There is general agreement among scientists that global temperatures are rising and will continue to increase in the future. It is also agreed that human activities are the most important causes of these climatic variations, and that water resources are already suffering and will continue to be greatly impaired as a consequence of these changes. In particular, it is probable that areas with limited water resources will expand and that an increase of global water demand will occur, estimated to be around 35-60% by 2025 as a consequence of population growth and the competing needs of water uses. This will cause a growing imbalance between water demand (including the needs of nature) and supply. This urgency demands that climate change impacts on water be evaluated in different sectors using a cross-cutting approach (Contestabile in Nat Clim Chang 3:11-12, 2013). These issues were examined by the EU FP7-funded Co-ordination and support action "ClimateWater" (bridging the gap between adaptation strategies of climate change impacts and European water policies). The project studied adaptation strategies to minimize the water-related consequences of climate change and assessed how these strategies should be taken into consideration by European policies. This article emphasizes that knowledge gaps still exist about the direct effects of climate change on water bodies and their indirect impacts on production areas that employ large amounts of water (e.g., agriculture). Some sectors, such as ecohydrology and alternative sewage treatment technologies, could represent a powerful tool to mitigate climate change impacts. Research needs in these still novel fields are summarized.

Riverine floods cause increasingly severe damages to human settlements and infrastructure. Ecosystems have a natural capacity to decrease both severity and frequency of floods. Natural flood regulation processes along freshwaters can be attributed to two different mechanisms: flood prevention that takes place in the whole catchment and flood mitigation once the water has accumulated in the stream. These flood regulating mechanisms are not consistently recognized in major ecosystem service (ES) classifications. For a balanced landscape management, it is important to assess the ES flood regulation so that it can account for the different processes at the relevant sites. We reviewed literature, classified them according to these mechanisms, and analysed the influencing ecosystem characteristics. For prevention, vegetation biomass and forest extent were predominant, while for mitigation, the available space for water was decisive. We add some aspects on assessing flood regulation as ES, and suggest also to include flood hazard into calculations.

The contamination of waters with nutrients, especially nitrogen and phosphorus originating from various diffuse and point sources, has become a worldwide issue in recent decades. Due to the complexity of the processes involved, watershed models are gaining an increasing role in their analysis. The goal set by the EU Water Framework Directive (to reach “good status” of all water bodies) requires spatially detailed information on the fate of contaminants. In this study, the watershed nutrient model MONERIS was applied to the Hungarian part of the Danube River Basin. The spatial resolution was 1078 water bodies (mean area of 86 km2); two subsequent 4 year periods (2009–2012 and 2013–2016) were modeled. Various elements/parameters of the model were adjusted and tested against surface and subsurface water quality measurements conducted all over the country, namely (i) the water balance equations (surface and subsurface runoff), (ii) the nitrogen retention parameters of the subsurface pathways (excluding tile drainage), (iii) the shallow groundwater phosphorus concentrations, and (iv) the surface water retention parameters. The study revealed that (i) digital-filter-based separation of surface and subsurface runoff yielded different values of these components, but this change did not influence nutrient loads significantly; (ii) shallow groundwater phosphorus concentrations in the sandy soils of Hungary differ from those of the MONERIS default values; (iii) a significant change of the phosphorus in-stream retention parameters was needed to approach measured in-stream phosphorus load values. Local emissions and pathways were analyzed and compared with previous model results.

A country scale analysis of diffuse source nutrient emissions have been undertaken previously on small catchments level using the MONERIS model, which needed a proper estimation of surface and subsurface runoff differentiation to support or contradict its own water budget based method. As reliable, country scale base flow estimation has not been available for the country at the time of the study, this knowledge gap has been tried to be filled by the current work. This has been done using multiple methods. Digital filter have been applied on continuous river discharge data on gauged catchments in order to determine base flow indices (BFI). Using multiple linear regression (MLR) and artificial neural networks (ANN), climatic, soil and land use properties of the catchments have been used to extend base flow indices to ungauged catchments. MLR brought acceptable results (adjusted r2 values around 0.7), however it proved to be sensitive of the selection of catchments used for validation, and therefore a mean of prediction by thirty different regression equation was used for the estimation. ANN was less sensitive for the change of the variables included and the number of nodes used for the learning. The results are comparable with the MLR method and show good agreement in most of the areas, however in some part of the country the two approach show significant differences in the predicted BFI values.

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