Hydrological drought trends and seasonality in selected Polish catchments between 1993 and 2022 using a threshold based approach

Abstract

Abstract Ongoing climate change and Land Use Change (LUC) in Europe are altering the frequency and seasonality of low-flow events. Increases in mean annual temperature, shifts in catchment land use, and reduced retention capacity contribute to intensifying streamflow deficits. This study examines long-term trends and seasonality of hydrological droughts in selected catchments of the Central European Lowland in Poland over hydrological years 1993–2022. Low-flow events were identified and characterised using tools in the R programming environment. Trends were assessed with the Mann–Kendall (MK) test and Sen’s slope estimator, and persistence was evaluated with the Hurst exponent. Significant correlations ( p  < 0.05) were found between the Total Number of Drought Events (TNDE) and LUC, particularly for events lasting ≥ 7 days at Q90 threshold, with the strongest effects in the Skora, Luciąża, Widawka and Grabia rivers. A marked increase in summer and autumn low-flow events was recorded after 2002, alongside rising Seasonal Number of Drought Days (SNDD) and Seasonal Cumulative Deficit Volume (SCDV), reflecting growing water deficits. The persistence of these trends suggests continued streamflow decline. The findings can inform the identification of catchments vulnerable to worsening summer water conditions.