The peak water concept has emerged to represent the trajectory of future water resources from glacierised basins, and has been widely adopted by the glaciology community. This is based on the notion that runoff from glaciers will increase up to a point in the near future and then decrease, because the melt rates of glaciers per unit area increase due to higher temperatures, while glaciers shrink. There is a point in the future that the glacier area becomes so small that the increase in melt rate per unit area cannot compensate for the area loss, and the absolute amount of glacier melt water starts to decrease. This peak water concept has been featured by several prominent papers and by the IPCC. However, we hypothesize that this peak water concept is an oversimplification of reality and can mask the real trajectory of changes in water resources from mountain catchments. It is only a valid concept for a single glacier, and the effect largely disappears when a mountainous catchment consists of multiple glaciers with different size, thickness, and mass balance sensitivity as result of extensive debris cover, for example. Moreover, and more importantly, it ignores climate change impacts on the non-glacierised part of the mountainous catchment, such as the buffering by snow and groundwater storages and the role of vegetation, and shifts in the partitioning between “green” (evapotranspiration) and “blue” (river runoff) water in particular. In this talk, we show a few examples of such oversimplifications, and argue for a broader and holistic perspective on the impacts of climate change on mountain water resources.

How to cite: Immerzeel, W. and Pellicciotti, F.: The peak water myth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7718, https://doi.org/10.5194/egusphere-egu24-7718, 2024.

The rise in annual mean temperature due to anthropogenic climate change is causing faster melting and thinning of glaciers leading to the formation of new glacial lakes and the expansion of existing ones in the Himalayan region. This exponential growth of glacial lakes increases the availability of freshwater resources and escalates the risk of future Glacial Lake Outburst Floods (GLOFs).
In the present study, Glacial lake inventories for the Upper Ganga basin were generated at the sub-basin level for 1990, 2000, 2010 and 2020 using Landsat (TM and OLI) images and semi-automated methods to understand the evolution of glacial lakes, altitudinal, orientational and typology changes. We were able to map 2,554 (area: 170.15 sq. km) glacial lakes in 1990, 2,783 (area: 191.03 sq. km) in 2000, 2,834 (area: 201.44 sq. km) in 2010, and 3,118 (area: 210.87 sq. km) in 2020. Between 1990 and 2020, the total number of glacial lakes increased by 564 (22.08%) and the total area increased by 40.72 sq. km (23.93%). In the year 2020, glacial lakes were found in 31 sub-basins of the Upper Ganga basin, out of 31 sub-basins, Arun sub-basin had the maximum number of glacial lakes (n: 734 & area: 61.66 sq. km).
The mean elevation of glacial lakes increased from 5,044.81 m asl (1990) to 5,052.30 m asl (2020), showing an increase of 7.49 m asl. In 2020, the majority of the glacial lakes were distributed in the elevation zone of 5,000-5,500 m asl (n:1,404 & area: 113.79 sq. km). In the upper Ganga basin, majority of the glacial lakes were south-facing (491) in 2020.
End moraine-dammed (M(e)) lakes dominate among differnt types of glacial lakes. In 1990, there were 2,081 (M(e)) lakes, which increased to 2,413 in 2020, indicating towards increasing risk of future Glacial Lake Outburst Floods (GLOFs) in the Upper Ganga basin. 
Therefore, the present study provides vital insights into the glacial lake dynamics of the Upper Ganga basin at the sub-basin level and will help in identifying potentially dangerous glacial lakes and developing robust policies to mitigate the impact of future GLOF events.

How to cite: Kumar, A., Mal, S., and Schickhoff, U.: Spatio-temporal evolution of glacial lakes in the Upper Ganga basin, Central Himalayas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3373, https://doi.org/10.5194/egusphere-egu24-3373, 2024.

The impacts of climate change and the retreat of mountain glaciers will significantly affect the headwaters of high mountain river systems. Accurate predictions of future water availability are essential to mitigate local impacts. Despite the availability of various glacio-hydrological modeling tools and high-quality input datasets, their effective application in less developed countries facing severe climate change impacts remains limited. Accessible and cost-effective tools are particularly scarce, hindering engagement with water management stakeholders, especially at the local level.

We present MATILDA, an open-source toolkit for glacierized catchments that allows users to acquire and process public data, apply well-established glacio-hydrological modeling routines, and estimate climate change impacts on the catchment of their choice. The workflow integrates Google Earth Engine, several state-of-the-art online data sources, and calibration algorithms. Published as a Jupyter book, it can be executed in an online Python environment, allowing users to generate scenario-based hydrological projections and analyze trends in runoff contributions, requiring only runoff observations.

The workflow is outlined and discussed in terms of practical application, sensitivity and uncertainty, limitations, and possible improvements. With a view to two regional studies in the Tian Shan Mountains, we evaluate MATILDA’s practical potential to support water management decisions in high mountain areas. The first study assesses the impacts of glacier change on lake levels and local agriculture in the endorheic Issyk-Kul basin in Kyrgyzstan. The second study focuses on the Chirchik River Basin in Uzbekistan and it's crucial role for hydropower production and fresh water supply for the Tashkent metropolitan area.

How to cite: Schuster, P., Georgi, A., Osmonov, A., and Sauter, T.: Assessing Climate Change Impacts on Glacierized Catchments in Central Asia Using an Open Source Toolkit, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19825, https://doi.org/10.5194/egusphere-egu24-19825, 2024.

The high mountains of Asia store large volumes of water in their glaciers and snowpacks. Twelve large river basins, fed with meltwater from these mountains, are home to almost 2 billion people. In their floodplains, a significant fraction of the global food is produced (34% and 23% of the global rice and wheat production respectively). This makes the snow and ice in the High Mountains of Asia a very important water reserve on which both water- and food security for a huge population depend.However, the water supply from the mountains faces many threats. Glaciers and snowpacks are melting at unprecedented rates, and large parts of these reserves are likely to disappear by the end of the 21st century. At the same time, the dependence of downstream populations on mountain water resources is increasing, mainly due to increasing water needs, continuing groundwater depletion and changes in (monsoon) precipitation.Agriculture in the predominantly irrigated floodplains in Asia is very intensive, with often 2 or even 3 crops grown per year. In some of these agricultural areas, irrigation water supply is largely depending on the seasonal availability of meltwater. Any changes in meltwater supply could therefore have large impacts on the crop production, but science has only just started understanding the impacts of melting glaciers and snowpacks on food and water security of downstream populations.In this presentation we will look back on our recent work in which we quantified the current en future dependence of downstream crop production on water from the mountains in the Indus and Ganges basins. We also describe remaining challenges, and look ahead to the upcoming (ERC) 3POLE2SEA project,  that aims to quantify these upstream-downstream linkages in all twelve river basins river basins originating from the High Mountains of Asia. We expect that the 12 river basins have very different upstream-downstream dependencies, resulting in different current and future risks for water and food security, and therefore need different responses for effective adaptation. We explain how our research can contribute to making agriculture in one of the largest food producing areas in the world more resilient to changes in the mountains.

How to cite: Biemans, H., Lutz, A., Smolenaars, W., Jamil, K., Ludwig, F., Dhaubanjar, S., and Immerzeel, W.: Impacts of melting glaciers and snowpacks in High Mountain Asia on downstream water and food security , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18462, https://doi.org/10.5194/egusphere-egu24-18462, 2024.

Runoff from the Tibetan Plateau (TP), known as the Asian water tower, is crucial to regional hydrological processes and the availability of water for large population living downstream. Climate change, especially marked atmospheric warming and altered precipitation patterns, have significantly affected the cryospheric hydrological process in the TP, particularly runoff. However, it is still unclear to what extent precipitation and temperature contribute to runoff change on the TP and the regional variability is not well understood. In this study, a large-scale, high-resolution, and well-calibrated distributed hydrological model was employed to simulate the long-term runoff of the TP over the past six decades (1961-2019). Then, spatiotemporal characteristics of runoff were analyzed. Furthermore, the impacts of precipitation and temperature on runoff variation were quantitatively estimated. The results found that the annual runoff decreased from southeast to northwest, and has been increasing over the past six decades. Notably, precipitation is a more important contributor than temperature across the plateau, contributing 72.08 % and 27.92 % to the runoff change, respectively. Besides, the influence of precipitation and temperature on runoff varies among basins, with the Daduhe Basin and the Inner Basin being the most and least influenced by precipitation, respectively. This research analyses historical runoff changes and provides insights into the contributions of climate change to runoff on the TP, which helps understand the hydrological response to climate change in mountain regions.

How to cite: Wang, Y. and Ye, A.: The quantitative attribution of climate change to runoff increase over the Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3551, https://doi.org/10.5194/egusphere-egu24-3551, 2024.

Glaciers in the Tien Shan act as natural reservoirs, storing freshwater in the form of snow and ice and releasing it during dry periods. This water source serves various purposes and is particularly crucial during dry periods, where it serves agriculture, hydropower, industry, and human consumption. Here, we use GloGEMflow to simulate the future evolution of all glaciers in the Tien Shan under CMIP6 SSP climate scenarios. In all climate scenarios, our results reveal an exceptionally pronounced retreat of the glaciers, surpassing the projected glacier loss for most regions of the world. By 2040, we project a loss of 30% of the glacier mass from 2020, which increases to 60% by 2100 under low emission scenarios (SSP1-1.9, SSP1-2.6) up to 90% under moderate to high emission scenarios (SSP3-7.0 and SSP5-8.5). This drastic retreat is driven by the unique climate of the Tien Shan, with most precipitation occurring during spring and early summer. Rising temperatures not only accelerate glacier melt but also reduce snow accumulation. Regardless of the scenario, we project that peak water from the glacier runoff will occur before 2050. By 2100, total annual glacier runoff decreases by 35% compared to the 2015-2020 mean level. The annual glacier runoff peak shifts from summer, when water demand is highest, to spring, presenting challenges for both agricultural and industrial sectors. We also examine and combine the simulated glacial runoff with information on water availability and demand from the ISIMIP framework. This helps to grasp and evaluate how important glacial meltwater is in the Tien Shan region. Our research provides essential insights for creating adaptive policies to handle water resources effectively at both local and regional level.

How to cite: Van Tricht, L., Zekollari, H., Huss, M., Vanderkelen, I., van Tiel, M., Compagno, L., Huybrechts, P., and Farinotti, D.: Future glacier mass loss in the Tien Shan strongly impacts summer water availability , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9575, https://doi.org/10.5194/egusphere-egu24-9575, 2024.

Glacier melt is known to provide an important source of water to streamflow in glacierized tropical regions, especially during the dry season. Groundwater also contributes a significant amount to streamflow. However, the linkage between the two is often unclear: How much groundwater originates from glacier melt? More broadly, how will groundwater and surface water contributions to streamflow change as glaciers retreat and climate changes? We developed a glacio-hydrological model in the Cold Region Hydrological Modelling platform to explore the complex interactions among the cryosphere, surface water, and groundwater in Peru's Cordillera Blanca, specifically in the Quilcayhuanca valley. The model uses meteorological observations from the valley and is parameterized using numerous data sources and process-based studies in the valley. Our findings reveal that during the dry season, 24 % of streamflow is routed through the groundwater reservoir, increasing to 40 % during the lowest flows. In a simulation without glaciers, streamflow discharge decreases by 34 % during the wet season and by 54 % during the dry season, with the groundwater contribution to streamflow decreasing by 55 % and 52 % for the wet and dry seasons, respectively. This simplified approach suggests that approximately half of the annual groundwater contribution to the stream originates from glacier wastage. We conducted sensitivity scenarios to evaluate the basin's resilience to the range of possible changes in precipitation, temperature and glacier cover expected by 2100. In a nearly deglaciated basin, the sensitivity to the range of tested temperature (+0 to 5 °C) produced a streamflow ranging from -60 to -49 % of current conditions in the dry season, and the range of tested precipitation (-20 % to +20 %) produced a streamflow ranging between -78 to -35 % of current conditions, indicating a larger sensitivity to potential changes in precipitation. Expected ratio changes were smaller during the wet season but followed a similar pattern. In the most likely scenarios by 2100, under RCP 8.5, wet season streamflow is predicted to decrease by 17 to 27 %, and dry season streamflow by 28 to 52 %. Despite a substantial decline in snow and ice contributions under climate change and deglaciation, the groundwater zone's contribution to streamflow shows relatively minor changes, demonstrating the low sensitivity of the groundwater system to climate shifts and glacier variations.

How to cite: McNamara, G., Aubry-Wake, C., Somers, L., McKenzie, J., Pomeroy, J. W., and Hellström, R.: Exploring the connectivity between glacier melt, groundwater and climate change in the Cordillera Blanca, Peru, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6606, https://doi.org/10.5194/egusphere-egu24-6606, 2024.

La Niña years are historically associated with precipitation deficits in central Chile. However, since the onset of the so-called Chile Megadrought in 2010, the teleconnection between the El Niño-Southern Oscillation phases and the hydroclimate in central Chile has either weakened or disappeared. This study investigates the hydrological response of high mountain watersheds to La Niña (LN) and megadrought conditions (MD) in the Andes of central Chile (30°S – 35°S) through physically-based simulation of processes at the watershed scale. It is shown that during LN years, winters and summers are colder, but spring seasons are warmer, while in MD years the summers are warmer. In addition, the hydrologic response to LN and MD is distinct and amplified during MD in terms of flow deficit.  Simulation results for five snow-dominated basins within the central Andes suggest lower efficiency in the transformation of precipitation to snowmelt flow (-3.7% and 1.6% with respect to the long-term average, for MD and LN, respectively), accompanied by higher evaporation (8.7% and 6.1%) and lower flow (-9.3% and -3.4%) relative to annual precipitation. Also, snow accumulation deficits at the end of winter propagate (-36.2% and -17.7%) with respect to the deficit of solid precipitation (-29.7% and -17.5%) and total precipitation (-26% and -19.3%), and during the MD the duration of snow is shorter compared to LN (-16.3 and -10.6 days). Thus, the key role played by snow processes and their variability in the hydrological response to droughts in central Chile is highlighted. The findings presented here are expected to inform ongoing discussion on adaptation strategies to climate change, as the observed climate during the megadrought (2010-?) is strikingly similar, on average, to GCM projections for this region toward the end of the 21^st century.

How to cite: McPhee, J., Hernandez, D., Courard, M., Mejías, A., Tesemma, Z., Pietroniro, A., and Pomeroy, J.: Hydrological implications of the Chile Megadrought in high mountain basins and lessons for climate adaptation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13616, https://doi.org/10.5194/egusphere-egu24-13616, 2024.

In alpine catchments, evapotranspiration (ET) is regularly considered a minor component of the hydrological system and is therefore only rudimentarily regarded in modelling studies and climate change projections. The focus is usually on snow and glacier related processes, projecting a rapid retreat of glaciers in central Europe within the next few years and decreasing snow volumes at lower elevations due to climate warming. This leads to a reduction in the dominance of snow and glacier related processes. Changes in vegetation characteristics due to climate- and/or land use change will presumably lead to a relative increase in the importance of other processes such as ET, interception and soil moisture, which will affect spatial and temporal variations in discharge generation.

To identify spatial and temporal patterns of changing process importance, a case study of the Fundusbach catchment in Tyrol, Austria is conducted using the fully distributed and physically based model WaSiM-ETH. As the process representation within all hydrological models is affected by parameter equifinality, substantially different parameter combinations and therefore process representations can lead to similar values of performance criteria when looking at discharge only. To address this issue, elevation dependent, spatial and temporal parameter sensitivity analysis is coupled with a multi-objective calibration. This approach aims to improve the spatial and elevation dependent process representation within the model domain. Instead of calibrating on different output variables, additional field and remote sensing data are used to constrain the parameter space of individual submodels and thus the process behaviour. In a final step, the constrained model is calibrated against discharge. Based on this reference model, scenario analyses are carried out to investigate individual process responses to changes in climate and land use.

The results show, that integrating additional field data and constraining the calibration parameter space considerably improves the process representation within the model. Furthermore, first results show, that changes of the land cover do not influence the overall discharge regime, but ET and soil moisture. Increasing amounts of shrub cover limit infiltration and evaporation, while interception and soil moisture increase. Most process responses intensify with increasing elevation and reflect the spatial patterns of land cover.

How to cite: Herzog, A., Vormoor, K., and Bronstert, A.: Shifting hydrological process importance in alpine catchments: Combined effects of climate and land cover change on alpine evapotranspiration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4133, https://doi.org/10.5194/egusphere-egu24-4133, 2024.

Snowmelt or ice melt typically control diurnal streamflow cycles during rain-free periods in high-altitude alpine catchments. Evapotranspiration-controlled streamflow cycles are less prominent, but can occur simultaneously (Mutzner et al., 2015). In general, the importance of evapotranspiration for the water balance of alpine catchments is likely to increase due to changing atmospheric boundary conditions and (related) changes in land cover. In this study, we focus on controls of diurnal streamflow cycles in the Fundusbach catchment (13 km²) in the Ötztal Alps (Austria). In addition to the official gauge at the catchment outlet, we have installed three further gauges along the longitudinal river profile. Here, we are recording the variability in water level/discharge at high temporal resolution (15 min) since June 2022. We have also adapted the deterministic spatially distributed hydrological model WaSiM with hourly and high spatial resolution (25 x 25 m²) for the Fundusbach catchment. Based on this model and the observation data, we are able to

• determine the diurnal streamflow dynamics and their change along the longitudinal profile,
• analyze the seasonal dynamics of diurnal streamflow patterns, and thus,
• draw conclusions about the spatially and temporally changing control variables of the diurnal streamflow cycles (data- and model-attributed) for rain-free periods outside winter.

Results show that (i) the diurnal streamflow variability decreases along the longitudinal profile, (ii) the amplitude of meltwater driven runoff cycles decreases exponentially over the year, whereby (iii) evapotranspiration-driven cycles always seem to attenuate meltwater-driven cycles. At later points in the snow-free season, the signal of the evapotranspiration-induced streamflow cycles can occasionally be inferred directly from the measurement data. For these days, catchment evapotranspiration amounts can be determined from runoff data as the integral between the daily maximum (during nighttime) and minimum (during daytime). The results also indicate an altitude-dependency of the control processes along the longitudinal profile, which needs to be further investigated.

Reference:

Mutzner, R., Weijs, S.V., Tarolli, P., Calaf, M.C., Oldroyd, H.J., Parlange, M.B. (2015): Controls on the diurnal streamflow cycles in two subbasins of an alpine headwater catchment. Water Resour. Res., 51, 3403-3418. doi.org/10.1002/2014WR016581.

How to cite: Vormoor, K., Francke, T., Herzog, A., and Bronstert, A.: Control processes of diurnal streamflow cycles along the longitudinal profile of an alpine river, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10041, https://doi.org/10.5194/egusphere-egu24-10041, 2024.

Groundwater plays a pivotal role in the water cycle but its interplay with hydrological processes has often been neglected or overly simplified in hydrological models of high-elevation catchments. This may increase uncertainties in future projections and impede a holistic understanding of the hydrological changes. High Alpine catchments, in fact, display complex surface and subsurface processes and lack of observations. Here, we investigate the role of alpine groundwater in the hydrologic response by partitioning the observed streamflow variations to glacier recessions, snowmelt, rainfall, and for the first time - groundwater fluxes at the Martell valley in Italy since the 2000s. To examine the dynamic interactions of these components in detail, we adopt a modeling framework that combines the physics-based model WaSiM (with an integrated groundwater module) with meteorological inputs obtained from the weather model WRF. Extensive field observations (meteorology, hydrology, geomorphology, piezometric levels, stable water isotopes) are collected to constrain the hydrological model parameters and for model evaluation. This study quantifies the contribution of groundwater in moderating the intensity and timing of hydrological extremes (high and low flows) in the selected high-elevation catchment and emphasizes the significance of groundwater in sustaining water availability in this sensitive environment subject to climate change.

How to cite: Fan, X., Hofmeister, F., Schaefli, B., and Chiogna, G.: Role of groundwater during hydrological extremes in the glaciated and snow-fed high Alpine catchment under climate change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2269, https://doi.org/10.5194/egusphere-egu24-2269, 2024.

Springs are vital water sources, and their vulnerability to environmental changes, particularly climate change, is of growing concern. The collaborative research project ECOSPRING, funded by the Austrian Academy of Sciences, focuses on the assessment of microbial communities and water quality patterns in selected springs all over Austria. Here, we will focus on understanding the response and vulnerability to hydrological events and climate change.

The first aim of the project is to characterize the springs based on their temporal dynamics in terms of physical-chemical characteristics. A detailed analysis of the dynamics in discharge, temperature, pH, EC, stable isotopes, essential nutrients, and major ions will provide valuable insights into the geological imprint and prevailing hydrological conditions, as well as on catchment areas.

Microbes are an integral component of aquatic ecosystems and can serve as sensitive indicators for environmental conditions. We will compare the microbial community composition in relation to the hydrogeological and physicochemical conditions.

Our research activities target two spatial scales, from a local perspective, with 14 springs in the province of Styria studied monthly, to a regional approach by sampling around 100 springs distributed all over Austria twice, in winter/spring and summer/autumn marking the expected hydrological extremes.

In the initial stages of our research, we gathered data from 15 selected springs of Styria. These springs exhibit a wide and dynamic spectrum in their physical-chemical properties. Together with records of discharge, springs could be categorized into stable, intermediate, and highly dynamic systems. Our preliminary results indicate a connection between these fluctuating physical-chemical conditions and the composition of the spring water microbiome. The underlying mechanisms driving these observed patterns are yet not fully understood and await further investigations.

In summary, this research project seeks to enhance our understanding of the vulnerability of spring waters to anthropogenic pressures such as climate change. The findings will provide a knowledge base for future water resources management and contribute to the sustainable use of these vital resources.

How to cite: Boanca, F. P., Seelig, M., Karwautz, C., Gerfried, W., and Griebler, C.: Temporal dynamics of water quality and microbial community composition in alpine springs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17858, https://doi.org/10.5194/egusphere-egu24-17858, 2024.

This study thoroughly compared two types of neural networks, namely Long Short-Term Memory (LSTM) and Gated Recurrent Unit (GRU) recurrent neural networks (RNNs), within the context of hydrological modeling for predicting runoff in the Oum Er Rabia sub-basins. By assessing their performance on both daily and monthly scales, we aimed to understand the dynamics of runoff, which is crucial in water resources management. The combined analysis of predictions at both time scales provides a comprehensive perspective, using daily outputs for short-term decisions and monthly predictions for longer-term planning.

Using a hydroclimatic time series dataset from 2000 to 2019, incorporating key factors such as snow cover area, temperature, and rainfall that influence hydrological processes and significantly impact flow patterns, the research evaluates the predictive accuracy of the models at both scales. The results reveal nuanced differences in predictive accuracy, with average Kling-Gupta Efficiency (KGE) values for LSTM and GRU at daily and monthly scales, respectively, being 0.64, 0.52, and 0.46, 0.54. These findings provide insights into the strengths and limitations of each architecture in the mountainous region of Morocco.

The study enhances our understanding of the applicability of LSTM and GRU architectures in hydrological modeling, aiding practitioners in selecting models tailored to specific needs. By establishing a robust framework for short-term decision-making and long-term planning in water resource management, this research contributes to advancing predictive modeling and promoting sustainable water use while mitigating flood risks. The knowledge acquired paves the way for improved decision support in the critical area of water resource management.

How to cite: Nifa, K., Boudhar, A., Elyoussfi, H., Eljabiri, Y., Bousbaa, M., Bargam, B., and Chehbouni, A.: Exploring Neural Network Performance in Hydrological Modeling in a Mountainous Region of Morocco: A Case Study on LSTM and GRU Architectures for Runoff Prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11621, https://doi.org/10.5194/egusphere-egu24-11621, 2024.

In North African countries where water scarcity and limited data prevail, employing predictive hydrological modeling is crucial to gain accurate insights into current and future water reserves. Hence, these models parameters exhibit instability in this context due to the climate variability observed through basins. Therefore, our efforts focus on using a combination of measured data, remote sensing information, and reanalysis data for calibration and validation, to check the improvement in the result accuracy. Through this study, we simultaneously investigate the spatiotemporal stability of the HBV model in several sub-catchments of Oum Er-Rbia Basin, by improving the performance of a bucket-type conceptual model. We created a Nested Cross-Validation (NCV) framework to assess spatiotemporal stability. The framework uses optimal parameters from a donor catchment of the Hydrologiska Byråns Vattenbalansavdelning (HBV) model as inputs for target catchment parameter ranges. In particular, we evaluated HBV's capacity for prediction over time and space, as well as its impact on model parametrization throughout the regionalization process in the setting of sparse data catchments. As results, the HBV model is spatially transferable from one basin to another, with NSE ranging from  0.5 to 0.8 and KGE values between 0.1 to 0.9, meaning a moderate to high performance. The HBV optimum parameter sets exhibit unpredictable behavior over space. On the contrary, their inter-annual behavior is nearly identical. It also detected a decrease in the model's predictive skills over time, which can be explained by the research area's tendency to dry out year after year. Furthermore, employing KGE for calibration rather than NSE improves model predictive performance significantly. The model  calibration process with the KGE outperformed those with the NSE metric, especially when simulating high flows. Furthermore, the findings demonstrate a significant relationship between high model performance and high values of several optimal parameter sets throughout the calibration and validation periods.

Keywords: HBV model, poorly gauged basin, arid and semi-arid region, KGE, NSE.

How to cite: El Garnaoui, M., Boudhar, A., Karaoui, I., and Chehbouni, A.: HBV Performance under complex and poorly gauged context, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14594, https://doi.org/10.5194/egusphere-egu24-14594, 2024.

Mountainous areas play a crucial role in global water resources. Orographic precipitation provides mountains with disproportionately high precipitation, which can be stored seasonally or over many years as snow and ice. Therefore, mountains are often referred to as ‘water towers’, emphasising their vital contribution to water provision for human use. Nevertheless, on a global scale, knowledge about their relevance for lowlands is limited, especially beyond long-term annual averages (Viviroli et al., 2020). Therefore, this study aimed to first assess differences in the water supply of mountains and lowlands in large river basins globally. Second, the share of mountain runoff in lowland water abstractions was evaluated with a focus on monthly averages and intra- and interannual variability to identify hotspots of mountain importance.

Our study is based on global simulations of the large-scale hydrological model CWatM (Burek et al., 2020) at a resolution of 5arcmin (~10km) from 1990 to 2019. The model simulates water availability, water demand and water use. A glacier representation was added to depict mountain water resources more realistically (Hanus et al., submitted). We compared water availability and demand in mountain and lowland areas within each river basin to identify the distinct patterns regarding water quantity, seasonality and interannual variability in mountains. Additionally, we derived the share of mountain runoff in lowland surface water abstractions to explore the relevance of mountains for human water use.

The analysis of around 600 river basins globally confirmed that precipitation and runoff are disproportionally higher in mountain areas in most river basins, whereas water demand is comparatively low. Additionally, we found mostly a larger intra-annual variability and lower interannual variability in mountain runoff compared to lowland runoff.

The estimated share of mountain runoff in lowland surface water abstractions is largest in High Mountain Asia, western North America, parts of South America and Southern Europe. In 250 basins, the maximum monthly relative mountain runoff share in lowland surface water abstractions exceeds 10%, and 25% of the world population lives in the lowlands of these basins. In comparison, only 7% of the world's population lives in lowlands of basins where the long-term mean annual share of mountain runoff in lowland surface water abstractions exceeds 10%. Thus, the relevance of mountains for lowland water supply becomes more apparent when distinguishing between different months compared to long-term annual averages.

Burek, P., Satoh, Y., Kahil, T., Tang, T., Greve, P., Smilovic, M., Guillaumot, L., Zhao, F., and Wada, Y.: Development of the Community Water Model (CWatM v1.04) – a high-resolution hydrological model for global and regional assessment of integrated water resources management, Geosci. Model Dev., 13, 3267–3298, https://doi.org/10.5194/gmd-13-3267-2020, 2020.

Viviroli, D., Kummu, M., Meybeck, M., Kallio, M., & Wada, Y.: Increasing dependence of lowland populations on mountain water resources. Nature Sustainability, 3(11), 917-928, https://doi.org/10.1038/s41893-020-0559-9, 2020.

How to cite: Hanus, S., Burek, P., Smilovic, M., Seibert, J., and Viviroli, D.: What is the monthly share of mountain water in lowland water abstractions?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10334, https://doi.org/10.5194/egusphere-egu24-10334, 2024.

The lack of comprehensive water supply prediction capacity in most areas of the U.S. poses challenges in evaluating water availability. In order to improve water availability prediction and assessment, in 2019, the U.S. Geological Survey initiated planning efforts to intensively study five medium-sized basins throughout the U.S. over the next decade, including the Upper Colorado River Basin (UCOL). Research in the UCOL aims to provide insight into how past, present, and future snow conditions – including amount, timing, melt, and transitions from snow- to rain-dominated systems – impact water supply (quantity and quality) and the ability to meet demand. A specific emphasis is placed on how these processes affect water budget components and dissolved solids concentration and loading in the UCOL. A fully integrated groundwater-surface water hydrologic model (GSFLOW), and temporally dynamic dissolved solids models (SPARROW) that explicitly represent the groundwater contribution to dissolved solids loading to streams are being applied to meet the study objective. Comprehensive information on water diversion and groundwater pumping has been compiled and is being explicitly represented in the models to better represent human demand.  Temporal and spatial patterns in predicted water quantity and quality conditions are being evaluated in the context of past and projected future changes, summarized over 30-year time periods, in snow metrics.  Historical trends in multiple snow metrics, water budget components, groundwater levels, and dissolved solids provide context for evaluations of current conditions and motivation for further investigation and modeling. The tools and concepts developed in the UCOL will contribute to ongoing work in the other regional study basins as well as a forthcoming national water availability assessment. 

How to cite: Miller, M., Day, N., Dickinson, J., Engott, J., Jones, C., Knight, J., Longley, P., Lopez, S., Masbruch, M., McDonnell, M., Miller, O., Schmadel, N., Tillman, F., and Wise, D.: Water Availability Assessment in the Upper Colorado River Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4160, https://doi.org/10.5194/egusphere-egu24-4160, 2024.