The Water Web: More about WaSSI

Southern forests are among the top providers of water supply in the Nation. (photo by Vekony Zoltan, courtesy of Dreamstime)

Water quantity and quality issues affect every living thing on Earth, yet, until recently, methods for projecting possible future water supply scenarios were fairly limited.

In the late 1990s, Southern Research Station (SRS) scientists participating in several national-scale assessments of climate change science and climate-related impacts discovered “a frustrating lack of landscape-scale, integrated ecosystem models from which to draw projections of future hydrologic conditions,” according to research ecologist Steve McNulty. So they set out to build their own hydrologic model—known as WaSSI—to examine how long-term climatic changes interacting with human factors could influence water availability.

WaSSI stands for the Water Supply Stress Index, which was originally developed in 2005 to assess the impacts of changes in temperature and precipitation, land use, and human population on the relationship between water supply and demand in the southern region of the United States. Now researchers with the Eastern Forest Environmental Threat Assessment Center (EFETAC) are expanding its scope.

“WaSSI is a comprehensive model that is being built and validated using data from NASA satellite imagery and measurements from more than 500 individual water and carbon monitoring sites around the world,” says Ge Sun, EFETAC research hydrologist and WaSSI’s lead developer. “It can simulate monthly water supplies as well as carbon sequestration—an essential ecosystem function for regulating climate—for approximately 2,100 watersheds across the entire continental United States.”

EFETAC’s WaSSI development team, including co-developers McNulty and research hydrologist Pete Caldwell, intend to use the model results to help natural resource managers and policymakers make informed decisions when faced with the uncertainties associated with future environmental change.

“Water is a very powerful controller of ecosystem structure and function,” explains Sun. “If you understand a forest’s water cycle, you can tell a lot about the carbon cycle, biodiversity, and how the ecosystem will respond to change.” WaSSI can also help a variety of other users such as educators, researchers, nongovernmental organizations, and the general public gain insight into the effects of global change on water, carbon, and biodiversity at both local and continental scales.

A range of projects are already using information generated by WaSSI, including the Southern Forest Futures Project  and Northern Forest Futures Projectconducted by SRS and the Northern Research Station, respectively. The Union of Concerned Scientists recently released a report about the impacts of power plants on freshwater supplies based on findings from WaSSI. (Read more about this on CompassLive).

The WaSSI model is also reaching an international audience. It’s been successfully applied in Mexico and Brazil to help address natural resource and land use challenges, and in several countries in Africa and Asia to quantify potential impacts of land use practices on water quantity and quality as part of an effort to develop economic incentives for conserving watershed ecosystem services.

“This application of WaSSI represents a true international collaboration effort that benefits many people,” says Sun. “This is especially true in regions with limited means for monitoring current or forecasting future water and carbon resources.”

WaSSI, now available online, can predict how climate, land use, and human population change may impact water availability, carbon sequestration, and biodiversity at the watershed level and across the lower 48 United States. WaSSI users can select and adjust temperature, precipitation, land cover, and water use factors to simulate an unlimited number of global change scenarios for user-determined timeframes through 2100. Simulation results are available as downloadable graphs and data files that users can apply to their unique information and project needs.

Explore WaSSI online




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