S24

In Mediterranean high mountain environments, the snow accumulation/melting regime determines the surface water balance, redistributing the fractions of infiltration/runoff and evaporation from the ground and conditioning the volume circulating in the river channels. Therefore, the snow cover adds another degree of complexity to the precipitation-flow relationships in these systems (e.g., rain-on-snow events). Thus, a process-oriented approach is necessary when studying these relationships.

The definition of indicators derived from satellite remote information is a widespread technique in the characterization of the hydrological state of a basin. Previous studies in these areas have identified the state of vegetation, through its vigorousness using the NDVI (Normalized Difference Vegetation Index), as a good indicator for the characterization of soil water content at the beginning of the hydrological year (Gómez-Giráldez et al., 2014).

Therefore, in this context, the objective of this study is to analyze the relationships between changes in the state of watershed vegetation and flow variations in snow-influenced watersheds as additional information to anticipate downstream seasonal inputs using previous remote sensing information. For this purpose, a 20-year series of daily flow rates at a gauged point in the Guadalfeo river basin, one of the headwater catchments of the Sierra Nevada National and Natural Paro river was used, together with meteorological time series and the simulation of snowpack water flows using the physical-based model SNOWMED. Hence, two flow events are selected: i) rainfall-runoff events and ii) melt-runoff events. The vegetation dynamics in the basin is analyzed through variations of NDVI, derived from Landsat data (TM and ETM+) during the same study period.

From the analysis, the lags between the local change in NDVI, the loss of snow-covered area at the headwaters and the occurrence of melt or mixed flow events allow us to establish the onset of the generalized melt state in the basin, as well as to estimate threshold antecedent states. The results deepen the understanding of the hydrological dynamics in the basin, as well as the capacity of the NDVI as a tracer of the hydrographs associated with the generalized states of melting in Mediterranean mountain basins.

How to cite: Torralbo, P., Pimentel, R., Herrero, J., Aguilar, C., Moreno, F., and Polo, M. J.: Using NDVI as an indicator of snowmelt runoff in Mediterranean mountain catchments: application to the Guadalfeo river basin, Sierra Nevada., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-681, https://doi.org/10.5194/iahs2022-681, 2022.

Aufeis are widespread in the territory of the North-East of Eurasia (including the basins of large rivers in permafrost, such as the Yana, Indigirka, Kolyma, Anadyr, Penzhina Rivers and rivers of the Chukchi Peninsula. They comprise an important water resource of the study region. Based on the analysis of Landsat satellite images for the period 2013-2019 the number and characteristics giant aufeis (area ≥0.1 km²) were estimated. As Landsat images do not always allow correctly assess the maximum area of aufeis, it was adjusted to get the maximum value before the beginning of ablation period for the assessment of aufeis resources.

After correction total maximum area of aufeis formed by groundwater reaches 4529 km². The aufeis resources of the North-East and of the large river basins were assessed. The aufeis resources vary from 0.4 to 4.25 km³ (or 3.7 – 11 mm) for individual basins of large rivers. They are at least 10.6 km³ in total or 5 mm of water depth in average for the study area.

The contribution of aufeis runoff to streamflow in different seasons was calculated for 58 hydrological gauges (area 523 – 526000 km²). Aufeis annual runoff varies from 0.3 to 29 mm (0.1 – 22%, average 3.8%) with the share in winter runoff amount about 6 – 712 % (average 112%) and the spring freshet 0.2 – 43% (average 7.1%).

The influence of aufeis and glaciers on the water balance is compared – in general, the aufeis runoff exceeds the glacial runoff. The response of aufeis to climate change depends on different factors of the natural system.

The dynamics of aufeis formation is directly related to winter runoff, which changes are observed in different parts of the cryolithozone. The presented results are relevant for studying the impact of climate change on the hydrological cycle and its components in the permafrost regions of the Northern Hemisphere.

The study was carried out with the support of RFBR (19-55-80028, 20-05-00666) and St. Petersburg State University (project 75295879).

How to cite: Nesterova, N., Makarieva, O., Shikhov, A., Ostashov, A., Zemlyanskova, A., and Alexeev, V.: Aufeis resources and their role in water balance of North-Eastern Eurasia, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-99, https://doi.org/10.5194/iahs2022-99, 2022.

Hillslope water tracks are landmark features of permafrost landscapes, yet their origin and future evolution are debated. Water track networks are believed to be fully developed fluvial networks constrained by permafrost. Hence one potential evolution scenario under future climate is rapid thermo-erosional development of water tracks. Permafrost tundra environment near Vorkuta, European Russian Arctic, N67°17’, E63°39’, is a model ecosystem for this scenario, developing under changing climate and permafrost degradation.

Figure 1 Hydrographical network of the study region, 30 km south of Vorkuta, European Arctic Russia

Field works at the study site were carried out in September 2017 and repeated in 2021. Local streams and groundwater, from both boreholes and soil pits, were sampled for dissolved organic carbon (DOC) and nitrogen (DON), major ions, stable water isotopes and trace elements. Electrical resistivity tomography (ERT) was used to study permafrost distribution.

First-order water tracks are minor linear depressions, occupied by Betula nana and rarely expressed in local topography, hosting fast subsurface runoff. Initial stages of permafrost perturbation, these forms are major pathways of DOC export from permafrost slopes, with mean DOC content is 29 ± 2 mg/L. Channelized runoff appears farther downslope, at the slope bend. Increased input from supra-permafrost groundwater is traced by Ca²⁺ increase, and rapid decline in DON content, from 0.1-0.3 mg/L to zero. At toeslopes adjacent to the Vorkuta R., larger streams coexist with polygonal depressions dissecting otherwise flat riverine terrace. In streams, the DOC content decreases to 12 ± 1.5 mg/L, while in depressions, it raises to 38-39 mg/L. Terrain perturbation by water tracks provides initial slope drainage and promotes fast DOC export from slope soils and its potential microbial consumption.

Permafrost is discontinuous, and open taliks are present under water tracks and polygonal depressions, as shown by ERT survey. Taliks allow upward groundwater movement and drainage to the fluvial network. Sub-permafrost groundwaters were sampled from two boreholes, draining two major regional aquifers, and their traces were found in both large streams and minor water bodies of the region.

How to cite: Tananaev, N., Isaev, V., and Sergeev, D.: Hydrological surface-subsurface connectivity in permafrost tundra environment, European Russian Arctic, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-604, https://doi.org/10.5194/iahs2022-604, 2022.

Inspired by own field studies on permafrost and hydrological variability, a study was launched to investigate changes in runoff in southern Siberian catchments on the large scale. Until now, the reasons for the sometimes-drastic changes in river discharge remained more or less unanswered or were speculative. We combined data assimilation techniques, statistical analysis and hydrological simulation to investigate in detail the different climatic and physiographic impacts on the runoff behaviour of the Selenga (northern Mongolia / southern Siberia), the upper Lena and the Aldan (tributary to the Lena). Through this selection, we have included two different climatic and vegetation zones (semi-arid, transition zone between steppe and boreal forest, and humid, with exclusively boreal forest) as well as three areas with different permafrost extension (sporadic, discontinuous, continuous) in our investigations. We have selected a period of maximum data availability covering the years 1954-2013.

First, we were able to establish that due to the oscillating, large-scale atmospheric circulation over Siberia, precipitation and runoff are subject to periodic natural changes between rather dry and wet conditions. In addition to these oscillations, precipitation in all catchments shows negligible long-term trends over the 60 years period. Thus, we associate the long-term trends in runoff with the impacts of permafrost degradation. In the predominantly semi-arid Selenga catchment, lateral permafrost degradation prevails, i.e. decreasing permafrost extent. We found that there is a strong loss of water due to increased infiltration and seepage, resulting in drier conditions and ultimately lower runoff. In the boreal Lena and Aldan catchments, on the other hand, vertical permafrost degradation is prevalent. However, a frozen and thus impermeable layer remains below the growing active layer, which leads to overall wetter conditions and increased runoff. This contrasting behaviour mirrors the "dry becomes drier, wet becomes wetter" phenomenon described in earlier research. We also found that the warming-induced increases in permafrost thaw have led to major changes in the hydrological regimes of the three investigated basins. This integrated approach enabled new insights into the complex and highly dynamic hydrological changes that will provide impetus for subsequent studies. 

How to cite: Menzel, L. and Han, L.: Impact of changing climatic conditions and permafrost degradation on discharge in southern Siberian catchments, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-454, https://doi.org/10.5194/iahs2022-454, 2022.

Climate change drastically threatens water supply systems and ecosystems especially in water towers that maintain water demands downstream. Analyzing future implications in the timing and amount of snowmelt runoff is a crucial mission to develop required adaptation strategies against climate change effects. This study aims to estimate future snowmelt runoff and snow extent in terms of various metrics i.e. timing and the quantity for the Upper Euphrates Basin (41,109 km²). As the most upstream basin of the water tower Mesopotamia, the basin is located in the Eastern mountainous part of Turkey. The future characterization of snowmelt runoff and snow cover area is investigated taking the regional climate model projections into account through hydrological model applications. Furthermore, changes in snow line elevation and lag time in the snowmelt processes are examined. The basin is divided into two major sub-basins as Karasu Basin and Murat Basin. The conceptual hydrological models, HBV and HEC-HMS, have been utilized to establish a rainfall-runoff relationship. The models are calibrated and validated with observed daily total precipitation and average temperature data for the 1980-2010 period. Future projections are employed for 2025-2100 periods using EU-CORDEX data with various global circulation models.  CNRM-CM5 and HadGEM2-ES data sets and RCP 4.5 and RCP 8.5 emission scenarios are used for future projections. Climate data sets are subjected to local bias corrections. The preliminary results indicate decreases in snow cover extent, snow duration, and snowmelt runoff. The overall assessment will help us to understand how these changes will affect operations of water resources systems (downstream reservoirs) in terms of flood control, energy production, irrigation, and water supply, etc.

How to cite: Uysal, G., Dogan, Y. O., Civelek, H. S., Sorman, A. A., and Sensoy, A.: Analyzing the Effects of Climate Change for the Water Tower of Mesopotamia, Turkey, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-367, https://doi.org/10.5194/iahs2022-367, 2022.