Water and water bodies are vital for people and nature. They provide both important resources and valuable habitats for life. The conservation and use of water systems must hence be reconciled to ensure the best possible path to sustainable development. Pressure on water resources and aquatic ecosystems increases continuously both in Germany and worldwide. Agriculture, industries, the energy and water economy, settlements and traffic, as well as recreation contribute to this development. Climate change, including increases in the frequency and severity of extreme events such as droughts and intense precipitation, exacerbates the situation. Water is becoming scarce for people and ecosystems or is getting out of control during extreme rainfall. Increased damage to infrastructure, water pollution and degraded ecosystems limited in their functionality ensue. Water policy must cope with conflicting goals of water resource use and conservation. The resulting conflicts are serious and complex, and have evident repercussions for practical water management, calling for new approaches to solve the pressing issues. In view of the complex task and rapidly changing framework conditions, a comprehensive understanding of water systems is imperative to implementing viable prevention and adaptation strategies. The topics to consider must range from individual hydrological, ecological and technical processes to system interrelationships and dynamics, and to economic, social and political issues. This breadth is a challenge for water research. Accordingly, the German Water Science Alliance aspires to link fundamental scientific insights across disciplines to practical solutions of water issues with a view to promote evidence-based water policy supporting sustainable water resource and ecosystem management – in Germany, Europe and worldwide. The present framework paper identifies four central thematic challenges along these lines: 1. Hydrological extremes - developing sustainable adaptation options to cope with increasingly frequent and intense heat, drought and heavy rainfall events 2. Water quality - ensuring a lasting high quality of water resources and aquatic ecosystems that are subject to increasing user demands 3. Biodiversity - preserving and restoring ecological structures and processes to maintain and restore a multifunctional aquatic biodiversity 4. Water infrastructures - adapting water infrastructures and optimizing management networks to ensure the long-term performance of water systems. These four thematic challenges are embedded in a whole-systems context to derive insights into water research and management needs that go beyond the individual themes. In addition to the goal of fostering scientific understanding of the complex interrelationships and emergent system properties, this framework paper focuses on the requirements of integrated water resource and aquatic ecosystem management. There is a particular need for investigations into the collation, mobilization, provision and integrative use of comprehensive data on water systems, as well as for developing simulation models capturing changes in water systems and their societal repercussions. This critically involves multi-, inter- and transdisciplinary cooperation in research and water management, and the blending of knowledge and methods from science, engineering and social science. Networking between university and non-university research institutions is necessary, just as a systematic dialogue between the scientific community, authorities, associations, and other stakeholders, including policy makers. The methodological challenges shared by the complementary disciplines contributing to integrative water systems research, are addressed in a separate section, as are the challenges of inter- and transdisciplinary cooperation and the transfer of knowledge to diverse target groups in society. The present framework paper provides an overview of the challenges and current and future research needs relating to water. Emphasis is on Germany, including suggestions on how the framework conditions for water research can be improved. Future so-called „Water Views“ will build on this framework to elaborate on selected topics. These position papers written by members of the water science community will address topical water research and management issues to serve as a basis for in-depth discussions. To this end, the Water Science Alliance invites all representatives of the German water research community to join competencies in order to provide answers to the most urgent water issues emerging at the national level, but also at the European and global scale.

Unter Mitarbeit von u.a. Rita Adrian, Ilona Bärlund, Arne Beermann, Thomas U. Berendonk, Viktoria Berger, Felix Bilek, Mareike Braeckevelt, Christoph Czichy, Michael Eisinger, Jörg Freyhof, Claudia Freimuth, Nadine Gerner, Georg Guggenberger, Daniel Hering, Sonja Jähnig, Ralf Klingbeil, Klaus Kümmerer, Marius Mohr, Insa Neuweiler, André Niemann, Torsten C. Schmidt, Ulrike Scherer, Ralf Schüle, Thomas Sommer, Kerstin Stahl, Stefan Stolte, Bernd Sures, Katja Tielbörger, Jale Tosun, Rita Triebskorn, Hans-Jürgen Ulonska, Barbara Waelkens und Markus Weitere.