Global uncertainty of various downward shortwave solar radiation products

Downwelling shortwave solar radiation, as the core driving force of the Earth's surface energy system, serves as the foundation for ecological assessment and solar energy utilization. The frequent occurrence of extreme disasters worldwide has raised higher demands for the certainty of solar radiation data. However, multi-source solar radiation products exhibit uncertainty yet globally-unclear. Here, we systematically investigate the spatiotemporal characteristics of uncertainties across six widely used solar radiation products on a global scale from 1991 to 2023, including remote sensing inversion (ISCCP-ITP, GLASS), reanalysis (ERA5, MERRA-2), and model simulation (SSP245, SSP585). Finally, we employed interpretable machine learning methods to explore the potential factors influencing such uncertainties. Results show that uncertainties in solar radiation products display remarkable spatiotemporal heterogeneity. ERA5 performed the best at the daily scale (R = 0.98, RMSE = 23.30 W/m2). While uncertainties vary significantly under different geographical conditions, products of the same category exhibit similar patterns. ERA5 exhibited the highest error over water surfaces, but its RMSE was only 20.61 W/m2 in snow covered areas. Remote sensing inversion products (ISCCP-ITP and GLASS) tended to underestimate solar radiation (with MBE values of −2.09 W/m2 and −3.79 W/m2, respectively), whereas reanalysis and model simulation products were generally overestimated. The two satellite remote sensing-based products showed similar uncertainties across different land cover types. Reanalysis products generally outperformed model simulation products. The potential factors influencing uncertainties in solar radiation products are complex and diverse, with solar zenith angle, air temperature, and humidity exerting greater impacts. This study facilitates the rational use of multi-source solar radiation products to address global climate change and energy crises.