Climate change is reshaping the future for freshwater. Water is the predominant means through which the impacts of climate change will be felt. Regardless of future greenhouse gas emissions trends, a certain amount of climate change is already unavoidable. Changes in freshwater systems are already being observed and water risks (shortage, excess, inadequate quality and disruptions to freshwater ecosystems) are expected to increase in a changing climate.

Water is the main channel through which the impact of climate change will be felt and the key to developing successful adaptation strategies. We are already observing changes in freshwater systems around the world, and water-related risks – whether there is too little, too much, too unreliable, or of poor quality – are expected to increase. These changes can be either gradual or dramatic, and can jeopardise water security over the long-term making it more costly, as time passes, for governments to adjust to changing circumstances.�

Climate change is reshaping the future for freshwater. It aggravates existing strains and complicates future planning, management and investment in water infrastructures. Reducing the adverse consequences and costs of climate change and tapping into any opportunities will require adjusting to new circumstances – that is, adaptation. Adaptation requires flexibility in a domain characterised by long-lived infrastructure with high sunk costs. It requires foresight where there is low confidence in climate projections for key water parameters at local scale. It also calls for adaptive water governance where inertia and poor water governance are more often the norm than the exception. In response to this challenge, OECD countries are making progress tackling this issue and a number of lessons learned can be drawn from experience to date.

This chapter provides an overview of the range of complex impacts on freshwater that can be expected in a changing climate. It also highlights the main sources of uncertainty and information gaps associated with climate change impact assessments on water systems that pose challenges for informing practical, on-site adaptation decisions. Finally, it examines the policy implications of the proposition that stationarity is dead, or in other words, that the future for freshwater will not look like the past.

This chapter sets out a risk-based approach for adapting water systems to climate change as a key component of improving water security over the long-term. It begins by setting out a rationale for a risk-based approach to inform policy decisions in the absence of reliable climate predictions. It then provides a framework to guide government action to know, target, and manage water risks and highlights the importance of considering risk-risk trade-offs. Finally, it proposes policy guidelines for addressing water risks in the context of a changing climate in order to improve the timeliness, efficiency, and equity of adaptation decisions.

Progress on adapting water systems to climate change has been advancing in recent years across OECD countries. In order to gauge progress and to gain insights from practical adaptation efforts for water systems, the OECD Secretariat undertook a survey of policies across all 34 member countries and the European Commission.This chapter looks at general trends, highlights innovative approaches, and draws out lessons learned from the survey. It provides practical insights into countries’ efforts to know, target and manage increasing water risks in a changing climate. It captures the primary concerns and vulnerabilities of countries. It documents the types of policy instruments most commonly used to tackle various water challenges and identifies a range of policy levers for adaptation illustrated by practical examples. Finally, it takes stock of efforts to date to finance adaptation for water systems.

An uncertain future for freshwater, the potentially rapid pace of change and the existence of possible irreversible tipping points increases the value of flexibility and calls for a dynamic, future-oriented approach to water governance and policy. This chapter highlights how adaptive water governance is gaining attention as a means to increase flexibility and deal with uncertainty related to long-term trends. It highlights how well-designed economic instruments can improve the efficiency and timeliness of adaptation responses by reducing baseline stress on water resources and providing flexibility to deal with increased variability, risks, and uncertainty. Based on a number of case studies it draws out lessons for adaptation on the use of insurance schemes, water trading, water pricing, and ecosystem-based approaches. Finally, the chapter examines some of the potential pitfalls in financing adaptation for water and looks at how a real options approach can be used to value flexibility in long-term investments.

The scientific evidence documenting the range and significance of climate change impacts on freshwater resources is compelling and growing. Given the importance of water as an essential resource as well as a potential threat, climate change impacts on freshwater will affect not only water and flood management per se, but also a number of key policy domains (e.g. energy, agriculture, infrastructure, biodiversity, and health). Despite the ever-expanding scientific basis, reliable information about the nature, magnitude and timing of impacts at the scale needed for practical, site-specific adaptation is generally lacking. Adaptation decisions need to accommodate significant uncertainty. Effective and timely adaptation can lower the cost of climate change impacts.