The Pliocene is the most recent epoch in which the Earth warmed under atmospheric CO2 levels similar to today (>400 ppm). The Pliocene then transitioned to the colder Pleistocene epoch, with the initiation of large-scale Northern Hemisphere glaciations. Although ocean temperature changes across these epochs are relatively well-known, quantitative estimates of the magnitude of land temperature change in the tropics are scarce. We provide a Plio-Quaternary quantitative air temperature record based on the distribution of bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) preserved in sediments of the Funza-II core in the Sabana de Bogotá, Colombia (~4°N). Using a refined age model based on new U-Pb zircon dates from ash layers, and a novel mixed-source model that disentangles contributions from lake- and soil-derived brGDGTs, we show that warm Pliocene (3.8 to 2.58 Ma) temperatures were [Formula: see text] °C warmer than the last ~800,000 y of the colder Pleistocene. The evolution of Pliocene-Pleistocene temperature in our record largely mirrors long-term tropical sea surface temperature (SST) cooling, highlighting the linkages between sea and land temperatures in the low latitudes via greenhouse-gas forcing. The median amplitude of Pliocene-Pleistocene cooling in the northern tropical Andes exceeds that predicted by theory, highlighting the importance of regional feedbacks including lapse rate adjustments and/or changes in Pacific SST gradients to the long-term evolution of Andean temperature. This first quantitative terrestrial temperature reconstruction within 5° of the equator over the past 3.8 My highlights that both regional and global processes must be considered when constraining uncertainties for future warming scenarios.

In the glacier-melt-dominated regions of Kyrgyzstan, accurate cryosphere monitoring is essential for Central Asian water resource forecasting. However, the lack of consistent in situ observations necessitates the integration of diverse remote sensing datasets and physically based models which often vary in their underlying assumptions and resolutions. This study presents a transparent, reproducible framework for the comparative evaluation of heterogeneous snow products in complex terrain, applied to SnowMapper (a NWP-driven physical model) and GlacierMapper (a MODIS-based NDSI product) for the period 2000–2024.The framework employs spatial harmonization via nearest-neighbor resampling to a common independent grid and temporal alignment across differing calendar conventions. To address variable incompatibility, Snow Water Equivalent (SWE) outputs from SnowMapper are transformed into binary snow/no-snow classifications using literature-derived thresholds. Sensitivity analyses reveal that product agreement is significantly influenced by these methodological transformations. Evaluation using complementary spatiotemporal diagnostics such as fractional snow cover area, balanced accuracy, Cohen’s kappa and snow depletion curves (SDCs) identifies periods of systematic divergence across decadal and seasonal timescales. Results demonstrate that apparent product discrepancies arise not only from physical inconsistencies but also from methodological treatment. This standardized intercomparison approach is transferable across sensors and regions enhancing the reliability of snow-product assessments in data-scarce mountain environments.

While several hypotheses exist to explain the development of large-scale perennial Northern Hemisphere ice sheets in the late Pliocene and early Pleistocene, the prevailing view is that a decline in atmospheric carbon dioxide (CO2) drove this substantial change in late Neogene climate. However, the primary mechanism responsible for this reduction in CO2 has yet to be fully explored. Mineral dust-derived iron enhancement of ocean organic carbon production and export to the deep ocean and marine sediments has previously been invoked to explain reductions in atmospheric CO2 on multiple timescales. Here we test the hypothesis that iron fertilization of the Pliocene subarctic North Pacific affected atmospheric CO2, and in turn drove the formation of Northern Hemisphere ice sheets. By compiling Pliocene dust and export productivity proxy data sets from across the North Pacific and then progressively filtering for the most reliable records, we find that there is no relationship between North Pacific dust inputs and export production in the Pliocene. Finally, we apply these new composites to broadly assess previously proposed drivers of Pliocene Asian dust dynamics as well as North Pacific Ocean circulation and biogeochemistry.

Abstract Tropical cities are frequently exposed to short and intense rainfall that poses a significant flood risk to rapidly growing populations, making it essential to predict how these extremes will evolve under climate change. However, local projections remain limited by the lack of high‐resolution climate simulations and long‐term meteorological records. To address this, we present a globally scalable framework that downscales gridded daily rainfall data to hourly resolution using a stochastic disaggregation model. The model is calibrated using satellite‐derived hourly rainfall statistics, and rainfall intensity‐temperature scaling is applied using General Circulation Model‐projected dew point temperatures, eliminating the reliance on local hourly records. By linking dew point temperature‐rainfall relationships to projected changes from climate models, we generate future intensity‐duration‐frequency curves across 20 tropical and subtropical cities. Results show hourly rainfall intensities increase by 10%–17% by 2080–2100 relative to 1995–2014 under SSP2‐4.5 and under the assumption of Clausius‐Clapeyron scaling, with rare high‐impact events becoming up to six times more frequent under SSP5‐8.5. Temperature‐rainfall scaling emerges as the dominant source of uncertainty, surpassing climate model and emission uncertainty. We further show that using only mean temperature shifts rather than changes in the entire temperature distribution may significantly underestimate rainfall intensification. These findings underscore the need to accurately quantify local temperature‐rainfall scaling and offer a pathway for improved global projections of rainfall extremes, particularly in data‐scarce regions, supporting more resilient urban infrastructure planning for a future climate.

Abstract. Across ecosystems, soil water is replenished by precipitation events and depleted by evapotranspiration. Evapotranspiration is driven by solar radiation and the aerodynamic evaporative demand of the atmospheric boundary layer (Eaero). However, vegetation regulates the rate of transpiration through species-specific stomatal closure mechanisms that depend on tree water status, which in turn depends on the tree’s water supply and the atmospheric water demand. Therefore, quantifying the effects of precipitation, solar radiation and Eaero on tree-mediated water fluxes is challenging. Here we use ERRA, a framework for de-mixing and de-convolving non-stationary system responses to multiple inputs, to quantify how atmospheric forcing affects ecosystem water fluxes and water content dynamics in a mixed beech and spruce forest. The resulting impulse-response functions describe how soil and tree water fluxes respond to three atmospheric forcing (precipitation, solar radiation, Eaero). Water contents of soils and trees responded positively and rapidly to precipitation pulses, indicating fast infiltration of precipitation into the soil and net increases in tree water contents. Tree water contents responded more clearly to precipitation inputs than sapflow rates did, suggesting that precipitation primarily reduced transpiration rather than enhancing tree water uptake. Trees responded quickly and strongly to impulses of solar radiation, but their responses to Eaero were less distinct, potentially reflecting stomatal closure effects on transpiration. The impulse-response functions reflected species-specific water use strategies and differences in hydraulic capacitance of trees, which buffered root water uptake during periods of high transpiration demand and thus prolonged the refilling of tree water storage after precipitation events. Impulse responses to solar radiation and Eaero were much less distinct in the soils than in the trees, illustrating how forest canopies shield the underlying soils from atmospheric forcing. Our study highlights how impulse-response functions can help to identify soil-plant-atmosphere relations, complementing our understanding of forest ecosystem functioning in response to atmospheric forcing.

The inter- and transdisciplinary research project TREBRDIGE (formally titled Transformation toward Resilient Ecosystems: Bridging Natural and Social Sciences) focuses on watershed management in Alpine regions in Switzerland. centuries, check dams have been constructed in streams to control erosion and flooding, while intensive forest management in these areas has further influenced both flood and erosion processes. The maintenance of flood management infrastructure requires high financial investments and at the same time affects the resilience of the ecosystems. The aim of TREBRIDGE is to identify alternative policy and management approaches of watersheds in Alpine regions. Such approaches aim on the one hand to increase the resilience of Alpine ecosystems in coping with extreme weather events and on the other hand meet societal needs regarding natural resource use and protection.The transdisciplinary aspect of TREBRIDGE focuses on creating and assessing alternative policy and management to explore different scenarios which are co-created in collaboration with researchers, policymakers, as well as national, regional, and local actors. We focus on three case study areas in the Swiss Alps: Alptal (Canton Schwyz), Gürbetal (Canton Bern) and Illgraben (Canton Valais). All case studies are prone to varying natural hazard risks but have a in place. The interdisciplinary aspect of TREBRIDGE takes a holistic view on watershed and forest functioning by assembling inter-​ and transdisciplinary scholars, geologists, geomorphologists, hydrologists, ecologists, economists, and policy analysts. To combine the socio-economic, ecological and geohydrological dimensions, we followed a structured method to develop a conceptual framework. The framework represents a comprehensive social-ecological system view and bridges three types of knowledge (systems, target, and transformation) as well as diverse disciplinary perspectives. Our poster contributes to this session in three ways: 1) We describe what steps can be taken to develop a conceptual framework when dealing with complex social-ecological systems that are influenced by drivers and processes of global change. The framework supports integration of diverse types of knowledge and perspectives from different disciplines. 2) We briefly present how such a framework could look like using the TREBRIDGE project as an example. 3) We outline how such a conceptual framework can be applied in interdisciplinary research settings to facilitate knowledge integration across disciplines.

Rainfall erosivity is a key dynamic factor of water erosion estimation, with a significant spatial and temporal variation. This study presents a comprehensive analysis of the spatial patterns and monthly distribution of rainfall erosivity across India, using data from 261 hourly and 2,525 monthly rainfall stations covering the period from 1969 to 2021. In India, monthly rainfall erosivity and related attributes—such as the kinetic energy of erosive rainfall, the number of erosive events, and peak hourly rainfall intensity—have been systematically examined for the first time. Monthly erosivity estimates derived from hourly data were linked with monthly rainfall, enabling a simplified and efficient estimation approach. To predict monthly erosivity based on rainfall, temperature, and topographic variables, we developed and evaluated three modeling approaches: linear regression, a machine learning-based XGBoost model, and an ensemble model. XGBoost outperformed the others, achieving a median coefficient of determination (R2) of 0.97, while the ensemble model also performed well with a median R2 of 0.96. Additionally, a Geographically Weighted Regression (GWR) approach was applied for spatial interpolation, yielding accurate high-resolution erosivity maps with a median R2 of 0.90. The results also demonstrate that erosivity peaks during the summer monsoon months (June to September), with July exhibiting the highest value due to intense rainfall and high kinetic energy. Notably, the analysis revealed that nearly 32% of India experiences monthly erosivity exceeding 2,000 MJ mm ha−1 h−1 month−1 in July alone. In contrast, non-monsoon months showed considerably lower erosivity levels across most of the country. A statistically significant long-term increase was detected in January, with an average rise of +0.86 MJ mm ha−1 h−1 month−1 in total erosivity and + 0.1 mm h−1 in maximum 60-min rainfall intensity annually. While acknowledging certain limitations, this study provides valuable insights into erosive rainfall characteristics, enhances rain-driven erosion assessment, and supports the development of timely and location-specific soil conservation strategies across India.

Highly engineered Alpine watersheds and forests face growing risks, requiring shifts in management and research. We use science integration and a participatory scenario process to integrate disciplines and co-create knowledge with stakeholders. We thus develop pathways for rethinking future management, aiming for higher resilience of Alpine ecosystems and delivering greater societal value than current systems.Given highly engineered Alpine ecosystems with monocultures and channelized streams, this project proposes radical changes to enable increased ecosystem resilience and societal wellbeing. We propose to rethink 1. management by including ecological and socio-economic aspects and 2. research by integrating natural, engineering, and social sciences. In this inter- and transdisciplinary project, we develop qualitative scenarios as storylines for future Alpine watershed and forest management. These scenarios serve as parameters for, on the one hand, the biophysical modelling of ecological quality (biodiversity, ecosystem function, ecological integrity) in Swiss case study regions. On the other, we assess residents’ preferences for the scenarios in relation to Nature’s Contributions to People and aspects of justice. We thus use science integration and a participatory scenario process to enable integration across disciplines as well as co-create knowledge with stakeholders throughout the research process. While this approach facilitates working across disciplinary boundaries and includes stakeholders from the onset, it also comes with challenges: finding a common language across disciplines and engaging meaningfully with stakeholders takes time and simultaneously does not cater to the traditional metrics in academia.

Experimental floods serving environmental or ecological purposes (e-floods) represent a strategic approach to managing sediment within river systems altered by hydropower operations and other regulation. The absence of natural sediment transport due to minimum flows below dams and intakes leads to various ecological challenges, including river incision and habitat degradation. By releasing water stored behind dams, e-floods aim to mimic natural flow regimes, facilitating the redistribution of fine sediments that have clogged the riverbed and rebuilding aquatic habitats. Our research examines the effects of e-floods on the Sp & ouml;l River, which flows into the Inn River in southern Switzerland. Through the deployment of a suspended sediment concentration (SSC) sensor network, 4 sensors in 2021 and 7 sensors in 2023, we monitored the release of previously stored sediment and the propagation of suspended sediment waves triggered by these e-floods at a high temporal resolution (1-2.5 mins). Our findings reveal SSC pulsations above 5 gL-1 (lasting 3 h) and above 8 gL-1 for at least 30 min, in both 2021 and 2023, respectively, which were larger in amplitude and lasting longer than previously measured, surpassing established thresholds. The peaks reached were 12.0 gL-1 (2021) and 10.8 gL-1 (2023). Moreover, the sediment wave was observed to extend into the Inn river, leading to potential siltation and ecological impacts downstream. We found a total fine sediment load of 1,297 +/- 75 t and 1,936 +/- 133 t (in 2021 and 2023, respectively) delivered by the Sp & ouml;l e-floods to the Inn, which is 0.8-1.1% of the total annual fine sediment load in the Inn. A simple steady-state solution to the advection equation suggests that for suspended sediments to settle before reaching the Austrian border, the discharge and SSC of the Sp & ouml;l and the discharge of the Inn must all be taken into consideration. We provide a proof-of-concept that high-resolution fine sediment sensing should accompany e-flood planning in order to capture the fluctuations in SSC during the release, to identify possible fine sediment inputs either from the dam or instream sources, such as river bed, banks and floodplain, and to provide first-order estimates of the fine sediment loads and their propagation downstream. Future work can use data from such a network to develop predictive models and adaptive management strategies to mitigate adverse ecological effects while optimizing sediment redistribution efforts.

The occurrence of extreme suspended sediment concentrations (SSCs) in rivers can have negative impacts on human infrastructure, water quality, and the health of aquatic ecosystems. However, most existing studies have focused on the SSC dynamics of individual catchments or single events. Consequently, large-scale patterns of suspended sediment dynamics remain poorly understood. The objective of this study is to identify spatial differences in (1) the seasonality of SSCs and (2) the occurrence of SSC extremes in the Alps. For our analyses, we use 10 years of observed sub-daily SSC data from 38 gauging stations in Switzerland and Austria. We show that the presence of glaciers, catchment elevation, and the onset of the melt season are important drivers of SSC seasonality. However, slightly different processes are important at the event scale, where rainfall is the main driver of SSC extremes, responsible for 85 % of all events. The remaining events are entirely or partly associated with snowmelt and glacial melt, which can account for up to 35 % of the events in high-elevation and partially glaciated catchments. This underscores the disproportionate influence of meltwater on sediment concentrations in high-altitude alpine rivers, which can be explained by the significant contribution of meltwater to overland flow and river discharge in combination with the high sediment availability in glacier forefields. A significant proportion of the extreme events (24 %) resulted in peak SSC values greater than 5 g L−1, highlighting their potential to cause significant harm to aquatic species and river ecosystems.

Sediment cascades are a convenient way of conceptualizing the transfer of sediment from hillslope production areas, through the river network, to the river basin outlet. Distributed hydrology-sediment models play an important role in the prediction of these source-to-sink links, because they can explicitly connect water and sediment fluxes along topographically-driven pathways. Here, we provide some examples of such cascade-based hydrology-sediment model applications in alpine environments and some problems related to their use. In particular, we highlight two critical problems with hydrology-sediment modelling that go beyond trivial model calibration difficulties. These address fundamental issues of (a) non-uniqueness in sediment source mixing, and (b) sediment supply limitations. The first problem of non-uniqueness is known in hydrological modelling as the curse when models perform well at basin outlets for the wrong reasons, misrepresenting hydrological processes within the basin. In geomorphology, this concept has not received the same level of attention. Here we show that even a calibrated physically-distributed hydrology-sediment model can be subject to non-uniqueness, and provide the same suspended sediment yields at the basin outlet with completely different combinations of sediment sources. Including sediment tracers in model validation helps to identify this problem, and it is also helpful to check simulations at sub-basin scales where we are closer to distinct sediment sources. The second problem of sediment supply limitations is a challenge for all models that rely on transport capacity formulas for sediment transport. In our experience, both supply and transport capacity limit sediment transport at the basin scale, and we need to include this in our models. For example, we show that supply limitations can completely change the seasonality of sediment yields and render many climate change impact studies worthless. Finally, we argue that both problems above, at least for suspended load, can be partially addressed by novel monitoring. For example by low cost smart sensors that allow a distributed sensing of sediment fluxes above and below potential sediment sources at high resolutions, or by high resolution remote sensing to capture space-time variability in river turbidity. This kind of data can dramatically improve our ability to calibrate models, reduce non-uniqueness, and over the long term identify the key signatures of sediment supply in river systems. It is our opinion that improving the predictions of climate and environmental change effects on sediment yields requires both better model validation as well as new data.

One of the major challenges posed by climate change in agriculture is the alteration in cropland suitability. This alteration has serious consequences for food security and economic stability at global, regional, and local scales, especially in smallholder and rainfed agricultural systems like in Ethiopia. A comprehensive understanding of the current state of croplands and future changes under warming temperatures and increasing rainfall uncertainty is critical for national climate adaptation planning. Here, we evaluated cropland suitability (CLS) for four major cereal crops (teff, maize, sorghum, and wheat), under both current and future climates across the rainfed agriculture (RFA) landscapes of Ethiopia. We utilized a novel suitability modelling approach that establishes functional relationships between crop yield, and climatic factors (rainfall, temperature, and solar radiation) and soil factors (texture, pH, and organic carbon). Furthermore, we analyzed the relative influences of the growing season rainfall and temperature on the changes in CLS. The results show that 54 % of the RFA area has a suitability index of 0.6 or higher (moderately to highly suitable) for teff and that 51 %, 63 %, and 29 % of the grid cells are suitable for maize, sorghum, and wheat crops, respectively. The suitable agroecologies of the four crops will likely undergo altitudinal shifts and areal contraction, with magnitudes of the changes depending on the emission scenarios. Under the SSP2-4.5, the suitable areas are projected to decrease by 25 % for teff, 7 % for maize, 10 % for sorghum, and 16 % for wheat in the 2080s. In semi-arid and hyper-humid climates, CLS is sensitive to changes in the growing season rainfall, whereas in low and high elevation regions, it is temperature- sensitive. In light of our results, we argue that adaptation actions tailored to agroecological conditions and topographic locations are vitally necessary to mitigate the long-term impacts of climate change on Ethiopia's rainfed agriculture.

High elevation headwater catchments are complex hydrological systems that seasonally buffer water and release it in the form of snow and ice melt, modulating downstream runoff regimes and water availability. In High Mountain Asia (HMA), where a wide range of climates from semi-arid to monsoonal exist, the importance of the cryospheric contributions to the water budget varies with the amount and seasonal distribution of precipitation. Losses due to evapotranspiration and sublimation are to date largely unquantified components of the water budget in such catchments, although they can be comparable in magnitude to glacier melt contributions to streamflow. Here, we simulate the hydrology of three high elevation headwater catchments in distinct climates in HMA over 10 years using an ecohydrological model geared towards high-mountain areas including snow and glaciers, forced with reanalysis data. Our results show that evapotranspiration and sublimation together are most important at the semi-arid site, Kyzylsu, on the northernmost slopes of the Pamir mountain range. Here, the evaporative loss amounts to 28% of the water throughput, which we define as the total water added to, or removed from the water balance within a year. In comparison, evaporative losses are 19% at the Central Himalayan site Langtang and 13% at the wettest site, 24 K, on the Southeastern Tibetan Plateau. At the three sites, respectively, sublimation removes 15%, 13% and 6% of snowfall, while evapotranspiration removes the equivalent of 76%, 28% and 19% of rainfall. In absolute terms, and across a comparable elevation range, the highest ET flux is 413 mm yr −1 at 24 K, while the highest sublimation flux is 91 mm yr −1 at Kyzylsu. During warm and dry years, glacier melt was found to only partially compensate for the annual supply deficit.

Debris-flow volumes can increase along their flow path by entraining sediment stored in the channel bed and banks, thus also increasing hazard potential. Theoretical considerations, laboratory experiments and field investigations all indicate that the saturation conditions of the sediment along the flow path can greatly influence the amount of sediment entrained. However, this process is usually not considered for practical applications. This study aims to close this gap by combining runout and hydrological models into a predictive framework that is calibrated and tested using unique observations of sediment erosion and debris-flow properties available at a Swiss debris-flow observation station (Illgraben). To this end, hourly water input to the erodible channel is predicted using a simple, process-based hydrological model, and the resulting water saturation level in the upper sediment layer of the channel is modelled based on a Hortonian infiltration concept. Debris-flow entrainment is then predicted using the RAMMS debris-flow runout model. We find a strong correlation between the modelled saturation level of the sediment on the flow path and the channel-bed erodibility for single-surge debris-flow events with distinct fronts, indicating that the modelled water content is a good predictor for erosion simulated in RAMMS. Debris-flow properties with more complex flow behaviour (e.g., multiple surges or roll waves) are not as well predicted using this procedure, indicating that more physically complete models are necessary. Finally, we demonstrate how this modelling framework can be used for climate change impact assessment and show that earlier snowmelt may shift the peak of the debris-flow season to earlier in the year. Our novel modelling framework provides a plausible approach to reproduce saturation-dependent entrainment and thus better constrain event volumes for current and future hazard assessment. We developed a predictive modelling framework to estimate bed erodibility based on antecedent saturation of the channel bed. The modelled saturation conditions and the RAMMS-calibrated bed erodibility exhibit a strong correlation when debris flows adhere to typical flow patterns, making the proposed framework a promising tool for hazard assessments under climate change. image

Using a novel dataset, this study assesses the impact of 21st-century climate change on the hydrology of 221 high-mountain catchments in Central Asia. We employed a parsimonious, steady-state stochastic soil moisture water balance model to project changes in runoff and evaporation across three future timeframes: 2011–2040, 2041–2070, and 2071– 2100, compared to the baseline period of 1979–2011. Baseline climate data were sourced from CHELSA V21 climatology, providing daily temperature and precipitation for each subcatchment. Future projections utilized bias-corrected CMIP6 outputs from four General Circulation Models under four scenarios. Global datasets informed the spatial soil parameter distribution, and glacier imbalance ablation data were integrated to refine discharge modeling, which was validated against long-term catchment norm data. The results indicate an upward trend in precipitation (+4.5%, +5.8%, and +8.4% for the three future periods) and median temperature increases of +1.3°C, +2.4°C, and +3.6°C, respectively. Modeling results predict an initial discharge increase of +4.1% in the first period, tapering off to +1.4% by the third, with glacier wastage in the Tien Shan impacting runoff zones and reducing discharge there. In contrast, the Gissar-Alay and Pamir ranges are projected to experience discharge increases throughout the century due to delayed peak water and enhanced glacier ablation. Shifts in precipitation patterns suggest potential alterations in hydrological extremes, a topic that warrants further investigation in the region. Our findings highlight the differentiated hydrological responses to climate change within Central Asian high-mountain catchments and underscore the critical role of glaciers in future water availability, with implications for local and regional water resource management.

Readers will be led down a random path from continental dynamics to paleoclimate. A key to understanding continental dynamics is recognizing that differences in gravitational potential energy per unit area between high and low terrain govern much of large-scale continental deformation. Removal of mantle lithosphere, not just crustal thickening, plays a crucial, but difficult-to-test, role in changes in surface elevation. Although measuring past surface heights remains a challenge, indications of such processes suggest that surface uplift associated with such removal can affect relative plate motion. Climate change, from a warmer to cooler climate, and associated changes in erosion and sedimentation introduce further complications to determining past elevations. The phenomena that led to such cooling include a number of possibilities, but I favor the emergence of islands in the Maritime continent, which transformed the Pacific Ocean from one with a warm eastern tropical Pacific, as during El Niño events, to the present-day La Niña–like background state. Teleconnections from the eastern tropical Pacific to Canada affect the duration of summers and the potential of high-latitude ice to accumulate. ▪Lateral gradients in gravitational potential energy per unit area (GPE), a force per unit length, govern large-scale continental dynamics.▪Removal of mantle lithosphere and thickening of crust raise GPE; knowledge of mean surface elevations provides a test of these processes.▪Climate change from a warmer to cooler climate and from one with less to more erosion can give the false impression of elevation change.▪Emergence of Indonesian islands, more rain over them, a stronger Walker Circulation, and cooler eastern Pacific may have led to ice ages.

Forest ecosystems depend on throughfall and stemflow fluxes for both water and nutrient input. Spatial and temporal variability of throughfall and stemflow fluxes are large and differ between tree species. The nutrient fluxes that accompany throughfall and stemflow are affected by climate, precipitation intensity, the seasonality of dry deposition, and canopy exchange processes. The interdependence of these factors make it challenging to quantify changes in throughfall and stemflow amounts as well as their nutrient content. Here we provide observation-based evidence from 3.5 years of record with 222 rainfall events, of the seasonal variability of throughfall and stemflow magnitude and ion concentrations under a beech (Fagus silvatica) and spruce (Picea abies) tree. Interception and canopy cover were seasonally variable, average annual interception was 53% below beech, 61% below spruce and 68% below young spruce canopies. Further we assess seasonality of ionic nutrients such as NH and NO as well as Mg, Ca and K and their dependence on both dry deposition and canopy exchange. Throughfall and stemflow were enriched compared to precipitation, with large differences between ions and different months. Antecedent precipitation was a main control on throughfall and stemflow enrichment. We developed a conceptual model of the potential drivers of throughfall and stemflow enrichment based on our observations. While NH and NO enrichment are likely dominated by dry deposition and dew and fog accumulation, Mg, Ca and K were additionally affected by canopy exchange. Observation based studies such as this one are needed to understand precipitation and nutrient partitioning across forests, which enables to predict how changes in climate and forest composition will affect local hydrology and nutrient inputs into forest ecosystems.

<p>Hydropeaking in rivers changes the flow regime, increases river clogging, mobilizes fine sediment, and causes major stress to fish, macroinvertebrates, and aquatic plants that suffer from the rapid water level fluctuations. One in four medium- to large-sized rivers in Switzerland is affected by hydropeaking. In this study, we investigated the effect of hydropeaking on fine sediment transport during an experimental flood on the Spöl river, a tributary of the Inn river, in the canton of Graubünden, Switzerland. The study was a proof-of-concept for new smart turbidity sensors, which were developed in our laboratory, calibrated, and tested in mixing tank experiments in 2021 and again in 2022 with a range of different sediment types. These sensors were deployed at two locations on the Spöl during an experimental flood release by the upstream Ova Spinne hydropower dam. The collected data reveal sudden sediment concentration increases and decreases (pulsing) as the discharge increases steadily throughout the day. The highest concentration of sediment is much larger (4-5 g/L) than would be expected and appeared with the onset of the flood and again with the peak discharge. Our findings also reveal clockwise and counter-clockwise hysteresis loops in the stage-concentration relation, which point to a switch in the sediment supply between supply limited and unlimited conditions during the experimental flood. This study shows that high spatial- and temporal-resolution monitoring of suspended sediment is possible with a low-cost sensor network. The applications of such a network are plentiful: from identifying sediment source activation and transport in small streams, glacier networks and deltas, to environmental monitoring of maximum sediment concentration levels for the survival of fry fish, for prevention of river bed clogging, and for pollutant monitoring (binding to sediments).</p>

Climate change is expected to affect precipitation, streamflow, and sediment transport. These changes are particularly relevant in mountainous environments that play a crucial role in water resources and sediment supply for downstream reaches. We investigated the impact of climate change on hydrology and geomorphology in the upper Emme catchment (127 km2) in the Swiss pre-Alps by simulating its hydromorphological response to present climate and three climate scenarios at the end of the century using the distributed CAESAR-Lisflood landscape evolution model. The mean seasonal changes, intensification of short-duration rainfall extremes, and snow processes were explicitly modeled. The results highlight the importance of the intensity of rainfall events to predict sediment transport at the outlet, while changes to snow processes are predominant to understand the seasonal hydrological shift. For the highest emission scenario (RCP8.5), the sediment yield at the outlet increased by 6% despite a reduction in precipitation by 7% compared to the present climate, as a result of heavy precipitation intensification. On a seasonal scale, discharge increased in winter while it decreased in spring in all scenarios due to changes in snow accumulation and melting. Furthermore, we found that erosion and deposition will change spatially by the end of the century, with a shift from erosion- to deposition-dominated valleys.