Effects of riparian buffer on streamflow response under changing land cover and climate in a developing watershed.

Background/Question/Methods

Land conversion and global environmental change are stressing freshwater resources. The conversion of land to impervious surfaces reduces the capacity of watersheds to maintain stable baseflow, slow storm runoff, and provide clean water resources. The effects of expanded land conversion on watersheds will be exacerbated by a changing climate, which may increase stormwater timing and amounts to levels that threaten human and aquatic ecosystem health. Riparian areas represent dynamic transition zones critical for regulating hydrologic processes and riparian buffers can be a best management practice for mitigating the effects of land conversion on water resources. However, our ability to anticipate the efficacy of current and alternative riparian buffers under changing conditions remains limited. To address this gap, we projected hydrologic responses to different levels of buffer protection under a coupled land cover/climate scenario for 2060. We used the Soil and Water Assessment Tool (SWAT) to project future streamflow in an urbanizing watershed in North Carolina, USA under three levels of buffer protection: no additional buffers, 15-m, and 30-m. We compared resulting future hydrology to a baseline period to address how streamflow hydrology will change in response to future conditions and to what extent riparian buffer protection could mitigate these changes.

Results/Conclusions

For the future model, we used the Coupled Model Intercomparison Project CSIRO GCM RCP 8.5 scenario of future climate, which is a future of high greenhouse gas emissions coupled with warmer and wetter conditions, and the FUTure Urban-Regional Environment Simulation model for future land cover. Trends from the climate model show a 7.6% increase in mean annual precipitation and an increase of 16.1ºC to 18.8ºC in mean annual temperature to 2060. Land cover projections indicate doubling of low-intensity development by 2060. Buffers decreased flow rates during the lowest flow events in developing areas by up to 7% but could increase overall baseflow in the highest developed areas compared to no buffer protection. Buffers had a dampening effect on flow during the highest flow events across the watershed by up to 3.3%. Our study represents an approach to incorporate riparian buffers into hydrologic modeling to account for their mitigative effects under changing conditions. Understanding if riparian buffer protection can stabilize water resources under global change is a complex, pressing issue in watershed science and management and buffer ability to alleviate effects of anthropogenic activities is particularly crucial in developing basins, where populations are facing increased flood risk and decreased water availability.