News

Sustainable management of rivers and waterways requires reliable data on the transport of substances, their influencing factors, and the expected trends, which are accelerated by anthropogenic environmental change. The high dynamics of rivers, which is reflected in a large spatio-temporal variability of (suspended) matter flows, places high demands on surface water monitoring. Therefore, it becomes more and more important to clearly describe existing scientific uncertainties, to reduce them if possible, and to communicate them to decision makers. The aim of the online symposium “Uncertainty in river water monitoring – New insights on spatio-temporal variability of suspended river water components” was to address these challenges within the scope of an international platform. The symposium is part of the BfG research project URSACHEN, (Uncertainties in the determination of spatio-temporal variable material loads in rivers), implemented until 2023. It was held as an online event on Nov. 30 and Dec. 1, 2022. With 230 registered participants from 45 countries, the symposium was well received internationally. Over the two days, a total of 27 presentations addressed spatial, temporal, and methodological uncertainties in the determination of substance loads. Joint discussions highlighted both the challenges and opportunities for surface water monitoring. In this context, the results of the URSACHEN project were presented as well. The virtual platform enabled the participation of scientists “around the globe”,  reflected by the keynotes given by speakers such as Ton Hoitink (Wageningen, the Netherlands), Magdalena Bieroza (Uppsala, Sweden) and Marwan Hassan (Vancouver, Canada).

The symposium was opened by Harald Koethe, the director of ICWRGC (International Centre for Water Resources and Global Change), who presented the interdisciplinary URSACHEN project, while emphasising the international networking of BfG and ICWRGC. He also made reference to the UNESCO International Sediment Initiative (ISI). In addition, Mr. Koethe underlined the global importance of the topic by emphasizing that an understanding of suspended sediment transport plays a central role for the monitoring of water quality as well as for the stability of river systems and deltas and thus for millions of people living along rivers.

The overarching topic of “uncertainty” in river water component measurements was addressed in three “sessions”, each focusing on methodological, spatial and temporal aspects. In the first session on methodological uncertainties, moderated by Harald Koethe (ICWRGC), the possibilities, but also the challenges and limitations of new and already established, direct and indirect sampling and monitoring methods were presented. Based on examples of sediment concentration determination using acoustic and optical sensors and in discussions, it became clear that even established methods can only provide reliable results if the controlling factors for suspended sediment concentration such as hydraulic conditions and sediment properties are included and adequate calibration of the sensors takes place.

Thomas Hoffmann (M3) and Lars Duester (G4) led through the following programme. The second and third sessions dealt with the recording of the spatial and temporal variability of suspended matter. The “Spatial Session” focused on the problem of the representative determination of substance concentrations at certain water body (cross)sections,while i.a. remote sensing methods were also presented. The “Temporal Session” focused primarily on the importance of continuous monitoring series. On the one hand, the analysis of seasonal courses and hysteresis curves allows conclusions to be drawn about the possible sources and influencing factors of suspended sediment loads, while on the other hand, a minimum time interval can be determined, which is necessary for a reliable determination of suspended compounds in water and their loads.

The need for further research concerning uncertainties in river monitoring was actively discussed and its importance has been recognized. The significance of the topic was also mirrored by the number of participants and the presented diverse research approaches along with their results. The symposium succeeded in promoting the international and interdisciplinary exchange in the “river monitoring community” and offered valuable chances and opportunities to establish new professional contacts and deepen existing ones.

Geneva, 29 November 2022

The World Meteorological Organization has published its first State of Global Water Resources report. It provides insights into the availability of freshwater in different parts of the world and highlights major flood and drought events. In its first edition, the assessment is limited to streamflow, terrestrial water storage and the cryosphere. However, it is intended to include groundwater, soil moisture and water quality in the future. The preparation of the 2021 report was largely based on simulated data from hydrological models and remote sensing information from satellite missions. These were compared and validated against observational data. Despite good correlation, the validation between modelled and observed results would benefit substantially from more hydrological information, as WMO Secretary-General Prof. Petteri Taalas pointed out. He called on Member States to share more hydrological information in line with the WMO Unified Data Policy. Thereby he acknowledged the importance and contribution of the Global Data Centres. The report provides world leaders, decision-makers and citizens with information on the state of water resources for the first time and is an important step towards accurate water data and early warning systems in preparation for the United Nations 2023 Water Conference, COP28 and the 2030 Agenda for Sustainable Development.

The classification of hydrological basins for the global streamflow analysis of the assessment was based on the WMO Basins and Sub-Basins dataset of GRDC. In addition, observational river discharge data from GRDC were used for the validation of simulated river discharge data from Global Hydrological Modelling Systems. Data of the International Soil Moisture Network (ISMN) have also been utilised for the assessment report. The head of GRDC, Ulrich Looser, was also involved in the preparation and review of the assessment report. Petteri Taalas states that WMO is committed to extending the variables in future editions of the report to include groundwater, soil moisture and water quality. Here, UNEP’s GEMS/Water Data Centre, operated by ICWRGC and BfG, will also contribute in the future. Most of the global water data centres are part of the Global Terrestrial Network – Hydrology (GTN-H), a joined initiative of WMO and the Global Climate Observing System, coordinated by ICWRGC. In this context it is gratifying that the gaps in water and climate observation systems are also emphasized in the COP27 Cover Decision. Closing Gaps in water data and observations are also discussed as Game Changers for the Water Action Agenda and will support the discussions in the proposed five interactive dialogues of the 2023 UN Water Conference.