Effects of Riparian Buffer on Streamflow Response to Land Use and Climate Change

Rapid land conversion, coupled with global environmental change, is stressing freshwater resources. Namely, the conversion of land into impervious surfaces hinders the ability of watersheds to provide clean water, slow run-off, and maintain regular base flow. Population growth, and subsequent development, in the Piedmont region of the southeastern United States between Atlanta, GA and Raleigh, NC is among the highest in the country. Uncontrolled growth in the Piedmont will exacerbate the effects of climate change and cause stormwater challenges that threaten human and aquatic ecosystem health. Riparian buffers represent a best management practice for maintaining the hydrologic balance and mitigating against the effects of land conversion. However, our ability to anticipate the effectiveness of current and alternative riparian buffers in mitigating the continued effects of urbanization and climate change remains very limited. To address this information gap, we projected hydrologic response to different levels of buffer protection under a coupled land use/climate scenario for 2060. We used the SWAT hydrologic model to project future streamflow in the Upper Neuse and Upper Catawba (HUC-8 developing watersheds) under three levels of buffer protection: none (currently applied in most NC watersheds), 50-ft (currently applied in the Neuse watershed), and 100-ft (applied in parts of the Chesapeake Bay watershed). Land use derived from the FUTURES urban growth model indicates increased impervious surface cover across the study area, particularly in areas located just outside main urban centers. Preliminary results from the SWAT model show that compared to the no buffer scenario, expanded buffers (50-ft and 100-ft) have a mitigative effect on water quantity by stabilizing extreme high and low streamflow in sub-basins that experienced a high percentage of forested-to-urban land conversion. Expanded buffers have a marginal effect on water quantity in sub-basins that were already highly urbanized. Therefore, buffer protection in developing sub-basins can potentially minimize the impact of land conversion on water quantity.