The process of propagation from meteorological to hydrological drought is studied using the Vistula basin in Poland (193,960 km²) as a case study. The study aims to set a background for the analysis of processes influencing drought propagation in the basin, including the availability of data on hydro-meteorological factors, groundwater, and major human activities that might influence the water cycle in the region. A recent history of drought events in the basin is derived based on a statistical analysis of flow measured at nine gauging stations located along the river, starting from upstream downwards in the 1951–2018 period. The study is enhanced by the analysis of the temporal and spatial variability of a number of drought indices. As a result, the factors affecting temporal and spatial variability of drought—with particular emphasis on the interaction between the variability induced by natural processes and human interaction—are identified. The drought dynamics is studied by analysis of the relationships between meteorological and hydrological drought indices. The results indicate that the Vistula River basin has been influenced in its upstream part mainly by the mining industry, and the middle and downstream parts are additionally affected by industry and agriculture.

The spatiotemporal variations in the water balance caused by environmental changes lead to unsteady-state conditions with long- and short-term implications on the social and economic conditions. The aim of this study is to extend the current knowledge of the Budyko approach in unsteady-state conditions and the importance of model structural uncertainties. We used three Budyko-based models (Turc-Pike, Zhang, Fu) with and without the concept of effective precipitation scenarios. The effective precipitation and model parameters were determined together during the calibration processes. The effective precipitation-based approach improved the model performance in predicting the annual water balance in most of the River Vistula catchment. We also discuss the importance of considering structural uncertainties in water balance modelling. Climate change is the main driver for the changes in the water balance of the River Vistula. The estimation of water balance dynamics, considering environmental changes, is essential to understand the changes in hydrological processes.

The scientists tend to assume that climatic factors are the only drivers in the development of drought. However, this classical assumption is no longer valid in the Anthropocene, as most catchments have been significantly modified by human factors. Recent theoretical developments have shown that there are mutual interactions and feedback mechanisms – drought shapes humans and vice versa. Therefore, this study aims to assess the role of human impacts on hydrological drought (HD) characteristics by considering runoff and baseflow separately. For this purpose, the two rainfall-runoff models: SWAT (Soil and Water Assessment Tool) and HBV (Hydrologiska Byrans Vattenbalansavdelning) models are compared. The results show significant differences in the magnitude of change between the two models, suggesting that the ensemble method of multiple models need to be considered for modelling human impact. However, the results confirm that despite significant differences in the magnitude of change, both hydrological models indicate similar impacts, i.e. positive and negative.

Water balance modelling is often applied in studies of climate and human impacts on water resources. Annual water balance is usually derived based on precipitation, discharge and temperature observations under an assumption of negligible changes in annual water storage in a catchment. However, that assumption might be violated during very dry or very wet years. In this study we apply groundwater level measurements to improve water balance modelling in nine sub-catchments of the River Vistula basin starting from the river sources downstream. Annual and inter-annual water balance is studied using a Budyko framework to assess actual evapotranspiration and total water supply. We apply the concept of effective precipitation to account for possible losses due to water interception by vegetation. Generalised Likelihood Uncertainty Estimation GLUE is used to account for parameter and structural model uncertainty, together with the application of eight Budyko-type equations. Seasonal water balance models show large errors for winter seasons while summer and annual water balance models follow the Budyko framework. The dryness index is much smaller in winter than in summer for all sub-catchments. The spatial variability of water balance modelling errors indicate an increasing uncertainty of model predictions with an increase in catchment size. The results show that the added information on storage changes in the catchments provided by groundwater level observations largely improves model accuracy. The results also indicate the need to model groundwater level variability depending on external factors such as precipitation and evapotranspiration and human interventions. The modelling tools developed will be used to assess future water balance in the River Vistula basin under different water management scenarios and climate variability.