Groundwater-induced flooding, a rare phenomenon that is increasing in low-elevation coastal cities due to higher water tables, is often neglected in flood risk mapping due to its sporadic frequency and considerably lower severity with respect to other flood hazards. A loosely coupled flood model is used to simulate the interplay between surface and subsurface flooding mechanisms simultaneously. This work opens new horizons on the development of compound flood models from a holistic perspective.

In this work, we proposed a multi-source data assimilation framework for near-real-time flood mapping. We used a quasi-2D hydraulic model to update model states by injecting both stage gauge observations and satellite-derived flood extents. Results showed improvements in terms of water level prediction and reduction of flood extent uncertainty when assimilating both stage gauges and satellite images with respect to the disjoint assimilation of both observations.

This short paper is the preface of the PIAHS volume of the IAHS/UNESCO FRIEND-Water conference of Cotonou in November 2021.

The sensitivity of a geomorphology-based hydrological modelling is evaluated according to four DEMs from 5 m to 50 m resolution in Brittany, France. A set of 8 basins (5–565.7 km²) is used in a pseudo-ungauged context to explore the potential of Prediction in Ungauged Basin (PUB). The results show that a coarse-worldwide DEM such as SRTM (25 m) supported similar performances than the finer one available from the French mapping institute.

The 8th Global FRIEND conference highlighted the advance in hydrological science and innovation in water management. 52 accepted papers cover study areas in precipitation and climate impact; observation, analysis and simulations of hydrologic processes; floods in the changing environments; drought monitoring and analysis; water resources and environmental impacts. The outcome of the conference presented in the proceedings will be shared and discussed widely among UNESCO IHP networks.

Global floodplain mapping has rapidly progressed over the past few years. Different methods have been proposed to identify areas prone to river flooding, resulting in a plethora of available products. Here we assess the potential and limitations of two main paradigms and provide guidance on the use of these global products in assessing flood risk in data-poor regions.

Retrospective forensics of the 1969 extreme hydrometeorological events in Tunisia – Tunisia experienced extreme rainfall-flood events in September and October 1969. These events have been gauged and reconstituted in such a detailed manner that they are now the best known extreme events in Maghreb. The retrospective forensics of these events are much valuable not only in terms of hydrological and geomorphological knowledge, but also in terms of actual and future water and infrastructure.