Changes in Streamflow Drought and Flood Distribution Over Poland Using Trend Decomposition

Raczynski, K., & Dyer, J. (2023). Changes in Streamflow Drought and Flood Distribution Over Poland Using Trend Decomposition. Acta Geophysica. 2023, 22. DOI:10.1007/s11600-023-01188-0.

The aim of this work is to analyze the changes in streamflow drought and flood distribution in Polish rivers through data decomposition and trend analysis. The study dataset constituted daily streamflow at 250 gauges located across Poland (eastern Europe) from January 1, 1965, to December 31, 2020. Hydrological extremes were identified by the means of the objective threshold method, and basic parameters such as occurrence frequency, duration times, and event volumes were calculated along with minimal and maximal flow information, aggregated on monthly and annual scales. The seasonal trend decomposition using Loess (STL) method was used to decompose long-term changes from raw datasets. Results indicated that the application of the STL decomposition significantly improved the ability to detect changes in the streamflow time series, which is crucial for further research on climate-induced changes in different parts of the world. The identified trends indicate a decrease in flooding and an increase in streamflow drought magnitudes across Poland, except for mountainous areas in southeastern Poland, where drought magnitudes increase during summer and decrease in winter, while flooding increases in late spring and early autumn.