Fresh Water, Land and Biologic Interactions: Changes and Impacts

The goal of this workshop was to explore the existing knowledge of and new approaches to the complex relationship between water cycles, biogeochemical cycles, and human actions. Considering available models of these systems, the session discussed the concept of different ecological-hydrological regions and their distinctive characteristics across the globe. An early study of major river systems of the world and how they may be affected by climate change was discussed.

Keywords: models and modeling, water cycle, biogeochemical cycle, human interactions, snow and ice

Overview & Relevance:
The terrestrial hydrological cycle is an essential component of the Earth’s climate and biogeochemical systems, and it supplies the necessary water resource for sustaining life on the land. Associated with this hydrological cycle is the cycling of energy, water, nutrients, and trace gases between land, atmosphere, ocean, solid earth, and the terrestrial biota. In some areas, food production to sustain human life is limited primarily by the availability of water; flood and droughts occasionally take their toll in other areas. The dynamics of the interacting hydrologic processes and the linkages between soils, vegetation, and the atmosphere are not well understood.

Greenhouse warming and other real or suspected changes in the earth system will affect the hydrological cycle, and these changes may have important social consequences as well as feedbacks to other components in the global biogeochemical system. Unfortunately, our ability to predict these changes and their impacts is severely constrained by our limited understanding of the basic processes and interactions.

CONTENT:
The goal of this workshop was to explore the present state of knowledge, and identify promising new approaches to an understanding of the complex hydrologic and biogeochemical system on human action. The session began with an examination of the state of climate and cliamte/hydrology models and then considered the state of knowledge of the coupled water and biogeochemical cycles. This led to a discussion of literature use/ecosystem interactions. As these varied enormously in different parts of the world, the session addressed the concept of eco-hydrological regions and their distinctive characteristics.

We then turned to more direct connections between water and humankind. The session discussed risk, uncertainty, and saliency in water management systems, and considered the effect of climate change on large international water systems, and the vulnerability of drainage basin developments. Finally, there was an open discussion on water, sustainability, and social response, including an attempt to identify new approaches.

Discussion Topics:
•  What are the regional differences and similarities in eco-hyrological regions (e.g. tropical wetlands, savannas, deserts, cold regions); what new understanding and/or modeling is needed in order to predict the response of these regions to changes in climate, land use, or other external forcings?
•  What controls the role of freshwater in biogeochemical cycling, including land-vegetation-atmosphere exchanges of moisture in these various eco-hydrological regions?
•  How will ground water depletion and increasing consumptive use of surface water, in a changing climatic environment, affect the water balance of continents, exchanges of water with ocean and atmosphere, and global sea level?
•  How can soil moisture, surface water, snow cover, and other components of the terrestrial hydrological cycle be modeled realistically at all spacial scales?
•  How can we define the macroscale interactions of humans, water, vegetation, and other species, in a systems approach, and use this understanding to answer questions of sustainability in water-limited societies?