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Updated 16 September 2008

The Global Water Cycle
USGCRP Program Element



The Global Water Cycle


Recent Accomplishments

Near-Term Plans

Archived News Postings [June 2000-July 2005]

Related Sites

Calls for Proposals

CCSP / USGCRP Water Cycle Working Group Members

For long term plans, see Water Cycle chapter of the Strategic Plan for the Climate Change Science Program (2003) posted on CCSP web site.


The Water Cycle
Basic background information from NASA's Earth Observatory Reference section.


Proceedings of the Tenth U.S. -Japan Workshop on Global Change: Climate and Water.  Workshop held 15-17 January 2003, Irvine, California.  Draft dated 30 May 2003.   Also available as MS Word file. (link posted 30 May 2003)

Global Water Cycle ImageResearch associated with this element involves studies of the crucial role the water cycle plays in climate variability and change, and the influence climate has on aspects of the global water cycle on which society and nature depend. Through countless interactions within the Earth system, the global water cycle integrates physical, chemical, and biological processes that sustain ecosystems and influence climate and related global change. The ultimate goal of CCSP water cycle research is to provide a better foundation for decisions and investments by policymakers, managers, and individuals. Achieving this goal requires a program of activities that test predictions and data products in real decision contexts, demonstrate techniques and their effectiveness to potential users, and provide tools and strategies to transfer the science from the experimental realm to operations. In FY 2009, emphasis will be placed on coordinated observations and modeling of selected sites, at the river basin or catchment scale, to improve understanding of terrestrial water cycle processes leading to better closure constraints on water budgets at this scale. The improvements to land surface and hydrological models resulting from this research will lead to an enhanced ability to more accurately represent global change projections at the regional scales that affect water resources and other applications sectors dependent on the water cycle.


Strategic Research Questions

5.1.  What are the mechanisms and processes responsible for the maintenance and variability of the water cycle; are the characteristics of the cycle changing and, if so, to what extent are human activities responsible for those changes?

5.2. How do feedback processes control the interactions between the global water cycle and other parts of the climate system (e.g., carbon cycle, energy), and how are these feedbacks changing over time?

5.3.  What are the key uncertainties in seasonal to interannual predictions and long-term projections of water cycle variables, and what improvements are needed in global and regional models to reduce these uncertainties?

5.4 What are the consequences over a range of space and time scales of water cycle variability and change for human societies and ecosystems, and how do they interact with the Earth system to affect sediment transport and nutrient and biogeochemical cycles?

5.5.  How can global water cycle information be used to inform decision processes in the context of changing water resource conditions and policies?

See Strategic Plan for the U.S. Climate Change Science Program, Chapter 5, for detailed discussion of these research questions.

The global water (and energy) cycle plays a critical role in the functioning of the Earth system. Through complex interactions, the global water cycle integrates the physical, chemical, and biological processes that sustain ecosystems and influence climate and related global change. Inadequate understanding of the water/energy cycle is one of the key sources of uncertainty in climate prediction and climate change projections. Clouds, precipitation, and water vapor play important roles in feedbacks that are not well represented in many climate models. These processes alter surface and atmospheric heating and cooling rates, leading to adjustments in atmospheric circulation and precipitation patterns. Improved understanding of these processes will be essential to developing options for responding to the consequences of water cycle variability and change. For assessing the impacts of global and regional climate change on human societies, industrial and economic systems, and natural and managed ecosystems, water is considered a more rigid or critical constraint or limiting factor than temperature. To address these issues the CCSP Global Water Cycle element expends considerable effort to improve observations, data assimilation, and modeling/prediction systems that in turn deliver the information necessary for decision-support tools and assessments that provide a basis for “best practices” in the management of water resources.

The ultimate goal of water cycle research is to provide a solid foundation for decisions and investments by policymakers, managers, and individuals, be it at the Federal, State, or local level. Achieving this goal requires a program of activities that significantly improves understanding of water/energy cycle processes, incorporates this understanding in an integrated modeling/prediction framework, and tests predictions and data products in real decisionmaking contexts. In order to demonstrate techniques and effectiveness to potential users, the Global Water Cycle program also aims to expedite the transfer of science results from the research/experimental realm to operational applications.

Significant progress is being made in the understanding of cloud properties, the direct and indirect effect of aerosols on cloud and precipitation processes, and the interaction of cloud systems with land surface hydrological conditions. To this end, the Global Water Cycle program’s first integrated priority activity was completed in June 2007 through multi-agency participation in DOE’s Cloud and Land Surface Interaction Campaign (CLASIC). Comprehensive satellite monitoring of water cycle parameters— such as global precipitation and cloud structure in storm systems and hurricanes [with the Tropical Rainfall Measuring Mission (TRMM) and Cloudsat], soil moisture [with the Special Sensor Microwave/Imager (SSM/I) and the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E)], and water bodies [with the Gravity Recovery and Climate Experiment (GRACE)], as well as more accurate atmospheric profiles of temperature, humidity, and land/ocean surface parameters (with the multisensor Terra and Aqua satellites)—have resulted in integrated data sets and improved models of the Earth system. Ensemble Kalman filtering techniques have demonstrated the potential use of satellite-derived surface soil moisture estimates to improve the characterization of soil moisture at depth in land information systems. The incorporation of research results in models has led to better simulation/prediction capabilities for hydroclimatic variables. Multi-model and ensemble modeling techniques developed by CCSP have led to improved seasonal predictions of both the atmospheric and terrestrial hydrological cycle. Techniques have also been developed by USDA’s Agricultural Research Service, DOI/USGS, and the DOI Bureau of Reclamation, in collaboration with NOAA, NASA, EPA, and DOE, among others, for the downscaling of intra-seasonal and seasonal precipitation forecasts to temporal scales consistent with the input requirements for agricultural and water resources management as well as conservation planning and decision-support tools. Experimental seasonal hydrological prediction systems have been developed that use multi-model climate forecast products and empirical tools to “force” land/hydrological prediction models.

Pretty WATER view



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