Assessment of Future Streamflow Variability in the Duck River Basin, USA under CMIP6 Climate Projections using HEC-HMS Model

The Duck River Basin in Tennessee, USA, is ecologically diverse but highly vulnerable to climate change, particularly in terms of streamflow dynamics. This study projects future streamflow under two greenhouse gas emission scenarios (SSP2-4.5 and SSP5-8.5) using three Global Climate Models (BCC-CSM2-MR, MPI-ESM1-2-HR, and MRI-ESM2-0) from Coupled Model Intercomparison Project Phase 6 (CMIP6), coupled with the HEC-HMS hydrologic model. The HEC-HMS model was calibrated and validated at the Hurricane Mills outlet in Tennessee (USGS site 03603000), achieving strong performance with a Nash-Sutcliffe efficiency (NSE) of 0.827 and a percent bias of -4.67% during calibration and reliable predictions during validation (NSE = 0.785, bias = -2.16%). Results across three future periods (2015–2040, 2041–2070, and 2071–2100) reveal consistent seasonal streamflow patterns: high flows in winter (December–March) and severe low flows in summer (June–October). This seasonal contrast becomes increasingly pronounced from the 2041–2070 period to 2071–2100. The warmest scenarios predict earlier snowmelt, leading to higher winter peaks (particularly between January and March), but drastically reduced summer flows, with median flows falling below 50 m³/s from June to September, increasing drought risks. Amid all three time periods, the coldest scenario for 2071–2100 also shows pronounced winter peaks driven by snowmelt and precipitation, but similarly low summer flows. The wettest scenarios for all times maintain higher winter flows and some summer flow, whereas the driest scenarios feature sharp winter peaks but minimal summer streamflow. Moderate scenarios provide more balanced flows, avoiding extremes and supporting smoother seasonal transitions. These findings point out the urgent need for adaptive water management, resilient infrastructure, and sustainable land practices to mitigate climate change impacts in the Duck River Basin.