Cluster Water balance and water management | Umweltbundesamt

On the relevance of the action field

In the natural water cycle, water moves continuously in its liquid, gaseous or frozen state through land, sea and the earth’s atmosphere. As a result of climate change, increased temperatures fuel this cycle, accelerating and intensifying the processes of evaporation. Any increase of water content in the atmosphere raises the likelihood of precipitation. Precipitation patterns are changing. Changes in the water cycle that have been observed already, have strong impacts on ecosystems, economy and society. This is because not just all living organisms – humans included – but nearly all economic processes are dependent on the availability of water, in some cases on high-quality water.

Water management encompasses the entirety of measures for regulating the water balance, for abstracting and distributing drinking water and for the management of various kinds of waste water. Climate change is one of the greatest challenges to the water management. It is primarily the incidence of extreme weather events which makes planning difficult. Given that the climate change impacts on water and groundwater are on the increase, the requirements for protecting and improving the resilience of these water sources to climate change impacts are increasing too. At the same time, the demand for the utilisation of water keeps rising. The experience of drought periods in the summer months of recent years shows that various regions in Germany are already now witnessing conflicts in respect of the utilisation of water.

DAS Monitoring –what is happening due to climate change

Previously, it was possible in Germany to assume that water would always be available in sufficient quantities. It was only the reliable supply of high water quality that has always been in focus. As demonstrated already by the 2019 DAS Monitoring Report, the development of groundwater levels requires greater attention. As indicated by data collected in the drought years of 2018 to 2020, the trend towards diminishing groundwater levels and reduced spring flows has continued. The development in northern Germany is of particular concern (cf. Indicator WW-I-2). In the drought years, all over Germany record shortfalls were determined in respect of the long-term lowest groundwater levels recorded at gauging stations. Comparable trends have also been observed with regard to water levels in lakes, which – especially in the North German Plain – are closely linked with groundwater levels. Between 2018 and 2020 massive water losses were recorded in some cases (cf. Indicator WW-I-7).

Precipitation deficits and high evaporation rates occurring in summer are also noticeable in the discharge rates of watercourses: The mean water discharge rates in the summer half-year have been decreasing significantly since 1961 (cf. Indicator WW-I-3), while the number of low-water level days in the summer half-year – in other words, days on which the level of the mean low-water discharge (MNQ1960-1991) has not been attained – is increasing (cf. Indicator WW-I-6). Evidence for decreases in the availability of water is also found in satellite gravimetric data. In Germany, the terrestrially stored water has diminished significantly in the course of the past 20 years (cf. Indicator WW-I-1).

A dearth of water on one hand is contrasted with a surfeit of water on the other. Increased frequency of heavy rainfalls – sometimes even extreme and persistent rainfalls resulting from so-called Vb (or Five B) weather patterns – repeatedly cause floods. However, so far the development of floodwater days has not indicated a significant trend, either for the summer or for the winter half-year (cf. Indicator WW-I-4). The formation of floodwater is always related to specific combinations of weather patterns which have so far not occurred either systematically or regularly. An analysis of peak discharge rates in watercourses (cf. Indicator WW-I-5) shows clearly that in former years, especially during summer half-years, there have been some very extreme flood events, when the long-term mean values for flood discharge were exceeded 8-fold at some of the gauging stations. The flood disasters in the Ahr and Erft valleys are not even included in the gauging stations selected for discharge readings in the DAS Monitoring Indicators.

Rising temperatures combined with water shortages in summer have grave impacts on water ecosystems. Water temperatures in lakes and reservoirs have been rising significantly since 1961 (cf. Indicator WW-I-8). This affected the onset of spring algal bloom (cf. Indicator WW-I-9) and lake stratification in summer, thus in turn strongly influencing the chemical and biological processes occurring in lakes. Likewise, watercourse temperatures increased significantly in the course of the last three decades (cf. Indicator WW-I-10). High water temperatures combined with reduced oxygen contents are problematic for aquatic organisms – fish, in particular.

Future climate risks – outcomes of KWRA

As mentioned in the 2021 Climate Impact and Risk Analysis towards the middle of this century, high risks of low water levels, of floodwater and the failure of flood protection systems have been forecast. The same applies to flash floods and the associated failure of drainage facilities and flood protection systems. Nevertheless, the certainty of this estimate is categorised as low. As far as sewer networks as well as outfall ditches and sewage treatment plants are concerned, a medium risk (according to a grid of low – medium – high) was estimated to arise by the middle and towards the end of this century. A high risk is forecast to arise as early as the middle of this century in respect of increases in the temperature of water bodies, a decrease in ice cover and the deterioration of water quality. The certainty of this estimate ´has been categorised as medium. The reason for this may be partly the fact that especially the recent extremely hot and dry years 2018–2020 have demonstrated graphically the associated direct impacts on water bodies. As far as the development of the chemical water quality is concerned, there is very little certainty at the moment. It is to be expected that a medium risk may arise towards the end of this century. By the same token, the risk of negative effects on the groundwater level and quality arising by the middle of this century was categorised as high, and by the end of this century this forecast is even given the attribute of high certainty. These developments entail consequential risks in respect of water utilisation. For example, it is expected that by the end of this century there will be a high risk in terms of a shortage of irrigation water, and that there will be a medium risk in respect of restrictions to the availability of drinking water and process water. These estimates were made subject to low certainty.

Where do we have gaps in data and knowledge?

Thanks to the close involvement of the Länder in working out the water-related DAS Monitoring Indicators via the Federal/Länder Working Group Water (LAWA) / Subgroup Climate Indicators, it was possible to build a wide-ranging database for the DAS Monitoring. Moreover, subgroup discussions have helped to prompt further initiatives to improve the availability of data and to deliver monitoring data on other relevant themes. For example, the LAWA expert group on lakes has selected lakes all over Germany for the installation of specific measuring equipment in order to obtain measured data such as temperature data, differentiated by different levels of depth. This will make it possible in future to obtain meaningful data on the development of circulation and stratification regimes prevailing in lakes. Furthermore, the LAWA Panel on Surface Waters and Coastal Waters awarded a contract for a better standardisation of mapping instructions regarding the mapping of water body structures thus enabling the homogeneous application of such instructions by all the Länder. The purpose is to generate comparable data in future on the development of the structure of water bodies and their shores. Against this background it was decided not to re-introduce the response indicators contained in the 2019 Monitoring Report regarding the shore vegetation of small and medium-sized water bodies. It was not possible to expand the case study in respect of Brandenburg, Rhineland-Palatinate and Saxony.

Within the framework of the UBA-commissioned research project on the use of satellite data conducted in parallel with the further development of DAS Monitoring, possibilities were examined for improving the monitoring indicators for water-related themes by means of generating data, whose in-situ collection would be quite laborious or even impossible to implement comprehensively. Primarily, the work covered the establishment of time series on temperature and ice cover and regarding the onset of spring algal bloom in lakes. The time series on spring algal bloom was incorporated in the DAS Monitoring indicator set. However, as far as ice cover and temperature are concerned, the time series are currently still relatively short.

There are major data deficits in respect of quality parameters for watercourses. The investigations carried out within the framework of the WRRL (WFD/Water Framework Directive) can be used only to a very limited extent for the purpose of monitoring the impacts of climate change. Overview monitoring is used for assessing the overall condition of surface water bodies. This is only carried out at major intervals. The operational monitoring complements the measurements taken in the course of overview monitoring; it is used in order to obtain sufficiently reliable data on prevailing fluctuation ranges. However, this type of monitoring is carried out at just a few gauging stations. Investigative monitoring is intended to produce further insights into the causes of negative impacts and to find opportunities for their elimination. These measurements are typically made more frequently. However, the gauging stations are located so that, in a targeted way, they can capture any negative effects caused by anthropogenic activity. This means that they are not compliant with the selection criteria employed for the monitoring of climate change impacts which require the exclusion of anthropogenic influences as far as possible. For the gauging stations underlying the DAS Monitoring Indicator on watercourse temperatures (cf. Indicator WW-I-10), it has been ensured, as far as possible, that they are not subject to any anthropogenic influences. However, it is not possible to achieve the complete exclusion of such influences. For the monitoring of climate change impacts it would be necessary to use a targeted approach for the identification of specific gauging stations for this monitoring purpose, and to ensure that these stations are suitable for very frequent investigations to be carried out.

As far as any impacts of climate change on the ecology of water bodies are concerned, indicators used currently in DAS Monitoring permit only the derivation of risk assessments. To date, there has been no direct collection or assessment of data on biological or material changes taking place in water bodies. This is partly due to the limited availability of data, in particular for the description and interpretation of changes in the ecology of water bodies. Notably, as far as material changes are concerned, there are numerous technical questions which remain to be answered. It is difficult to differentiate the specific impacts of climate change from other – especially from anthropogenic – influences.

While DAS Monitoring contains several meaningful indicators at the impact level, it is true to say that there is still a shortage of meaningful indicators at the response level. In this respect too, the development of indicators comes up against the limitations of data availability. For example, the nationwide indicator for the water use index (WW-R-1) only shows a ‘proxy’ entry, in order to generate a theme in the monitoring report for the issues pertaining to a sustainable use of water in accord with the availability and use of water. Further considerations including the subject of a high-frequency collection and interpretation of data on peak utilisations of water are required. So far the theme of waste water management has not yet been embedded in the monitoring report either. Likewise, it is becoming increasingly important to examine the landscape water balance as well as the question how to improve the retention of water and the issue of rewetting at the landscape scale; these subjects have so far only been touched on as marginal themes in the monitoring report.

What’s being done – some examples

With regard to the stabilisation of the landscape water balance, flood protection issues, the maintenance and restoration of a good ecological condition of water bodies as well as the availability of sufficient groundwater, there is broad agreement on objectives regarding the adaptation to climate change with the WRRL objectives and the EU Floods Directive (HWRM-RL). Owing to climate change, the implementation of the measures embodied in this directive has attained greater urgency.

As far as flood protection is concerned, there have already been direct political responses to the prevailing increased flood risks. This includes the National Flood Protection Programme (NHWSP) and the special framework plan ‘Preventative Flood Protection’ (Präventiver Hochwasserschutz), which includes the restoration of natural retention areas in its focus. The funds made available for flood protection have been distinctly increased in recent years (cf. Indicators WW-R-2 and WW-R-3). In the context of dealing with low-water levels and drought periods, the Länder are in the process of developing precautionary strategies for a sustainable management of water resources and for the prevention and management of water utilisation conflicts. In view of the extreme drought from 2018 to 2020, the work on these issues has gained a particular urgency. A strategic framework was provided for this work by the Federal government when the national water strategy⁵⁶ was adopted by the Federal cabinet on 15th March 2023. This strategy is to achieve sustainable use of water resources for people and the environment by 2050, ensuring the conservation and restoration of a near-natural water balance, and enhancing climate-adapted water infrastructures. This strategy has made it possible, for the first time, to pool water-related measures regarding all relevant sectors (agriculture and nature conservation, administration and transport, urban development and industry) with the involvement of Federal government, Länder, municipalities, the water management and all water-using economic sectors and groups. The action programme envisions 78 measures to be implemented immediately and to be completed by 2030. The implementation of the national water strategy is closely interconnected with funding from the action programme ‘Natural Climate Protection’ (ANK), which also provides funding for climate-related measures in water management, for the purpose of developing water bodies and for measures regarding water-sensitive urban development. Further measures at Federal level include the publication of research findings and information materials such as low-water level reports compiled by the Federal Institute of Hydrology (BfG) which is currently also developing a nationwide user-group specific low-water level information system entitled ‘NIWIS’.

^{56 - BMUV – Bundesministerium für Umwelt, Naturschutz, nukleare Sicherheit und Verbraucherschutz: Nationale Wasserstrategie. https://www.bmuv.de/wasserstrategie}