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The young water fraction (Fyw*), defined as the fraction of catchment outflow with transit times of less than 2–3 months, is increasingly used in hydrological studies that exploit the potential of isotope tracers. The use of this new metric in catchment intercomparison studies is helpful to understand and conceptualize the relevant processes controlling catchment functioning. Previous studies have shown surprising evidence that mountainous catchments worldwide yield low Fyw*. These low values have been partially explained by isolated hydrological processes, including deep vertical infiltration and long groundwater flow paths. However, a thorough framework illustrating the relevant mechanisms leading to a low Fyw* in mountainous catchments is missing. The main aim of this paper is to give an overview of what drives Fyw* variations according to elevation, thus clarifying why it generally decreases at high elevation. For this purpose, we assembled a data set of 27 study catchments, located in both Switzerland and Italy, for which we calculateFyw*. We assume that this decrease can be explained by the groundwater storage potential, quantified by the areal extent of Quaternary deposits over a catchment (Fqd), and the low-flow duration (LFD) throughout the period of isotope sampling (PoS). In snow-dominated systems, LFD is strictly related to the snowpack persistence, quantified through the mean fractional snow cover area (FSCA). The drivers are related to the catchment storage contribution to the stream that we quantify by applying a cutting-edge baseflow separation method to the discharge time series of the study sites and by estimating the mean baseflow fraction (Fbf) over the PoS. Our results suggest that Quaternary deposits could play a role in modulating Fyw* elevation gradients via their capacity to store groundwater, but subsequent confirmation with further, more detailed geological information is necessary. LFD indicates the proportion of PoS in which the stream is sustained and dominated by stored water coming from the catchment storage. Accordingly, our results reveal that the increase of LFD at high elevations, to a large extent driven by the persistence of winter snowpacks and the simultaneous lack of a liquid water input to the catchments, results in lower Fyw*. In our data set, Fbf reveals a strong complementarity with Fyw*, suggesting that the latter could be estimated as Fyw*≃1-Fbf for catchments without stable water isotope measurements. As a conclusion, we develop a perceptual model that integrates all the results of our analysis into a framework for how hydrological processes control Fyw* according to elevation. This lays the foundations for an improvement of the theory-driven models.

River networks in the Alps are very complex and hold many unanswered research questions. For example, various assumptions must be made to when studying tributaries and small rivers. Namely, there is not a widely accepted tool to measure streamflow in small, mountain streams that can overcome their specific challenges affordably without large installations. For example, alteration between extremely high and no discharge volume is characteristic of intermittent rivers and ephemeral streams (IRES). Conventional measuring devices all require streambed installation, which exposes them to displacement or destruction by abruptly rising water levels. One solution, thus, is to remove the sensor from the streambed and measure from a distance. We have experimented with an acoustic sound recorder mounted above the stream as an alternative tool to assess water level. We designed a low-cost audio sensor powered by a microcontroller with an audio shield specifically for recording IRES. To ensure reproducibility, we used Arduino for programming the Teensy 3.2. Images of the water level in an IRES were simultaneously captured when possible (daylight) and used for calibration. The water level visible in the images correlated well with that determined from the audio recordings from our self-developed audio sensor (R2 = 95%). Based exclusively on the audio recording of an IRES, we can obtain a time series of the water level, at least when water was present. We are currently unable to determine consistently whether water is present nor state with certainty when the streambed is dry based solely on acoustic data. Nevertheless, this new sensor allows us to measure an alpine channel network at more locations and over longer time periods than previously feasible.

Past studies on the impacts of climate change (CC) on Alpine hydropower production have focused on high-head accumulation power plants. We provide one of the first comprehensive, simulation-based studies on CC impacts on Alpine Run-of-River (RoR) production, also considering effects of environmental flow requirements and technical increase potential. We simulate future electricity production under three emissions scenarios for 21 Swiss RoR plants with a total production of 5.9 TWh a-1. The simulations show an increase in winter production (4 % to 9 %) and a decrease in summer production (-2 % to -22 %), which together lead to an annual decrease of about -2 % to -7 % by the end of the century. The production loss due to environmental flow requirements is estimated at 3.5 % of the annual production; the largest low-elevation RoR power plants show little loss, while small and medium-sized power plants are most affected. The potential for increasing production by optimising the design discharge amounts to 8 % of the annual production. The largest increase potential is related to small and medium-sized power plants at high elevations. The key results are: i) there is no linear relationship between CC impacts on streamflow and on RoR production; the impacts depend on the usable streamflow volume, which is influenced by the Flow Duration Curve, environmental flow requirements, and design discharge; ii), the simulated production impacts show a strong correlation (>0.68) with the mean catchment elevation. The plants at the highest elevations even show an increase in annual production of 3 % to 23 %, due to larger shares of precipitation falling as rain instead of snow. These general results are transferable to RoR production in similar settings in other Alpine locations and should be considered in future assessments. Future work could focus on further technical optimisation potential, considering detailed operational data.

Preprint of a manuscript as submitted to the Elsevier journal of Ecologial Engineering

Rapid climate change is impacting water resources in Afghanistan. The consequences are poorly known. Suitable mitigation and adaptation strategies have not been developed. Thus, this paper summarizes current status of knowledge in relation to Afghan water resources. More than 130 scientific articles, reports and data sources are synthesized to review the potential impacts of climate change on the cryosphere, streamflow, groundwater and hydrological extremes. The available information suggests that Afghanistan is currently witnessing significant increases in temperature, less so precipitation. There is evidence of shifts in the intra-annual distribution of streamflow, with reduced summer flows in non-glaciated basins and increased winter and spring streamflow. However, in the short-term there will be an increase in summer ice melt in glaciated basins, a “glacial subsidy”, which sustains summer streamflow, despite reduced snow accumulation. The future prognosis for water resources is likely to be more serious when this glacier subsidy ends.

Intermittent rivers and ephemeral streams (IRES) account for 50% of the world's flows. Climate change leads to an increase in intermittent streams from perennial streams. Recently, IRES have been found to be very important for carbon and nitrogen cycling and ecosystem functions. Despite recent attention towards IRES, spatial and temporal data lack, especially in mountain areas. Conventional measuring techniques depend on devices that have certain limitations, for example, they are placed in the streambed, where they get destroyed or displaced during a heavy stream flow event. This thesis presents a self-developed, low-cost audio sensor that can derive the water level of an IRES using only sound. In addition to an audio sensor, a time-lapse camera constantly documented the streambed and captured the water level at thirty-minute intervals. The water level determined from the images and the audio files is strongly correlated with a 95% coefficient of determination (R2). We can calculate the water level using the audio data with the exponential regression function, as long as there is some water in the stream. This work demonstrates the possibility of an audio sensor to obtain reliable water level data in an IRES and offers a legitimate alternative to conventional measuring methods. This technological advance offers a new affordable, accessible tool that can be widely used and thus increase monitoring of the flow of IRES at a large scale.&nbsp

Durch den Klimawandel verändern sich die Abflussmengen sowie die Abflussverteilungen in der Schweiz. Abflussveränderungen im Niedrigwasserbereich haben Auswirkungen auf den Niedrigwasserindikator Q347, der nach dem Gewässerschutzgesetz (GSchG) als Richtwert zur Herleitung von Restwassermengen dient. In der vorliegenden Studie zeigen wir anhand von vier exemplarischen Laufkraftwerken, wie sich ein veränderter Q347-Wert auf die Restwasserbestimmungen und auf die Wasserkraftproduktion bei einer Neukonzessionierung auswirkt. Eine Veränderung des Q347-Werts bedeutet laut Artikel 31 GSchG eine Veränderung der Restwassermenge, die jedoch von einem 1:1-Zusammenhang abweicht: Bei einer Zunahme von Q347 nimmt die Restwassermenge weniger stark zu. Bis Ende Jahrhundert wird für höhergelegene Kraftwerke (> 2000 m ü. M.) ein höherer Q347-Wert erwartet, was bei einer Neukonzessionierung eine höhere Restwassermenge bedeuten würde. Für tiefergelegene Kraftwerke (< 1500 m ü. M.) nimmt Q347 ab und somit auch die Restwassermenge. Eine Abschätzung zu- künftiger Produktionsveränderungen kann jedoch nicht aufgrund der Veränderung des Grenzwerts Q347 hergeleitet werden, sondern erfordert die Berücksichtigung des gesamten für die Wasserkraft nutzbaren Abflussvolumens. Für zukünftige Produktionsveränderungen spielen die Restwasserbestimmungen eine untergeordnete Rolle, entscheidend sind primär die klimabedingten Abflussveränderungen sowie die Ausbauwassermenge eines Kraftwerks., Le changement climatique modifie les volumes d’écoulement ainsi que la répartition des débits en Suisse. Les modifications de débit en période d’étiage entraînent des répercussions sur l’indicateur d’étiage Q347 qui, selon la Loi sur la protection des eaux (LEaux), sert de valeur de référence pour la détermination des débits résiduels. Dans la présente étude, nous utilisons quatre exemples de centrales au fil de l’eau pour montrer comment une modification de la valeur Q347 se répercute sur les dispositions relatives aux débits résiduels et sur la production hydroélectrique dans le cas d’une nouvelle concession. Selon l’article 31 de la LEaux, une modification de la valeur Q347 implique une modification du débit résiduel, qui s’écarte toutefois d’une relation 1:1 : si Q347 augmente, le débit résiduel augmente moins fortement. D’ici la fin du siècle, on s’attend à une valeur Q347 plus élevée pour les centrales situées à plus haute altitude (> 2000 m), ce qui signifierait un débit résiduel plus élevé en cas d’octroi d’une nouvelle concession. Pour les centrales situées à une altitude inférieure (< 1500 m), Q347 diminue et donc aussi le débit résiduel. Cependant, une estimation des futurs changements de production ne peut pas être déduite sur la base de la modification de la valeur limite Q347, mais nécessite la prise en compte de l’ensemble du volume d’écoulement utilisable pour la force hydraulique. Pour l’évolution future de la production, les dispositions relatives aux débits résiduels ne jouent qu’un rôle secondaire. Ce sont en premier lieu les modifications des débit inhérentes au climat ainsi que le débit équipé d’une centrale qui sont déterminants.

Spatiotemporal information on water resources and their dynamics is essential for evidence-based decision making to support sustainable water management, particularly under environmental changes and competitive water uses. This study investigates the integration of satellite remote sensing (SRS) data with spatially explicit hydrological modelling to report on water resources at multiple scales in the Volta River basin (VRB) in West Africa. The Water Accounting Plus (WA+) framework is used as a standardized reporting framework to present water conditions and management practices, explicitly accounting for interactions between water and land use. The fully distributed mesoscale Hydrologic Model (mHM), spatially calibrated with multiple SRS products, is forced with a large ensemble of climate change projection data under the representative concentration pathway RCP8.5. Changes in water resources over the historical baseline period 1991-2020 and the near-term future 2021-2050 are investigated across multiple spatial domains including four climatic zones, four sub-basins and six riparian countries.Results indicate that water availability is projected to increase in the near future due to the increase in rainfall, along with higher inter-annual variabilities, thereby highlighting the need for adaptation strategies to optimize the water-energy-food-ecosystem nexus in the VRB. The proposed integrated modelling framework shows a good potential in supporting evidence-based decision and policy making for sustainable water management in large river basins., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The transition towards decarbonized power systems requires accounting for the impacts of the climate variability and climate change on renewable energy sources. With the growing share of wind and solar power in the European power system and their strong weather dependence, balancing the energy demand and supply becomes a great challenge. We characterize energy compound events, defined as periods of simultaneous low renewable production of wind and solar power, and high electricity demand. Using a logistic regression approach, we examine the influence of meteorological and atmospheric drivers on energy compound events. Moreover, we assess the spatial coherence of energy compound events that pose a major challenge within an interconnected power grid, as they can affect multiple countries simultaneously. On average, European countries are exposed to winter energy compound events more than twice per year. The combination of extremely low temperatures and low wind speeds is associated with a higher probability of occurrence of energy compound events. Furthermore, we show that blocked weather regimes have a major influence on energy compound events. In particular, Greenland and European blocking lead to widespread energy compound events that affect multiple countries at the same time. Our results highlight the relevance of weather regimes resulting in synchronous spatial energy compound events, which might pose a greater risk within a potential fully interconnected European grid.