. E-mail: [email protected]

Elena Shevnina, Finnish Meteorological Institute, PO Box 503, FI-00101, Helsinki, Finland. E-mail: [email protected]

Joel D.L.C. Siopongco, Crop and Environmental Sciences Division, International Rice Research Institute, Los Baños, Laguna, Philippines. E-mail: [email protected]

Vladimir Smakhtin, International Water Management Institute, Colombo, Sri Lanka. E-mail: [email protected]

Aditya Sood, International Water Management Institute, Colombo, Sri Lanka. E-mail: [email protected]

Diana Suhardiman, International Water Management Institute, South-east Asia Regional Office, Vientiane, Lao PDR. E-mail: [email protected]

Tran Quang Tho, Southern Institute for Water Resource Planning, Ho Chi Minh City, Vietnam. E-mail: [email protected]

To Phuc Tuong, International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines. E-mail: [email protected]

Stefan Uhlenbrook, UNESCO-IHE Institute for Water Education, PO Box 3015, 2601 DA, Delft, the Netherlands. E-mail: [email protected]

Karen Villholth, International Water Management Institute, Regional Office for Southern Africa, Pretoria, South Africa. E-mail: [email protected]

Jinxia Wang, Center for Chinese Agricultural Policy, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China. E-mail: [email protected]

Reiner Wassmann, Crop and Environmental Sciences Division, International Rice Research Institute, Los Baños, Laguna, Philippines. E-mail: [email protected]

Jun Xia, State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, China and Key Laboratory of Water Cycle and Related Land Surface Processes, Chinese Academy of Sciences, Beijing 100101, China. E-mail: [email protected]

Changrong Yan, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081 and Key Laboratory of Dryland Agriculture, Ministry of Agriculture, Beijing 100081, China. E-mail: [email protected]

Jianying Yang, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081 and Key Laboratory of Dryland Agriculture, Ministry of Agriculture, Beijing, China. E-mail: [email protected]

Preface

Water used for agriculture is the largest water consumer globally, about 70% of all freshwater withdrawals. Climate change impacts on water resources – through changes in precipitation, snowfall, soil moisture, river flow and groundwater recharge – translate into impacts on agricultural production. With current trends in population growth, rising incomes and changing diets, the demand for food will double over the next 50–80 years. Significant improvements are necessary in agricultural water management now to reduce the vulnerability of poor people in developing countries to climate-induced changes in precipitation and water availability.

The objective of this book is to provide experiences from studies on agricultural water management under climate change as references for agriculture and irrigation planners, decision makers, researchers and students. Chapters in this book present an overview on global assessment of climate change impacts and water requirement for future agriculture, detailed crop water requirements in case studies in developing countries, irrigation management under sea-level rise in deltas, and agricultural adaptation options to climate change such as water-saving techniques and groundwater exploitation, and related policy settings. Findings and conclusions from the studies presented in this book may help in identifying subjects for further research and actions in management to filling the information and knowledge gaps in agricultural water management.

This book was edited by a team of scientists based at the International Water Management Institute (IWMI). It is produced as part of the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), which is a strategic partnership of CGIAR and Future Earth. The views expressed in this book cannot be taken to reflect the official opinions of CGIAR or Future Earth.

The Editors

1 Climate Change and Agricultural Development: A Challenge for Water Management

Chu Thai Hoanh,* Robyn Johnston and Vladimir Smakhtin

International Water Management Institute (IWMI), Colombo, Sri Lanka

Abstract

Freshwater-related risks of climate change increase significantly with increasing global temperatures. Globally, the negative impacts of future climate change on freshwater systems are expected to outweigh the benefits, and agriculture and irrigation, as the largest consumers of water globally, are most at risk. This book analyses the potential impacts of climate change on water for agriculture, and the adaptation strategies in water management to deal with these impacts, drawing on global assessments and regional studies.

This chapter introduces the book, sets the scene for research on climate change in agricultural water management, and synthesizes the issues, methodologies and findings in the chapters to follow. Chapters 2 and 3 provide an overview of global assessment of climate change impacts and water requirement for future agriculture. Chapters 4–7 provide analyses of crop water requirements in four case studies in developing countries. Chapters 8 and 9 are studies of irrigation management under sea-level rise in Vietnam’s Mekong Delta. Chapters 10–12 discuss examples of adaptation alternatives such as water-saving techniques and groundwater exploitation, and related policy settings. The last chapter links the dominant approach of uncertainty presented in the climate change discourse with policy discussions on climate adaptation strategies.

1.1 Climate Change and Agricultural Water Management

Observational records and climate projections provide abundant evidence that freshwater resources will be strongly impacted by climate change, with wide-ranging consequences for human societies and ecosystems. Observed global warming over several decades has been linked to changes in the large-scale hydrological cycle such as: increasing atmospheric water vapour content; changing precipitation patterns, intensity and extremes; reduced snow cover and widespread melting of ice; and changes in soil moisture and runoff (Bates et al., 2008). Over the 20th century, precipitation changes show substantial spatial and inter-decadal variability. Since the 1970s, increases in precipitation have been observed over land in high northern latitudes, while decreases have dominated from 10°S to 30°N. Climate model simulations for the 21st century are consistent in projecting trends of increasing annual average river runoff and water availability at high latitudes and in some wet tropical areas, and decrease over some dry regions at mid-latitudes and in the dry tropics (IPCC, 2007b). These trends are reconfirmed in the Fifth Assessment Report by IPCC (2013).

Freshwater-related risks of climate change increase significantly with rising temperatures associated with increasing greenhouse gas (GHG) concentrations. Globally, the negative impacts of future climate change on freshwater systems are expected to outweigh the benefits. By the 2050s, the area of land subject to increasing water stress due to climate change is projected to be more than double that with decreasing water stress (Bates et al., 2008). In particular, frequency of short hydrological droughts is likely to increase in the presently dry regions (IPCC, 2014).

Rainfed agriculture is vulnerable to climate change through the direct impacts of changed rainfall and temperature conditions; irrigated agriculture bears the additional risk of changes in availability of surface and groundwater. Irrigation is the largest water consumer globally: about 70% of all freshwater withdrawals go to irrigated agriculture (UN Water, 2009). Increasing water scarcity may limit food production in rainfed systems, putting pressure on food prices and increasing countries’ dependence on food imports or investments into irrigation. Shifting from rainfed to irrigated agriculture is a front-line adaptation strategy to hotter, drier conditions, but will in turn increase demand for water. According to FAO (Food and Agriculture Organization for the United Nations) projections, developing countries, with 75% of the global irrigated area, will need to expand their irrigated areas by 0.6% per year until 2030 to meet food demand (Bruinsma, 2003), although a smaller expansion of irrigated area is assumed under all four scenarios of the Millennium Ecosystem Assessment, with global growth rates of only 0–0.18% per year until 2050 (Millennium Ecosystem Assessment, 2005).

Regarding crop water requirement, the physiological effect of CO2 is associated with an increased intrinsic water use efficiency of plants, which means that less water is transpired per unit of carbon assimilated (IPCC, 2014). For C3 plant species, including most food crops, the CO2 effect may be relatively greater for crops that are under moisture stress compared to well-irrigated crops. The large-scale implications of CO2–water interactions (i.e. at canopy, field and regional level) are highly uncertain. In general, the positive effects of elevated CO2 on plant–water relations are expected to be offset by increased evaporative demand under warmer temperatures (IPCC, 2007b); therefore the impact of elevated CO2 on water demand is usually not considered in studies of agricultural water management under climate change.

Higher water temperatures and projected changes in water extremes, including floods and droughts, are projected to affect water quality and exacerbate many forms of water pollution such as sediments, nutrients and dissolved organic carbon, with possible negative impacts on agricultural production, although the extent of these changes is highly uncertain and depends on rainfall seasonality, land cover and soil management practices (IPCC, 2014). Mullan and Barrett-Lennard (2010) suggested that climate change is expected to reduce water availability in general, making the use of low quality water resources more common.

In low-lying coastal areas, sea-level rise is projected to increase flooding depth, resulting in shorter duration for crops, and to extend salinity intrusion into the surface and groundwater systems in estuaries, causing a decrease of freshwater availability for agricultural production. Without adaptation, it is projected that hundreds of millions of people will be affected by coastal flooding and displaced due to land loss by the year 2100; the majority of those affected are from East, South-east and South Asia. Protecting against flooding and erosion is considered economically rational for most developed coastlines in many countries under all socio-economic and sea-level rise scenarios analysed (IPCC, 2014).

Locally, irrigated agriculture may face new problems linked to the spatial and temporal distribution of streamflow. For instance, at low latitudes, especially in South-east Asia, early snowmelt may cause spring flooding and lead to a summer irrigation water shortage (IPCC, 2007b). In most dry subtropical regions, climate change is projected to reduce renewable surface water and groundwater resources significantly. This will intensify competition for water among agriculture and other sectors, and affect regional water supply, energy generation and food security. In contrast, water resources are projected to increase at high latitudes. Proportional changes are typically one to three times greater for runoff than for precipitation. The effects on water resources and irrigation requirements of changes in vegetation due to increasing GHG concentrations and climate change remain uncertain (IPCC, 2014). There is high confidence that irrigation demand will increase significantly in many areas (by more than 40% across Europe, USA and parts of Asia). Other regions – including major irrigated areas in India, Pakistan, and south-eastern China – might experience a slight decrease in irrigation demand, due for example to higher precipitation, but only under some climate change scenarios.

However, region-to-region variations in different studies were very heterogeneous. For example, using seven global hydrological models with a limited set of projections, Wada et al. (2013) estimated a global increase in irrigation demand by the 2080s (ensemble average 7–21% depending on emissions scenario). By contrast, based on projections from two general circulation models (GCMs) and two emissions scenarios, Zhang and Cai (2013) suggested a slight global decrease in crop water deficits in both irrigated and rainfed areas by the 2080s, which can be explained partly by a smaller difference between daily maximum and minimum temperatures.

With the changes in temperature and precipitation under climate change, shifting of crops from present locations to new locations will occur as one option in adaptation to climate change. In a study assessing the impact of climate change on agricultural land for 16 crops by comparing the global spread of farmland between the ‘current’ period (1981–2010) and a future period (2071–2100), Zabel et al. (2014) calculate a potential global net increase in land climatically suitable for crops of 4.7 million km², from 54.2 million km² to 58.9 million km². These figures include land that is both rain-fed and irrigated, and exclude protected areas and dense forest because of the importance of conserving these to protect ecosystem services, such as carbon storage. However, the authors emphasize a downward shift in land quality: 3.9 million km² is projected to be ‘highly suitable’ for crops, compared with 4.6 million km² for the current period. In turn, more land will be classified as ‘marginally suitable’ or ‘moderately suitable’, with increases of 3.8 million km² and 1.6 million km², respectively, under these categories. In this study, irrigation areas are assumed not to change, but in practice, it is likely that irrigation systems will be expanded to the areas highly suitable for crops in terms of soil, terrain and climate.

IPCC (2007a, 2014) warn that increased demand for irrigation, from both surface and groundwater sources, will result both from changed climatic conditions and from increased demand for food by a growing population. Globally, the impacts of climate change on increasing irrigation water requirements could be nearly as large as the changes projected from socio-economic development in this century (Turral et al., 2011). Agricultural production systems and water resources will be critically shaped in the coming decades by the interaction of climate with non-climatic drivers: demographic, socio-economic, technological and lifestyle changes.

IPCC (2013) stress that current water management practices may not be robust enough to cope with the impacts of climate change on agriculture and other water use sectors. Adaptive water management techniques, from field-scale water-saving techniques, to basin-level scenario planning, learning-based approaches, and flexible and low-regret management solutions, can help create resilience to uncertain hydrological changes and impacts due to climate change. Much of the adaptation cost in water management will be needed in developing countries, which face barriers including lack of human and institutional capacity, financial resources, awareness and communication.

1.2 Global Assessment on Agricultural Water Management

Maskey et al. (Chapter 2, this volume) review the global literature on impacts of climate change on agriculture and prospects for adaptation. They find that sensitivity of agriculture to climate change varies across the globe, and in general, developing countries, where more than 800 million people are already undernourished, will be hardest hit. There has been considerable progress in approaches for assessing the impact of climate change on agriculture and irrigation and in evaluation of adaptation measures, but critical challenges and constraints associated with climate change impact and adaptation remain. Limited understanding of the interactions between, and relative importance of, factors like elevated ozone and CO2 levels, extreme weather conditions, weed variety, socio-economic changes and adaptation responses mean that diverse adaptation options from farm to policy level are essential. Most published studies on adaption focus on modification of existing management practices to improve crop yield, using process-based models, but do not account for trade-offs between crop production and resource availability, which influence the farmer’s decision-making and profitability. The authors propose that more effort is required to incorporate social, financial, institutional and technical constraints and the limitations of resources and adaptive capacity into adaptation frameworks and planning.

Sood (Chapter 3, this volume) warns that, with world population increasing to about 9 billion and the per capita GDP rising, the future demand for water for domestic and industrial sectors will compete with the agricultural water demand. Results from a water accounting and global food trade model, the Water, Agriculture, Technology, Environmental and Resource Simulation Model (WATERSIM), indicate that the proportion of consumptive water demand for agriculture will decrease from around 72% of the total demand in 2010, to 37% in case of business-as-usual, 27% in case of an optimistic socio-economic scenario and 50% in case of a pessimistic socio-economic scenario. The greatest increase in demand for consumptive water comes from domestic and industrial sectors, although to maintain optimum yields, around 16–19% more irrigation water will be required on average due to higher evaporative demand. Sood concludes that with improved agricultural water management and liberalized global food trade, there are enough resources globally not only to meet the future demand but also to reduce malnutrition.

1.3 Crop Water Requirements under Climate Change

Analysing past climate data is one way to assess potential impacts of climate factors on crop water requirement. Liu et al. (Chapter 4, this volume) evaluate the effects of climate in the Huang-Huai-Hai Plain (3H Plain) in the northern China using observed climate data for the period 1981–2009 to estimate reference evapotranspiration (ET0), then analyse the sensitivity of crop water requirement (ETc) of major climatic variables and regional responses of precipitation deficit in different crop growth stages. The results show that temperature was the most sensitive variable in general for the 3H Plain, followed by solar radiation, wind speed and relativity humidity. Relative humidity was the factor most closely correlated with precipitation deficit.

Working in the same region in China, where water is scarce and climate change is likely to exacerbate water stress, Xia et al. (Chapter 5, this volume) explore regional crop responses to climate change, using the wheat–maize double-cropping system as an example. Their results indicate that under likely climate change scenarios, production of winter wheat will increase (with slightly intensified evapotranspiration), but in contrast, summer maize production will slightly decline (with a significant increase of evapotranspiration). The results also indicate that wheat is more resilient to climate change than maize. To mitigate the impacts of climate change on agricultural water use, they propose a range of agricultural water management measures and policies, including improving the performance of participatory irrigation management reform, establishing a water rights system, reforming agricultural water price, and promoting the adoption of agricultural water-saving technology.

Lansigan and Dela Cruz (Chapter 6, this volume) also report local observational evidence of changing climate based on available historical weather data sets in the Philippines. The authors select plausible climate scenarios and downscaled climate projections, both dynamic and statistical, for analysing crop yields using a calibrated crop simulation model for a standard rice variety (IR-64) and a local maize variety (IPB-911). Their results indicate a reduction from 8 to 14% in crop yields for every 1°C temperature increase depending on season and location. For adaptation strategies in agricultural water management, the authors propose location-specific measures based on best practices including adjusting the planting calendar, improving water use efficiency and irrigation water management, water impoundment, planting stress-tolerant varieties, and weather index-based insurance for crop production.

Since the agriculture sector is highly vulnerable to climate change in many parts of the world, there is an increasing concern among farmers, researchers and policy makers about the potential impacts of climate change on food security and livelihoods. Kakumanu et al. (Chapter 7, this volume) review the current state of understanding of climate change impacts on irrigation water in South Asia and specifically on the crop yield and relevant adaptation measures in three major river basins, the Godavari, Krishna and Cauvery in India. An optimization model was used to evaluate the different adaptation practices and their potential to maximize rice production and income, and minimize water use for the mid- and end-century climate change scenarios. The authors conclude that adaptation practices at farm level, such as system of rice intensification, machine transplantation, alternate wetting and drying and direct seeding, could reduce the water and labour use by 10–15% and stabilize rice production in the long term. They suggest that to adapt to the impacts of climate change on agricultural water management, technology upscaling is an alternative but should be backed up with well-planned capacity-building programmes for farmers.

1.4 Agricultural Water Management under Sea-level Rise

The Mekong River Delta is one of the regions most seriously impacted by sea-level rise (World Bank, 2007), which will aggravate inundation and salinity intrusion and hence strongly influence agricultural production. Phong et al. (Chapter 8, this volume) focus on the impacts of sea-level rise in Bac Lieu province, a low-lying coastal province in the Mekong River Delta of Vietnam. The province receives fresh water from the Mekong mainstream on the east side, and dyke and sluices for protection from salinity intrusion were built at the south-west. The authors use a hydraulic and salinity model for simulating water level, flow and salinity in the canal network for years of low, average and high water volume from upstream, and different levels of projected sea-level rise from 12 to 75 cm. Their results indicate that flooding depth increases directly with sea-level rise but that for sea-level rise less than 30 cm, salinity slightly decreases, due to increasing freshwater inflows from the mainstream. This contradicts many previous studies, which generally conclude that the area of salinity intrusion is always larger under sea-level rise. However, when sea-level rise is higher than 30 cm, saline water intrudes into the mainstream and freshwater intake canals, and additional structures (dykes and sluices) will be needed for salinity control.

Most of the Mekong Delta’s aquaculture production occurs in the floodplains and coastal areas that are highly exposed and vulnerable to climate change impacts and sea-level rise. Adaptation in water management for cropping systems, such as upgrading dykes to reduce flooding and salinity intrusion, will benefit other production systems, particularly aquaculture. Kam et al. (Chapter 9, this volume) present an example of economic evaluation of autonomous adaptation by shrimp and catfish farms in the Mekong Delta of Vietnam. The study shows that planned adaptation measures can help defray catfish farmers’ escalating costs of raising pond dykes in response to increased flooding in the delta, if government policy and public investment in adaptation to climate change, particularly for water management, take account of socioeconomic development targets of the aquaculture industry. Because of the high level of uncertainty surrounding commodity prices and changes in production technologies, a ‘no-regrets’ strategy of reducing the high dependence on shrimp and catfish culture and diversifying into more ecologically oriented production systems is recommended, to hedge the aquaculture industry against the increasing risks and uncertainties brought about by climate change.

1.5 Adaptive Agricultural Water Management

Groundwater resources have been exploited in many regions to respond to the increase in water demand for agriculture under climate variability and climate change. Villholth (Chapter 10, this volume) considers groundwater resources in transboundary aquifers as significant water reserves for sustainable agricultural and socio-economic development in the context of Africa, Asia, the Middle East and Latin America. The author highlights that integrated surface and groundwater measures are important for local, smaller-scale, no-regrets adaptation, as well as for larger-scale, strategic adaptation. Socio-economic and institutional aspects, encompassing international law and specific adapted international agreements as well as bottom-up participatory processes, are critical for attaining success on the ground.

Although climate change challenges the traditional assumption that past hydrological experience provides a good guide to future conditions (IPCC, 2007b), adaptation to climate change is still based on past experiences. An approach in adaptation is to compare future water demand with lessons from similar conditions in the past, to select possible alternatives. In an example of this approach, Savoskul and Shevnina (Chapter 11, this volume) model the future inflow to the irrigation scheme of the Syr Darya Basin in Central Asia under two climate scenarios based on IPCC core models. Simulating water allocation in the basin in 2070–2099 shows that 14–21% of water demands in the agriculture sector in a normal hydrological year and 28–51% in a dry year are likely to be unmet. The challenges expected from future climate change can be paralleled to those resulting from the political change due to the collapse of the USSR, which left 18% (normal year) and 46% (dry year) of agricultural water demands unmet in 1992–2001. Therefore the authors suggest that the adaptation measures employed in the post-Soviet transitional period can serve as a basis for future climate change adaptation strategies.

Water-saving techniques in agriculture are considered as potential measures to adapt to climate change impacts. These techniques do not only improve water use efficiency but can also contribute to mitigation of