Hydrological Pollutant Export Responses to Rain-fall Intensity in Paddy Fields

Agricultural non-point source pollution threatens water quality, and climate change intensifies this risk by increasing rainfall intensity. This study examined how rainfall intensity affects runoff and pollutant export (COD, TN, TP) from paddy fields in the Yangtze River Basin. Simulation experiments with rainfall rates of 40 mm/h (S40) and 120 mm/h (S120) showed that high-intensity rainfall nearly doubled runoff volume and coefficients. Pollutant loads rose sharply: COD export increased from 2.21 to 4.90 kg/ha, TN from 211.71 to 585.16 g/ha, and TP in May was 2.5 times higher under S120 than S40. Correlation analysis identified runoff volume as the main driver of pollutant export, with coefficients under high intensity often exceeding 0.20. These results demonstrate that extreme rainfall events dominate annual pollutant export and provide a basis for climate-adaptive nutrient management in monsoon-affected agricultural regions.