Global Hydrology

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THE SCIENCE OF GLOBAL HYDROLOGY

Water is arguably the single most critical factor supporting nature and humanking on this, our "blue planet". Water is a central component of the Earth system, providing important controls on the world's weather and climate. Water is central to survival itself, and without it plant and animal life would be impossible. Water is also central to human well-being, by supporting rainfed and irrigated agriculture, forestry, navigation, manufacturing, waster processing, and hydroelectricity. In the more than 250 international river basins, water moving across international boundaries makes for sensitive and potentially dangerous international diplomatic challenges. Our understanding of present-day climate systems and the predicted consequences of future climate change, together with population growth and economic development, demonstrate that water will be of paramount importance for many years to come.

Based on the traditions of scientific hydrology lasting more than 100 years, our current knowledge of water systems relies heavily on studies cast over the plot, hillslope, and small catchment scales. At the same time, through the development of data sets, statistical analysis, and modeling, the Earth systems science community is poised to make important contributions to understanding the critical linkages, feedbacks, and thresholds within the global water system.

Quantifying elements of the land-based hydrological cycle is a key focus of major international observational and modeling programs. General circulation models (GCMs) and, more recently, regional atmospheric models of increasing sophistication are widely employed to help understand how complex landscapes regulate surface water and energy fluxes. Global, real-time weather forecast models built on assimilatin of satellite and land-based station data sets demonstrate increasing skill in making predictions of water cycle variables. Major field campaigns mobilize the community toward coordinated water cycle observations and serve as focal points for the improvement of land surface hydrology models. Earth Systems Models with coupled energy-water-biogeochemistry algorithms are also under development and are shedding light into the importance of the land-based water cycle in regulating climate dynamics and terrestrial primary production. New technologies are on the horizon in terms of innovative remote sensing systems to monitor the state of inland waters. New capabilities are also emerging to simulate riverine constituent fluxes at the global scale. Taken together, these capabilities provide a scientific and technical context through which to assess the changing nature of water systems in the face of climate change and of the growing role of humans in modifying water systems across the planet.

When we speak today about "global hydrology" we are thus referring to a branch of hydrology that is developing rapidly, is inherently synthetic and beginning to take on an interdisciplinary character that unites the biogeophysical and human dimensions research communities. The research, education, and outreach mission of the Water Systems Analysis Group is dedicated to supporting these new developments in global-scale hydrology.