Yukyeong Jang
|
oh Jong-Min
|
I Song Choi
| 2026, 35(5)
| pp.362~378
| number of Cited : 0
This study forecasts water quality at Paldang Lake and interprets the basis of its predictions to identify priority nonpoint source (NPS) areas in the watershed. Because rainfall-driven NPS pollution originates from widely dispersed sources, evidence is needed to allocate limited management resources. To this end, 63 monitoring stations across the Namhan River, Bukhan River, and Gyeongan Stream were represented as graph nodes, and Graph WaveNet was used to forecast BOD, COD, T-N, and T-P at the Paldang Lake station from 1 to 10 days ahead. SHapley Additive exPlanations (SHAP) was then applied to quantify variable- and station-wise contributions, which were compared according to whether rainfall occurred. For 1-day-ahead forecasts, the explanatory power (R²) was at least 0.89 for all variables (0.94 for T-N), equal to or higher than the LSTM, TCN, and Transformer baselines, and T-N maintained an R² of 0.37 even at the 10-day horizon. Conditional SHAP analysis showed that nutrient contributions from the remote Bokha Stream system in Icheon increased markedly under rainfall; for T-P, rainfall contributions exceeded dry-condition contributions in all 250 training runs, indicating a rainfall-sensitive NPS source. The same tendency appeared in the Gyeongan Stream watershed. These results can serve as a basis for prioritizing watershed-scale NPS reduction projects.