HS2.1.6

The hydrological cycle is generally known as a recurring result of various forms of water movement and changes in its physical state in nature over a specific area of ​​the earth (river or Lake Basin, a continent, or the whole earth). It is most likely that the increase in global warming will intensively affect the hydrological cycle regionally and globally which will ultimately affect the ecosystem, public health, and municipal water demand. Therefore, the resiliency of watershed to extreme events play a vital role to understand the health of the watershed. This study aims to quantify the resiliency of the Hunza watershed, which lies in the Western Karakoram, to dry conditions under the climate change projections i.e. RCPs 2.6, 4.5, and 8.5. We used a fully distributed hydrological model SPHY to simulate the impact of climate change on future water availability. The SPHY Model was calibration and validation for the time periods (1994-2000) and (2001-2006) respectively. The performance of the model was tested through statistical analysis such as Nash-Sutcliffe efficiency (NSE), coefficient of determination (R²), percentage of bias (PBIAS), and root mean square error (RMSE).To develop future water scenarios, the daily temperature, and precipitation data were obtained from the CORDEX South Asia domain under three Representative Concentration Pathways (RCPs). The empirical quantile mapping method was used for the correction of the daily temperature and precipitation biases under the regional scale. The model was run for near (2007-2036), mid (2037-2066), and far-future (2067-2096) climate projections i.e. RCP2.6, RCP4.5, and RCP8.5. The resilience of watershed defined as the speed of recovery from dry conditions. The monthly Streamflow Drought Index (SDI) was used as an indicator of the dry condition. The resiliency of the watershed determines with the threshold levels of -0.5 and -1.0. The analysis indicates that the resiliency of the watershed has increased from 0.3 to 0.5 in the future under the RCP of 2.6. The value of resilience under the RCP of 4.5 is 0.29, 0.45, and 0.52 for near, mid, and far futures respectively. Under extreme climate conditions RCP 8.5, the watershed resilience is 0.2 in the near future and 0.3 in the mid-future, and 0.6 for the far future. Therefore, it can be concluded that the health of the reservoirs will be very good in the future to stabilize the drought.  

How to cite: Fatima, E., Rahim, A., ul Hasson, S., Hassan, M., Aziz, F., and Yousaf, M.: The Resiliency of High-Altitude Watershed to Dry Condition Under the Changing Climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-386, https://doi.org/10.5194/egusphere-egu21-386, 2021.

Mountain lakes are distinctive water bodies that not only serve as a crucial water resource for the inhabitants of the upland regions but also as an important destination for millions of tourists who are attracted by their beauty. Mountain lakes are fragile water bodies that are experiencing changes in their hydrological processes owing to global warming. Understanding the consequences is important as it can help identify whether climate change causes degradations in lake hydrological functioning. The interactions of hydrological processes in mountain lakes with external drivers are usually hard to explain explicitly owing to their complexity. To deal with that problem, scholars develop conceptual frameworks. The focus was on the Canadian Rocky Mountains where 5155 lakes were identified using GIS. To identify factors influencing lake hydrological function and their sensitivity to changing climate, a literature review was undertaken. Identified in the literature review were 13 natural drivers that reflected climate change impacts to lake hydrological functioning and 38 additional sub-factors that characterize the drivers. Using these factors, a conceptual framework for mountain lake hydrological functioning was developed. The major limitation to thorough testing of the conceptual framework was a small number of observations for lakes in the research area. Nevertheless, the conceptual framework is flexible and should be tested across many mountainous regions worldwide. Overall, the conducted research stresses the problem of limited hydrological understanding of lakes in the Canadian Rockies and presents a useful framework of the complex interactions of natural drivers and intra-lake processes under rising temperatures.

How to cite: Amaro Medina, D. and Westbrook, C.: Climate change impact on the hydrological functioning of the mountain lakes: a conceptual framework, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-998, https://doi.org/10.5194/egusphere-egu21-998, 2021.

Mountain watersheds often act as water towers that supply water to large human populations in valley aquifers. Therefore, their susceptibility and resilience to droughts are of outsize importance particularly, as global climate change projections suggest more frequent droughts in the future. Previous studies have examined the impact of climate warming on mountain hydrology, but they have not explicitly linked impacts of multi-year droughts to subsurface water storage. In this study, we use the 2012-2015 California drought to examine the mechanisms via which subsurface flow paths and storage affect the hydrologic response to drought in the Kaweah River watershed in the Sierra Nevada mountains. We build and test an integrated hydrologic model using the coupled land surface-groundwater model ParFlow.CLM. The model is able to simulate the observed hydrology with a high degree of accuracy. Results reveal that mountain aquifer recharge sourced from snowmelt (MAR_snow) is the primary input to the groundwater system, and much of the simulated streamflow. We find that increases in air temperature and decreases in precipitation during the drought reduces snow water equivalent (SWE), and causes a 73% reduction in MAR_snow compared to the pre-drought period. Reduction in MAR_snow initially results in subsurface storage losses along the ridgelines and areas of low topographic convergence. Topography induced draining of the regolith storage causes groundwater depletion and provides supplemental water to maintain streamflow and riparian evapotranspiration (ET). As the drought develops, drying of the subsurface alters lateral connectivity of the shallow groundwater system, and reduces streamflow and riparian ET. We apply machine learning models to examine the spatial patterns in groundwater storage depletion and recovery. These models reveal that topography induced draining and filling of subsurface storage in response to drought and precipitation recovery, respectively, is the key control on the streamflow response in this mountainous watershed. Warmer conditions and more frequent droughts that reduce SWE in the future are likely to amplify this cycle.

How to cite: Schreiner-McGraw, A. and Ajami, H.: Subsurface mechanisms control hydrologic response to a multi-year drought in a mountainous watershed with a Mediterranean climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1784, https://doi.org/10.5194/egusphere-egu21-1784, 2021.

Mountain System Recharge (MSR) is one of the main components of recharge in many arid and semi-arid aquifers, yet the mechanisms of MSR in high-elevation mountain ranges are poorly understood. The complexity of recharge processes and the lack of groundwater observations in mountain catchments contribute to this problem. MSR consists of two distinct pathways: 1) mountain bedrock aquifer recharge (MAR) consists of snowmelt or rainfall derived infiltration into the mountain bedrock, which either discharges to streams as baseflow or reaches an alluvial aquifer in an adjacent valley via lateral subsurface flow referred to as mountain block recharge (MBR), and 2) Mountain front recharge (MFR) consists of streamflow infiltration at the mountain front. Here, we apply streamflow recession analysis across 11 anthropogenically unaffected catchments in the Sierra Nevada to derive seasonally distinct storage-discharge functions and quantify MAR in response to changes in precipitation. Median annual recharge efficiencies (ratio of annual MAR to precipitation) range from 4 to 28% and can reach up to 60% during the wettest years on record. We implement a global sensitivity analysis to identify parameters that significantly impact MAR rates. Results illustrate that MAR estimates are mostly sensitive to the filter parameters for streamflow data selection used during the recession analysis, and the number of dry days after a rain event where streamflow data are excluded has the greatest impact. Our results demonstrate that storage-discharge functions are useful for quantifying groundwater recharge in mountainous catchments under perennial flow conditions. However, estimated MAR rates are impacted by the uncertainty in streamflow data, filtering of streamflow time series and model structure. Future work will be focused on quantifying uncertainty in MAR estimates caused from various sources.

How to cite: Ajami, H. and Schreiner-McGraw, A.: Quantifying Mountain Aquifer Recharge Rates Using Storage-Discharge Functions in the Sierra Nevada, California, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1921, https://doi.org/10.5194/egusphere-egu21-1921, 2021.

From snow-covered peaks to urban heat islands, this gradient, in its most concentrated form, is the essence of Alpine regions; it spans not only diverse ecosystems, but also diverse demands on water resources. Continuing climate change modifies the water supply and accentuates the pressure from competing water uses. Large Alpine lakes play hereby a key role, for water resource and natural hazard management, but surprisingly, are often only crudely modelled in available climate change impact studies on hydrology. Indeed, regulation of Alpine lake outlets, where daily specifications for lake level and outflow are defined, are the crux to bringing together diverse stakeholders. Ideally, a common regulation is agreed upon with an annual pattern that both corresponds to natural fluctuations and respects the different needs of the lake ecosystem, its immediate environment and upstream and downstream interests, such as fishery, shipping, energy production, nature conservation and the mitigation of high and low extremes. Surprisingly, a key question that remains open to date is how to incorporate these anthropogenic effects into a hydrological model?

To estimate climate change impacts, daily streamflow through this century was calculated with the hydrological model PREVAH, using 39 climate model chains in transient simulation from the new Swiss Climate Change Scenarios CH2018, corresponding to the three different CO₂ emission scenarios RCP2.6, RCP4.5 and RCP8.5. PREVAH is based on a 200×200 m grid resolution and consists of several model components covering the hydrological cycle: interception, evapotranspiration, snow, glacier, soil- and groundwater, runoff formation and transfer. In order to implement the anthropogenic effect of lake regulations, we created an interface for the hydrodynamic model MIKE11. In this work, we will present the two hydraulically connected Swiss lakes, Walensee (unregulated) and Zurichsee (regulated), that are located on the gradient between snow-covered peaks and urban environments. This catchment area was already affected by water scarcity in isolated years.

The hydrological projections at the end of the century show minor changes in mean annual lake levels and outflow for both lakes, but there is a pronounced seasonal redistribution of both level and outflow. The changes intensify over time, especially in the scenario without climate change mitigation measures (RCP8.5). In the winter, mean lake levels rise and outflow increases; in the summer, mean lake levels fall and outflow decreases. Walensee’s (unregulated) level change is significantly higher, with a difference of up to 50 cm under RCP8.5, than Zurichsee’s (regulated), which only changes around 5 cm; the changes in outflow are of the same order of magnitude in both lakes. The extremes show an increased frequency of reaching the drawdown limit, but no clear change in frequency of reaching the flood limit.

In order to estimate future hydrological developments on lakes and downstream rivers, it is important to use models that include the impact of such regulations. Hydrological models including anthropogenic effects allow a separation of climatic and regulatory impacts. Timely hydrological projections are crucial to allow the necessary time horizon for both lake and downstream interests to adapt.

How to cite: Wechsler, T., Inderwildi, A., Schaefli, B., and Zappa, M.: Between high mountain processes and urban needs: implementing lake regulations into a hydrological model to anticipate climate change impacts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2594, https://doi.org/10.5194/egusphere-egu21-2594, 2021.

Floods are the natural phenomenon that causes more victims worldwide and is probably the most devastating, widespread and frequent natural disaster in society. According to the IPCC, the frequency and magnitude of extreme flooding is likely to increase as a result of the water-holding capacity in a warmer atmosphere. An increase in flooding events requires the development of appropriate adaptation measures that are based on sound scientific knowledge and assessments based on the analysis of extreme flood events, in order to carry out hazard zoning and design of structural and non-structural measures to reduce risk levels. 

Due to the above, different databases have been developed in Europe with documented information (affected areas and damage) and instrumental information (meteorological and hydrological records) that integrate the Geographic Information Systems (GIS), with the aim of providing an efficient way of representing the information and a useful tool for its analysis.

The PIRAGUA project addresses the characterization of the hydrological cycle in the Pyrenees region, which includes three countries, France (Nouvelle-Aquitaine and Occitanie), Spain (Basque Country, Navarre, Aragon, and Catalonia) and Andorra. This summary presents the main results for one of its objectives, which consists on the analysis of the impact of floods in the Pyrenees, especially on water resources, and the design of the most suitable adaptation strategies. In a first phase, a database of floods was developed, which includes meteorological data, caused impacts, affected areas and the classification of the event according to the impact (ordinary, extraordinary, and catastrophic) for all the Pyrenean massif covering the period 1981-2015, starting from different databases and information sources of each one of the regions. The results show that at the level of the massif there have been 181 flood events, of which 128 have affected Spain, 43 France and 46 Andorra. Of these, 34 have been cross-border and have affected more than one region. Similarly, trend analysis has shown an increase in flood events that have caused significant damage (extraordinary and catastrophic) due to an increase of such events in Aquitaine, Occitanie, Andorra and Catalonia.

On the other hand, all flood events have been characterized with pluviometric data from the daily rainfall gridded dataset generated by SAFRAN. This has made it possible to carry out a statistical analysis and identify the precipitation thresholds associated with the different types of floods. Similarly, SAFRAN has been used to corroborate the flood events in the database and identify possible flooding episodes not included in the historical records. These results and the identification of the municipalities that have historically been most frequently affected by flood events are a starting point for the analysis and creation of more efficient adaptation measures.

How to cite: Pardo, E., Llasat, M. C., Llasat-Botija, M., and Quintana-Seguí, P.: Analysis of flooding events in the Pyrenees and adaptation measures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5313, https://doi.org/10.5194/egusphere-egu21-5313, 2021.

The ongoing intensive deglaciation in high mountain areas is resulting in great instability of mountainous headwater regions, which could significantly extreme hydrological events In this research a model “chain” of hydrodynamic and runoff formation models is adopted to simulate a glacier lake outburst flood (GLOF) from Bashkara Lake, situated in headwater region of the Baksan River and its effect on the downstream.

Two-dimensional hydrodynamic model for the Adylsu River valley was developed, based on the STREAM_2D software (author V. Belikov). The ECOMAG runoff formation model (author Yu. Motovilov) for the entire Baksan River basin was adopted. The output flood hydrograph from the STREAM_2D model was set as additional input into the Baksan River runoff formation model in the upper reaches of the Adylsu River below Bashkara and Lapa Lakes.

Based on field surveys and remote sensing data, actual Bashkara Lake GLOF on September 1, 2017 was modelled. The GLOF event was triggered by extreme precipitation that caused overwetting of the dam and increase in the lake water level. The peak GLOF discharge according to modeling was estimated as 710 m³/s at the dambreak section and 320 m³/s at the Adylsu River mouth 40 minutes after the outburst. Two possible mechanisms for re-outburst of Bashkara Lake were taken into account: the rock avalanche impact, forming displacement waves, and the lake outburst due to increase in the water level, accompanied by expansion of the existing dam break. Under the rock avalanche scenario, there was no significant model response. Based on the results of modeling of the second re-outburst scenario, the maximum discharge of the outflow was estimated as 298 m³/s at the dambreak section and 101 m³/s in the Adylsu River mouth.

As a result of model chain application contribution of GLOFs and precipitation to an increase in peak discharge along the Baksan River was estimated. The actual outburst flood amounted to 45% and the precipitation - to 30% of the peak flow in the Baksan River at the mouth of the Adylsu river (10 km from the outburst site). In Tyrnyauz (40 km from the outburst site) the components of the outburst flood and precipitation were equalized, and in Zayukovo (70 km from the outburst site) the outburst flood contributed only about 20% to the peak flow, whereas precipitation - 44%.

Similar calculations were made for a potential re-outburst flood, taking into account expected climate changes with an increase in air temperatures by 2°С and an increase in precipitation by 10% in winter and decrease by 10% in summer. The maximum discharge of the re-outburst flood in the Adylsu river mouth according to modeling can be approximately 3 times less than discharge of the actual outburst on September 1, 2017 and can contribute up to 18% to peak discharge in the Baksan River at the confluence with the Adylsu river.

The Baksan River runoff formation model was developed under support of RFBR, project number 20-35-70024. The glaciation changes and climate impact scenarios analysis was funded by RFBR and the Royal Society of London (RS), project number 21-55-10003.

How to cite: Kornilova, E., Krylenko, I., Rets, E., Motovilov, Y., Bogachenko, E., Krylenko, I., and Petrakov, D.: Modeling impact of GLOF on the the Baksan River runoff (the Central Caucasus, Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7765, https://doi.org/10.5194/egusphere-egu21-7765, 2021.

The behaviors of flood runoff are related to the soil and geological conditions of basin as well as rainfall, basin scale, and topography. However, the effects of surface conditions on flood runoff in natural basins have not been sufficiently investigated until now. Under the situation of an increasing frequency of disasters due to heavy rainfall, it is important to clarify the contribution of basin conditions to flood runoff to enable flood control planning. The aim of this study is to investigate the relationship between flow duration curves mainly for flood runoff and the areal ratios of different types of soil and geology in the basin. We selected eight mountainous basins with areas from 103 to 331 km², located in regions of different topographical, geological, and climatological conditions in Japan. The one percentile flow duration curves out of more than 14 years at hourly time steps are used for evaluation. To clarify the properties of flow duration curves, the discharge into the dams, which means the runoff from basins, is shown as runoff height ( Q ), and are normalized, the highest value being, by dividing by the maximum runoff height (Qmax). The flow duration curves are approximated as straight lines on the log-log graph, and the relationships between the slopes and the areal ratios of the different types of soil and geology are shown as scatter plot graphs. The results indicate that the slope of flow duration curves focusing on flood runoff have correlations and significant differences with the areas of (a) Brown Forest soils, and (b) Neogene rock formation, and with the (c) the Andosols/volcanic rock formation ratio.

How to cite: Fujimura, K., Yanagawa, A., Iseri, Y., Murakami, M., Kanae, S., and Okada, S.: Flow duration curves focusing on flood runoff in relation to different distributions of soil and geology in mountainous basins in Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9716, https://doi.org/10.5194/egusphere-egu21-9716, 2021.

Glacierized catchments are of great importance for water supply sustaining diverse human livelihoods, economies, and cultures. Despite their importance, both glacierized headwaters and downstream areas remain poorly monitored. Nevertheless, a considerable amount of international and local research has dealt with hydrological models including different levels of complexity, data sources, and goals. In addition, the increasing availability of free software and powerful automatic model calibration tools facilitates the use of complex models even to non-expert users. As a result, models could show a good performance despite misconceptions. That is also true for the tropical Andes where low data availability and quality combined with large uncertainties on glacio-hydrological and meteorological processes prevail.

Accordingly, this study aims to identify if simple or more complex glacio-hydrological models can perform robust simulations for tropical glacier-fed basins combined with scarce data. The study case was carried out in the Sibinacocha (4,822 m a.s.l) and Phinaya (4,678 m a.s.l.) catchments, both located in the headwater of the Vilcanota-Urubamba river basin, in the Cusco region, Peru. These outer-tropical catchments are characterized by pronounced dry and wet seasons and hold a glacier extent of about 8 and 18%, respectively. Three conceptual models were implemented, in order of increasing complexity: 1) the lumped Shaman model (developed in this study), and the semi-distributed 2) HBV-light, and 3) RS Minerve. All simulations were implemented on a monthly time step from 1981 to 2010. Hydroclimatological data series were obtained from the gridded PISCO dataset at 10 km spatial resolution and two local weather stations. Furthermore, changes in glacier surface were delineated for three years (1986, 1994 and 2004) by using a semi-automatic NDSI approach based on satellite imagery. Finally, a comprehensive evaluation was performed using common measures of model performance, the associated flow signatures, and different runoff components.

Results show that all model complexities allow for an acceptable performance (R² > 0.65, Nash-Sutcliffe > 0.65, Nash-Sutcliffe-ln > 0.73) with small differences related to the model structure. However, more complex models require a more comprehensive calibration strategy and assessment to avoid simulations with apparently high model performance driven by inadequate assumptions. Moreover, more complex models require a better understanding of the underlying hydrological processes that is often hampered by data scarcity, limited knowledge and field accessibility in the Peruvian Andes. Results suggest that a careful calibration strategy, additional data collection, and the implementation of simple models can provide more robust simulations rather than opt for increasing model complexity. For robust hydrological modeling, a comprehensive assessment of the flow signatures and runoff components is pivotal. These findings have been incorporated into a framework that aims for expert and non-expert conducted robust glacio-hydrological simulation under data scarcity. Nevertheless, high uncertainty and limited knowledge hamper a more thorough process understanding and the improvement of related model results which illustrates the limitations of their predictive character. In such a context, additional data collection with local participatory approaches combined with policy-making for climate change adaptation and water management can benefit from approaches that support decision making under high uncertainty.

How to cite: Muñoz, R., Huggel, C., Drenkhan, F., Vis, M., and Viviroli, D.: Comparing model complexity for glacio-hydrological simulation in the data-scarce Peruvian Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10006, https://doi.org/10.5194/egusphere-egu21-10006, 2021.

Water scarcity is increasingly becoming a problem in many regions of the world. On the one hand, this can be attributed to changes in precipitation conditions due to climate change. On the other hand, this is also due to population growth and changes in consumer behaviour. In this study, an analysis is carried out for the highly glaciated Vilcanota River catchment (9808 km² – 1.2% glacier area) in the Cusco region (Peru). Possible climatic and socioeconomic scenarios up to 2050 were developed including the interests from different water sectors, i.e. agriculture, domestic and energy.

The analysis consists of the hydrological simulation at a monthly time step from September 2043 to August 2050 using a simple glacio-hydrological model. For historic conditions (1990 to 2006) a combination of gridded data (PISCO precipitation) and weather stations was used. Future scenario simulations were based on three different climate models for both RCP 2.6 and 8.5. Different glacier outlines were used to simulate changes in glacier surface through the time for both historic (from satellite data) and future (from existing literature) scenarios. Furthermore, future water demand simulations were based on the SSP1 and SSP3 scenarios.

Results from all scenarios suggest an average monthly runoff of about 130 m³/s for the Vilcanota catchment between 2043 and 2050. This represents a change of about +5% compared to the historical monthly runoff of about 123 m³/s. The reason for the increase in runoff is related to the precipitation data from the selected climate models. However, an average monthly deficit of up to 50 m³/s was estimated between April and November with a peak in September. The seasonal deficit is related to the seasonal change in precipitation, while the water demand seems to have a less important influence.

Due to the great uncertainty of the modelling and changes in the socioeconomic situation, the data should be continuously updated. In order to construct a locally sustainable water management system, the modelling needs to be further downscaled to the different subcatchments in the Vilcanota catchment. To address the projected water deficit, a new dam could partially compensate for the decreasing storage capacity of the melting glaciers. However, the construction of the dam could meet resistance from the local population if they cannot be promised and communicated multiple uses of the new dam. Sustainable water management requires the cooperation of all stakeholders and all stakeholders should be able to benefit from it so that they will support future projects.

How to cite: Meier, S., Munoz, R., and Huggel, C.: Impact of climate change on water availability in Tropical Andean catchments: a case study in the Vilcanota catchment, Peru, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10292, https://doi.org/10.5194/egusphere-egu21-10292, 2021.

Climate change has and will have many impacts on natural and human systems, and many of these impacts are already well described in the literature. One impact of climate change that received less attention is the increase in river temperature, even though it is recognized as a key variable controlling the water quality of freshwater ecosystems. It influences both the metabolic activity of aquatic organisms and biochemical cycles. It is also a key variable for many industrial sectors, and favorable for the spreading of certain diseases affecting fish.

In a previous study (Michel et al., 2020) we showed a clear increase of +0.33 ± 0.03 °C per decade in water temperature over the last four decades in Switzerland. Important differences between lowland and alpine catchment were identified. Indeed, the warming rate in alpine catchments is only half of that observed in lowlands rivers. This difference is attributed mainly to the contribution of cold water from snow and glacier melt in mountainous area during summer, mitigating the impact of air temperature warming.

As a follow up, the response of selected Swiss catchments in lowland and alpine regions to the future forcing is numerically assessed using the CH2018 climate change scenarios for Switzerland. This is done using a sequence of physics-based models. The CH2018 climate change scenarios have been extended to a new set of alpine meteorological stations and downscaled to hourly resolution (Michel et al., 2021).

The results show an increase in water temperature for any of the RCP (2.6, 4.5, and 8.5) scenarios and a strong impact of climate change on alpine catchments caused by changes in snowfall/melt, glacier melt, and surface albedo. Indeed, we see a rapid acceleration of the warming in alpine catchments which “catch-up” with the warming already observed in lowland catchments. This can lead to a warming of up to +7 °C by the end of the century in some alpine rivers with the RCP8.5 scenario. An important shift in the hydrological regime is also observed, particularly in high-altitude rivers.

As a result, river ecosystems will be severely impacted. In addition, the combined changes in water temperature and discharge have an important impact on the groundwater temperature annual cycle, as we discussed in Epting et al. (2021). Seasonal shifts in rivers water infiltration associated with increased groundwater recharge during high runoff periods could be an important factor affecting future groundwater temperatures.

REFERENCES

Epting, J., Michel, A., Affolter, A., & Huggenberger, P.: Climate change effects on groundwater recharge and temperatures in Swiss alluvial aquifers, Journal of Hydrology X, 11, 100071, 2021, doi:10.1016/j.hydroa.2020.100071.

Michel, A., Brauchli, T., Lehning, M., Schaefli, B., & Huwald, H.: Stream temperature and discharge evolution in Switzerland over the last 50 years: annual and seasonal behaviour, Hydrological and Earth System Science, 24, 115–142, 2020, doi:10.5194/hess-24-115-2020.

Michel, A., Sharma, V., Lehning, M., & Huwald, H.: Climate change scenarios at hourly time-step over Switzerland from an enhanced temporal downscaling approach, International Journal of Climatology, under review

How to cite: Michel, A., Epting, J., Lehning, M., and Huwald, H.: River Temperature Evolution in Switzerland over the 21st Century, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13001, https://doi.org/10.5194/egusphere-egu21-13001, 2021.

Glacier peak water describes the initial increasing and subsequent decreasing trend of glacier melt water as a response to global warming. The phenomenon might encourage excessive water use that cannot be sustained in the long-term. Knowing magnitude and time scale of its effect on streamflow trends and changes in partly glacierized catchments is therefore needed. This comparative regional study examined August streamflow records from 1976-2015 in the European Alps, Norway, Western Canada, and Alaska. It aimed to detect whether and when a peak was reached or passed and how strong decreasing post-peak streamflow trends were. A one-peak hypothesis could not be confirmed in many of the records and the variability of individual series' detected peaks and trends is large. Some common patterns in the timing of peaks and general trend directions in the records could be generalized. These suggest: a peak early in the period in Western Canada followed by mostly declining streamflow trends, pre-peak conditions in Alaska resulting in mostly positive streamflow trends, variable peaks in Norway and the Alps from the mid-1990s on with differences for low and highly glacierized catchments. Trends and peaks in climate-variability corrected August streamflow broadly related to phases of regional glacier retreat, but local variability is more complex.  Only weak systematic deviations were found related to catchment characteristics. This multi-record and multi-region comparison of streamflow observations suggests that knowledge on a regional phenomenon will need to be complemented with local monitoring and modelling to provide useful information for water resources planning.

How to cite: Stahl, K., van Tiel, M., and Moore, R. D.: Peak water in observed glacier-fed streamflow time series, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13065, https://doi.org/10.5194/egusphere-egu21-13065, 2021.

The vast majority (~70%) of tropical glaciers in the world are located in the Peruvian Andes. The Santa River Basin, in the Ancash region of Peru, is bound by two parallel mountain ranges; the Cordillera Blanca to the east and the Cordillera Negra to the west. The main water sources in the Cordillera Blanca are rivers and lakes originated from glacier melt, while the Cordillera Negra has no glaciers and depends on seasonal rainfall. In the last decades, water resources have decreased due to climate change, while demand has increased due to population growth and intensification of agricultural and industrial activities. Moreover, higher water levels in glacial lakes due to accelerated glacier melt has reduced their flood attenuation capacity that, along with other triggers of outburst floods, can have catastrophic consequences. One of the strategies adopted by the regional government is the construction of dams, floodgates and siphon drainage systems to reduce the risk of outburst floods. The lowering of lake water levels to provide flood attenuation conflicts with the need for increasing water regulation in the basin (to compensate glacier mass loss) and alters the natural downstream flow regime.

This study responds to the need for long-term planning of the major glacial lakes in the Santa River Basin to satisfy all water uses, including environmental ones, and contributing to flood reduction under alternative future climate change scenarios. We adopt a systems analysis approach with the support of the Water Evaluation and Planning system (WEAP) coupled with the hydro-glaciological model TOPographic Kinematic APproximation and Integration (TOPKAPI). They are driven by high-resolution climate projections from the Weather Research and Forecast (WRF) model for future emission scenarios and global climate models available in the CMIP5, for the period 2022-2050. The integration of these models allows representing the complex hydrology of the catchment, explicitly accounting for glacier mass change, and water resources management including the main lakes and water demands. A large spectrum of climate change and lake management scenarios are analysed with a no-regret approach using criteria related to the reliability of water supply for human demands and environmental flows, along with flood abatement and water scarcity. The results of this study that interface hydrology, water demands and infrastructures support local decision-making and exchange with stakeholders in the Santa River Basin, which will strengthen water security across water uses, fostering development and economic growth in the region.

How to cite: Celmi, G., Momblanch, A., Hess, T., Fyffe, C. L., Potter, E., Orr, A., Drenkhan, F., Walker-Crawford, N., Loarte, E., Bustamante, M. G., and Pellicciotti, F.: No-regret adaptation to climate change through management of glacial lakes in the Santa River Basin in Peru, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13369, https://doi.org/10.5194/egusphere-egu21-13369, 2021.

As a result of altitude and latitude amplified impacts of climate change, widespread alterations in vegetation composition, density and distribution are widely observed across the circumpolar north. The influence of this vegetation change on the timing and magnitude of hydrological fluxes is uncertain, and is confounded by changes driven by increased temperatures and altered precipitation (P) regimes. In northern alpine catchments, quantification of total evapotranspiration (ET) and evaporative partitioning across a range of elevation-based ecosystems is critical for predicting water yield under change, yet remains challenging due to coupled environmental and phenological controls on transpiration (T). In this work, we analyze 6 years of surface energy balance, ET, and sap flow data at three sites along an elevational gradient in a subarctic, alpine catchment near Whitehorse, Yukon Territory, Canada. These sites provide a space-for-time evaluation of vegetation shifts and include: 1) a low-elevation boreal white spruce forest (~20 m), 2) a mid-elevation subalpine taiga comprised of tall willow (Salix) and birch (Betula) shrubs (~1-3 m) and 3) a high-elevation subalpine taiga with shorter shrub cover (< 0.75 m) and moss, lichen, and bare rock. Specific objectives are to 1) evaluate interannual ET dynamics within and among sites under different precipitation regimes , and 2) assess the influence of vegetation type and structure, phenology, soil and meteorological controls on ET dynamics and partitioning.  Eddy covariance and sap flow sensors operated year-round at the forest and during the growing season at the mid-elevation site on both willow and birch shrubs for two years. Growing season ET decreased and interannual variability increased with elevation, with June to August ET totals of 250 (±3) mm at Forest, 192 (±9) mm at the tall shrub site, and 180 (± 26) mm at the short shrub site. Comparatively, AET:P ratios were the highest and most variable at the forest (2.4 ± 0.3) and similar at the tall and short shrub (1.2 ± 0.1).  At the forest, net radiation was the primary control on ET, and 55% was direct T from white spruce. At the shrub sites, monthly ET rates were similar except during the peak growing season when T at the tall shrub site comprised 89% of ET, resulting in greater total water loss. Soil moisture strongly influenced T at the forest, suggesting the potential for moisture stress, yet not at the shrub sites where there was no moisture limitation. Results indicate that elevation advances in treeline will increase overall ET and lower interannual variability; yet the large water deficit during summer implies a strong reliance on early spring snowmelt recharge to sustain soil moisture. Changes in shrub height and density will increase ET primarily during the mid-growing season. This work supports the assertion that predicted changes in vegetation type and structure will have a considerable impact on water partitioning in northern regions, and will also vary in a multifaceted way in response to changing temperature and P regimes.  

How to cite: Nicholls, E., Drewitt, G., and Carey, S.: Hydrological implications of vegetation change in a subarctic, alpine catchment, Yukon Territory, Canada, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13916, https://doi.org/10.5194/egusphere-egu21-13916, 2021.

The majority of the freshwater input from Greenland stems from the Greenland Ice Sheet. Despite its importance in terms of freshwater totals, there is a much higher number of individual catchments disconnected from the ice sheet contributing on average about 26% of the total Greenland freshwater flux. Most of those catchments have local glacier cover, only very few of them are instrumented and little scientific literature exists. We present a dataset of 12 years of discharge of four catchments less than 15 km apart, that are different in size (between 7 and 32 km²), local glacier coverage (4-11%) and lake cover (0-5%). They all drain into Kobbefjord, a well-studied fjord in West Greenland, near Greenland’s capital Nuuk. We find that annual specific discharge totals vary greatly (between 1.2 and 1.9 m/yr on a 12-year average within 15 km) due to a general climatic gradient and different strengths of orographic shading. The seasonal cycle differs among the sites mainly due to different exposure to solar radiation as a driver for major snowmelt; small ice coverage in the catchments plays only a minor role in discharge variability. Dry years generally increase the magnitude of spatial gradients in specific discharge and no significant temporal trends have been found in the studied catchments. On the sub-daily scale, the presence and elevation of lakes determines the catchment’s response during sunny days, leading to a difference in the timing of maximum discharge of between 7 and 12 hours depending on the site and the time of the year. The response of discharge to major precipitation events is discussed, where uniform reaction is found for the catchments with no lakes near the gauge and a delay of between 5 and 7 hours in the catchment with low-lying lakes. A comparison with a recently published modelled discharge time series on individual catchment scale shows the model’s capability of reproducing both snowmelt and large-scale storm events; however, the strong spatial heterogeneity of discharge magnitude and timing as well as the presence and variability of base-flow is not captured. We discuss methods to combine observational data with existing model output in order to improve the potential of their combined usage on the Greenland-scale.

How to cite: Abermann, J., Langley, K., Myreng, S., Petersen, D., Rasmussen, K., and Peßenteiner, S.: Freshwater input into a low-Arctic Fjord in West Greenland: Timing, drivers and model evaluation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14149, https://doi.org/10.5194/egusphere-egu21-14149, 2021.

Climate change is expected to have a significant impact on water resources in mountain areas, as it is the case of the Pyrenees range between France, Spain and Andorre. Independently of future changes on rainfall patterns, global temperature rise is likely to provoke larger and earlier snowmelt, and enhanced precipitation deficits during the dry summer season. Exploring the impacts of this future situation on groundwater is essential, as this resource is often important for drinking water, irrigation and breeding uses in mountain regions. However, studies on groundwater recharge in the context of climate change are relatively scarce, as compared to studies focusing on surface water resources.

We assessed potential groundwater recharge (part of effective precipitation that infiltrates and potentially reach the aquifers) over the Pyrenean range in the framework of the PIRAGUA project, a collaborative multi-national effort funded by the EU’s Interreg POCTEFA program. Based on a gridded (5x5 km²) meteorological dataset derived from observational data by the CLIMPY project, we estimated effective precipitation for each grid cell using a conceptual water balance scheme. The effect of the seasonal change of land cover / land use (based on the Corine Land Cover dataset) on the water budget model has been assessed, and showed the need to include this component for a more accurate simulation. Based on a spatial characterization of the land infiltration capacity, the potential groundwater recharge has been computed for homogeneous groundwater bodies. Results have been compared to the outputs of groundwater models applied on selected karstic catchments using the BALAN code, and to a general knowledge of groundwater recharge rates for different regions within the study zone. Finally, climate change impacts on future IDPR have been explored using scenarios provided by the CLIMPY project.

The Pyrenees range is a hot-spot for water resources with a tremendous impact over a much broader region in SW Europe, as Pyrenean rivers are fundamental contributors to large systems such as those of the Adour and Garonne (France) or Ebro (Spain), as well as smaller systems in the western and eastern sectors such as the Bidasoa (Spanish Basque Country), Llobregat-Ter-Muga (Catalonia), or Têt-Tech-Aude (France). Our results are relevant for the planning and management of water resources for this important transboundary region in the future, as changes in groundwater recharge will also affect water resources availability.

Acknowledgments: the project PIRAGUA, is funded by the European Regional Development Fund (ERDF) through the Interreg V-A Spain France Andorra programme (POCTEFA 2014-2020).

How to cite: Caballero, Y., Lanini, S., Le Cointe, P., Pinson, S., Hevin, G., Jódar, J., Lambán, J., Zabaleta, A., Antigüedad, I., and Beguería, S.: Groundwater recharge and groundwater water resources under present and future climate over the Pyrenees (France, Spain, Andorre), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16471, https://doi.org/10.5194/egusphere-egu21-16471, 2021.