1. Introduction

The goal of the thesis was to evaluate changes in the surface- and groundwater quality during periods of hydrological drought. The Upper Nitra river catchment was selected as a study area. Before the evaluation of the drought in this catchment, the occurrence and character of hydrological drought in 75 profiles of Slovak rivers was processed. This regional evaluation was used for comparison of the relationship between the local and regional drought occurrences. Subsequently, the occurrence and nature of meteorological and hydrological droughts in the surface water and groundwater were analysed in the evaluated area. Partial results were compared afterwards. The study of hydrological drought was followed by the assessment of the surface water and groundwater quality at various quantitative conditions. The water quality within periods of water scarcity was assessed at the two levels. As the threshold levels, value of median and 90th percentile estimated from the flow duration curve were used. Individual results were summarized. The last chapter deals with a general assessment of the dependence between quantitative and qualitative conditions of the surface- and groundwater within the drought periods. In addition to the described work, a new software tools for the hydrology and hydrogeochemistry were developed and used for the data processing and results assessment.