Water and forests in Southern US

In the coming decades, water quality, rainfall patterns, and streamflow regimes will continue to change, according to a new report on water.

The report is part of the Southern Forest Outlook from the USDA Forest Service and the Southern Group of State Foresters. In it, a team of seven hydrologists, foresters, economists, and other experts assessed water resources in the 13 southern states, from Virginia to Texas. They found:

• Precipitation extremes, both low and high (droughts and floods), will continue to increase in magnitude and frequency.
• Streamflow is projected to change but the amount and direction of change (increase or decrease) will vary across the South. Most future scenarios considered agree that portions of Arkansas, Louisiana, Oklahoma, and Texas will be most vulnerable to climate-driven streamflow reductions by 2070.
• Projected land use change will further alter streamflow regimes and water quality in developing watersheds.
• Hydrologic changes due to climate and land use changes may be exacerbated by hurricanes, seal level rise, wildfire, nonnative invasive plants, and insect and disease outbreaks.

"Fortunately, forestry best management practices are well-established and will help mitigate the effects of climate and land use change on water quality and availability," says Peter Caldwell, Forest Service researcher and lead author of the report.

The team used the Water Supply Stress Index model to project the effects of climate and land use change on water resources across four future scenarios and five climate projections. The future scenarios and climate models are from the 2020 Resources Planning Act Assessment and represent different assumptions about population and economic growth, land use change, and global climate change from 2020 to 2070. Under some future scenarios, forestry best management practices could be challenged by extreme precipitation events, according to the new report.

"Given these challenges and the uncertainty of changing future conditions, adaptive management informed by local knowledge will continue to be an important component of forest water management," says Caldwell.

Caldwell contributed to the Forests to Faucets assessment and a large body of research on how forests supply drinking water to people in the South and across the nation, with the goal of providing actionable information to prioritize forests and watersheds for management, restoration, and conservation to protect or enhance water supplies.

"For the new report we combined hydrologic modeling with a literature synthesis to answer forest and water related research questions that the public and state and national forestry agencies identified as important," says Caldwell.

The Southern Forest Outlook is designed to inform forest sector decisionmakers and the interested public about observed trends, anticipated futures, and critical issues based on authoritative synthesis and interpretation of existing science, data, and 50-year projections.

The report builds on a rich history of regional assessments of southern forests. Urbanization, markets, and climate change were identified as factors in previous assessments and remain highly relevant.

The water report emphasizes the value of keeping forests as forests. Converting forests to other land uses (especially urban use) results in higher concentrations of sediment, pathogens, and other pollutants in waterways. Increases in extreme rainfall events coupled with land use change could wash even more pollutants into waterways.

The water report is the second of four in the assessment. A report focused on markets was released in November, and additional reports on fire and forest change are forthcoming.