This applies not only to freshwater systems but also to the oceans, their levels and what lives in them. Water is becoming a central issue in this new period. Some call this new geological period the Anthropocene. The momentum and acceleration of the impacts of business as usual threaten to tip the complex Earth System out of the environment in which everything living on this Earth has evolved and developed. In the last 50 years or so we have come to recognize the movements in all Earth's layers, including the plates at the surface, the mantle and the core as well as the atmosphere and ocean. Without interlocked cycles and recycling, the components of our Earth could not function as an integrated system. The various parts of the Earth system – rock, water, and atmosphere – are all involved in interrelated cycles where matter is continually in motion and is used and reused in the various planetary processes. These challenges to effective planetary stewardship must be addressed and soon. The challenges of our current decade-resource constraints, financial instability, religious conflict, inequalities within and between countries, environmental degradation-all suggest that business-as-usual cannot continue. Earth is currently confronted with a relatively new situation, the ability of humans to transform the atmosphere, degrade the biosphere, and alter the lithosphere and hydrosphere. Our planet no longer functions in the way it once did. We have done this mainly to satisfy short-term economic goals, often goals that may not have included the long-term environmental-or even economic-sustainability of region or basin, and indeed our own health. 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 disrupted and overallocated river flow regimes-sometimes to the point of drying them up, along with their downstream lakes. 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. There are no substitutes and while it is renewable there is only a finite amount of it. Water plays a role in the creation of everything we produce. We depend on water not only for life itself, but indeed for our economic wellbeing as well. 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. This in turn impacts the amounts and spatial and temporal distributions of precipitation that falls on watersheds and the timing of its runoff. Our actions are impacting our global environment, including our climate. We humans have become the principal driver of environmental change. Throughout 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. 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. 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. How best to meet these challenges requires research in all aspects of water management. 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. All of us involved in research must find ways to remove these constraints. 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. There are many regions where our freshwater resources are inadequate to meet domestic, economic development and environmental needs. 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. Water distinguishes our planet compared to all the others we know about.
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