The International Association of Hydrological Sciences (IAHS) coordinates two initiatives in hydrology:
- The Panta Rhei hydrological decade 2013- 2022, focusing on gains in our understanding of water cycle processes, their changing dynamics in respect of interactions and feedbacks with human systems. 
- The 23 Unsolved Problems in Hydrology (UPH), launched in 2017 after a public consultation process, in collaboration with the Hydrology Divisions of EGU and AGU as well as the IAH. 
This session presents works related to these initiatives.
Approaching the end of this Panta Rhei decade (2013-2022), it is time to synthesize the achievements of this decade. The main focus of this grand synthesis, which will be published in an IAHS book, is on coevolution and prediction of coupled human-water systems, including understanding of emergent phenomena, mechanisms, and implications for predictions and practices. Focus is put on theoretical/conceptual framework for understanding changes in hydrology and society; coevolution and emergent phenomena; dynamic models; data needs and acquisition; benchmark datasets in various context and scales, including human-flood, human-drought, agricultural, transboundary and global systems. Case studies from Panta Rhei working groups, IAHS Commissions and beyond are also welcome.
The 23 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. A crucial issue is to put together fragmented knowledge to address the questions raised and enhance coherence in hydrological sciences. The purpose of this session is to present research results that advance the understanding of any of the 23 UPH, review (or present a contribution to review) the state of the art of one (or more) of the UPH, pointing towards directions where progress is most promising.
 Panta-Rhei: https://iahs.info/Commissions--W-Groups/Working-Groups/Panta-Rhei.do
 23 UPH: https://doi.org/10.1080/02626667.2019.1620507
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