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Drought is an important natural hazard with large impacts on society. Changes in drought characteristics have been studied for different parts of the hydrological cycle, but insights into changes of groundwater resources are obscured due to the lack of long-term observations and large heterogeneity of hydrogeological conditions. Moreover, predicted future changes in precipitation are uncertain and have a lagged effect on streamflow and groundwater. We investigated past changes and potential future changes in catchment baseflow as a reflection of groundwater drought for 338 headwater catchments across Germany based on catchments' characteristic response times. First, baseflow dynamics as a proxy of groundwater storage and outflow on a catchment scale were derived from streamflow records and related to precipitation input. Second, past trends in baseflow minima were calculated and attributed to climate and catchment controls. Last, response times and the timing of yearly baseflow minima were combined into estimates of the sensitivity to future precipitation changes. Baseflow response times of the studied headwaters are heterogenous across Germany, ranging from a few months to several years, and depend significantly on hydrogeological conditions. Few significant trends were found in past baseflow minima, and trends are highly dependent on the period of analysis. Based on the assumption of a typical regional scenario of increasing winter precipitation and decreasing summer precipitation, increases in hydrological drought hazard or no changes are projected for most parts of Germany. Catchments with longer response times can buffer interannual precipitation shifts, whereas catchments with fractured rocks are sensitive to summer precipitation decreases. These results urge for a surface water and groundwater management based on local groundwater response to precipitation and help to assess impacts of climate change on overall water supply. [ABSTRACT FROM AUTHOR]

This study investigates 72 catchments across the federal state of Baden-Wuerttemberg, Germany, for changes in water quality during low-flow events. Data from the state's water quality monitoring network provided seven water quality parameters (water temperature, electrical conductivity, concentrations of chloride, sodium, sulfate, nitrate, and phosphate), which were statistically related to streamflow variability. Water temperature changes during low-flow showed seasonal dependence. Nitrate concentrations revealed high spatial heterogeneity with about one third of the stations showing decreasing values during low discharge. For most other parameters, concentrations increased during low-flow. Despite consistent trend directions, the magnitudes of changes with streamflow differed markedly across the state. Both multiple linear regression and a multiple analysis of variances were applied to explain these differences with the help of catchment characteristics. Results indicated that for sulfate and conductivity, geology of the catchments was the most important control, whereas for chloride, sodium, and nitrate, sewage treatment plants had the largest influence. For phosphate, no clear control could be identified. Independent from the applied method, land use was a less important control on river water quality during low-flow than geology or inflow from sewage treatment plants. These results show that the effects of diffuse and point sources, as well as those of natural and anthropogenic sources differ for different water quality parameters. Overall, a high diversity of potential water quality deterioration signals needs to be considered when the ecological status of rivers is to be protected during low-flow events. [ABSTRACT FROM AUTHOR]