Water Management : A Balancing Act

A balanced approach to water resource management can support aquatic life and meet the needs of current and future generations. Photo by Ge Sun.

It may come as little surprise that human activities and climate influence the volume of water in rivers, but U.S. Forest Service research is now revealing just how much.

Scientists with the Eastern Forest Environmental Threat Assessment Center are examining the individual and combined effects of changing land cover, human water use, and climate through time. Their efforts are providing a clearer picture of how these factors impact river flows needed to support healthy aquatic life and provide water for domestic use, agriculture, and energy.

In a study recently published in the journal Hydrology and Earth System Sciences, Eastern Threat Center researchers first determined how river flows are currently affected by human water use and impervious land cover—those developed surfaces such as buildings and paved roads and parking lots that do not allow rain water to soak into the ground. To do this, they used a tool called the Water Supply Stress Index (WaSSI) model, which provides information about water availability, water demand, and water flow routes.

Next, they used WaSSI to estimate how river flows could change with future projections for increasing human water use and impervious surface area in addition to an altered climate. They considered two future climate scenarios to estimate river flow changes for almost 2,100 watersheds (drainage basins that are sources of water flowing into rivers) across the continental United States through the year 2060.

Researchers found that, while impervious surfaces can route more water directly into rivers and thereby increase river flows due to reduced evapotranspiration (plant water use), human water use and climate change decrease river flows, sometimes to a much greater extent. The exact impacts on river flows vary from watershed to watershed.

“Our results suggest that higher temperatures and decreased precipitation associated with climate change will have a larger impact on river flows than either impervious cover or human water use at the national scale. Unfortunately, climate change is also the most uncertain of the global change drivers,” says Peter Caldwell, Eastern Threat Center research hydrologist and the study’s lead author.

The findings of this study will be important for natural resource managers and planners who must ensure adequate and sustainable water supplies in the face of growing demands and a changing climate.

“Although impervious cover increases river flows, it should not be considered as a management strategy for increasing water supply due to the negative impacts on aquatic habitat and water quality,” says Eastern Threat Center research hydrologist Ge Sun. “The climate change impacts on river flows as well as the changes to infrastructure required to support human water needs will affect human communities and downstream aquatic life, requiring a balanced approach to water resource management. It is important to evaluate the individual and combined effects of factors influencing river flows to develop management options and strategies to lessen negative impacts on water supplies.”

Read the full text of the article.
Note: This article appears in a special issue of the journal Hydrology and Earth System Sciences. Ge Sun served as a co-editor for this special issue.

For more information, contact Peter Caldwell at pcaldwell02@fs.fed.us.

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