A hybrid data‐driven and data assimilation method for spatiotemporal forecasting: PM2.5 forecasting in China

Abstract

Spatiotemporal forecasting involves generating temporal forecasts for system state variables across spatial regions. Data-driven methods such as Convolutional Long Short-Term Memory (ConvLSTM) are effective in capturing both spatial and temporal correlations, but they suffer from error accumulation and accuracy loss as forecasting time increases due to the nonlinearity and uncertainty in physical processes. To address this issue, we propose to combine data-driven and data assimilation (DA) methods for spatiotemporal forecasting. The accuracy of the data-driven ConvLSTM model can be improved by periodically assimilating real-time observations using the ensemble Kalman filter (EnKF) approach. This proposed hybrid ConvLSTM-EnKF method is demonstrated through PM2.5 forecasting in China, which is a challenging task due to the complexity of topographical and meteorological conditions in the region, the need for high-resolution forecasting over a large study area, and the scarcity of observations. The results show that the ConvLSTM-EnKF method outperforms conventional methods and can provide satisfactory operational PM2.5 forecasts for up to 1 month with spatially averaged RMSE below 20 μg/m3 and correlation coefficient (R) above 0.8. In addition, the ConvLSTM-EnKF method shows a substantial reduction in CPU time when compared to the commonly used NAQPMS-EnKF method, up to three orders of magnitude. Overall, the use of data-driven models provides efficient forecasts and speeds up DA. This hybrid ConvLSTM-EnKF is a novel operational forecasting technique for spatiotemporal forecasting and is used in real spatiotemporal forecasting for the first time.