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This paper aims to quantify the uncertainty in the projections of future hydrological extremes in the BialaTarnowska River basin, south Poland. We follow a multi-model approach based on several climate projections obtained from the EUROCORDEX initiative, raw and downscaled realizations of catchment precipitation and temperature, and flow simulations derived using the hydrological HBV model. The projections cover the 21st century. Three sources of uncertainty were considered: one related to the hydrological model parameters uncertainty, the second related to climate projection ensemble spread and the third related to the distribution fit. The uncertainty of projected extreme indices related to hydrological model parameters was conditioned on flow observations from the reference period using the Generalised Likelihood Uncertainty Estimation approach, with separate weighting for high and low flow extremes. Flood quantiles were estimated using Generalize Extreme Value (GEV) distribution at different return periods and were based on two different lengths of the flow time series. The sensitivity analysis based on ANOVA shows that the uncertainty introduced by the HBV model parameters can be larger than the climate model variability and distribution fit uncertainty for the low-flow extremes whilst for the high-flow extremes higher uncertainty is observed from climate models than from hydrological parameter and distribution fit uncertainties. This implies that ignoring one of the three uncertainty sources may cause great risk to future hydrological extreme adaptations and water resource planning and management. [ABSTRACT FROM AUTHOR]

The nature of drought conditions is estimated using a range of indices describing different aspects of drought events. Three drought indices are evaluated, namely the Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Runoff Index (SRI), using observed hydroclimatic data and applying them to hydro-meteorological projections into the 21st century. The first two indices are evaluated using only meteorological variables and from this point of view, are better suited to meteorological drought projections than the third index, SRI, which is based on catchment discharge and represents hydrological drought. We assess information contained in those indices and their suitability to catchment scale climate projection drought assessment in ten selected Polish catchments, representing different hydro-climatic conditions, which are used as a case study. Projections of climatic variables (precipitation and temperature) are obtained from the EURO-CORDEX initiative derived from seven climate models at a grid resolution of 12.5 km for the time period 1971--2100. Future runoff projections for the catchments are obtained using a conceptual rainfall-runoff model (HBV). The results of analyses of indices based on observations in the reference period show consistent estimates for most of the catchments. Hydro-meteorological climate model projections for three periods, including the reference period 1971--2000, and two 30-year periods, near-future 2021--2050 and far-future 2071--2100, are used to estimate changes of future drought conditions in the catchments studied. The results show a substantial variation of temporal drought patterns over the catchments and their dependence on projected precipitation and temperature variables and the type of indices applied. Of the three indices studied, only SPEI projections indicate drier conditions in the catchments in the far-future period. The other two indices, SPI and SRI, indicate wetter climates in the future. [ABSTRACT FROM AUTHOR]