Modélisation robuste de l'impact agrégé de retenues collinaires sur l'hydrologie de surface

En raison du développement de l'industrie légumière, les retenues collinaires à vocation d'irrigation se multiplient dans le département du Morbihan (Bretagne, France). Même si de tels aménagements hydrauliques ont une influence individuelle faible, leur multiplication et leur concentration géographique peuvent avoir des conséquences dommageables sur l'hydrologie de surface. Nous proposons d'utiliser une fonction de transfert de type Hydrogramme Unitaire Géomorphologique, basée sur l'identification de la fonction aire normalisée du bassin versant contribuant effectivement à l'écoulement et sur l'estimation d'une vitesse moyenne d'écoulement dans les thalwegs. Le déterminisme de cette fonction de transfert permet de semi-distribuer l'afflux pluviométrique. Il nous permet en outre de proposer une méthodologie de simulation explicite de l'effet agrégé des retenues collinaires, connaissant leur mode de fonctionnement hydraulique local. Puis, pour le bassin versant pilote de l'Yvel (302 km2), nous étudions a priori l'impact de l'implantation de retenues collinaires selon un scénario géographique de développement préférentiel et pour différents degrés d'intensification.In response to the increasing demand from the food industry for fresh produce, many farms located in the administrative county of Morbihan (Brittany, France) have intensified their vegetable crop production (e.g. peas, beans, spinach) due to their high value. To obtain the best yields and to respect contracts signed with industrial partners, irrigation has been widely used by the farming community to support this production. Since 1989, 500 to 600 ha/year of irrigated farmland have been developed with financial support from state, regional and county agencies. The official purpose of this financing program is to irrigate 50% of the fields cultivated for vegetable crops. Water use for irrigation was estimated to be 6 million m3 in 1999. The demand for irrigation coincides with the period of low water levels in the stream. Thus, there is strong competition with drinking water demands and ecological flow requirements. Moreover, the potential use of groundwater to fulfill these demands is not possible. One of the solutions is to build small headwater dams to store winter flows and use this resource during the growing season. In order to help local public authorities assess their strategy, we need to develop a robust quantification method to study the impact of this development.The 302 km2 Yvel watershed is the site of a highly developed region of small headwater dams because the geological substratum is composed mainly of schist with low groundwater reserves, precipitation is less than the regional average, and the industrial demand for vegetable crops is high. For all these reasons, this watershed is particularly vulnerable. Moreover, from a regional policy point of view, the downstream part of the watershed is located within the Morbihan county whereas the upstream part is located within the Côtes d'Armor and Ille et Vilaine counties, which do not provide any financial support for irrigation development. The current concentration of headwater irrigation dams reflects these regional development incentives as dams are mostly built in the downstream part of the watershed.To study the impact of small headwater dams on watershed hydrology, we propose a conceptual tool built around a geomorphological instantaneous unit hydrograph (GIUH) modelling approach. The GIUH structure, which is based on the effective watershed normalized area function and an estimated mean flow velocity, allows for the explicit accounting of dams and, and thus, can be used for a priori assessment studies. It can also be used in a semi-distributed perspective, where spatial discretization is determined from rainfall variabilities instead of gauging station constraints. These two points allowed us to study three regional irrigation development scenarios: construction of 100, 200 and 300 future headwater irrigation dams. Using two observed rainfall events, we showed that the simulated hydrograph shape at the watershed outlet can be significantly modified. In conclusion, in situ observations and simulation results suggest that : (1) headwater dams do not have any impact when reservoirs are full - lamination is locally observed and thus, does not have any impact on the watershed hydrograph; (2) a spatially homogeneous implementation of headwater dams modifies the watershed hydrograph according to a contributing watershed area ratio; similar behaviour is observed for low water level periods; and (3) localized implementation can be studied through modelling with enough precision to give relevant information to decision makers

Challenges in operationalizing the water–energy–food nexus

Concerns about the water–energy–food (WEF) nexus have motivated many discussions regarding new approaches for managing water, energy and food resources. Despite the progress in recent years, there remain many challenges in scientific research on the WEF nexus, while implementation as a management tool is just beginning. The scientific challenges are primarily related to data, information and knowledge gaps in our understanding of the WEF inter-linkages. Our ability to untangle the WEF nexus is also limited by the lack of systematic tools that could address all the trade-offs involved in the nexus. Future research needs to strengthen the pool of information. It is also important to develop integrated software platforms and tools for systematic analysis of the WEF nexus. The experience made in integrated water resources management in the hydrological community, especially in the framework of Panta Rhei, is particularly well suited to take a lead in these advances

100 Years of IAHS – Graphic capitalisation and poetic celebration

In centenary celebration of IAHS, Converging knowledge, shared in global embrace, Hydrological sciences in captivating displays, A graphic chaptering, and poetic interlace.</p

Can we use indicator-based farm sustainability assessment tools for the WEFE Nexus?

Fair and safe allocation of natural resources for the Euro-Mediterranean area, especially for semi-arid regions, strongly relies on the adoption of WEFE (Water Energy Food Ecosystem) Nexus strategies. Transitioning to WEFE Nexus requires novel quantifiable assessment for interlinked analysis of the four WEFE sectors. Several indicator-based tools exist for agricultural sustainability at the farm scale. This contribution investigates on the application of such tools in relation for WEFE Nexus approaches. The IDEA method was selected for extending its applicability as a novel WEFE Nexus indicator toolkit and the following challenges are identified: (1) some WEFE aspects need to be reinforced in order to expand the scope beyond the actual agro-ecological focus; (2) the application at the farm scale needs to be articulated with larger scales where the WEFE Nexus displays emerging consistencies; (3) Nexus interactions, trade-offs and synergies could be further accounted for. These three challenges help identify how the IDEA indicator-based tool could be adapted to assimilate the WEFE Nexus approach, and so to allow applications in new agro-hydrological contexts.</p

Epistemological dimensions of the water–energy–food nexus approach: reply to discussions of “Challenges in operationalizing the water–energy–food nexus”

We thank the authors, Varis and Keskinen, and Nauditt, for their constructive contributions. We endorse their key comments, further referring to recent literature and events, including the UN 2018 High Level Political Forum on sustainable development. Here, we elaborate on the epistemological perspective of the water–energy–food nexus conceptualization, assessment, discourse and operationalization

Uptake by end-users of a PUB approach made available as a Web Service

A consolidated geomorphology-based approach for discharge hydrograph Prediction in Ungauged Basins (PUB) through deconvolution of discharge signals from gauged donor catchments, their transposition and their convolution towards target outlets, has been made available online to end-users through a Web Service (Web Processing Service Application Programming Interface – WPS API) for the synoptic peninsular region of Brittany, France. In the spirit of hydrological services, the SIMFEN Web Service allows anyone to execute the hydrological modelling online through OGC® interoperability standards; collection of public hydrometric data; connection to a pre-existing Web Service for geomorphometric analysis; and online visualization. Thanks to tangible indicators, we here show how the users' community is actually active in using the Web Service, i.e. in uptaking the recent science-operational translation of a scientific development into a Service.</p

WST -- Widefield Spectroscopic Telescope: design of a new 12m class telescope dedicated to widefield Multi-object and Integral Field Spectroscopy

The Wide-Field Spectroscopic Telescope (WST) is a concept for a 12-m class seeing-limited telescope providing two concentric fields of view for simultaneous Multi-Object Spectroscopy and Integral Field Spectroscopy. The specified wavelength range is 0.35-1.6 microns. The baseline optical design relies on a corrected Cassegrain solution feeding Multi-Object spectrographs through fibres, while the central area of the field is propagated down to a gravity-stable Integral Field Station housing 144 spectrographs. The Cassegrain corrector also provides for atmospheric dispersion compensation. All optical components are within commercially available dimensions. With a view to minimizing risks and costs, to the maximum possible extent the telescope relies on proven subsystem solutions. An exception is the tip-tilt secondary mirror, which would likely have to provide some rejection of wind shake. An iteration of the optical design is ongoing, with a view to mitigating the weaknesses of the first baseline design. The telescope would be wavefront-controlled on-sky at the common-path MOS focus. Controls in the IFS path will need to compensate for the effect of subsequent differentials - wavefront and line of sight. There is no shortage of degrees of freedom and metrology solution to do so. The size of the dome is driven by the Nasmyth footprint and the height of the pier, which houses the IFS station. The baseline assumption is that a VLT-like enclosure would provide suitable shielding and ventilation.Comment: 8 pages, 4 figures, SPIE Astronomical telescopes and instrumentation. 16-21 June 2024. Yokohama. Japan Conference 13094-61 Ground-based and Airborne Telescopes

Invigorating hydrological research through journal publications

Over the past five years, the editors of a number of journals in the discipline of hydrology have met informally to discuss challenges and concerns in relation to the rapidly changing publishing landscape. Two of the previous meetings, in Götenborg in July 2013 and in Prague in June 2015, were followed by joint editorials (Blöschl et al. 2014; Koutsoyiannis et al. 2016) published in all participating journals. A meeting was convened in Vienna in April 2017 [during the General Assembly of the European Geosciences Union (EGU)] that was attended by 21 editors representing 14 journals. Even though the journals are published in very different settings, the editors found common cause in a vision of the editor’s role beyond just that of gatekeeper ensuring high-quality publications, to also being critical facilitators of scientific advances. In that enabling spirit, we as editors acknowledge the need to anticipate and adapt to the changing publishing landscape. This editorial communicates our views on the implications for authors, readers, reviewers, institutional assessors, and the community of editors, as discussed during the meeting and subsequently

Food and agriculture

Food security has long been a challenge for human societies and will become an increasingly pressing global issue over the coming decades (Fischer, 2018). Although global food production has kept pace with population growth, close to 750 million people (or 10% of the global population) were exposed to severe levels of food insecurity in 2019 (FAO/IFAD/ UNICEF/WFP/WHO, 2020). Unfortunately, this number has increased even further over the course of 2020 due to the COVID-19 pandemic and its economic impacts worldwide. In the 2030 Agenda for Sustainable Development, Sustainable Development Goal (SDG) 2 aims to “end hunger, achieve food security and improved nutrition and promote sustainable agriculture” (UNGA, 2015). The food system is almost entirely supported by water, and agriculture uses the major share of global freshwater resources. However, water use for food production is being questioned continually as intersectoral competition for water intensifies and water scarcity increases. Additionally, in many regions of the world, water for food production is used inefficiently (D’Odorico et al., 2020). This is a major driver of environmental degradation, including depletion of aquifers, reduction of river flows, degradation of wildlife habitats, and pollution (Willett et al., 2019). A fundamental transformation of how water is being managed in the food system is therefore necessary if most of the SDG 2 targets are to be achieved by 2030, without further degradation of water resources to concurrently achieve SDG 6 to “ensure availability and sustainable management of water and sanitation for all” (IFPRI, 2019)

Ensuring consideration of water quality in nexus approaches in the science–practice continuum : reply to discussion of "water quality: the missing dimension of water in the water–energy–food nexus?"

We thank Arnbjerg-Nielsen and co-authors for their constructive contribution. We endorse their key comments and suggestions on how to increase awareness of and action on water quality interactions in the water–energy–food (WEF) nexus. Here, we advance the discussion, commenting on the scope of water quality to embrace ecosystem as well as human needs, and the importance of transdisciplinarity and focusing at the city/aquifer/drainage basin scale in WEF nexus hotspots in ensuring that water quality is considered in WEF nexus approaches. We also identify how recent global events, the COVID-19 pandemic and the 26th Conference of the Parties to the UN Framework Convention on Climate Change (UNFCCC COP 26), may intensify the WEF nexus and its water quality interlinkages, highlighting the need to weave WEF considerations into addressing the United Nations Sustainable Development Goals and the climate and biodiversity emergencies