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

This dataset provides a set of hydrometric indices for about 1500 stations across Africa with daily discharge data. These indices represent mean flow characteristics and extremes (low flows and floods), allowing us to study the long-term evolution of hydrology in Africa and support the modeling efforts that aim at reducing the vulnerability of African countries to hydro-climatic variability.

Rising availability of remote sensing imagery provide novel opportunities to improve the understanding of the hydrology of multiple water bodies. The analysis of 443 Landsat images between 1984–2017 and 48 Sentinel-2 images between 2015–2017 confirms the possibility of monitoring floods within individual depressions of the Senegal River floodplain. First results based on in situ data also reveal the potential to refine hydrological relationships between the water height and the flooded area.

Accurate monitoring of surface water extent is essential for hydrological investigation of small lakes (1–10 ha), which supports millions of smallholder farmers. Landsat monitoring of long-term surface water dynamics is shown to be suited to lakes over 3 ha based on extensive hydrometric data from seven field sites over 15 years. MNDWI water classification optimized here for the specificities of small water bodies reduced mean surface area errors by 57 % compared to published global datasets.

Urbanization, resulting from a sharply increasing demographic pressure and the development of infrastructure, has made the population of many tropical areas more vulnerable to extreme rainfall hazards. Characterizing extreme rainfall distribution is thus becoming an overarching need in hydrological applications. Using 14 tipping-bucket rain-gauge series, this study provides IDF curves and uncertainties over Senegal. Climate change requires warning end-users that they should be used with care.

Socio-economic and hydroclimatic data were integrated in a modeling framework to simulate water resources and demand. We successfully modeled water stress changes in space and time in two basins over the past 40 years, and explained changes in discharge by separating human and hydroclimatic trends. The framework was then applied under 4 combinations of climate and water use scenarios at the 2050 horizon. Results showed that projected water uses are not sustainable under climate change scenarios.

During a flood event over a karst watershed, the karst may attenuate surface floods by absorbing water or contribute to the surface flood by direct contribution of karst waters in the rivers and by diffuse resurgence along the hillslopes. If it is possible to monitor each known outlet of a karst system, the diffuse contribution is yet difficult to assess. We present here a new, original method to do it, based on chemical analysis and a hydraulic study.

This study aimed at reducing structural uncertainty in the conceptual modelling of a semi-arid Andean catchment. A multiple-hypothesis framework was combined with a multi-criteria assessment scheme to characterize both model non-uniqueness and model inadequacy. This led to retaining eight model structures as a representation of the minimum structural uncertainty that could be obtained with this modelling framework.

Socioeconomic and hydro-climatic data were used to model water resources, water demand and their interactions in two river basins. By using an integrative framework we successfully modeled variations in water stress over the past 40 years, accounting for climate and human pressures and changes in water management strategies over time. We explained past changes in discharge by separating human and hydro-climatic trends. This work will help assess future water stress and design adaptation plans.