Analysis of low flow indices under varying climatic conditions in Poland

Abstract

Changes in low flow indices under future climates are estimated for eight catchments in Poland. A simulation approach is used to derive daily flows under changing climatic conditions, following RCP 4.5 and RCP 8.5 emission scenarios. The HBV rainfall-runoff model is used to simulate low flows. The model is calibrated and validated using streamflow observations from periods 1971-2000 and 2001-2010. Two objective functions are used for calibration: Nash-Sutcliffe and log transformed Nash-Sutcliffe. Finally, the models are run using the bias-corrected precipitation and temperature data simulated by GCM/RCM models for the periods 2021-2050 and 2071-2100. We estimate low flow indices for the simulated time series, including annual minima of 7-day mean river flows and number, severity and duration of low flow events. We quantify the biases of low flow indices by N-way analysis of variance (ANOVA) analysis and Tukey test. Results indicate a large effect of climate models, as well as objective functions, on the low flow indices obtained. A comparison of indices from the two future periods with the reference period 1971-2000 confirms the trends obtained in previous studies, in the form of a projected decrease in the frequency and intensity of low flow events.