Water distinguishes our planet compared to all the others we know about. While the global supply of available freshwater is more than adequate to meet all current and foreseeable water demands, its spatial and temporal distributions are not. There are many regions where our freshwater resources are inadequate to meet domestic, economic development and environmental needs. In such regions, the lack of adequate clean water to meet human drinking water and sanitation needs is indeed a constraint on human health and productivity and hence on economic development as well as on the maintenance of a clean environment and healthy ecosystems. All of us involved in research must find ways to remove these constraints. We face multiple challenges in doing that, especially given a changing and uncertain future climate, and a rapidly growing population that is driving increased social and economic development, globalization, and urbanization. How best to meet these challenges requires research in all aspects of water management. Since 1965, the journal Water Resources Research has played an important role in reporting and disseminating current research related to managing the quantity and quality and cost of this resource. This paper identifies the issues facing water managers today and future research needed to better inform those who strive to create a more sustainable and desirable future. Human Ambitions and Earth's LimitsThroughout the world, demographic, economic, and technological trends have accelerated our ability to knowingly and unknowingly modify the environment we live in and that sustains us. We humans have become the principal driver of environmental change. Our actions are impacting our global environment, including our climate. This in turn impacts the amounts and spatial and temporal distributions of precipitation that falls on watersheds and the timing of its runoff. Coupled with changes in landscapes, due to growth in food and energy production and from the movement of people into urban centers, we are altering the quantity and quality of our freshwater resources on which we depend to survive, both physically and economically. We depend on water not only for life itself, but indeed for our economic wellbeing as well. Water plays a role in the creation of everything we produce. There are no substitutes and while it is renewable there is only a finite amount of it.In the past, we have made decisions regarding the management of our water resources that have not always helped us become more secure or sustainable. We have disrupted and overallocated river flow regimes-sometimes to the point of drying them up, along with their downstream lakes. We have overdrawn groundwater aquifers; polluted many, if not most of our water bodies including estuaries, coastal zones and even oceans; and degraded ecosystems. We have done this mainly to satisfy short-term economic goals, often goals that may not have included the long-term environmental-or even economicsustainability of region or basin, and indeed our own h...

Fresh water figures prominently in the machinery of the Earth system and is key to understanding the full scope of global change. Greenhouse warming with a potentially accelerated hydrologic cycle is already a well‐articulated science issue, with strong policy implications. A broad array of other anthropogenic factors—widespread land cover change, engineering of river channels, irrigation and other consumptive losses, aquatic habitat disappearance, and pollution—also influences the water system in direct and important ways. A rich history of site‐specific research demonstrates the clear impact of such factors on local environments. Evidence now shows that humans are rapidly intervening in the basic character of the water cycle over much broader domains. The collective significance of these many transformations on both the Earth system and human society remains fundamentally unknown [Framing Committee of the GWSP, 2004].

This paper presents one of the first quantitative scenario assessments for future water supply and demand in Asia to 2050. The assessment, developed by the Water Futures and Solutions (WFaS) initiative, uses the latest set of global climate change and socioeconomic scenarios and state-of-the-art global hydrological models. In Asia, water demand for irrigation, industry, and households is projected to increase substantially in the coming decades (30-40% by 2050 compared to 2010). These changes are expected to exacerbate water stress, especially in the current hotspots such as north India and Pakistan, and north China. By 2050, 20% of the land area in the Asia-Pacific region, with a population of 1.6-2 billion, is projected to experience severe water stress. We find that socioeconomic changes are the main drivers of worsening water scarcity in Asia, with climate change impacts further increasing the challenge into the 21st century. Moreover, a detailed basin-level analysis of the hydro-economic conditions of 40 Asian basins shows that although the coping capacity of all basins is expected to improve due to gross domestic product (GDP) growth, some basins continuously face severe water challenges. These basins will potentially be home to up to 1.6 billion people by mid-21st century.Plain Language Summary Home to almost 4.5 billion people, Asia has experienced unprecedented economic and population growth in recent decades. In order to sustain growing food demand and increasing standard of living, water use has been increasing rapidly in many parts of Asia. At present, water withdrawals in Asia represent 65% of the global total. This huge abstraction of water resources has resulted in many Asian regions undergoing pervasive water scarcity conditions. The imminent global changes from climate change and socioeconomic development in Asia are expected to place additional pressures on water resources in the coming decades. In such a context, it is imperative to evaluate future water scarcity conditions and identify regions at highest risk in Asia. We found that by 2050, 20% of the land area in Asia, with population exceeding 1.6-2.0 billion, is projected to experience severe water scarcity. Here, we for the first time highlight that socioeconomic changes are the main driver of worsening water scarcity in Asia, much larger than the climate change impacts.

ABSTRACT. The two cultures theory argues that policy makers and scientists have different cultures and difficulty in communicating with each other. Others argue that there is increasing co-production of knowledge. This essay aims to assess the concerns of policy makers based on our policy work, policy-related research work, and our day-to-day experiences in terms of three questions: What are the perceived major issues for water governance? What are the major challenges in the structure of the existing global water governance approach? What is the vision for improving global water governance? This essay combines views from governmental, hybrid, inter-and non-governmental policy makers. It argues that water covers so many issues, aspects, and sectors that a key challenge is whether water should be governed as a sector or as a cross-cutting issue. It looks at how this challenge plays out within the United Nations system and leads to specific goal setting, while missing an overall visionary approach and a legally binding system of governance; within the hybrid arena, where it leads to inclusive discussion but not necessarily triggering consensus decisions; within nation states, where it has led to a loss of focus and a multitude of gaps and overlaps; and within transnational cooperative projects, where it has led to multiple interpretations of what is good practice. It then identifies a series of research questions.

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