Changes in Precipitation Patterns in Poland Derived From Projected Downscaled Future Climate Data From CMIP5 and CMIP6

Climate change is affecting the intensity and frequency of precipitation. The main objective was to assess future changes in precipitation patterns in Poland. Ensembles of daily precipitation projections for 70 stations from CMIP5 and CMIP6 under RCP(SSP)4.5, RCP(SSP)8.5 pathways were statistically downscaled using the Quantile Perturbation Method (QPM), covering the reference period 1961–1990 and future period 2071–2100. We assessed annual and seasonal (winter, summer) changes in 12 extreme Precipitation Indices (PIs), their distributions across Poland, and shifts in design annual maximum (AM) precipitation intensities. Statistical measures included distribution fitting, Intensity-Duration-Frequency curves, and return periods. The projected changes (CMIP6-8.5) in summer include: increase in the length of consecutive dry days (5%, on average), number of heavy precipitation days (4%) and 1-, 3-, 5-day maximum intensity (8%, 6%, 5%), and decrease in the number of wet days (6%) and length of consecutive wet days (6%). In winter, projections show an increase in the number of heavy precipitation days (30%), 1-,3-, 5-day maximum intensity (15%, 13%, 12%), and total precipitation (11%). The changes vary across Poland, with a more intense increase in the number of heavy precipitation days in the north-west (summer) and in the 1-day maximum intensity in the south (winter), higher precipitation totals in the south, southeast and coastal areas (winter), and a decrease in total precipitation in the south and east (summer). Uncertainty is large for the number of heavy precipitation days and maximum intensities, while it is low for total precipitation and the number of wet and dry days. Future return periods of extreme events are projected to shorten. A 100-year 1-day AM intensity can become a $49-66$-year intensity. The results can be applied in flood and drought management plans, helping to adapt to future changes in precipitation patterns.