This PICO session aims to discuss progress and way forward on the 23 Unsolved Problems in Hydrology (UPH), in general, and, in particular, on transdisciplinary approaches to foster the interface between hydrology and society.
The International Association of Hydrological Sciences (IAHS), in collaboration with the Hydrology Divisions of EGU and AGU as well as the IAH, have recently called for compiling a list of unsolved scientific problems in hydrology that would invigorate research in the 21st century. In a public consultation process, a large number of potential science questions were collated, prioritised and synthesised, which resulted in a set 23 UPH (see https://doi.org/10.1080/02626667.2019.1620507). The UPH are articulated around 7 themes: Time variability and change, Space variability and scaling, Variability of extremes, Interfaces in hydrology, Measurements and data, Modelling methods, and Interfaces with society.
Some of the UPH have already been partially studied and recent research may shed light on how to move forward in a more holistic way. A crucial issue is to put together fragmented knowledge to address the questions raised and enhance coherence in hydrological sciences.
The following themes are of interest in this session:
1. Research results that advance the understanding of any of the 23 UPH as well as review of the state of the art of one (or more) of the UPH, pointing towards directions where progress is most promising and reflections on how the community could evaluate if an UPH can be considered solved or not.
2. Co-production of knowledge and policy. What approaches are available to support a fruitful collaboration between hydrological science and practitioners for tackling the real-world challenges of operational hydrology? How do we deal with uncertainty, adaptation, path dependencies but also with aspects of power, inequality and vested interests in these co-production processes? Who are the users of our knowledge, how useful is our knowledge for those societal users.
3. Interdisciplinary collaborations. How do we create the interdisciplinary knowledge needed to address the questions faced by decision-makers and societal stakeholders? What is the role of hydrologists in these processes? What are the mutual expectations of collaborating researchers from different disciplines and from societal stakeholders?

INVITED PICO TALK: Dr. Daniel Loucks, “Solving the 23 Major Mysteries in Hydrology: Who cares and Why?”