Investigating transformer-based models for spatial downscaling and correcting biases of near-surface temperature and wind-speed forecasts

High-resolution and accurate prediction of near-surface weather parameters based on numerical weather prediction (NWP) models is essential for many downstream and real-world applications. Traditional dynamical or statistical downscaling methods are insufficient to derive high-resolution data from operational NWP forecasts, making it essential to devise new approaches. In recent years, an increasing number of researchers have explored the implementations of deep learning (DL) based models for spatial downscaling, motivated by the similarity between the super-resolution (SR) problem in computer vision (CV) and downscaling. Furthermore, while transformer-based models have become state-of-the-art models for many SR tasks, they are rarely applied for downscaling of weather forecasts or climate projections. This study adapted transformer-based models such as SwinIR and Uformer to downscale the temperature at 2 m (T2m$$ {T}_{2\mathrm{m}} $$) and wind speed at 10 m (WS10m$$ W{S}_{10\mathrm{m}} $$) over Eastern Inner Mongolia, encompassing the area from 39.6-46 degrees N latitude and 111.6-118 degrees E longitude. We used high-resolution forecast (HRES) data from the European Centre for Medium-range Weather Forecast (ECMWF) with a spatial resolution of 0.1 degrees as the input and gridded observation data from the China Meteorological Administration (CMA) Land Data Assimilation System (CLDAS) at a spatial resolution of 0.01 degrees as the target. Given that the models use observation data rather than a coarse-grained version of forecast data as the target, they accomplish both bias correction and spatial downscaling. The results demonstrate that the performance of SwinIR and Uformer is superior to that of two convolutional neural network (CNN) based models (UNet and RCAN). Additionally, we introduced a novel module to extract features of varying resolution from the high-resolution topography data and applied a multiscale feature fusion module to merge features of different scales, contributing to further enhancement of Uformer's performance. For the first time, transformer-based models such as SwinIR and Uformer are applied for weather downscaling. Comparison with CNN-based models demonstrates that transformer-based models outperform CNN-based models such as UNet and RCAN. Furthermore, topography feature extraction and multiscale feature fusion modules are proposed to improve Uformer's downscaling performance.image