In the last decade (2011-2020), Slovakia has experienced a significant decrease in flows in most river basins. The aim of this study is to statistically analyse the changes in the hydrological regime of selected Slovak streams based on observations over a 90-year period (1931-2020), using measured average daily discharges. Several regions in Europe, particularly in the Mediterranean area, including Spain, Italy, and Greece, have been affected by significantly dry years. The occurrence of dry years is not unusual, as extreme droughts have also occurred in the Danube River basin in the past, such as in 1863, 1921, 1947, 1992-93, and 2003. Our goal is to analyse changes in the low flow regime of rivers in Slovakia, which have long observation records. Understanding the low flow regime is one of the inputs for determining hydro-ecological limits, which is essential for maintaining and achieving good ecological status of surface waters. Several flow and non-flow characteristics were evaluated when assessing hydrological drought. Flow characteristics include: minimum average daily flows (in monthly or annual steps, over the entire period), M-day flows (the exceedance curve of average daily flows), minimum monthly and annual flows, and T-year minimum flows. Non-flow characteristics evaluated include changes in the timing of dry periods (date of occurrence), the number of low flow days, the longest drought episode, and the deficit volumes. Individual flow characteristics were calculated from the series of average daily flows. The trend analysis showed that in the given sub-catchments there is a decrease in the T-year minimum flows, as well as a decrease in the basic runoff. The comparison of the 100-year minimum specific runoff with the values of the specific base runoff shows that the 100-year minimum runoff can be up to ca. 4 times lower than the estimated specific base runoff in an extremely dry year.

Acknowledgement

This work was supported by the project VEGA No. 2/0015/23 “Comprehensive analysis of the quantity and quality of water regime development in streams and their mutual dependence in selected Slovak basins”, and by the project APVV No. 20-0374 “Regional detection, attribution and projection of impacts of climate variability and climate change on runoff regimes in Slovakia”

How to cite: Miklanek, P., Pekárová, P., Bačová Mitková, V., Bajtek, Z., Halmova, D., and Pekár, J.: Historical drought occurrence on Slovak rivers during the period 1931–2020, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8738, https://doi.org/10.5194/egusphere-egu24-8738, 2024.

This study aims to analyse the changes in the long-term average monthly runoff regime on the territory of Slovakia. For the analysis, the average monthly discharges from 57 gauging stations of the whole territory of Slovakia, which the Slovak Hydrometeorological Institute provided for the period 1961-2020, were used. The selected basin areas range from approximately 10 km2 to 1000 km2. The monthly discharge data available were divided into two periods: the old one, 1961-2000, and the new reference period, according to the World Meteorological Organization (WMO), from 1991 to 2020.  The appropriate number of clusters was determined according to the statistical analysis using the average Silhouette Width and the Elbow method. Subsequently, the PCA method and K-means clustering were performed to pool the catchments into groups. The results present the outputs of the particular runoff regime in the selected gauging stations divided into five clusters. South-central Slovakia and central Slovakia characterise Cluster No. 1; Cluster No. 2 by the northwest and northeast of the country; Cluster No. 3 for the centre of northern Slovakia; Cluster No. 4 for central Slovakia, and Cluster No. 5 for the east, south and west part of Slovakia. When comparing the changes in the regime of both periods, we can state that the best, 89% agreement was in Custer No.2, representing the High Tatras region, and 86 % agreement was in Cluster No.5 for the western part of Slovakia, with is 44% in Custer No.4, where the highest long-term average monthly flows remain in April, but the lowest normalized long-term average monthly flows shift from January to February. In Custer No.3, with 40 % agreement of catchment forming the clusters, we find a similar shift of peak long-term average monthly flows from April (1961-2000) to March (1991-2020). The most significant changes in the long-term average monthly runoff regime were found for the catchment in Cluster No.1.

Finally, the most important characteristic features of the individual clusters of gauging stations created were also analysed, which could help incorporate other catchments into appropriate regional types in the future. The methodological procedure developed could also be used in further studies to predict future flow regime changes on the territory of Slovakia.

Acknowledgements

This study was supported by the Slovak Research and Development Agency under Contract No. APVV-20-0374 and VEGA Grant Agency No 1/0782/21. The authors thank the agencies for their research support.

How to cite: Sabová, Z., Kohnová, S., and Liová, A.: Spatial-temporal changes of the long-term average monthly runoff in Slovakia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8056, https://doi.org/10.5194/egusphere-egu24-8056, 2024.

Runoff is one of the essential indicators for designing measures that retain or safely divert water in the country. However, in the 21st century, rural basins face changes caused by climate or land use. These alters force society to think about the transformation that time brings and to change the view on some parameters of the country's functioning within the outflow processes. The presented contribution deals with runoff changes over the last decades, in which the difference in the values ​​of peak runoff coefficients in small watersheds is analysed using direct and indirect estimation methods.

The first part of the study deals with the indirect approximate calculation of the peak runoff coefficient in 128 small catchments up to an area of 150 km² (approx. 58 mi² ) located on the territory of the Slovak Republic. Input data consisted of estimated concentration times according to Nash and Kirpich formulae, estimated design values for maximum floods and IDF curves for all available rain gauge stations in each analysed basin. The results were compared to previous studies.

In the second part, for two selected basins (Parná – Horné Orešany and Belá – Liptovský Hrádok), we estimated the peak runoff coefficient using the direct method. The chosen watersheds represent different landscape structures, where the first is a lowland type, and the second a high-mountain type of landscape. The analysis was based on direct measurements of hourly peak flows from 1989 to 2021. The flood wave parameters for calculating the peak runoff coefficients were obtained by substituting the causative precipitation. These data were subsequently statistically analysed using the Johnson probability distribution. The peak runoff coefficient for a 100-year return period was separately modelled for the summer and winter periods in both basins and compared to the indirect estimation results.

The study's results are intended to highlight the differences in the methods used to estimate peak runoff coefficients in small watersheds.

Acknowledgements

This study was supported by the Slovak Research and Development Agency under Contract VEGA Grant Agency No 1/0782/21. The authors thank the agencies for their research support.

How to cite: Paulíková, L., Kohnová, S., and Výleta, R.: Estimation of the Peak Runoff Coefficient on Small Catchments in Slovakia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8187, https://doi.org/10.5194/egusphere-egu24-8187, 2024.

While the familiar path of experimenting with multi-objective calibrating a conceptual rainfall-runoff model involves the whole catchment area, this study examines and compares various spatial divisions of the catchment during the calibration process. The input data that is used includes runoff values (Q), precipitation (P), air temperature (T), and potential evapotranspiration (PET). Additionally, values of soil moisture obtained by the sensors of the remote sensing source (advanced scatterometer (ASCAT) remote sensing product-ASCAT SWI) were also incorporated into the analysis within a selected catchment in Slovakia. This study provides insights into the best practices for integrating satellite soil moisture data into multi-objective calibration. Moreover, including satellite soil moisture data is particularly significant, offering a novel perspective on moisture dynamics within the catchment. One of the objectives of this research is to identify the optimal spatial division of the catchment, explicitly evaluating the effectiveness of elevation-based division versus land cover-based division. These different catchment subdivisions should point to the impact on the accuracy and reliability of the rainfall-runoff model. The calibration strategy chosen for this study is divided into the period from 2007 to 2014 for the calibration run and for the validation run chosen period from 2015 to 2019. First results show improvement of soil moisture correlation results in land cover-based division contrary to elevation zone subdivision, in the whole period of calibration (2007-2014), as well as in only summer months period (June, July, August and September). Different established calibration strategies should offer a robust framework for calibrating the rainfall-runoff model in future.

Acknowledgement

This study was supportedby the VEGA Grant Agency No. VEGA 1/0577/23.

How to cite: Aleksić, M., Kubáň, M., Szolgay, J., and Párajka, J.: Different strategies of the catchment division in the process of multi-objective calibrating the conceptual rainfall-runoff model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8047, https://doi.org/10.5194/egusphere-egu24-8047, 2024.

Waterbodies across the world undergo changes. This influences the communities in the ecosystems. Groundwater is no exception. However, few studies focused so far on how the combined effects from environment, groundwater recharge, and a changing climate, impact the organisms living in the groundwater. In 2019-2021 in southwestern Czech Republic, we sampled fauna and microorganisms in 37 wells that had been monitored by CHMI for up to 40 years and that varied in the trends in chemical and physical characteristics. The wells tapped the shallow quaternary and deeper aquifers of seven major hydrogeological zones. Some of the wells represented recharge zones, others tapped artesian aquifers. Trends in temperature over the past decades were ambiguous. Carbon and nutrients did not show clear patterns, neither over time, nor predicting fauna and microorganisms. Fauna was, however, significantly more abundant in wells representing recharge zones. Most unexpected were the observations that silica increased significantly in all but one well, and that faunal numbers were lowest in the wells with the highest silica values, although there is no reason for fauna being harmed by silica, - on the contrary. The correlation is thus believed to show indirect effects, with the increase in silica probably being the (by)product from either climate change or land use change, or the combination of the two, and groundwater fauna being impacted by the underlying developments. This may have implications for ecosystem functions, and ultimately, the use of groundwater for drinking water production.

How to cite: Schmidt, S. I., Svátková, M., Kodeš, V., and Shabarova, T.: Changing groundwater ecosystems and recharge – neither temperature nor nutrients or carbon are the main drivers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5353, https://doi.org/10.5194/egusphere-egu24-5353, 2024.

The drought is becoming more frequent and severe with changing precipitation pattern in the future. How the water use efficiency responds to drought in different periods during the growing season has become a key scientific issue to explore the response mechanism of carbon and water cycle coupling process to drought in alpine meadow ecosystem. This project focused on the response mechanism of alpine meadow ecosystem productivity to drought and the relationship between productivity, evapotranspiration (or rainfall) and water use efficiency under simulated drought events in the early and middle growth seasons, and discuss the response mechanism of water use efficiency of alpine meadow ecosystem to drought. The result showed that (1) the delayed green-up under early growing season drought and advanced withered date under middle growing season drought occurred in graminoids, weeds and plant community, which indicated ‘escape strategy’ to drought. (2) the effect of advanced withered date was divergent among graminoid and weeds on the aboveground net primary production, which may lead to a stronger resistance of community productivity to middle growing season drought. (3) besides soil water deficit, the limited accumulation of aboveground biomass inhibited the physiological process of carbon exchange in alpine meadow community either. However, the carbon exchange process presented an over compensation mechanism, and the material distribution strategy may vary after rainfall restoration. (4) early growing season drought had no significant effect on water use efficiency of alpine meadow community (p > 0.05), while water use efficiency increased significantly under middle growing season drought (p < 0.05). The main reason is that the plant community is more sensitive to early growing season drought, which depressed the aboveground biomass, while aboveground productivity of alpine meadow plant community has stronger resistance to middle growing season drought. This project studied the response mechanism of alpine meadow ecosystem to extreme drought events in different periods, which has great scientific significance to the study of ecosystem response to extreme climate events, and provides a scientific basis for predicting and simulating the response of alpine meadow ecosystem in Northern Tibet to climate change in the future, especially the change of precipitation pattern.

How to cite: Hu, G.: Water use efficiency response of plant communities to drought in different growing periods in alpine meadow, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7326, https://doi.org/10.5194/egusphere-egu24-7326, 2024.

The increasing frequency of drought events in recent years has become a major hurdle for reforesting forests after natural disturbances in many areas globally, including parts of Central Europe. As an example, reforestation projects after bark beetle disturbances have faced notable failures and losses due to prolonged drought conditions in Northern Bavaria (Germany). Irrigation is a potential measure increasing reforestation success and is currently funded by the regional government. However, historically irrigation was not a common technique in this area and there is a lack of both practical and scientific knowledge concerning irrigation strategies. The optimal timing for the irrigation of the saplings as well as the water amount applied are crucial aspects in this context.

This study addresses this knowledge gap by conducting a drought stress experiment within a greenhouse environment, focusing on four commonly planted tree species prevalent in our study region in northern Bavaria. Various approaches were explored to reliably detect drought stress and identify the irrigation demand both concerning timing and amount of water applied: the experimental design integrates environmental data with ecophysiological measurements and employs drought stress indices derived from close-range remote sensing. The most promising methodology for detecting the irrigation demand, identified through rigorous experimentation, will be further explored on forest sites post-planting. Implementing such optimized irrigation strategies holds promise for safeguarding reforestation endeavors, particularly in regions prone to drought, and contributes to the sustainable management of forest ecosystems and water usage.

How to cite: Hahn, L., Schmidt, M., Lorz, C., Rothe, A., Rammig, A., and Zang, C.: Optimizing Irrigation Strategies for Mitigating Drought Stress in Reforestation Areas: Lessons from a Drought Stress Experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5802, https://doi.org/10.5194/egusphere-egu24-5802, 2024.

Over the past decades, extensive groundwater extraction has disturbed the water balance in the Hessian Ried region of Germany, resulting in a deepening of the groundwater table. Consequently, the forests in this area, which were initially reliant on groundwater, are now solely dependent on precipitation. The increasing frequency of summer droughts further jeopardizes the vitality of these forests. To address these issues, above-ground irrigation as an alternative to restoring the groundwater table could be pivotal. Implementing irrigation strategies may allow to revitalize trees and/or reduce mortality rates.

To assess the impact of irrigation on tree vitality, an experiment is conducted since 2021 in the municipal forest of Gernsheim, located in the Hessian Ried region, Germany, a region, where large forest areas are suffering from groundwater abstraction. The experiment involved designated control and irrigation plots, each in threefold replication covering 2500 m² per plot. Perforated pipes were installed at the irrigation plots on the ground, delivering water based on real-time field measurements of soil water content, matric potential, and precipitation regime. The irrigation plots received 186 mm, 505 mm, and 332 mm of additional water in 2021, 2022, and 2023, respectively.

Phenological observations indicated that irrigation prevented premature senescence of the foliage compared to control plots following a drought in 2022. Even in the following year, non-irrigated plots showed 10% less canopy cover. Additionally, leaf area index was significantly higher in 2022 and 2023 at the irrigated compared to the control plots, despite starting lower there in 2021. The negative impact of drought on tree growth was also significantly reduced by irrigation: the diameter increment of trees at irrigated plots during the drought year 2022 was similar to previous moist years for oak trees, while the increment was even higher for hornbeam trees. Tree mortality rates remained consistent at 3-5% in 2022 regardless of irrigation. However, tree mortality decreased to 0% in 2023 under the irrigation scheme, while it remained high at 10% in the control plots.

To conclude, forest irrigation effectively reduced premature senescence of tree foliage during the severe drought of 2022, and thus prolonged the growing period. Irrigation significantly contributed to preserving tree vitality and reducing tree mortality in the subsequent year. Given that trees might endure the adverse effects of drought for several years, long-term studies are necessary to determine to what extent forest condition can be revitalized over time with irrigation.

How to cite: Köhler, M., Bilyera, N., Gerdes, H., and Meesenburg, H.: Effect of irrigation on tree vitality in a temperate forest in Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22121, https://doi.org/10.5194/egusphere-egu24-22121, 2024.

Streamflow prediction, especially extreme events, poses a significant challenge due to the intricate and unpredictable nature of the rainfall-runoff process. Recently, promising results have been observed in time series problems by applying deep learning methods, including Long Short Memory (LSTM) and sequential modelling. This study investigates the application of the LSTM network to predict daily streamflow in the Dez River basin, Iran, during 2012–2019. Accordingly, observed precipitation, temperature, empirical evapotranspiration, and runoff were utilized as predictor variables. The performance of the LSTM model was compared with an established process-based approach, the Hron rainfall-runoff model, which served as a benchmark to evaluate the effectiveness of this innovative model. The models were evaluated using Kling-Gupta efficiency (KGE), Nash-Sutcliff efficiency coefficient (NSE), normalized root mean square error (NRMSE), and mean absolute percentage error (MAPE). Through evaluation and analysis, the NSE and MAPE indices were, respectively, 0.95 and 15.6% for the LSTM model in the validation stage. The results demonstrated that the LSTM model performed better than the Hron model in predicting daily streamflow. The superior performance of the LSTM network represents its efficiency in capturing and utilizing inherent temporal dependencies in hydrological data. This finding highlights the potential of the proposed model for improving the accuracy and reliability of real-time hydrological forecasts.

How to cite: Tanhapour, M., Hlavcova, K., Kohnova, S., Shakibian, H., Soltani, J., and Malekmohammadi, B.: Investigating the applicability of long short-term memory model for streamflow prediction , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8216, https://doi.org/10.5194/egusphere-egu24-8216, 2024.

Over the past centuries, many changes have occurred in addition to climate change, from human encroachment to deforestation and drainage, and much more. Research has shown that lowland forests use a significant amount of groundwater, without which it is much harder to imagine their existence, even as a dominant source of water. It is therefore crucial to understand how much and how forests can be maintained under the expected conditions, because groundwater levels are sinking year by year in large parts of the Hungarian lowlands.

From a conservation perspective, it is also crucial to investigate the activities taking place in the Ohat oak forest, which is a remnant area along the Tisza. Two groundwater wells were drilled in the region in 2021, and automated measuring equipment was put in each of them to track the daily variations in groundwater levels. In order to estimate the groundwater abstraction from the forest, we will utilize the White method to compute the groundwater recharge during times when there is no precipitation.

Additionally, we will look at how the local conditions have changed in relation to the region's long-term meteorological data series. We will be able to compare the soil water recharge in various years thanks to the multi-year data series, and search for connections between the recharging and the monthly and yearly weather conditions. We will also compare the summer and winter periods of the recharging.

This three years are very good for the examination, because there was also drought and wet years, the groundwater level was deeply subslided, and after that, in 2023, it was recharged a lot, because of the rainy weather. These conditions caused a big difference between every year’s recharging, which is instructive for the ecosystem functioning.

The following joint projects (143972SNN project and the TKP2021-NKTA-43 project) supported the preparation of this paper. TKP2021-NKTA-43 has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.

How to cite: Kele, Z., Kalicz, P., and Gribovszki, Z.: Examining the groundwater turnover in a lowland salt steppic oak forest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13016, https://doi.org/10.5194/egusphere-egu24-13016, 2024.

Nowadays, extreme precipitation events are becoming more and more prevalent, which, in some
situations, can cause serious problems and damage. To avoid the impacts of extreme rainfall events,
blue-green infrastructure elements are used to retain and slow down stormwater runoff. Examples are
vegetated (green) roofs, widely considered a promising nature-based solution for urban stormwater
management.
This experiment is focused on studying the influence of the retention capacity and the depth of the
selected commercial substrate of extensive vegetated roofs. The rainfall intensity testing aims to
demonstrate and explore new insights into vegetated roofs during severe extreme precipitation. The
actual experimental process was performed under laboratory conditions, where extreme rainfall
intensities (2 - 4 mm/min) with a duration of 15 minutes were subsequently simulated using a rainfall
simulator. The main identifier of the quality and capability of the substrate used on the vegetated roof
is the amount of runoff captured from the simulated rainfall intensity. The measured outputs will be
used as inputs to predictions reducing stormwater runoff. The knowledge gained and the different
variations of the simulations can significantly help in constructing and designing vegetated roofs and
effective urban stormwater management.

Keywords: precipitation, retention capacity, vegetated roof, runoff,

How to cite: Grečnárová, J., Danáčová, M., and Tomaščík, M.: The experiment of the effects of rainfall intensity and substrate depth of an extensive vegetated roof, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8142, https://doi.org/10.5194/egusphere-egu24-8142, 2024.

Rainfall intercepted by vegetation is, in many regions, an important part of the hydrological water cycle. Part of the intercepted rainfall evaporates into the atmosphere, and throughfall and stemflow contribute to runoff generation, control soil moisture and runoff connectivity patterns and affect soil erosion. The question of how changing climate and land cover conditions impact rainfall interception, raindrop microstructure, and their erosive power still needs to be better understood.

This presentation introduces the main aims of a bilateral research project between TU Wien, University of Ljubljana and the Slovenian Forestry Institute that focuses on the understanding of the effect of meteorological and vegetation characteristics on changes in raindrop microstructure and, therefore, on the erosive power of rainfall. The main idea of the research cooperation is to analyse and understand the main mechanisms of the rainfall interception process in different climate conditions and vegetation settings. The high-resolution disdrometer measurements from the experimental urban and forest plots in Slovenia and a small agricultural basin in Austria are used to determine and compare raindrop distributions and their changes. The high-resolution observations of discharge, sediment concentrations and isotope analyses contribute to the understanding of the erosion processes and sediment transport in the streams.

Acknowledgment: This contribution is part of the ongoing research project entitled “Evaluation of the impact of rainfall interception on soil erosion” supported by the Slovenian Research and Innovation Agency (J2-4489) and it was funded in part by the Austrian Science Fund (FWF) I 6254-N.

How to cite: Parajka, J., Széles, B., Marjanovic, D., Zabret, K., Lebar, K., Vilhar, U., Bezak, N., and Šraj, M.: How rainfall interception influences soil erosion in agricultural, urban and forest catchments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15021, https://doi.org/10.5194/egusphere-egu24-15021, 2024.

A changing climate brings more extreme weather and uneven distribution of rainfall events. These effects are already being observed, and although the average of the many annual rainfall totals is not changing significantly, the length and frequency of periods without rainfall and droughts have increased significantly. These changes are also felt by forest stands and their sensitivity to drought is a crucial factor in their growth and health. Our research team has been collecting data on the organic matter content and water-holding capacity of Hungarian soils for many years and has now also produced pF measurements. The sub-region of the Transdanubian Mountains region has provided a comprehensive picture of coarse-textured soil on which forest soil-forming processes take place. Soil samples were taken up to the limit of the occurrence of soil-forming processes, but at least up to 100 cm. Acidic Arenosols developed on the sand parent material. On these, mixed stands of beech and turkey oak-sessile oak associations developed. The pH, CaCO₃ content, organic matter content, texture, and bulk density of the soils were determined under laboratory conditions in 10 cm layers. The majority of the soil samples had an acidic pH between 4.4-6.4, with fine sand and sandy loam physical texture and free of calcium carbonate, with low humus content (0.9% in the upper 40 cm) compared to forest soils. From the pF measurements and using pedotransfer functions, we determined the potential water availability for plants, and using local climate data and measured soil data, we constructed a Thornthwaite-type water balance model for the area and used it to estimate the drought sensitivity of the area. These models improve and speed up the methods and therefore its accuracy and applicability to forest soils is a primary concern of this research.

The present publication was supported by the National Research Development and Innovation Fund of the Ministry of Innovation and Technology (successor: Ministry of Culture and Innovation) under the project TKP2021-NKTA-43, funded by the TKP2021-NKTA grant programme, and by the New National Excellence Programme of the Ministry of Culture and Innovation, code number ÚNKP-23-3-I-SOE-172, funded by the National Research, Development, and Innovation Fund. The field and laboratory tests were also carried out using equipment purchased with the support of the project "GINOP-2.3.3-15-2016-00039 - Investigation of the conditions for growing woody biomass".

How to cite: Katona, M., Végh, P., Balázs, P., Bidló, A., and Horváth, A.: Water retention of soils with coarse texture under forest stands using classical method and PTFs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1047, https://doi.org/10.5194/egusphere-egu24-1047, 2024.

We made our investigation in the Gemenc forest, which is situated beside the Danube river near to the southern border of Hungary. Mainly in the last decades, watercourse management played a significant role in landscape evolution. Most of the area is on the saved side today, so it doesn’t get flooded. The Danube usually brings CaCO₃ to this area with its sediment. The flooded areas are built from fine sediment materials. Meadow soils rich in CaCO₃ are characteristic, and the forests of this land grow healthy here (assuming that are high-quality forest types). Farther away from the river, higher plains have sand with humus soils and Chernozem soils. On our Polish investigation we took samples from the northern floodplains of Vistula, in 2 different areas, which located on the saved side. Overall the samples were very similar to the Hungarian ones.

Forest ecosystems of this area are probably one of the most important members of the continental vegetation that store carbon. Because of their size, they take a huge part of the global carbon cycle. During our examinations, we visited six Quercus petraea and Robinia pseudoacacia forests and took samples from the soil profiles of those forest soil besides the determination of water holding capacity. The humus content of the examined soil samples varied between 0.7 and 6.9 %. Since the study areas are no longer or rarely affected by flooding, the highest organic matter content was found in the topsoil layer for each sample. SOM content gradually decreased with depth. The effect of flooding is clearly shown by the fact that we found organic matter in the samples even in the layer below 100 cm, and in several cases, we found buried humus levels. Accordingly, the organic carbon stock of these soils may be higher than average. However, the decreasing number of floods endangers the vitality of forest stands. With less flooding, decreasing groundwater level and an increase in the temperature at night, dew formation becomes more limited, and evaporation increases. These changes also affect the decomposition processes taking place in the soil, the circulation of nutrients, and soil respiration. Increasing temperature, the speed of decomposition, and the intensity of soil respiration increase, which can further increase the decrease in the soil's C pool.

In the Polish samples, the SOM varied between 0,4 and 20,9 %, with an extremety of a soil with peaty features. The ph varied between 2,0 and 8,0, with the former also being the „extremety”, otherwise the avarage value being 7,7. If we compare the two study areas, we can conclude that the soils themselves are less vulnerable to the effects of the climate change, due to the differences in the microclimate, the precipitation and the evaporation

This article was made in frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.

How to cite: Szász, D., Bidló, A., Balázs, P., Hulisz, P., Végh, P., and Horváth, A.: Comparison of Polish and Hungarian floodplain soils’ reaction to the climate change , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-441, https://doi.org/10.5194/egusphere-egu24-441, 2024.

The beech stands ratio of Hungarian forests barely reaches 6%. However, beech is a native tree species with high production capacity; therefore, its importance in nature conservation and economy is significant. Due to global climate change, the focus is on the ability of carbon fixing and storage capacity in beech forest ecosystems. While we can estimate the amount of biomass above ground with relative precision, we have little data about organic carbon in soils.

The primary goal of our work was to collect as much data as possible on the amount of organic carbon stored in the soil of these native forest stands. Furthermore, the most significant factors were determined that influenced the sequestration.

During the research, undisturbed and disturbed soil samples were collected from every 10 cm layer in 40 beech stands. The depth depended on the bedrock. On loessy or sandy bedrock, the depth was 110 cm. In the case of rocky structure, samples were taken from 0-40 cm depth. Moreover, litter samples were taken and analyzed. The properties of the stands were also recorded on the sampling sites (tree species, diameter, etc.).

The soil pH was 5.17 on average, while the minimum value was 3.87 and the maximum was 8.4. The humus content varied between 0.16 and 15.65% because it decreased with depth. The average organic carbon stock was 6.39 C t/ha (Cminimum  1.46 C t/ha, Cmaximum 34.03 C t/ha). Moisture determines the organic carbon stock of the soil most of all.

This article was made in the frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme. Some of the tools used during the research were acquired within the framework of the "Investigation of the conditions for the cultivation of wood biomass - GINOP-2.3.3-15-2016-00039" project.

How to cite: Bidló, A., Balázs, P., Katona, M., Végh, P., and Horváth, A.: Examination of the organic carbon stock of the soil of Hungarian beech stands and the determining factors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12022, https://doi.org/10.5194/egusphere-egu24-12022, 2024.

Increasing carbon presence in the atmosphere prompts scientists to understand carbon sequestration processes better. Forest is one of the most promising ecosystems where this sequestration can take place with higher efficiency. In this research, we analysed long-term land use change processes and carbon content of soils in present Hungarian forests, searching for the answer: is there any relationship between the former land use and the carbon content of soils?
We selected 183 forest stands scattered across the country, where the age of the trees were approximately 60-70 years old. Soil samplings were carried out in the depth of 40-110 cm (in 10 cm layers). In order to derive long-term land use change information, we used historical map series dating back to the 18th century.
Results will contribute to the understanding of the carbon sequestration processes of terrestrial ecosystems.
This article was made in frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.

How to cite: Balázs, P., Bidló, A., Horváth, A., Katona, M., and Végh, P.: Legacy of former land use and its effect on carbon content of soil in present forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15203, https://doi.org/10.5194/egusphere-egu24-15203, 2024.

An investigated old-growth Scots pine (Pinus sylvestris L.) forest is located in a protected area. Climate, soil, and local hydrological conditions highly influence the health conditions of this relict forest stand. Drought symptoms are already visible thus complex analyses assessing of these site factors were investigated. Site conditions always influence vegetation. Conversely, vegetation always affects site conditions. Therefore, the relationship between forest stand vitality and stand growth becomes more complicated in the case of damage chain appearance in an elderly, resistant forest stand. Our research aimed to answer the following questions:

• How have site conditions changed in the research area in recent decades?
• Which are the most significant site-limiting factors in this case?
• Can a relict and protected ecosystem adapt to the changed conditions?

To identify the complex causes of tree mortality, climatic and soil conditions were analyzed and completed with bryological and biotic (pests) surveys. Altogether unfavorable soil conditions (coarse sand) and increasing aridity have led to a decline in tree vitality. Bark beetles have a high population density in the stand, so the beetles contributed to tree mortality. New spreading invasive moss species have appeared in the recently formed gaps, where crone projection is low. The disappearance of this relict forest stresses the urgent need for Hungarian forest management to prepare strategies for adaptive tree species selection.

This article was made in the frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.

How to cite: Horváth, A., Lakatos, F., Szűcs, P., Patocskai, Z., Végh, P., Winkler, D., Bidló, A., and Gálos, B.: Tree Mortality in a Relict Scots pine forest due to climate change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10271, https://doi.org/10.5194/egusphere-egu24-10271, 2024.

Numerous research based on long-term weather data sets proves a drier and warmer climate in Hungary. Research related to climate change and carbon sequestration is developing dynamically, so it is notable to show how climate change affects the quality and quantity of organic matter content in soils. The importance of changes in soil organic carbon stocks follows from its effects on ecosystems on a global level. In the last decades, afforestation programs were also started in Hungary to promote carbon sequestration. However, there have been several criticisms of afforestation efforts by experts and researchers dealing with agriculture, according to which agricultural areas, particularly grasslands, can sequestrate more organic carbon than forest stands. It is also not suggested to plant forest stands in dry, sandy areas, as it has a drying effect on the soil due to its high water demand compared to the fields, thereby reducing the net carbon sequestration. This research aim was to examine the above proposition at 5 locations where wooded and treeless, different land-used areas were managed next to each other. Based on our scientific investigation, it cannot be clearly stated that the soil of the forests we examined has a richer carbon stock than the neighboring arable land or pasture, but together with the amount of carbon stored in the O horizon, the forests surplus prevailed upon every examined point. Due to the slow process of carbon sequestration and organic matter entering the soil, we also plan to conduct long-term tests.

This article was made in the frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.

How to cite: Csorba, M., Bidló, A., Balázs, P., Végh, P., and Horváth, A.: Comparison of soil carbon stock of afforested and treeless sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9482, https://doi.org/10.5194/egusphere-egu24-9482, 2024.

The presence of soil fauna is essential for healthy soil life. As part of the soil mesofauna, Collembola are significant contributors to humus formation and the spread of mycorrhizal fungi, which are of major importance for plants, and they also help to decompose organic matter and mineralise the soil. Among the soil parameters, organic matter content is one of the most significant determinants of the abundance and diversity of Collembola. Our study aimed to explore these relationships in a forest-open landscape mosaic in a dry, sandy area in the Danube-Tisza Mid-Region of Hungary. Soil samplings were carried out in different forest types and nearby open areas (grassland and abandoned cultivated habitats). Five non-destructive soil samples of 100 cm3 were taken at each site using a soil corer with a 3.6 cm diameter and a 10 cm depth for the soil fauna survey. In total, 2,018 specimens from 13 families, and 49 species were sampled and identified. We used a multivariate ordination method (CCA) to investigate the relationship of individual species and life forms to specific soil parameters. It was found that mainly hemiedaphic species (such as Appendisotoma franzi, A. juliannae, Lepidocyrtus nigrescens) showed the strongest connection to soil organic matter. In contrast, euedaphic species (e.g., Doutnacia xerophila, Mesaphorura krausbaueri, Protaphorura cancellata) showed a weaker binding. The epedaphic, soil surface-dwelling species (e.g., Entomobrya multifasciata, Orchesella cincta) did not show a strong preference for soil organic matter content or other soil parameters. Based on similarity analyses (cluster analysis, Bray-Curtis distance), open habitats showed a distinct separation according to the Collembola species composition and abundance.

This article was made in frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.

How to cite: Winkler, D., Csorba, M., Bidló, A., Balázs, P., Végh, P., and Horváth, A.: The role of soil organic matter content in the composition and abundance of Collembola communities in a forest-open landscape mosaic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16602, https://doi.org/10.5194/egusphere-egu24-16602, 2024.

L band vegetation optical depth (L-VOD) is a widely used remote sensing variable for investigating the spatiotemporal variation in aboveground biomass (AGB). A key step of this method is to fit L-VOD against AGB, then use a space-for-time assumption to infer AGB change from fitted L-LOD change. In this study, we evaluated the performance of different fitting equations and explored their implications in predicting AGB. We used the SMOS-ICV2 L-VOD dataset and four AGB reference datasets. Specifically, we examined the implications of the space-for-time assumption in predicting the AGB interannual variations. We find that all the statistical fitting methods can capture the AGB spatial variation, yet introducing tree cover as a predictor significantly improves the AGB prediction, especially in regions with small and medium L-VOD values. However, these methods all fail to capture AGB spatial variation in dense forests. The AGB reference data also show large discrepancies in these regions. Our results also show that the spatial AGB sensitivities to L-VOD are much larger than the temporal AGB sensitivities to L-VOD, implying considerable uncertainties in temporal AGB changes predicted with spatially built models. By providing a comprehensive evaluation of fitting methods, our results offer a cautionary tale to the use of L-VOD data to infer AGB dynamics and the necessity of developing long-term field-based biomass change datasets for further constraining and evaluating AGB predictions from remote sensing observations.

How to cite: Zhang, Y., Ciais, P., Wigneron, J.-P., Chave, J., Cong, N., Li, X., Yang, Y., and Saatchi, S.: How accurately does L band vegetation optical depth predict aboveground biomass?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4841, https://doi.org/10.5194/egusphere-egu24-4841, 2024.

Dynamic global vegetation models (DGVMs) are essential for quantification of the response of land carbon storage to changes in atmospheric chemistry, climate, and land cover. While DGVMs are often evaluated concerning carbon responses to changes in CO₂ and climate, local responses to changes in land cover have received less attention. This is of concern as DGVMs are needed to project the long-term consequence of afforestation or deforestation on the land carbon balance under climate. Here, we present an assessment of the Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) model, one of the state-of-the-art DGVMs, aiming to evaluate the simulated growth in forest biomass carbon stocks across the European Union against comprehensive observational data.

We conduct a model-data comparison of biomass growth using databases that contain paired observations of above-ground biomass (AGB) and plant age, categorized across various age groups spanning from very young (0-19 years) to old (>99 years) forests for boreal and temperate forests. The biomass dataset encompasses a harmonized collection from multiple open forest inventory databases, comprising 603 sites across Europe for six plant functional types (PFTs). On average, the stands are approximately 58 years old, with a mean AGB of 6.4 kgC.m^-2. The findings indicate that simulations replicate the observed trend: AGB increases rapidly in young stands (<60 years old) and moderately saturates in later ages (>60 years old). However, the observed AGBs exhibit broader ranges and have more extremes than the simulated values. This is expected as observations refer to individual species, while our simulations are on the level of PFTs, which are an assemblage of species. Moreover, the comparisons reveal that the model underestimates AGB for temperate needleleaf evergreen forests, with a median deviation of approximately 60% from observed values. We propose a recalibration of the maximal rate of carboxylation and gross primary production fraction lost as growth respiration to reduce this deviation to less than 10%.

Our study highlights the potential of using observational biomass data to assess and calibrate DGVMs. This approach significantly enhances the ability of DGVMs to accurately reproduce the short-term land carbon sink response to reforestation. We provide a protocol that can easily be adapted to evaluate and recalibrate other DGVMs for the same purpose.

How to cite: Dinh, T. L. A., Goll, D., Ciais, P., Carvalhais, N., and Lauerwald, R.: Benchmarking simulations of forest regrowth across Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1784, https://doi.org/10.5194/egusphere-egu24-1784, 2024.

The role of the terrestrial biosphere in regulating the global carbon cycle is critical, and it is crucial to comprehend the regional-scale source-sink dynamics and the underlying mechanisms for developing effective mitigation strategies. The present study investigated the dynamic relationship between atmospheric CO₂ levels and environmental factors in South Asia (SA), Southeast Asia (SEA) and West Asia (WA); these regions are home to diverse ecosystems, including tropical rainforests, mangroves, and coral reefs. Understanding carbon dynamics in these ecosystems is crucial as they play a significant role in sequestering and storing carbon. Utilizing data from 2015 to 2021 from the OCO-2 satellite, we analyzed the column-averaged dry air mole fraction of atmospheric CO₂ (XCO₂) along with variables such as precipitation, temperature, and Leaf Area Index (LAI), which distinguishes between high and low vegetation types. These environmental factors were synchronized with the spatial and temporal attributes of bias-corrected Lite (V11) level-2 daily files obtained from OCO-2. The majority of the zones in the area showed a positive relationship between their temperature anomalies and XCO₂ anomalies, albeit with varying lag periods (ranging from 0 to 4 months). This suggests that these zones could potentially act as sources of CO₂ during warmer periods. This trend was not observed in some regions, including the western plateau and hills, eastern coastal planes and hills, Pakistan, and Nepal, where the relationship between temperature and CO2 exhibited varying lag effects. The correlations were examined between the inter-annual variability (IAV) of detrended and depersonalized monthly-resampled anomalies of XCO₂ datasets and various environmental factors (anomalies) across diverse agroclimatic zones. In tropical savannah and humid subtropical climates, observed a positive correlation, between XCO₂ anomalies and precipitation whereas arid and semi-arid areas displayed negative correlations. These patterns indicate that increased rainfall in certain regions might enhance vegetation productivity, thereby reducing atmospheric CO₂ levels. Furthermore, in areas dominated by tropical aseasonal forests, a dense LAI correlated negatively with XCO₂, suggesting that more dense vegetation leads to increased CO₂ absorption through photosynthesis. In contrast, tropical seasonal forests showed a positive correlation between LAI and XCO₂, each with a unique lag period. Our analysis demonstrates the complex patterns of CO₂ anomalies distribution in SA, WA and SEA influenced by climatic factors (precipitation and temperature) and vegetation density (LAI). These insights are crucial for understanding regional CO₂ source-sink dynamics and formulating effective climate change mitigation strategies.

How to cite: Jagadish, B., Patra, P. K., and Behera, M. D.: Exploring Regional-Scale Covariation: Atmospheric CO2 Anomalies Distribution Patterns, Vegetation Spread, and Climate Variables, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18551, https://doi.org/10.5194/egusphere-egu24-18551, 2024.

Ecosystems may exhibit various equilibrium behaviors (e.g., linear and threshold), which will dramatically affect how we understand and regulate ecosystem dynamics under different environmental conditions, thus reshaping ecosystems’ sustainable development. Studying equilibrium behaviors is particularly crucial for the Loess Plateau because hundreds of billions of Chinese Yuan have been paid to alter ecosystem structure and thereby to reduce soil erosion. Resultant increasing vegetation, however, exhausts soil water, which heavily threatens the sustainability of ecosystem function and services therein. It has been a widespread and long-lasting controversy over whether and where to afforest. However, one of the most fascinating equilibrium behaviors of alternative stable states, which permits more than one states under the similar conditions, has largely ignored in the framework. By integrating remote sensing products, a minimal model, and environmental data, this study explored alternative tree-cover states and its effects on functions and services of forest ecosystems in the Loess Plateau. The equilibrium behavior along annual precipitation gradient appeared to a threshold-type (uni-stability) combined with a fold bifurcation. That is, tree cover showed a threshold-type uni-stability when annual precipitation was lower than 400 mm, beyond which alternative stable states of high tree cover (forest, >35% tree cover), and medium tree cover (open woodland, 7%~35% tree cover) co-existed. Increasing spatial heterogeneity, and especially vegetation-precipitation positive feedback would advance the thresholds of transitions between alternative states towards to higher annual precipitation. Furthermore, regime shift from forest to open woodland states increased carbon stock, while reduced water yield, i.e., carbon and water formed a trade-off. This unusual balancing behavior not only enriches our understanding theoretically but also substantially benefit afforestation planning in the Loess Plateau practically, thereby promote forest ecosystem functions and services of forest ecosystems.

How to cite: Chen, N., Ma, L., and Yang, L.: Unusal equilibrium behavior of forest ecosystems in the Loess Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2330, https://doi.org/10.5194/egusphere-egu24-2330, 2024.

Understanding the intricate relationships between climate and vegetation remains a fundamental challenge in contemporary ecology. The ability to anticipate the specific climatic factors affecting different tree species and understand how they respond is crucial for mitigating the impacts of climate change on forested ecosystems. Additionally, quantitatively assessing habitat loss resulting from anthropogenic activities is essential for informed conservation efforts.
Our objective is to evaluate the potential distribution of pitch pine (Pinus rigida) in North America and assess the associated habitat loss. To achieve this, we employ a stepwise multidimensional climate envelope modeling approach, comparing two data-intensive models—the Variable Interaction Model (VIM) and the Variable Non-Interaction Model (VNM). These models discern the influence of diverse combinations of climatic characteristics on the distribution of the species. Both VNM and VIM employ Shapley values for factor ranking during construction. VNM assumes independent effects, resulting in a hyperrectangle-shaped climate envelope, while VIM considers interactions, yielding a complex, data-driven multidimensional envelope. Data integration involves mining the US Forest Inventories and climatic data  encompassing 19 parameters.  The results unequivocally highlight the VIM superior predictive accuracy compared to the Variable Non-Interaction Model VNM. Our findings reveal a habitat loss of approximately 91 %, primarily attributed to anthropogenic activities. This underscores the critical importance of comprehending the interplay between climatic factors in the development of climate envelope models for species ranges. The modeling approach developed in this study has the potential to enhance species distribution models for various tree species in the context of evolving climatic conditions.

How to cite: Strigul, N. and Rumyantseva, O.: Multidimensional climate envelop modeling of pitch pine (Pinus rigida) distribution in North America, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20540, https://doi.org/10.5194/egusphere-egu24-20540, 2024.

The recent consolidation of global carbon monitoring systems has been coupled with notable advances in methods for estimating the carbon cycle components in terrestrial ecosystems. These developments include a comprehensive assessment of the uncertainty and biases associated with these estimations. Gross primary productivity (GPP) is the most significant component of the terrestrial carbon cycle. Accurate estimation of GPP and its fluctuations over space and time is crucial not only for assessing ecosystem functioning and carbon balance but also for evaluating the resilience of ecosystems to adapt, survive and thrive in response to climate changes. Unfortunately, direct measurement of GPP through remote sensing (RS) signals is not feasible. Several RS signals associated with vegetation pigments and canopy structures can indeed function as proxies for GPP. These signals can be effectively integrated with various modelling approaches, considering different types and levels of complexity, to generate an estimation of global GPP at high spatio-temporal resolution.

This study aims to explore how Sentinel satellites can improve the remote global GPP estimation. Specifically, we evaluated the quality of the 10-daily GDMP product of Sentinel-3, ensuring its reliability and credibility, with a specific focus on evergreen forests, particularly Aleppo pine stands. The outcomes of this study are expected to contribute to refining and calibrating GDMP algorithms for improved accuracy.

The first aspect of our methodology involves the selection of several Aleppo pine forests across South-East Spain, where eddy covariance towers were installed, to study inter-site variability including soil characteristics, vegetation dynamics and forest management. Then, direct cross-comparisons between eddy covariance measurements and satellite observations were conducted for 4 independent study sites covering different periods (i.e., 2015-2018 and 2019-2023) to quantify uncertainties and biases in the GDMP product.

The results revealed that the GDMP product exhibits improved performance during wet periods, ranging across sites from the highest R² of 0.83 to the lowest R² of 0.71, but it encounters challenges in accurately simulating Gross GPP under drought conditions. This funding was expected because some potentially important factors such as drought stress among others were omitted in the current computation model of Copernicus Global Land Service. Therefore, it is suggested that the product could be more accurately labelled as a potential GDMP. Similarly, our analysis showed that Aleppo pine demonstrates high plasticity in response to local conditions that is not adequately captured by this GDMP model.

To address the challenges encountered in accurately simulating the GDMP product, we are working on developing a potential solution. This involves incorporating drought stress factors to enhance the model by integrating relevant physiological and environmental variables that influence specific responses of Aleppo pine to water shortage.

How to cite: Chebbi, W., Rubio, E., García-Morote, F. A., Andrés-Abellán, M., Picazo-Córdoba, M. I., Arquero-Escañuela, R., and López-Serrano, F. R.: Evaluation of the Sentinel-3A Gross Dry Matter Productivity (GDMP) product for evergreen forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12680, https://doi.org/10.5194/egusphere-egu24-12680, 2024.