Understanding the total water flows and pollutant loads to the Baltic Sea is important for effective coastal-marine ecosystem management. Current assessments often overlook the unmonitored flows and submarine groundwater discharge (SGD). This study proposes and outlines a conceptual modelling framework for overcoming this common neglect by integrated quantification of (1) the monitored surface water flows, and the unmonitored (2) surface water flows and (3) SGD from land to the Baltic Sea. The study outlines how unmonitored runoff and SGD can be estimated by various quantification approaches based on commonly available hydro-climatic, hydrogeological, and other characteristic catchment data. It also describes how modules for the different monitored and unmonitored discharge components are linked and should be integrated in modelling to total annual, seasonal, or finer-resolved water flows to the Baltic Sea, and analogously also in other coastal regions around the world. Though quantitative modelling remains ongoing, the conceptualization opens pathways to improve assessments and management of freshwater flows and associated pollutant loads to the Baltic Sea.

Hydrogeodesy is the discipline that measures the Earth's solid and aquatic surfaces and gravity field from space to study water resources and their changes over time. The Special Collections on Hydrogeodesy: Understanding Changes in Water Resources Using Space Geodetic Observations, in Water Resources Research (WRR) and Geophysical Research Letters, was envisioned as a community initiative to: (a) understand the state-of-the-art of the approaches, concepts, and tools of hydrogeodesy, (b) explore hydrogeodetic innovations that improve the understanding of the water cycle and water resources, and (c) assess the potential of hydrogeodesy to address complex water-related and sustainability questions. The Special Collection includes 41 published articles studying various types of water resources and hydrological properties using the main four hydrogeodetic technologies: Altimetry, Interferometric Synthetic Aperture Radar, Gravimetry, and Global Navigation Satellite Systems. The collection is also timely in highlighting the novel hydrogeodetic advances and opportunities on the 60th anniversary of WRR, and showcasing the potential of the field to solve water-related and sustainability challenges.

The climate change impacts on hydrological conditions may be strongly modulated by the spatial variability of the intensity of human activities within watersheds. Despite growing recognition of climate and anthropogenic influences on hydrological regimes, comprehensive and spatially explicit assessments remain limited, hindering the development of robust watershed management and climate adaptation strategies. In this study, we propose an integrated framework for such analysis and deciphering by combining principal component analysis, hydrological modeling, and a range of variability approach to diagnose and attribute hydrological regime changes. The framework is tested on the case of the Taoer River Basin as a representative watershed system with pronounced human-activity variation along the upstream to downstream direction. Our results show that human activities contribute only 18% to hydrological regime changes in the upstream regions, where anthropogenic influence is relatively low, compared to 49% in the downstream areas with substantially greater human interference. While the upstream areas exhibit more pronounced changes in daily maximum streamflow (78%–79%) and count of low pulses (79%), the downstream areas experience more substantial alterations in monthly average streamflow (84%–99%) and high pulse durations (85%). Overarching the human-activity variability, the climate change impacts increase the risk of flooding, while the human activities exert greater influence in amplifying drought risk. Simulations based on CMIP6 climate projections further indicate a significant increase in the likelihood of upstream flooding. Overall, our findings highlight the necessity of spatially differentiated management and adaptation strategies, tailored to steep human-activity gradients across watershed zones, to effectively address hydrological changes under climate stress.

Many scientific disciplines address, and societal sectors interact with, various aspects, components, and subsystems of water on land, which together form the terrestrial hydrosphere within the Earth System. Advancing knowledge of this sphere as a coherent, integrated whole requires a consistent and realistic understanding across the water-related domains. Achieving such knowledge convergence requires systematically and synergistically identifying and bridging major gaps across the domains. A network-based standard model is proposed as a foundation for this.

Addressing global challenges and advancing knowledge in the Earth and space sciences requires an equitable, diverse, and inclusive scholarly community where researchers must be freely able to conduct, collaborate on, share, review, and discuss their research on important economic and societal topics such as climate change. The current Executive Orders in the United States focus on censoring research and researchers by banning specific words, removing access to data sets, or by restricting what type of research can be funded or published, therefore compromising the knowledge that researchers are able to produce. As Editors-in-Chief of AGU publications we stand by our mission to support the publication of evidence-based, rigorously vetted research without political pressure. Collectively, our peer-reviewed journals and books provide inclusive publication outlets for the global research community to advance Earth and space sciences and to strengthen the public's trust in scientific evidence.

It is largely unknown, yet essential for the Baltic Sea state, the nutrient and pollutant loads from land, and the coastal-marine ecosystem health how freshwater discharges to the sea and their drought and flood extremes vary and change over the Baltic Sea Drainage Basin (BSDB). Based on four different (types of) datasets, we here compare these variations and changes over 1980-2010 across 69 large hydrological catchments in the BSDB. The datasets agree that the precipitation changes over the study period do not necessarily propagate to analogous changes for runoff and related discharges to the sea, with results showing various contrasting precipitation and runoff changes. The datasets differ markedly in that some model-based reanalysis datasets yield directly opposite water balance closures, implying persistent 30-year average regional storage wetting or drying depending on the dataset. For droughts and floods, dataset differences are overall greater for runoff than for precipitation, and widely used reanalysis data do not fully capture how extremely high and low flood- and drought-related runoff fluxes can be, as observed in the BSDB. These findings are important for plans and preparations to mitigate and/or adapt to changes and extremes in the Baltic freshwater conditions and discharges to the sea.

Undertaking systemic risk assessments of critical infrastructures (CIs) is necessary to improve understanding, mitigate impacts, and increase resilience to cascading effects of intensifying hydrometeorological hazards. This paper presents a novel quantitative approach with stakholder participation for simulating local physical interdependencies between multiple infrastructure sectors that may be disrupted by floods. The model comprised power, water, telecommunications, emergency, and transport systems. Local (node-edge) resilience metrics were computed to identify critical, vulnerable, and non-redundant CIs in the network. For infrastructures located in areas under risk of floods, global resilience metrics (for whole-network degradation) evaluated failure propagation. The approach was tested in a case study of Halmstad Municipality, Sweden, with a history of extreme hydrometeorological events. Results identified key power, water, and communication infrastructures with high disruption potential under flood exposure, as well as specific residential and industrial areas near hazard zones being the most vulnerable due to their extensive dependencies.