Simulating the effect of climate change scenarios on surface water quality in the Bosque watershed, Central Texas, United States

Changes in precipitation, temperature, and extreme events affect surface water quality through various processes, such as transport, deposition, and concentration. Coupling robust climate change scenarios and hydrological modeling, this study simulated the impact of climate change on surface water quality in the Bosque watershed in Central Texas, USA. Streamflow, Organic Nitrogen (ORGN), Organic Phosphorus (ORGP), Mineral Phosphorus (MINP), and Nitrate (NO 3 ) concentration were simulated under different climate change scenarios using the Soil and Water Assessment Tool (SWAT). A multi-site and multi-variable calibration/validation and Differential Split Sampling approach was used to calibrate and validate the SWAT. In the future climate scenarios, a steady decline in organic nitrogen, organic phosphorus, and mineral phosphorus was found, primarily associated with decreased precipitation and streamflow. The reduction in organic nitrogen, organic phosphorus, and mineral phosphorus was 22–57%, 35–65%, and 10–56%, respectively. However, the hotter and drier future climate scenarios would result in a statistically significant nitrate increase (61–104%). Changes in water quality parameters were higher in the RCP4.5 emission scenario compared to the RCP2.6 and RCP8.5 emission scenarios. This study highlights the dire effect of climate change on the NO 3 concentration, which requires urgent water management interventions to mitigate detrimental repercussions for watershed health.