Andrei Ioniță

Snow depth and persistence strongly influence ground–atmosphere energy exchange, meltwater input, and the thermal regime of rock glacier systems, yet high-resolution snow monitoring remains scarce in the Southern Carpathians. This study uses multi-temporal Unmanned Aerial Vehicle (UAV) Structure-from-Motion (SfM) photogrammetry to map snow-depth variability and microtopographic controls on the Galeșu Rock Glacier, Retezat Mountains. Eight UAV surveys were conducted between 2023 and 2025, including seven snow-covered acquisitions and one snow-free reference survey in August 2025. Snow depth was derived by DEM differencing and analyzed against morphometric indices, mainly profile curvature and relative topographic position. Results reveal strong spatial heterogeneity, with recurrent snow accumulation in furrowed, concave, and depressional sectors and reduced snow depth on local topographic highs. The 2024 surveys showed substantially deeper snow than 2025, with mean snow depths of 1.82 m in February and 1.62 m in March 2024, compared with 0.72 m and 0.83 m in February and March 2025. April 2023 displayed the deepest snowpack, with a mean snow depth of 2.27 m. Class-based analysis showed median contrasts of 2.30 m in 2024 and 1.20 m in 2025 between strong negative and strong positive curvature classes. These findings demonstrate that rock glacier microtopography exerts a first-order control on snow accumulation and persistence, providing a basis for future studies linking snow redistribution to ground thermal regimes, meltwater pathways, and ground-ice preservation in marginal periglacial environments.

Rock glaciers are among the most important indicators of mountain permafrost, yet long-term ground thermal observations remain scarce in marginal periglacial environments where permafrost occurs as isolated bodies with a patchy spatial distribution. This study presents one of the most extensive ground surface temperature (GST) monitoring datasets currently available from southeastern Europe, comprising up to 15 years of observations (2009–2024) from 17 sensors installed on 13 rock glaciers in the Southern Carpathians, Romania. This study examines the thermal regime of rock glaciers in the Southern Carpathians, explores the factors controlling their interannual variability, evaluates the implications for permafrost occurrence, and investigates recent changes in ground thermal conditions. Mean annual ground surface temperatures at sites located above 2050 m generally ranged from about −1 to 1.5 °C whereas winter equilibrium temperatures (WEQT) were commonly below −2 °C and often below −3 °C. Such values point to ground thermal conditions favourable for permafrost preservation. Marked year-to-year variability was evident throughout the monitoring network. Particularly cold conditions occurred during 2016–2017 and 2018–2019, whereas the warmest conditions were recorded in 2022–2023 and especially in 2023–2024. Correlation analyses indicate that atmospheric forcing is the primary control on GST variability, while snow-cover dynamics and ventilation processes within coarse blocky debris substantially modulate local thermal conditions. Despite the generally marginal climatic setting, most monitored rock glaciers still display thermal conditions compatible with the persistence of isolated permafrost. This interpretation is supported by both regional permafrost modelling and previous geophysical investigations. The longest GST record indicates a significant increase in both mean annual ground surface temperature and WEQT, providing evidence of ongoing ground warming.These results provide valuable observational evidence from a poorly documented mountain region and highlight the importance of long-term monitoring for understanding the future evolution of isolated permafrost in marginal environments.

Understanding long-term snow cover dynamics is essential in mountain regions with limited meteorological or in situ observations. This study examines seasonal snow cover evolution across the Romanian Carpathians (2000–2025) using daily MODIS/Terra MOD10A1 Cloud-Gap-Filled data at 500 m resolution. Snow-covered pixels were identified using an NDSI ≥ 40 threshold, and snow cover duration (SCD), snow onset date (SOD), and snow end date (SED) were analyzed in relation to elevation and aspect from the FABDEM, complemented by snow-covered area (SCA) and snowline elevation (SLE) metrics. Across the entire range, the snow season shortens mainly due to later onset (+0.28 days/year) and earlier melt (−0.78 days/year), resulting in an SCD decrease of −1.14 days/year. High-elevation (>2000 m) areas show only small changes (SCD: −0.13 days/year; SOD: +0.46 days/year; SED: +0.32 days/year), while the strongest reductions occur at low and mid elevations, where snow persistence is most sensitive to warming; consistent declines in seasonal SCA and a pronounced monthly SLE cycle further document the spatial expression of this variability. Uncertainty was assessed by comparison with station-based snow cover duration (n = 230 station-years), indicating strong agreement (r = 0.95) with a modest negative bias (median: −8 days) and a mean absolute error (MAE) of 16.7 days. Climate correlations highlight air temperature as the dominant covariate of interannual snow-phenology variability, whereas precipitation associations are weaker. Overall, these shifts in snow phenology highlight increasing instability of the Carpathian snow regime and emphasize the value of long-term MODIS observations for tracking cryospheric change in a warming southeastern European mountain system.

This study provides the first estimate of the water volume equivalent (WVEQ) of ground ice in intact rock glaciers within the Southern Carpathians, based on an ice content range of 10 % to 20 %. The research focuses 48 intact rock glaciers, most of which are located in the Retezat Mountains. Using existing geophysical measurements, the ice content was determined to range between 10 % and 20 %, representing the first attempt to estimate WVEQ at such a low ice content. Using the thickness-to-area scaling method, subsurface ice volumes were estimated and converted to WVEQ using an ice density factor of 0.9 g/cm3. The results show that the total estimated water volume ranges from 0.009 km3 at 10 % ice content to 0.014 km3 at 15 %, and 0.018 km3 at 20 %. The largest water volumes are stored in the rock glaciers of the Retezat Mountains, with most of the water concentrated between elevations of 2000 and 2200 m elevation, in north-facing valleys underlain by granite bedrock. The study highlights the critical role of lithology, orientation, and elevation in permafrost preservation in mid-latitude mountains. The findings emphasize that while the water equivalent in intact rock glaciers within marginal periglacial environments is relatively low, their hydrological and ecological significance should not be underestimated, particularly in the context of climate change and permafrost degradation. Significant changes in mountain stream runoff, along with a notable decline in the biodiversity of rock glaciers, are expected to occur within this century at high altitudes in the Southern Carpathians.

Mountain watersheds play a crucial role in sustaining freshwater resources, yet they are highly vulnerable to climate change. In this study, we investigated the summer water temperature of 35 alpine springs in the highest part of the Retezat Mountains, Southern Carpathians, between 2020 and 2023. During the four-year monitoring period, water temperatures across all springs ranged from 1.2 °C to 10.5 °C. Springs emerging from rock glaciers had the lowest average temperature (2.37 °C), while those on cirque and valley floors were the warmest (6.20 °C), followed closely by springs from meadow-covered slopes (6.20 °C) and those from scree and talus slopes (4.70 °C). However, only four springs recorded summer temperatures below 2 °C, suggesting a direct interaction with ground ice. The majority of springs exhibited temperatures between 2 and 4 °C, exceeding conventional thresholds for permafrost presence. This challenges the applicability of traditional thermal indicators in marginal periglacial environments, where reduced ground ice content within rock glaciers and talus slopes can lead to spring water temperatures ranging from 2 °C to 4 °C during summer. Additionally, cold springs emerging from rock glaciers displayed minimal daily and seasonal temperature fluctuations, highlighting their thermal stability and decoupling from atmospheric conditions. These findings underscore the critical role of rock glaciers in maintaining alpine spring temperatures and acting as refugia for cold-adapted organisms. As climate change accelerates permafrost degradation, these ecosystems face increasing threats, with potential consequences for biodiversity and hydrological stability. This study emphasizes the need for long-term monitoring and expanded investigations into water chemistry and discharge dynamics to improve our understanding of high-altitude hydrological systems. Furthermore, it provides valuable insights for the sustainable management of water resources in Retezat National Park, advocating for conservation strategies to mitigate the impacts of climate change on mountain hydrology and biodiversity.

Advective heat fluxes (chimney effect) in porous debris facilitate ground cooling on scree slopes, even at low altitudes, and promote the occurrence of sporadic permafrost. The spatial distribution of ground surface temperature on an overcooled, low-altitude scree slope in the Romanian Carpathians was analyzed using UAV-based infrared thermography in different seasons. The analysis revealed significant temperature gradients within the scree slope, with colder, forest-insulated lower sections contrasting with warmer, solar-exposed upper regions. Across all surveyed seasons, this pattern remained evident, with the strongest temperature contrasts in December and April. February exhibited the most stable temperatures, with thermal readings primarily corresponding to snow surfaces rather than exposed rock. Rock surfaces displayed greater temperature variation than vent holes. Vent holes were generally cooler than rock surfaces, particularly in warmer periods. The persistent presence of ice and low temperatures at the end of the warm season suggested the potential existence of isolated permafrost. The results confirm the chimney effect, where cold air infiltrates the lower talus, gradually warms as it ascends, and outflows at higher elevations. UAV-based thermal imagery proved effective in detecting microclimatic variability and elucidating thermal processes governing talus slopes. This study provides valuable insights into extrazonal permafrost behavior, particularly in the context of global climate change.