Evaluating High-Resolution Gridded Precipitation for the Adige Catchment: Comparison of Interpolation Methods and Benchmarking Against Existing Products

High-resolution precipitation data is essential for hydrological modeling and climate risk assessment, particularly in Alpine regions where complex terrain and fragmented data sources present ongoing challenges. In this study, we introduce a new 1-km daily gridded precipitation dataset covering the extended Adige River catchment (~40,000 km²) for the period 1990–2023. The domain spans cross-border areas of northern Italy, Austria, and Switzerland and integrates approximately 700 rain gauge series provided by nine regional and national agencies.

A key focus of the work is the comparison of multiple interpolation techniques, including kriging with external drift, local linear regression and machine learning, and their performance across diverse topographic settings. We tested several methods and identified those that offered the most reliable spatial estimates, with particular attention to areas of complex orography. The gridded outputs were evaluated against widely used precipitation products, including reanalysis datasets and lower-resolution observational grids such as SPARTACUS, ARCIS, E-OBS, EMO, CHIRPS,  CHELSA and APGD to assess improvements in spatial accuracy and representation. Both the climatological conditions and local-scale variability of the precipitation regime were analysed.

Results show that combining a dense observational network with carefully selected interpolation approaches significantly improves the spatial representation of precipitation, particularly in areas with complex topography. However, issues related to the underrepresentation of precipitation amounts at higher elevations due to rain-gauge undercatch and the data scarcity in mountain areas remained, and were further investigated to improve the quantification of the uncertainty of the final gridded fields and its implications for impact-oriented applications.

The dataset is developed within the framework of the RETURN Extended Partnership and is intended to support research and operational use across multiple sectors, including water resources, natural hazards, and climate adaptation planning.