In 2013, the International Association of Hydrological Sciences (IAHS) launched the hydrological decade 2013-2022 with the theme "Panta Rhei: Change in Hydrology and Society". The decade recognizes the urgency of hydrological research to understand and predict the interactions of society and water, to support sustainable water resource use under changing climatic and environmental conditions. This paper reports on the first Panta Rhei biennium 2013-2015, providing a comprehensive resource that describes the scope and direction of Panta Rhei. We bring together the knowledge of all the Panta Rhei working groups, to summarize the most pressing research questions and how the hydrological community is progressing towards those goals. We draw out interconnections between different strands of research, and reflect on the need to take a global view on hydrology in the current era of human impacts and environmental change. Finally, we look back to the six driving science questions identified at the outset of Panta Rhei, to quantify progress towards those aims.

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Digital elevation models (DEM) are fundamental for hydrologic and hydraulic modelling. Many practitioners rely on open-access global data sets due to the cost and sparse coverage of sources of higher resolution. In 2016, the Japanese Aerospace Exploration Agency released the ALOS World 3D-30m (AW3D30), an open-access global elevation model at an horizontal resolution of 30 m. So far no published study has done an assessment of the flood modelling capabilities of this new product. The purpose of this investigation is to (a) assess the utility of the AW3D30 for flood modelling purposes and (b) compare its performance with regards to computed water levels and flood extent maps calculated using other freely available 30m DEM (e.g., SRTM and ASTER). For this comparison, the reference to reality is given by the maps computed using a light detection and ranging (LiDAR)-based digital terrain model. This study is carried out in two catchments with contrasting topographic gradients. Results show that AW3D30 performs better than the SRTM. In mountainous regions, the results derived with the AW3D30 are comparable in skill to those obtained with a LiDAR-derived digital surface model. This encouraging performance paves the way to more accurate modelling for both data-scarce regions and global flood models. K E Y W O R D S ALOS, AW3D30, digital elevation model, flood