Extending Daily River Discharge Records Across China Using Satellite-Derived River Widths

Abstract. Long-term monitoring of global river discharge has been hindered by the uneven distribution of gauging stations and limited data accessibility, a challenge that is particularly acute in China. Although China contains one of the world’s densest river networks, high-frequency in situ discharge observations remain largely unavailable in the international public domain. To address this gap, we compiled daily discharge records from 1,196 gauges across China, comprising approximately 2.33 million observations – 39 times as many gauges as are currently available for the region in the Global Runoff Data Centre (GRDC). Leveraging this unprecedented collection of in situ discharge records, along with river width time series derived from Landsat and Sentinel-2 imagery and gauge-specific hydraulic geometry relationships, we reconstructed and extended daily river discharge observations for 310 gauges from 1990 to 2024, resulting in the China Daily River Discharge Records (CDR²) dataset. Compared with existing global satellite-derived discharge products, CDR² increases the number of available gauges in China by at least fivefold. It achieves substantially improved performance, with a median Kling–Gupta efficiency of 0.66 during validation. Sensitivity analyses further indicate that discharge estimation accuracy increases markedly with greater river width variability and stronger hydraulic sensitivity. Trend analysis reveals that nearly 65% of gauges exhibit declining discharge over 1990–2024, with a median relative trend of −0.21%/yr, most pronounced in the Haihe, Liaohe, Yellow River, and middle Yangtze River basins. As the most extensive satellite-derived, gauge-constrained daily discharge dataset currently available for China, CDR² bridges a critical geographic gap in global river monitoring and provides a valuable benchmark for future discharge estimation, hydrological studies, and satellite calibration efforts.