Mountain hydrology faces a number of specific challenges, such as the high spatial variability of conditions and processes in horizontal and vertical dimension, and the comparatively low density and limited representativity of hydrometeorological observation networks. Vít Klemeš (1990) characterized these challenges very pointedly when he noted that mountainous areas, despite their hydrological importance, represent “some of the blackest black boxes in the hydrological cycle”.

In the meantime, our knowledge about mountain hydrology has improved considerably, although the challenges can still be characterized as greater than for most lowland regions. Also, global hydrological models have become a research field in their own right since the time of Klemeš’ statement, and even though these models face similarly increased challenges in mountain regions, they can be useful for studying mountain regions and their water resources in a larger context. In addition, valuable information can be extracted from an overview of regional studies, as has been done, for example, in the mountain-specific parts of the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate and the IPCC Sixth Assessment Report.

This contribution will discuss a comprehensive view from the mountains looking downstream, with a focus on the importance of mountain water resources for the lowlands.

Reference

Klemeš V, 1990. Foreword. In: Molnár L, ed. Hydrology of Mountainous Areas. Proceedings of a workshop held at Strbské Pleso (Czechoslovakia), June 1988. IAHS Publication 190, IAHS, Wallingford, ISBN 0-947571-42-6, p. 7

How to cite: Viviroli, D.: Mountain water resources and the importance of looking downstream, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1408, https://doi.org/10.5194/egusphere-egu23-1408, 2023.

Hydrological models are currently used to simulate the water cycle at the catchment scale using climatic forcing. For water management purposes, one of the most important components to be determined is drainage. The estimation of drainage into an aquifer is directly related to the water input (precipitation), the outputs through evaporation and transpiration, and water flow dynamics in the unsaturated zone. The output fluxes are difficult to estimate through direct measurements and are often estimated using mathematical models build on climatic processes and data. Amongst the climatic data that are used, solar radiation is a key parameter since it estimates the energy available for open surface or soil evaporation and plant transpiration. Solar radiation can be computed directly knowing the sun’s position, provided by satellite surveys (with a spatial resolution down to 6x6km² and a time resolution of one hour) or interpolated from values measured at meteorological stations. Values based on observations should be preferred because direct computation is strongly biased due to the effects of weather conditions (cloud for example). In mountainous regions, the orientation of the hillslope regarding the sun's position can strongly impact the amount of solar energy arriving on the canopy or the soil.

The questions we address in this communication are the following: when applying physically based hydrological models to mountainous regions, is it really necessary to consider the potential sky obstruction due to the mountainous terrain of each grid cell to assess solar radiation? By rebound, does this strongly impact the estimation of evapotranspiration and water drainage to the aquifer?

To answer these questions, a mixed methodology that relies on two steps is proposed and tested. The first step consists of a theoretical computation of solar radiation for each grid cell of a given Digital Elevation Model using GIS tools. The second steps aim at correcting the first step computations to be consistent with measured or satellite data. For the first step, the (Scharmer, Greif 2000) model - which computes the 3 components of global radiation (direct, diffuse, and reflected by surrounding surfaces for clear sky conditions) – is used. The model also considers the local terrain to estimate the sky obstruction. In the second step, the data are averaged at the scale of the prescribed data (satellite or interpolated) and linearly corrected with a proportionality coefficient so that the average computed value fits the prescribed average value.

This methodology is then applied to a water catchment in the Vosges Mountains located close to Strasbourg (France). The proportionality coefficient varies locally between 0.2 and 2.5 showing that the local impact of topography on radiation is very significant. Using this correction coefficient in the Penman-Monteith formula, the relative difference in evapotranspiration is respectively -80% and +180% from the mean value for shaded areas and sunniest areas. For water drainage estimated through a conceptual model, the relative differences vary from -20% for the most exposed areas to +20% for the less exposed areas, demonstrating that orientation should be accounted for when simulating the response of mountainous watersheds.

How to cite: Luttenauer, D., Weill, S., and Ackerer, P.: Impact of mountain topography on potential evapotranspiration and water drainage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-982, https://doi.org/10.5194/egusphere-egu23-982, 2023.

In snow-dominated regions, snowmelt water plays a critical role in recharging the subsurface and generating streamflow. With a changing climate, the fraction of annual precipitation that falls as snow will probably decline. Rainfall and snowmelt water have different interactions with the subsurface and potentially vegetation, thus affecting the partitioning of precipitation into subsurface storage and streamflow. Currently, our understanding of how snow-to-rain transition affects this hydrologic partitioning in mountainous catchments is still limited. To take the best management practices for climate change adaptation, it is of critical importance to study how a catchment responds to such environmental disturbances.

In this study, we use the geophysics-informed hydrologic modeling to study the effect of snow-to-rain transition on hydrologic partitioning in a snow-dominated mountainous catchment in Idaho, USA. In the modeling, the subsurface structure was extracted from velocity map obtained from seismic refraction tests. Many studies has highlighted the importance of the heterogeneous subsurface in water partitioning in catchments, but accurate characterizations with traditional field techniques such as drilling are challenging. The hydrologic model developed from geophysical results is then calibrated with historical hydrometeorological measurements. Two climate change scenarios are designed to study the impact of warming on streamflow generation and water storage. In Scenario 1, a uniform warming is considered throughout the year, and an air temperature increase (+2.5 °C) is applied to change the phase of precipitation. In scenario 2, warming is only applied to the snow season (i.e., from December to April). The numerical modeling results show that a uniform warming (scenario 1) significantly promotes evapotranspiration (ET), and streamflow becomes less productive. Warming in the snow season only (scenario 2) induces an earlier, flashier streamflow but the partitioning of precipitation between storage and streamflow is not significantly changed. Compared to simulation results from traditional hydrologic modeling (without the heterogeneous deep subsurface), geophysics-informed hydrologic modeling reveals the importance of water storage in the fractured bedrock in response to the climate change.

How to cite: Chen, H. and Niu, Q.: Effect of snow-to-rain transition on precipitation partitioning in a mountainous catchment: insights from geophysics-informed hydrologic modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2920, https://doi.org/10.5194/egusphere-egu23-2920, 2023.

Tropical Alpine Ecosystems are high-altitude grasslands located above 3000 m.a.s.l. along the tropical belt of three continents. Their unique vegetation and soil characteristics, in combination with low temperature and abundant precipitation, create the most advantageous conditions for regulating and storing surface and groundwater. However, increasing temperatures and changing patterns of precipitation due to greenhouse-gas-emission climate change are threatening these fragile environments, reducing their extent and modifying their altitudinal distribution range. Here, we investigate the impact of climate change on the distribution and extent of global Tropical Alpine Ecosystems. We use an ensemble of historical and projected climate data (SSP585) from seven General Circulation Models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to estimate annual average values of temperature and annual accumulated values of precipitation for reference (1985-2014) and far future (2070-2100) 30-year periodos. We produced the 95% probability current and future hydroclimatic spaces for every ecosystem to determine the range at which Tropical Alpine Ecosystem currently thrives in the climatic space, and investigate a number of hydroclimatic variables. Then, we used the projected climate time-series data to assess the current Tropical Alpine Ecosystem areas that will be unable to keep up with the temperature and precipitation changes by exceeding their reference climatic boundaries in the far future. Overall, our results showed that the Tropical Alpine ecosystem would drastically reduce its extent. Approximately 45% of its current extent will experience hydroclimatic conditions beyond their reference climatic boundaries. For example, the Ethiopian montane moorlands in Africa will be the most impacted ecoregion with a reduction of approximately 95% of its current extent. For the case of páramos in the North of the South American continent, increasing temperatures and changing precipitation will render ~50% of the current extent unsuitable for these ecosystems during the dry season. Our results highlight the magnitude of the impacts of climate change on Tropical Alpine Ecosystem and the vulnerability of water security of millions of people who depend on its ecological functioning. These results also have implications for biodiversity conservation, as endemic species will be threatened by habitat reduction and shifts in their distribution ranges.

How to cite: Jaramillo, F., Rubiano, K., Clerici, N., and Sánchez, A.: Tropical Alpine Ecosystems under climate change: Paramos and moorlands in peril, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13389, https://doi.org/10.5194/egusphere-egu23-13389, 2023.

Water resources availability is one of the main concerns for policy makers around the World. In the Mediterranean basin, this problem has been increased given the extreme variability in climate and the land use changes that have occurred during the last century (i.e. land abandonment). Streamflow and other environmental variables related to vegetation have been analysed in three Mediterranean mid-mountain basins under conditions of Climate Change (CC), under conditions of Land Use Change (LUC) and under its Combined Action (CA). The Land Use changes have been defined in the framework of the Life MIDMACC project and are related to land management through shrubland cleaning activities in abandoned fields and forest management that is determined by a 50% decrease in tree density in a forest community.

Three basins (Leza, Estarrún and L'Anyet) have been simulated using the Regional Hydro-Ecologic Simulation System (RHESSys) for the periods 2035-2064 and 2070-2099. The aim of the study is to determine the impacts of climate change and land management on both streamflow and other variables such as Net Primary Production or Potential Evapotranspiration in these basins (representative of Mediterranean mid-mountains) in order to analyse how the management proposed can be used to adapt these basins to climate and whether it is capable of mitigating the forecast reduction in streamflow associated with climate trends.

The results with LUC reveal a clear positive trend, increasing the streamflow in the basins of Leza and L'Anyet rivers (+9.76% and +4.70%) and slightly decrease (-0.13%) in Estarrún river due to the limited area to be managed. The combined action (CA) shows, in general, an attenuation in the clear negative trend of streamflow under climate change (CC) conditions. This suggests that the land management proposed in the LIFE MIDMACC project could help the adaptation of Mediterranean mid-mountain basins to climate change and the mitigation of its effects.

Acknowledgements: This research project was supported by the Life MIDMACC project ((LIFE18 CCA/ES/001099)) project funded by the European Commission. Melani Cortijos-López is working with an FPI contract (PRE2020-094509) from the Spanish Ministry of Economy and Competitiveness associated to the MANMOUNT project. Manel Llena has a “Juan de la Cierva Formación” postdoctoral contract (FJC2020-043890-I/AEI/ 10.13039/501100011033) from the Spanish Ministry of Science and Innovation.

How to cite: Zabalza-Martínez, J., Nadal-Romero, E., Llena, M., Cortijos-López, M., Lasanta-Martínez, T., López-Moreno, J. I., Vicente-Serrano, S. M., Pascual, D., and Pla, E.: Could land management modify water resources in Mediterranean mountain areas?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7013, https://doi.org/10.5194/egusphere-egu23-7013, 2023.

Streamflow seasonality in mountain regions is besides climate often shaped by reservoir regulation. Such regulation is particularly important in the Alps where meltwater from glaciers and the snowpack are captured in reservoirs to generate hydropower during the winter season. While reservoirs affect streamflow seasonality, information on past seasonal reservoir operation patterns is rarely publicly available. Consequently, little is known about spatial variations in reservoir storage and release signals in dependence of climate and catchment characteristics. Here, we develop a generalized additive modelling approach to reconstruct daily and seasonal reservoir patterns from observed streamflow time series that encompass a period before and a period after a known year of reservoir construction.

We apply this approach to reconstruct the seasonality of reservoir regulation, i.e. information on when water is stored in and released from a reservoir, for a dataset of 74 regulated catchments in the Central Alps. Using these reconstructed seasonal regulation patterns, we identify groups of catchments with similar reservoir operation strategies using functional clustering. We find that reservoir management varies by catchment elevation. Seasonal redistribution from summer to winter is strongest in high-elevation catchments, where reservoirs are mostly used for hydropower production, while seasonal redistribution is much weaker in the downstream regions, where reservoirs are used for a range of different purposes. The clear relationship between reservoir operation and elevation has practical implications. First, these elevational differences in reservoir regulation can and should be considered in hydrological model calibration. Furthermore, the reconstructed reservoir operation signals can be used to study the joint impact of climate change and reservoir operation on different streamflow signatures, including extreme events. Last, the potential of regulation as a climate adaptation measure may vary for the high-elevation and downstream regions.

How to cite: Brunner, M. I. and Naveau, P.: Disentangling reservoir regulation patterns from natural streamflow in the Alps and their downstream regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1948, https://doi.org/10.5194/egusphere-egu23-1948, 2023.

The Andes are among the regions most affected worldwide by water insecurity with an increasing number of vulnerable people. Particularly seasonally dry regions such as the Bolivian-Peruvian Altiplano and the Dry Andes of Central Chile and Western Argentina exhibit considerable water stress due to increasingly adverse impacts from climate and land use changes, and growing water demand.

Adaptation to changing water availability is therefore a priority, but systematic scientific and diverse knowledge on adaptation policies and experiences has barely been documented for the Andean region. Here we present the first comprehensive assessment of climate change adaptation in the entire Andes for different adaptation types (management and planning, monitoring system, nature-based solutions, grey infrastructure, financing, and awareness and behaviour) and policies (climate change law, glacier law, Nationally Determined Contributions). This study is based on work contributed to and recently published in the IPCC’s Sixth Assessment Report, Working Group II (Chapter 12: Central and South America).

In the last two decades, several policies on climate change, water protection, regulation and management laws for adaptation in the mountain water sector have been implemented. The first Framework Law on Climate Change was implemented in Peru (2018) and is under way in Colombia, Chile and Venezuela. One milestone represents the Glacier Protection Law in place in Argentina (2010–2019) and under construction in Chile (since 2005). Furthermore, new water laws that include principles of integrated water resource management have entered into force, for example, in Peru (2009) and Ecuador (2014), or are under way in Colombia (since 2009). However, current realities in the Andes show major challenges in implementing integrated and sustainable water management mechanisms and policies. These are related but not limited to political and institutional instabilities, governance structures, fragmented service provision, lack of economies of scale and scope, corruption and social conflicts.

Although a growing body of climate change adaptation-related policies and initiatives exist for the Andes, evidence on their effectiveness is scarce. In many parts of the region the level of success of adaptation measures depends largely on the governance of projects and stakeholder-based processes and is closely related to their effectiveness, efficiency, social equity and sociopolitical legitimacy. Examples of successful implementation linked to e.g. watershed protection include water funds (e.g. Quito, Ecuador) and stakeholder platform processes (e.g. Moyobamba, Peru). Even less evidence has been reported for limits of adaptation or maladaptation experiences in the water sector. Most barriers to advance adaptation in the Andes are associated with missing links of science–society–policy processes, institutional fragilities, pronounced hierarchies, unequal power relations and top-down water governance regimes.

Adaptation gaps could be bridged by strengthening transdisciplinary research at the science-policy interface with blended bottom-up and top-down approaches in locally tailored adaptation agendas. Recently, the inclusion of indigenous and local knowledges in current adaptation baselines has attracted increasing attention, particularly in regions with a high share of indigenous peoples, such as Ecuador, Peru and Bolivia. Important questions centre around how to integrate diverse knowledge from the early planning stages on, to achieve enhanced or transformational adaptation building on co-produced knowledge.

How to cite: Huggel, C. and Drenkhan, F.: Assessment of climate change adaptation to improve water security in the Andes: current policies, remaining gaps and future opportunities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11312, https://doi.org/10.5194/egusphere-egu23-11312, 2023.

The Himalayan cryosphere is shrinking at an accelerating rate. This alarming trend is accompanied by more frequent natural hazards that threaten exposed mountain communities. Problems range from damages of irrigation canals and eroded fields to massive destruction of human habitat. Predicted changes in meltwater supply, modelled under the generic term ‘peak water’, require greater and concerted effort to understand and support local adaptation strategies to cope with experienced and predicted water scarcity. Regional development processes are further characterised by rapid and largely unplanned urbanisation, infrastructure development and related environmental degradation exacerbating risks for large numbers of people already affected by climate change. To meet these grand challenges, an interdisciplinary research perspective is needed for the Himalayan region based on the integration of natural and social sciences. Therefore, an improved understanding of socio-hydrological pathways is necessary to capture local and regional particularities and dynamics, including cryosphere changes, glacio-fluvial runoff, socioeconomic processes, indigenous environmental knowledge, and external development interventions. Based on a long-term study conducted in the Trans-Himalayan region of Ladakh, we explore the role of land use changes, water harvesting infrastructures, including implementation of ice reservoirs (so-called “artificial glaciers”) and construction of improved irrigation networks. Furthermore, the role of social institutions ranging from village to non-governmental organizations and state-sponsored development programs are considered. The presentation uses the case study of Ladakh to develop a grounded socio-hydrological framework for the fragile Trans-Himalayan region that may be used as a basis for sustainable development pathways.

How to cite: Nüsser, M., Brombierstäudel, D., Soheb, M., and Schmidt, S.: Socio-hydrological pathways: Cryosphere changes and adaptation strategies in the Trans-Himalaya of Ladakh, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15315, https://doi.org/10.5194/egusphere-egu23-15315, 2023.

Mountain regions supply around 22% of the world's population with freshwater — from precipitation over these water towers to melt water from snow packs and glaciers. However, the frozen reservoirs of water that usually act to buffer precipitation deficits are diminishing as a result of climate change. As a consequence, precipitation will become the main source of freshwater supplied by these water towers. Yet, already today, precipitation deficits over many water towers frequently cause severe droughts that further induce supply deficits in downstream regions. 

Here, we unravel the origins of precipitation over the most important water towers worldwide and illustrate their dependency on upwind land regions. Using a moisture tracking framework constrained by satellite observations, we disentangle the local and remote surface drivers of drought over these water towers and highlight the role of forested and irrigated regions during these events. Our results indicate that many water towers can self-sustain their precipitation during drought events through an increased self-supply of moisture for precipitation: over the water tower of the Ganges-Brahmaputra, for example, around 80% of the precipitation during drought events is supplied by the water tower itself and its dependent downstream region. Our findings highlight the vulnerability of the world's most important water towers to drought from an atmospheric perspective and outline the potential of localized forest and land management practices to secure freshwater to billions of people in the future.

How to cite: Keune, J. and Brunner, M.: Unravelling the origins of precipitation over the world’s water towers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1746, https://doi.org/10.5194/egusphere-egu23-1746, 2023.

The stable isotopes of water, ¹⁸O and ²H, are impacted by climatic events that give them a distinct fingerprint of their source. Investigating the origin of river water requires this fingerprint as a precursor. On an annual basis and at the global level, the flow of moisture from the oceans and its return via rainout and runoff is similar to a dynamic equilibrium. Rivers in the Himalayan region have their moisture source in various end members which include glacier/snow melting, rainfall/runoff, and groundwater/springs. Sutlej River is one such river that travels across the Himalaya and receives its waters from all the aforementioned regions. 105 water samples from 36 different locations have been collected from the Upper Sutlej River Basin in the pre-monsoon, post-monsoon, and lean seasons to study the isotope system of surface water in the basin. A seasonal cycle with high δ¹⁸O and δD values (‰) during the pre-monsoon (March to May; −14.42, −114.94), intermediate values during the winter (lean season) (December to February; −12.63, −105.10), and low values during the post-monsoon (October to November; −12.13, −101.6) is observed. The river falls in the western Himalaya that receives precipitation both from the Indian Summer Monsoon (ISM) as well as from the Western Disturbances (WDs). The intercept and the d-excess values in the water samples fluctuate due to the variable contributions from these two moisture sources and the related rainfall in different seasons which are generally higher than the global meteoric waters. The 168-hour back trajectories in different seasons using HYSPLIT model converging at a height of 4,200 m a.s.l. (mean elevation of the Upper segment of the catchment) for moisture source identification have shown that winds mainly blow from south or south-east with moisture source from the Arabian Sea and the Bay of Bengal in summer and monsoon seasons, whereas in winter and spring seasons winds blow mainly from the west bringing moisture from the Central Asian and Eurasian water bodies through Western Disturbances. The results of HYSPLIT model and isotopic analysis indicate a dominant contribution of Western Disturbances and glacier melt in the upper segment of the basin which is consistent with recent data on glacier retreats in the Himalayan region.

Keywords: Himalayan Rivers, Sutlej River, Stable Isotopes, Western Disturbances, Indian Summer Monsoon.

How to cite: Sharma, K., Gupta, A. K., Tiwari, S. K., and Chatterjee, N.: Seasonal variation in stable isotope compositions of surface waters from Upper Sutlej River Basin: Estimation of the moisture source, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1676, https://doi.org/10.5194/egusphere-egu23-1676, 2023.

High mountains, which exhibit alpine and subalpine characteristics, represent 15% of the earth’s land area and are estimated to contribute about 17% of global runoff. Depending on hydrogeological setting, a significant amount of catchment water can be stored in high mountainous underground as groundwater, which can contribute substantially to streamflow and represent an important water source. However, high-alpine catchments are often characterized by great geological complexity and highly heterogeneous hydraulic properties. For that reason, proper system characterization, monitoring and modeling remain challenging. In this study, we investigated a geologically complex alpine catchment in the Dolomites (Italian Alps) by combining hydrogeological investigation, hydrological monitoring and numerical modelling. A process based but spatially lumped hydrological model was applied to simulate the continuous measured catchment discharge in a period of three years, which covers a large variation of hydrodynamic conditions. The current model structure couples the sequential hydrogeological units within the studied catchment: (1) the fractured dolomitic rocks as bedrock aquifer and 2) the unconsolidated deposits accumulating on the slopes and at the valley floor as porous aquifer. In order to evaluate the model structure and parameterization in depth, we applied a multi-step evaluation approach considering both parameter sensitivity and uncertainty. The current modelling results demonstrate that the newly developed model can reproduce most discharge behavior of aquifers. The model indicates a dynamic linkage between surface and subsurface storage units during different flow conditions. Besides the matrix and conduit flow in fractured dolomitic aquifer, it highlights the important role of unconsolidated sediments (porous aquifer) to the storage and discharge behavior of the entire groundwater system. Furthermore, with the comprehensive model evaluation we learned the model structure deficit during extreme high flow condition and proposed a more detailed hydrogeological conceptual model to improve the model realism.

How to cite: Chen, Z., Lucianetti, G., and Hartmann, A.: Understanding collective behavior of bedrock and porous aquifers and their contribution to the total water storage and discharge dynamics of a high mountainous catchment – Dolomites, Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8899, https://doi.org/10.5194/egusphere-egu23-8899, 2023.

A limitation in generating reliable projections of the impact of climate change on subarctic glacierized watersheds is a lack of understanding of the involved processes. While glaciers are often the targets of glacierized watershed research, glaciers are only one of the many features controlling headwater hydrology. Recent studies suggest that the contribution and evolution of other hydrological components under climate change conditions, as well as their interactions with groundwater and surface runoff, must be considered to fully predict future climate change impacts. For example, rock glaciers are recognized for their hydrogeological significance, but their hydrologic processes remain understudied. We present a research program focused on a 5 km² glacier and rock glacier continuum in the upper section of Shar Ta Gà’ (Grizzly Creek) in the Kluane First Nation territory, Yukon, Canada. The continuum is characterized by the absence of an apparent surface hydrology outlet and no substantial groundwater exfiltration has been detected in the Shar Ta Gà’ River situated directly downstream of the rock glacier. Some diffuse groundwater seepages have been mapped but their yield represent a fraction only of the volumes that are expected from the glacier drainage area.

We apply a multimethod approach (including geophysics, hydrochemistry, and UAV based surveying) to characterize the hydrological and hydrogeological behavior of the Shar Ta Gà’ rock glacier in a context where drilling is prohibited. Here we present results from a distributed hydrologic monitoring network of extreme precipitation events that occurred between 2018 and 2022. The network records water pressure, electrical conductivity, water temperature, hydrometeorological data and time lapse images. The results depict the rock glacier as a complex, multi-channel, evolutive hydrogeological system that collects water from upstream channels and from a porous surface. The water is distributed among different reservoirs and/or preferential channels. The rock glacier appears being a node in the hydrological and hydrogeological system, collecting the waters from the continuum and allowing their transfer to granular aquifers and possibly fractured aquifers.

How to cite: Charonnat, B., Baraer, M., McKenzie, J. M., Valence, E., and Masse-Dufresne, J.: Are rock glaciers preferential meltwater pathways to alpine aquifers?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10266, https://doi.org/10.5194/egusphere-egu23-10266, 2023.

The Himalaya is a massive cryospheric reserve, which provides a significant amount of fresh water to major Asian rivers like the Indus, Ganges, Brahmaputra, etc. Climate-induced cryospheric change is one of the major worldwide concerns, particularly in the Himalaya. Meltwater from glaciers and snow stabilises the downstream river runoff, and it buffers against drought during the driest years to some extent. The hydrological impact due to climate change in the high Himalayan catchments is potentially amplified by the shrinkage of snow and ice reserves. Therefore, it is important to analyse the potential hydrological changes at catchment to regional scales in the Himalaya. Hydrological changes at the regional scale are mainly determined by glacier catchment scale hydrology. Presently, understanding the regional scale discharge in the Himalaya suffers from large uncertainties, and one major source is the lack of glacier catchment scale hydrological understanding. Motivated by the above, here we are studying the glacio-hydrological characteristics of the Sutri Dhaka Glacier (debris-free glacier) catchment, which is located in the Chandra basin, western Himalaya. The glacierised area is ~20 km², and the total catchment area is ~45 km².

To the glacier catchment, we are applying an hourly timescale glacio-hydrological model to simulate discharge and the corresponding hydrograph components from 1980 to 2022. We also obtained extensive long-term field measurements of glacier mass balance, meteorological parameters, and discharge for the ablation season of 2016 to 2022 (with some gaps). These field data are used to calibrate the model parameters using a Bayesian framework and validate the simulated discharge and glacier mass balance. The simulated discharge variability from the diurnal to inter-annual time scale matches with the observations with reasonable accuracy (R²>0.75). Also, the model is able to capture the strong seasonality of the diurnal discharge amplitude, which has a direct relation to the storage-release properties of the glacier. Particularly, the diurnal discharge variability from the Himalayan glacier catchment is not well explored in the literature. We have also computed the associated uncertainties in the model as we as in the observations. Our present analysis will help to improve the existing process-based understanding of the glacier catchment scale discharge from the glacierised Himalayan region.

How to cite: Laha, S., Sharma, P., Oulkar, S. N., Patel, L., Pratap, B., and Thamban, M.: Hydrological characteristics of Sutri Dhaka glacier catchment in the western Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1662, https://doi.org/10.5194/egusphere-egu23-1662, 2023.

The hydrology of large mountainous basins is sensitive to climate and land use change and impacts downstream availability in a diverse way. Our knowledge of the spatial and temporal variation of the water balance for large-scale mountainous basins like the Karnali (40,000 km²) is very limited.  Studies focus either on small alpine catchments or on major river basins of near continental scale. Studies focusing on the intermediate scale, where mountain water supply is directly linked to people and ecosystems downstream are scarce, but needed. In this study, we provide insight into the seasonal and spatial differences in meltwater contribution to streamflow, rain runoff, evapotranspiration and groundwater baseflow, with a particular focus on upstream-downstream dependencies. We use a high-resolution SPHY model, which we calibrate step-wise using satellite data of glacier mass balance and snow covers and observed river flow data. We explore the hydrological variability at the sub-basin scale, discuss the seasonal and spatial heterogeneity of the water balance components, and seek to understand the major drivers. Our results provide a baseline against which impacts of climate and land use changes will be assessed in a subsequent study.

How to cite: Pokhrel, P., Griffioen, J., and Immerzeel, W.: Understanding the seasonal and spatial variation of water balance in the Karnali basin in Nepal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15451, https://doi.org/10.5194/egusphere-egu23-15451, 2023.

Mountain rivers are threatened by various natural and human-induced impacts, all of them potentially altering the availability of habitats for fish communities. These impacts include, among others, climate- change-associated reduction of discharge and water abstraction by humans, e.g., for hydropower production and irrigation. A quantitative assessment of future water, and subsequent fish habitat, availability is therefore pivotal to the effective and sustainable management of water resources in mountain basins.

In this work, we investigated the effect of climate change on discharge and fish habitat availability in two alpine catchments in the Western Italian Alps.

Historical discharge was modeled by means of a relatively simple rainfall-runoff model (TUWmodel), whereas discharge projections were computed under different state-of-the-art greenhouse gas scenarios both for the near future (2041-2060) and the far future (2080-2099). Discharge was then translated into habitat availability with the MesoHABSIM (Mesohabitat Simulation Model) methodology, an approach that allows to simulate the variations in habitat availability for the local fish population (brown and marble trout).

We found significant changes in future runoff, in turn leading to marked changes in fish habitat availability, with contrasting response in glaciated vs non glaciated basins.

We demonstrated that the combination of a hydrological model, climate scenarios and habitat modeling allows the depiction of future ecological scenarios for alpine rivers, thereby representing a potential support for water resources management and decision-making.

How to cite: Filippa, G., Vassoney, E., Viglione, A., Vezza, P., Negro, G., Mammoliti Mochet, A., and Comoglio, C.: The impact of climate change on fish habitat availability in mountain rivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7654, https://doi.org/10.5194/egusphere-egu23-7654, 2023.