Temporal Consistency of Long-Term Seasonal Precipitation Trends in Italy from High- Resolution Regional Reanalyses

Reanalyses are widely used by the scientific community to assess precipitation trends across a broad range of disciplines. In particular, high-resolution regional reanalyses offer unique opportunities to monitor small-scale processes and evaluate the impacts of extreme precipitation events. Nevertheless, previous studies based on ERA5 and other global reanalyses have highlighted limitations in the temporal consistency of long-term annual precipitation estimates, calling for caution regarding their suitability for detecting robust climatological signals. This study extends the analysis of temporal consistency to four state-of-the-art convection-permitting reanalyses specifically developed for the Italian domain (MORE, CHAPTER, MERIDA HRES, and VHR-REA_IT) by dynamically downscaling ERA5 using different numerical models (MOLOCH, WRF, and COSMO). Long-term seasonal precipitation trends are evaluated against a homogenized observational dataset (UniMi/ISAC-CNR), specifically designed for climate analysis and ensuring temporal consistency. This comparison allows for a detailed quantification of uncertainties in precipitation trends across regions and seasons, helping to disentangle the climate signal from potential artefacts. Such inhomogeneities may be inherited from ERA5 in some cases or further introduced during the assimilation of local observations through techniques such as observational nudging. Finally, similarities and differences among the various reanalyses are discussed in the context of the specific architecture and configuration of each product. By providing an uncertainty assessment of seasonal precipitation trends, this work will deliver crucial information to reanalysis users on the extent to which trend results can be reliably employed in climate studies and impact assessments. At the same time, it will offer valuable feedback to reanalysis developers, supporting the design of reanalysis products that meet the highest standards of temporal consistency for Italy.