Agnieszka Sulikowska

Winter plays a key regulatory role in the natural environment of the temperate zone. It determines the dormancy period of plants, enables the accumulation of water in the form of snow, and limits populations of pests and pathogens. Rising temperatures during the winter season, the shortening of thermal winter, and increasingly frequent warm episodes are leading to the loss of a stable, long-lasting cold phase, which is an important factor regulating ecosystem functioning.The aim of this study is to assess winter warm episodes and heat waves in the context of the duration of thermal winter in Central Europe. Cases of anomalously high air temperature were analyzed, taking into account the spatial extent of the extreme event, its intensity, and its duration. Variability in the frequency, affected area, and magnitude of the region’s heat load in recent decades was examined using high-resolution (2 km × 2 km) gridded data developed for the years 1961–2024.The obtained results clearly confirm the shortening of thermal winter in Central Europe – sometimes to only a few to a dozen days – while it is increasingly interrupted by prolonged episodes of above-zero temperatures. An extended area of the region is exposed to thermal extremes (positive values of minimum air temperature and days with maximum temperature exceeding the 95th percentile), and heat surpluses anomalous for the winter months are leading to a progressive destabilization of climate seasonality.The research findings indicate that the observed changes are not limited solely to an increase in mean temperature but also involve a transformation of the seasonal structure of the climate. The shortening and fragmentation of thermal winter, together with the increasing frequency of warm episodes, weaken the regulatory mechanisms of the natural environment, increasing ecosystem vulnerability to thermal stress and phenological disturbances. In light of projections of continued climate warming, this process may intensify further, making winter one of the key seasons in the analysis of contemporary climate change in Central Europe.Research funded by the National Science Centre, Poland under the OPUS call in the Weave programme 2022/47/I/ST10/02144

Spring phenology in temperate trees is strongly controlled by air temperature, yet the role of short-term thermal anomalies preceding phenological events remains insufficiently understood. In our previous analyses of silver birch (Betula pendula) phenology in Poland, we showed that the timing of both ground-observed leaf unfolding (LU) and satellite-derived start of season (SOS) was closely related to temperature anomalies in March and April, and that not only the magnitude but also the within-season timing of warming played an important role in shaping spring onset. Preliminary anomaly-based analyses further suggested that the period of approximately 20 days preceding leaf-out may be particularly important. However, contrasting early-spring seasons indicated that similar phenological outcomes may arise from different thermal trajectories, including both sustained warming and short but intense late-season warm pulses.In this study, we revisit these relationships using an extended dataset comprising LU observations for 2007–2026 and SOS estimates for 2018–2026. LU data were obtained from the Institute of Meteorology and Water Management – National Research Institute, while SOS was derived from Sentinel-2 imagery using the Enhanced Vegetation Index. Temperature conditions were assessed from in-situ measurements and a high-resolution station-based gridded dataset. We focus specifically on pre-event temperature anomalies, examining their magnitude, persistence, and timing in relation to the observed dates of spring onset. Rather than relying solely on calendar-month means, we analyse temperature anomalies in moving windows preceding LU and SOS to identify the period of greatest phenological sensitivity and to test whether exceptionally early spring onset is more strongly associated with sustained positive anomalies or with brief but intense warm episodes occurring shortly before the event.By combining long-term ground observations with satellite-based estimates, this study provides a more process-oriented perspective on spring phenology and its thermal controls. The results are expected to improve our understanding of how silver birch responds to anomalous thermal conditions and to help refine interpretations of phenological sensitivity under ongoing climate warming.

This study explores how exposure conditions affect the carbonation process of cementitious materials that include incinerated sewage sludge ash (ISSA), to evaluate ISSA’s potential as a sustainable additive in cement-based construction materials and its role in CO₂ sequestration. Hardened cement pastes with different amounts of ISSA (0 %, 20 %, 25 %, 30 %, and 35 %) were subjected to two carbonation experiments: indoor and outdoor in a natural environment. The carbonation process was tracked using phenolphthalein tests, scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), and calcium carbonate content measurement. Results show that ISSA-modified cement pastes have increased carbonation potential, especially at 20–25 % ISSA, with a rise in CaCO₃ formation and diverse calcite morphologies. However, higher ISSA levels (>30 %) led to decreased carbonation efficiency. The outdoor experiment revealed the significant influence of temperature and humidity changes on carbonation rates, resulting in slower CO₂ absorption compared to laboratory conditions.

Vegetation phenophases serve as indicators of long-term climate-driven environmental changes, impacting ecosystem functions like the carbon cycle and plant–animal interactions. Satellite-based phenology assessments, particularly with high-spatial and temporal resolution Sentinel-2 data, enable large-scale monitoring where field observations are scarce. This study modeled the start of the season (SOS) for deciduous species in Poland using Sentinel-2 data (2018–2023). We tested four vegetation indices [MTCI (MERIS Terrestrial Chlorophyll Index), EVI (Enhanced Vegetation Index), NDMI (Normalized Difference Moisture Index), VARI (Visual Atmospheric Resistance Index)] for their ability to correctly capture SOS in silver birch stands by comparing Sentinel-2 based SOS dates with ground observations, which were available only for this species. We then used the best-performing index to map SOS for black alder, pedunculate and sessile oak, and common beech. Results showed that Sentinel-2 indices effectively track SOS patterns at national scale, though different indices yielded varying SOS dates: EVI and NDMI estimates were similar, MTCI indicated later SOS with high variability, and VARI showed the earliest dates. Correlations with ground data were moderate (coefficients >0.5) and varied yearly. EVI provided the most stable results, making it most suitable for tracking other species. The earliest SOS dates appeared in 2018 and the latest in 2021, with birch generally showing the earliest SOS and oak the latest. Spatially, SOS started earlier in western lowlands and later in the Baltic moraine hills, northeast, and mountainous areas. Annual shifts likely reflected air temperature variability in spring, as shown in a preliminary growing degree days analysis. Our findings enhance understanding of forest phenology and demonstrate remote sensing’s potential for tracking large-scale seasonal changes. Uncertainties resulting from limited and variable ground observations, spatial mismatches between field and satellite estimations, and possible gaps in Sentinel-2 coverage highlight the challenges of validating SOS estimates; nonetheless, Sentinel-2 enables the detection of meaningful regional and species-level phenological patterns. Expanding the Sentinel-2 archives will further enhance this capability. Future studies should explore the relationship between SOS and temperature metrics, drawing on high-resolution gridded meteorological data to capture spatial patterns in spring temperature conditions and support spatial analysis of SOS–temperature relationships.

Climatological normal periods are used to describe the typical climate conditions that can be expected in a given location. These climate normals – statistical values such as means or totals for specific climate elements – are calculated for non-overlapping 30-year periods. The 1961–1990 period was probably the most widely used reference baseline in modern climatology, as it was recommended by the World Meteorological Organization for long-term climate change assessments. Now that 2020 has passed, a new climatological normal period (1991–2020) can be adopted. This raises an important question: how will this updated baseline affect the way we define anomalies and extremes, given that climate warming has already shifted what is now considered “normal” in many regions? With ongoing climate change, the statistical definition of “normal” itself is evolving – potentially influencing climate assessments and regional comparisons.The main aim of this study is to assess how the selection of the reference period (1961–1990 vs. 1991–2020) influences how extremes are defined and distributed across Central Europe, based on a new high-resolution dataset. First, we compared how the choice of baseline period affects spatial and seasonal patterns of air temperature and precipitation indices. These indices include mean values and counts of extreme days defined by absolute thresholds. Next, we assessed how standard percentile thresholds used to define extremes (such as the 90th percentile) vary depending on the baseline period, and how these differences impact the spatial distribution of corresponding extremes. The analyses are based on a newly developed, high-resolution gridded daily dataset for Central Europe (1 × 1 km), covering the years 1961–2020, which includes daily maximum and minimum temperatures and precipitation totals. The dataset is based on in-situ measurements covering Poland, Czechia, Slovakia, and the border regions of Germany and Austria.The results show large differences in temperature and precipitation patterns between indices computed using the two baseline periods, demonstrating that the 1991–2020 reference is strongly affected by recent climate change. The selection of a more recent baseline can significantly understate the extent of ongoing warming, especially when extremes are defined using percentile thresholds. Precipitation indices appear less sensitive to baseline changes, although differences still exist. The 1961–1990 period may offer a more stable reference for climate studies, and careful consideration is needed when communicating changing baselines to decision-makers.

Plant phenology is primarily driven by air temperature, although this relationship is complex and not yet fully understood – particularly regarding the influence of temperature extremes on the timing of individual phenophases. In recent decades, observed springtime warming has led to significantly earlier green-up in temperate deciduous forests. Furthermore, spring temperatures in Central Europe are projected to rise by 2–5°C by the end of the century, depending on the scenario. Such changes are expected to profoundly affect forest structure and functioning, including ecosystem processes such as water, carbon, and nutrient cycling. These shifts may, in turn, have far-reaching consequences for ecosystem productivity, food webs, and species interactions.To improve our understanding of deciduous trees responses to temperature changes – and how such shifts may affect ecosystems – we examined the relationship between the onset of spring activity in silver birch (Betula pendula) and recent springtime temperature anomalies in Poland (2018–2024). This period includes several extreme spring seasons (e.g. 2018, one of the warmest on record), offering a unique empirical basis for evaluating how future climate conditions may influence temperate forest phenology.The phenological data used in this study included both ground-based observations of leaf unfolding and satellite-derived estimates of the start of season (SOS) for silver birch, one of the most abundant deciduous tree species in Poland. Ground-based data were obtained from the Institute of Meteorology and Water Management – National Research Institute. The SOS metric was derived from Sentinel-2 imagery (10 × 10 m resolution), based on derivatives of the Enhanced Vegetation Index. Temperature conditions for individual seasons were assessed using in-situ measurements and a newly developed high-resolution gridded dataset (1 × 1 km) for Central Europe. The relationship between air temperature and the onset of the season was explored using both temperature anomalies and the Growing Degree Days index.The study provides empirical evidence of the sensitivity of spring phenology in deciduous trees to temperature conditions in Central Europe, offering valuable insights into potential future shifts under ongoing climate change. Our findings show a significant advancement in silver birch phenology during exceptionally warm springs and notable delays during colder ones. Most importantly, the results suggest that not only the magnitude, but also the timing of temperature anomalies within the season plays a crucial role in shaping spring phenological responses.

As the climate continues to warm, patterns of air temperature and precipitation in Central Europe (CE) are changing, affecting the frequency, intensity, and spatial extent of extremes in this region. Studying and understanding these variations is crucial due to natural hazards such events trigger and is essential for refining climate predictions. However, the reliability of climate reanalysis or gridded datasets regarding extreme weather is still uncertain at varying temporal and spatial scales, especially in areas of diversified geography like CE. In this study we aim to evaluate the performance of two reanalysis, ERA5 and ERA5-Land, and two gridded observation datasets, EOBS and newly developed high-resolution data for CE, alongside in-situ observations, regarding the occurrence, spatial extent, and intensity of extreme temperature and precipitation events. The study is based on daily maximum and minimum temperatures (Tmax, Tmin), and precipitation totals (RR) for the 1961-2023 period, covering CE defined as the area encompassing Poland, Czechia, Slovakia, and eastern Germany. The extreme events are defined based on absolute as well as local percentile thresholds. The newly introduced daily gridded dataset for CE is based on quality-controlled and homogenised station data from approx. 500 climatological stations and approx. 1000 rain gauges, with a spatial resolution of 1×1 km and additionally 0.5×0.5 km in the mountainous areas to better capture details of complex terrain.Gridded datasets validation procedure comprises of the comparison of in-situ data with the results extracted from the nearest grid points as well as from the predefined areal buffer. The co-occurrence of extremes between the datasets will be examined using statistics based on a contingency table, such as the hit rate, while the other extreme events’ characteristics, i.e. their spatial extent and intensity, will be studied employing the most common statistical measures, i.e. correlation coefficients, bias estimation, cross validation.The results indicate that the data accuracy regarding the representation of the temperature and precipitation extremes in CE depends strongly on the subregional topography features as well as varies with the intensity and severity of the events. These conclusions highlight the necessity of local datasets development, alongside with already existing regional or global databases, especially when specialised environmental modelling is taken into consideration.

Recent advancements in satellite phenology research demonstrate its effectiveness as a robust tool for monitoring vegetation and its responses to climate drivers. Satellite data provides insights distinct from ground-based observations, yet both sources complement each other well. Utilizing new-generation satellites, with high spatial and temporal resolution, facilitates a deeper understanding of climate-phenology relationships. These satellite-derived indices prove especially valuable in regions with scarce ground-based observations like Poland. Air temperature plays a crucial role in driving various plant developmental processes, among which the initiation of spring activity is the most prominent. However, drawing ultimate conclusions regarding this relationship remains challenging as quantitative estimates strongly diverge. Recent observations indicate that climate warming has altered plant phenology across many European regions. Investigating these complex connections is crucial, given that changes in plant phenology affect fundamental ecosystem functions, including water, carbon, and energy fluxes, as well as interactions between plants and animals, ultimately shaping ecosystem productivity. The main aim of this study is to evaluate the impact of air temperature conditions on the onset of spring activity of silver birch (Betula pendula) in Poland over the years 2007-2024. The phenology data used in the study include both ground observations of leaf unfolding and satellite-derived estimates of start-of-season (SOS) for silver birch, which is among one of the most abundant deciduous tree species in Poland. Ground-based data were sourced from the Institute of Meteorology and Water Management – National Research Institute and spans years 2007-2024, while the satellite-based SOS metric was derived from Sentinel-2 imagery and covers the 2018-2024 period. The SOS metric was based on EVI (Enhanced Vegetation Index) derivatives. Temperature conditions during individual seasons were assessed using in-situ measurements as well as the E-OBS (v28.0e) gridded dataset, and the relationship between air temperature and the start of the season was studied using temperature anomalies and the Growing Degree Days (GDD) index for 5°C base temperature. The study showed large inter-annual variability in silver birch phenology – the estimated SOS varied between studied seasons by more than 20 days. The results also proved the usefulness of Sentinel-2 data in monitoring the phenology of deciduous tree species, while indicating that satellite-based estimators pertain to a slightly different phenological phase than ground-based observations. The study provided insights into the links between temperature conditions and the spring phenology of birch, showing that responses to air temperature are complex. The relationship remains evident, as, for instance, in 2018, characterized by extremely warm April and May, an advanced start of the season was observed. Conversely, in 2021, a delayed start of the season was noted as a consequence of cold temperatures during these months. However, quantitatively describing these relationships remains a challenge and further research is necessary.

Air temperature is a crucial driver of many plant developmental processes, among which the initiation of spring activity is the most prominent. Recent climate warming has been found to alter plant phenology in many European regions. However, ultimate conclusions regarding this relationship are still challenging as quantitative estimates are strongly diverging. Moreover, the results concerning the role of temperature extremes, i.e., unusually warm or cold periods, are equivocal. Studying these complex links is of utmost importance as changes in plant phenology affect basic ecosystem functions, including water, carbon, and energy fluxes, as well as plant-animal interactions and ecosystem productivity. Recent progress in research based on satellite phenology indicates that it is a powerful tool to monitor terrestrial vegetation and its responses to climate drivers. It provides qualitatively different traits than ground-based observations, but these two sources of information complement each other well. The use of new generations of satellites with high spatial and temporal resolution helps to gain a better insight into the climate-phenology relations. The main aim of this study is to assess the effect of air temperature conditions on the start of the spring activity of deciduous trees in Poland during 2018-2023. Data used in the study include the E-OBS (v27.0e) gridded daily mean, maximum and minimum temperatures, and the Sentinel-2 imagery over March-June. The tree species chosen for the analysis are common beech (Fagus sylvatica), silver birch (Betula pendula), and two species of oak (Quercus), which are among the most abundant in Poland. Several hundred single species stands were delimited across the area of Poland to study inter- and intraspecific differences in temperature-phenology relations. General temperature conditions during six individual seasons were assessed using the growing degree days (GDD) for 0°C and 5°C base temperatures. Special attention was paid to extremely warm or cold events, i.e., warm and cold spells, defined using percentile-based thresholds. Their effects were evaluated regarding their intensity and timing within the season. Trees’ response to temperature conditions was assessed using satellite-derived start-of-season (SOS) metric based on derivatives calculated from two indices: MTCI (MERIS Terrestrial Chlorophyll Index) and EVI (Enhanced Vegetation Index). This preliminary study provided insights into complex links between temperature conditions and spring phenology of deciduous trees, showing that responses to climate drivers, especially extreme events, are species-dependent. Large inter-annual variability in phenology has also been shown – estimated SOS varied between studied seasons by more than 20 days. The results also proved the Sentinel-2 data to be useful in the monitoring of individual tree species phenology.

Ekstrema ciepła w zmieniającym się klimacie Europy: definicje, przyczyny, tendencje, skutki