Climate change and archaeological heritage: risk identification and monitoring of a lakeshore archaeological site in Smuszewo (Poland) - A case study

47 Renata GRAF(*),Lech KACZMAREK(**),Sławomir KRÓLEWICZ(*), Włodzimierz RĄCZKOWSKI(***) & Lidia ŻUK(***) (*)Adam Mickiewicz University in Poznań - Institute of Physical Geography and Environmental Planning - Poznań, Poland (**)Adam Mickiewicz University in Poznań - Biological Spatial Information Laboratory - Faculty of Biology - Poznań, Poland (**) Adam Mickiewicz University in Poznań - Faculty of Archaeology - Poznań, Poland Corresponding author: r[email protected] CLIMATE CHANGE AND ARCHAEOLOGICAL HERITAGE: RISK IDENTIFICATION AND MONITORING OF A LAKESHORE ARCHAEOLOGICAL SITE IN SMUSZEWO (POLAND) - A CASE STUDY ExTENDED AbSTRACT Il cambiamento climatico rappresenta una minaccia crescente per il patrimonio culturale, in particolare per i siti archeologici situati sulle sponde dei laghi, dove le fluttuazioni dei livelli dell’acqua e i cambiamenti nell’equilibrio idrico influenzano direttamente le condizioni di tutela. Il documento presenta una strategia di identificazione e monitoraggio del rischio a più livelli, sviluppata per un insediamento fortificato dell’età del Bronzo Finale / Prima Età del Ferro a Smuszewo, in Polonia, come parte del progetto TRIQUETRA. Il sito, situato all’interfaccia tra ambienti terrestri e acquatici, è caratterizzato da strutture in legno ben conservate, identificate lungo la sponda orientale e nel Lago di Czeszewo, così come all’interno dell’insediamento fortificato. La conservazione di questi reperti dipende dalla stabilità idrologica del lago, che è stata influenzata da cambiamenti climatici a lungo termine e da attività umane. La ricerca si basa su una metodologia di valutazione del rischio a tre fasi, che integra analisi di dati storici, tecniche di telerilevamento e monitoraggio in loco. Sono stati analizzati documenti cartografici storici, fotografie aeree e immagini satellitari per tracciare i cambiamenti ambientali, evidenziando l’impatto delle modifiche nell’uso del suolo dal XIX al XXI secolo, le attività di bonifica e i cambiamenti climatici. Inoltre, i dati meteorologici pluriennali hanno fornito approfondimenti sulle minacce indotte dal clima nella regione. Una sfida importante durante lo studio è stata la mancanza di misurazioni sistematiche dei livelli dell’acqua nel Lago di Czeszewo, che ha impedito di stabilire una correlazione diretta tra i cambiamenti idrologici osservati e il rischio associato alla conservazione dei reperti archeologici. Per affrontare queste limitazioni, nel 2023 è stato avviato un sistema di monitoraggio che include banche dati geospaziali tematiche, l’acquisizione di immagini aeree con droni e misurazioni dirette dei livelli dell’acqua. Queste attività mirano a quantificare i principali fattori che influenzano le fluttuazioni del livello dell’acqua e il loro impatto sull’integrità strutturale del sito. I dati raccolti supportano la creazione di una mappa dinamica del rischio, necessaria per lo sviluppo di strategie di conservazione a lungo termine. I risultati preliminari indicano che sia fattori climatici che antropici contribuiscono in modo significativo ai cambiamenti idrologici nel bacino del lago. La variabilità pluriennale e stagionale delle precipitazioni, l’aumento delle temperature e i periodi prolungati di siccità accentuano la variabilità del livello dell’acqua, accelerando potenzialmente il degrado delle strutture in legno. Allo stesso tempo, i progetti storici di bonifica e drenaggio hanno modificato la capacità naturale di ritenzione idrica, destabilizzando ulteriormente l’idrologia del lago. Questo studio mette in evidenza la vulnerabilità dei siti archeologici sulle sponde dei laghi ai cambiamenti climatici e all’impatto dell’attività umana. Utilizzando un approccio interdisciplinare che combina analisi di materiali cartografici storici e contemporanei, dati di telerilevamento e monitoraggio in loco, i risultati dell’analisi possono fornire una base per la mitigazione del rischio e la protezione del patrimonio archeologico. La metodologia del progetto TRIQUETRA è intesa come un modello per condurre ricerche simili in tutta Europa, evidenziando la necessità di migliorare l’acquisizione e la raccolta dei dati, la modellizzazione predittiva e le politiche di conservazione adattative. Italian Journal of Engineering Geology and Environment www.ijege.uniroma1.it IJEGE, Special Issue 1 (2025): 47-64, DOI: 10.4408/IJEGE.2025-01.S-04 E-ISSN 2035-5688 | ISSN 1825-6635 / ©Author(s) 48 Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it R. gRaf, L. KaCZMaREK, S. KRÓLEWICZ, W. RĄCZKOWSKI & L. ŻUK AbSTRACT The aim of this paper is to present a multi-level approach to risk identification and monitoring strategies for the lakeshore archaeological sites. Within a range of the cultural heritage typologies that are addressed by the TRIQUETRA project, the Late Bronze Age/Early Iron Age fortified settlement at Smuszewo (Poland) occupies a transitional position between mainland and water environment. Archaeological excavations and other surveys conducted between the 1950s and 2010s revealed wellpreserved wooden structures on land and on the east shore of Czeszewo Lake. Crucial to their preservation is the waterlogged environment which is directly related to the condition of the lake, water balance and particularly the water level. The problem of deteriorating water conditions (e.g. decreasing water level) in neighboring areas - resulting in recurrent droughts – has already been identified. However, its impact on the fragile wooden relics of the fortified settlement has not yet been assessed. Keywords: climate change, cultural heritage, risk assessment, lakeshore archaeology, remote sensing, hydrological monitoring, Smuszewo INTRODUCTION It is difficult to dispute the view that we are experiencing anthropogenic climate changes that impact the world around us, leading to numerous challenges. The multifaceted nature of climate change directly and indirectly modifies the conditions in which we live, affecting environmental contexts, economic activities, social relations, and the broader cultural sphere. Archaeological heritage is one such area that is and will continue to be affected by the consequences of climate change (Cassar, 2005; Hollesen, 2018). Considering that this heritage is nonrenewable , the challenges associated with its protection become even more significant (Heathcote et alii, 2017; Rockman & Hritz, 2020). Among the most vulnerable cultural resources are archaeological sites located in transitional environments, such as lakeshores, where changes in water balance and hydrological dynamics directly threaten the preservation of organic structures (Holden et alii, 2006; Bonazza et alii, 2021). This issue is increasingly recognized, leading to the formulation of research projects (both national and international) aimed at identifying threats on local and regional scales and developing strategies to minimize the negative impacts of ongoing climate and environmental changes (Bosher et alii, 2019; Howard et alii, 2016). TRIQUETRA: Toolbox for assessing and mitigating Climate Change risks and natural hazards threatening cultural heritage is currently one of the projects addressing the identification, assessment, and mitigation of risks to cultural heritage resources as a consequence of ongoing climate changes. The identification of threats to cultural heritage involves the need to pinpoint the most significant factors and determine methods for recognizing and assessing their impact (Sesana et alii, 2020; Orr et alii, 2021). This can be done at both regional and local levels. Regional considerations permit the creation of general models that indicate trends across different areas of Europe. In the context of individual archaeological sites, general models provide a broader context for considerations, but the analysis of local conditions also seems particularly important (Daly, 2014). Taking this aspect into account in the assessment of a specific archaeological site, it is worth identifying local factors deemed significant. These can be categorized into relatively stable factors (i.e., those not subject to rapid processes) and dynamic factors, which can be observed relatively continuously. The objective of this study is to present a multi-tiered approach to risk assessment and monitoring at lakeshore archaeological sites, using the fortified settlement at Smuszewo (Poland) as a case study. This text was created as part of the TRIQUETRA project and contributes to its goal by investigating how environmental variability affects the structural integrity of organic (including wood) archaeological remains. The diversity and specificity of relics from past human activities shape how questions are formulated. In the case of Smuszewo, site 3, the location of the archaeological remains particularly their position along the lakeshore gives rise to a range of site-specific questions (Fig. 1). Crucial to their preservation is the waterlogged environment which is directly related to the condition of the lake, water balance and particularly the water level (e.g. Broda & Hill, 2021; Lucejko et alii, 2020). The research addresses key questions: (1) how do water level dynamics in lake influence the preservation of wooden relics, (2) what are the main climatic and anthropogenic factors affecting hydrological conditions in the region, (3) can predictive tools and monitoring systems improve long-term conservation strategies? These questions arise from a broader need to understand how dynamic and static environmental variables intersect at vulnerable archaeological sites. Fig. 1 - Location of the Smuszewo archaeological site (No 3) on the orthophoto map and hypsometric map of Poland (source: Head Office of Land Surveying and Cartography, orthophoto map of Poland 2023, hypsometric map 2024. Available at: https:// www.geoportal.gov.pl) 49 Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it CASE STUDY The assumptions of the TRIQUETRA project led to the selection of a case study in Central Europe. The Smuszewo site 3 (AZP 4232/95) consists of the remnants of the Late Bronze Age/Early Iron Age fortified settlement. These remains were identified in 1863 and referred to as the Czeszewo lake-dwelling, in reference to previously discovered pile dwellings in Germany and Switzerland. The wooden structures observed at that time were located in the coastal zone of the eastern part of the lake and were found underwater and in peat sediment layers outside the embankment surrounding the settlement. They were revealed due to the lowering of the lake’s water level resulting from drainage works (Libelt, 1870-1871; Łepkowski, 1871). Archaeological excavations conducted in the 1950s and 1960s indicated the presence of wooden structures within the settlement, similar to those extensively excavated in Biskupin (Kostrzewski, 1938; Durczewski, 1985). These wooden structures related to internal buildings were located approximately 0.80–1.10 meters below the current ground level (Rajewski, 1957; Malinowski, 1961), which roughly corresponds to an elevation of 88.60/89.00 meters above sea level (Polish vertical datum – KRON86). Noninvasive investigations (geophysical surveys and interpretation of aerial photographs) conducted in 2004 and 2010 showed a very clear plan of internal structures (wooden buildings, paved wooden streets, hearths, etc.) (Harding & Rączkowski, 2010). Only a few such settlements have been recorded, but all of them share similar threats. APPROACH AND DATASETS The complexity of environmental variables requires an interdisciplinary approach. This involves geomorphological, soil, hydrological, meteorological, flora and fauna, archaeological data, as well as contemporary human activities. All these factors are interconnected but may highlight different aspects of threats. The vulnerability of material relics of cultural heritage to threats is interpreted as the degree to which an object is exposed to damage or destruction due to natural factors or human activities (Sabbioni et alii, 2008). Assessing vulnerability is a complex process that requires considering many interrelated factors (Brimblecombe et alii, 2006). In this study, it was conducted based on the analysis of selected components of the natural environment and anthropogenic pressure factors (Table 1). To assess the role of individual factors from a historical perspective, we utilized a wide range of data: archaeological, topographical, environmental (thematic), climatic, and remote sensing data (Table 2). Additionally, in the years 2023–2024, detailed data about the immediate surroundings of the site were acquired through regular monitoring using RGB and thermal aerial photographs from an altitude of up to 120 meters (UAV) (Fig. 2). Simultaneously, regular water level measurements were conducted using a probe that measures the water level and records it with a Datalogger DL/N series 64. Historical cartographic data were used in the analysis of environmental component transformations, while remote sensing and UAV-based surveys were employed in monitoring landscape Tab. 1 - Factors considered in cultural heritage vulnerability assessment (Smuszewo case) Fig. 2 - Examples of UAV’s aerial survey/orthoimages for monitoring environmental conditions; with dates of acquisition CLIMATE CHANGE AND ARCHAEOLOGICAL HERITAGE: RISK IDENTIFICATION AND MONITORING OF A LAKESHORE ARCHAEOLOGICAL SITE IN SMUSZEWO (POLAND) - A CASE STUDY 50 Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it R. gRaf, L. KaCZMaREK, S. KRÓLEWICZ, W. RĄCZKOWSKI & L. ŻUK and hydrological changes. Remote sensing data for this area have been available since 1966 and include aerial photographs with a spatial resolution of up to 25 cm collected in Poland for cartographic purposes, laser scanning used to develop a highly accurate terrain surface model, satellite spy images from the Corona and Hexagon programs, medium-resolution images from the Landsat programs (approximately 1000 cloud-free terms from 1984 to the present with the spatial resolution 15/30m), and from the Sentinel program (both radar and multispectral, with a spatial resolution of up to 10 m), as well as commercial high-resolution images (e.g., WorldView, Ikonos, QuickBird, PlanetLab). Meteorological records, including data from the Institute of Meteorology and Water Management – National Research Institute’ (IMGW-PIB) meteorological stations and historical climate data sets, were used to assess trends in air temperature, precipitation, and extreme weather events. Hydrological databases supported the analysis of water regime transformations within the fortification’s range and catchment area, as well as changes in the lake’s water level to assess their impact on the site’s wooden relics. Geological and soil data were used in the analysis of stability and susceptibility of the terrain to erosion and water retention for long-term environmental balance assessment. Tab. 2 - Data available and acquired for research purposes 51 Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it CLIMATE CHANGE AND ARCHAEOLOGICAL HERITAGE: RISK IDENTIFICATION AND MONITORING OF A LAKESHORE ARCHAEOLOGICAL SITE IN SMUSZEWO (POLAND) - A CASE STUDY IDENTIFICATION OF CONTExTS AND PROCESSES Geomorphological and geological contexts The archaeological site in Smuszewo is located by Czeszewo Lake, a ribbon lake formed during the Baltic glaciation. Its morphology results from genetic conditions and subsequent processes that transformed the lake and its surroundings (Kozarski, 1981). The retreat of the ice sheet left behind a deep depression filled with mineral sediments and surrounded by a moraine upland zone (Krygowski, 1961; Bartkowski, 1965). During the late glacial period, Czeszewo Lake took the form of a large proglacial lake, filling almost the entire ribbon lake depression. Studies by Sołowiej (1975) in the 1970s showed that the lake occupies only a small part of the original depression, extending along an east-west axis. Over time, the water level in the lake decreased, peatlands formed, and vegetation gradually encroached on the shallower areas, as documented by the presence of gyttja (lake sediment) directly deposited on clays. The layout and structure of the lake basin and its immediate surroundings were transformed by natural processes such as sedimentation, vegetation succession, and the accumulation of peat layers, as well as erosion processes, which were later intensified by human activities (land use changes, drainage works, cutting reeds, digging peat for heating). Considering the hypsometric criterion, three distinct levels were identified within the ribbon lake of Czeszewo Lake (Sołowiej, 1975) (Fig. 3): • the lower level (approximately 87 m a.s.l.), constituting the contemporary bottom of the ribbon lake; • the higher level (2.5-5.0 m above the bottom), with hills forming a kind of ‘islands’ in the peat-filled ribbon lake; • the edges of the ribbon lake, more pronounced on the southern side (relative height over 12 m) than on the northern side (7.5-9.5 m). The deposition of organic and inorganic materials over centuries has led to the gradual filling of the lake. Currently, the lake bottom, filled with organic and mineral sediments, has a slight slope towards the west and is characterized by constrictions made of mineral formations surrounded by peat. The sediments reach a thickness of up to 0.5 meters, and vegetation covers 98% of the shoreline and 25% of the lake basin (Fig. 1). The coexistence of sedimentation processes and vegetation growth has contributed to the formation of peatlands in shallow areas and, in some places, to the quasi-stabilization of the shoreline, reducing erosion activity. The northern edge of the ribbon lake, more geomorphologically stable, limits erosion and anthropogenic influences. In contrast, the southern edge features numerous erosional incisions, which drain the upland. This zone is characterized by more intense erosion processes. Additional morphological elements increasing the dynamics of the slope zone include anthropogenic scarps and denudation basins, while within the ribbon lake and kettle holes, there is a dense network of drainage ditches and channels that emphasize the features of the discussed landscape. Morphological changes in the Smuszewo site area are associated with the presence of two genetically distinct groups of surface forms: postglacial (organic accumulation plains, dry and wet closed depressions, erosional valleys, erosional edges, alluvial fans) and anthropogenic (peat extraction pits, excavations, trampling and plowing terraces) (Sołowiej, 1975). The geological-lithological stability (quasi-stability) of the area results, among other things, from the nature of morphological structures, lithological types, and sediments forming the deeper geological substrate. The analysis of the geological and soil-agricultural maps of the Smuszewo settlement area and its surroundings (Fig. 4) highlights key features of the area related to the presence of various lithological types, such as sands and glacial tills, the appearance of Fig. 3 - Geomorphological sketch of the surroundings of Czeszewo Lake. Legend: 1) ribbon lake bottom, 2) drainless depressions, 3) moraine outcrops in the channel bottom, 4) undulating moraine plateau, 5) dead - ice moraines, 6) surface waters, 7) edge of the subglacial channel. Source: own study based on DTM 5 x 5 m (https://geoportal.gov.pl) and explanations to the Detailed Geological Map of Poland (https://geologia.pgi.gov.pl/karto_geo) Fig. 4 - Lithological map of the surroundings of Czeszewo Lake. Legend: 1) clays, 2) clayey sands, 3) sands on clays, 4) sands, 5) peat and muck soils, 6) no data (bottom of the ribbon lake), 7) surface waters. Source: own study based on digital soilagricultural map at a scale of 1:5k (https://geoportal.gov.pl) 52 Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it R. gRaf, L. KaCZMaREK, S. KRÓLEWICZ, W. RĄCZKOWSKI & L. ŻUK organic soils, and products of washing and leaching in closed depressions and the ribbon lake. This indicates the dynamics of processes leading to changes in the lithology of formations and, indirectly, changes in soil conditions related to lithology. The organic deposits and peatlands surrounding most of the lake are associated with wetland areas. Compared to mineral soils, they are generally less stable; peat itself is prone to compaction, subsidence, and oxidation upon drying. The sands and sandy soils near the lake indicate past fluvial or glacial processes. Sandy soils provide moderate stability but are susceptible to erosion, especially on slopes or areas with concentrated water flow. In contrast, glacial tills, common in the moraine upland surrounding the lake, provide a more stable substrate. Their stability can be compromised by human activities that disrupt their structure. The analysis of the stability of the edges of the Czeszewo Lake ribbon lake, considering the lithology of the formations, indicates significant differences between its southern and northern parts. The southern edge of the ribbon lake, characterized by a higher proportion of loose sandy formations and greater slope, is more prone to erosion processes and potential landslides, especially during heavy rainfall. The slope map (Fig. 5) confirms that areas with the highest slopes (>12°) are found in this part of the ribbon lake, making them particularly vulnerable to degradation. The northern edge of the ribbon lake is gentler (slopes <9°), with a higher proportion of glacial tills that stabilize the slope structure. An additional factor limiting erosion is the vegetation cover, which reduces surface runoff and soil loss. The slope map with enhanced contrast (Fig. 6) confirms that the southern edge is more susceptible to destructive processes, and this is evidenced by the preservation state of another fortified site (Smuszewo, site 1, north side) dated to the early medieval period (Fig. 6). Field studies by Sołowiej (1975) showed the presence of results of abrasion processes. In the past, these processes may have led to the destruction of part of the fortification (site 3), as seen in the analyzed terrain profiles. Climate changes and monitoring Currently, it seems that climate change can be considered a significantly dynamic factor shaping environmental conditions in the region of Czeszewo Lake. Historical, contemporary, and projected changes are observed, which may be crucial for the functioning of the lake’s ecosystem and the preservation of archaeological relics. Archaeological relics are particularly susceptible to climate-related changes. Their wooden structures are located in the lake’s coastal environment and ‘islands’ in the peat-filled ribbon lake, where water level fluctuations, seasonal changes in precipitation, and air temperature variations play a significant role in their conservation processes. The climatic region (central Greater Poland), in which the Smuszewo fortified site is located, is characterized by more frequent occurrences of very warm and simultaneously cloudy weather without precipitation compared to other regions of Poland (Woś, 1999). Measurements of basic meteorological parameters – precipitation and air temperature – allow us to identify the main trends in this part of Poland. The nearest measurement station to the fortification is the IMGW-PIB station in Gołańcz (9 km northwest of the fortification), where precipitation is recorded. The nearest IMGW-PIB measurement station where air temperature is recorded is in Chrząstowo (32 km north of the fortification). The average annual precipitation for the Gołańcz station in the period 1954-2023 is 511 mm, one of the lowest in Poland – the average for Poland is 600 mm (Table 3). The figure (Fig. 7) shows the annual precipitation totals for the Gołańcz station, divided into the winter-cold half-year (months from November to April) and the summer-warm half-year (months from May to October). Annual precipitation totals show an upward trend, particularly noticeable after 2000, but also exhibit significant variability, ranging from 290 to 720 mm. During the measurement period, three years Fig. 5 - Hypsometric map of the surroundings of Czeszewo Lake. Legend: 1) hypsometric color scale (values in meters above sea level), 2) steep slopes (>12°), 3) surface waters. Source: own study based on a 5×5 m DTM (https://geoportal.gov.pl) Fig. 6 - The erosion of the shoreline slopes has led to the destruction of parts of the fortified settlements, as shown on the synthetic slope gradient map. Smuszewo, site 1 (early medieval hillfort) – the north section of the rampart (on the lakeside) is missing. Smuszewo, site 3 (Late Bronze Age/Early Iron Age fortified settlement) – the most severe damage affects the western part of the ramparts on the lakeside 53 Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it CLIMATE CHANGE AND ARCHAEOLOGICAL HERITAGE: RISK IDENTIFICATION AND MONITORING OF A LAKESHORE ARCHAEOLOGICAL SITE IN SMUSZEWO (POLAND) - A CASE STUDY with precipitation totals exceeding 700 mm were recorded, namely 1967, 1970, and 2017. The lowest precipitation totals were recorded in 1982 and 1989 (Fig. 7). From the perspective of Czeszewo Lake’s water balance, the amount of precipitation during the cold season, along with periods of persistent snow cover that delay surface runoff and contribute to retention, is significant. The precipitation total in the cold half-year shows an upward trend, in contrast to the trend of precipitation totals in the warm half-year, which shows a weak downward trend. The graph in the figure (gray line) shows that there may be periods when the precipitation total in the cold season may be close to or less than 100 mm, with an average of 189 mm (1995/1996 and 1996/1997). The highest precipitation total in the cold half-year was recorded for the 2023/2024 season, 339 mm. Precipitation change forecasts for Poland until 2100 indicate that in future climate conditions, the precipitation total may further increase, but with noticeable seasonality (Raport, 2020). Forecasts based on climate change scenarios suggest more intense precipitation during the autumnwinter periods and a potential decrease in summer precipitation totals. However, observational data from the Gołańcz station (Fig. 7) show only weak trends with high interannual variability and do not yet clearly confirm these projected seasonal shifts. Figure 8 shows the average monthly air temperatures for the Chrząstowo Station from 1981 to 2024, located 34 km north of the Smuszewo site. An upward trend in air temperature is visible, with a notable increase in average monthly temperatures during the winter months. In the 1980s, the average monthly temperature in winter (January/February) even dropped below −10°C. This increase in evaporation and decrease in water accumulation during the cold period for Czeszewo Lake may, in turn, affect the minimum water level in the summer season. Hydrology and its dynamic According to the hydrographic division of Poland, Czeszewo Lake is located in the Wełna River catchment area (a tributary of the Warta River), with which it is connected via the Wapno– Laskownica Canal flowing into the Gołaniecka Stream (a tributary of the Wełna River) (Fig. 9). The watershed delineating the total catchment area of the lake, covering 81.9 km² (JCWP Czeszewo Lake Card: https://wody.isok.gov.pl/pdf/JCW/LW10215.pdf), is mostly clearly marked in the terrain’s topography. The direct catchment area of the lake constitutes only 3.3% of the total catchment area. In the immediate vicinity of Czeszewo Lake, about 0.4 km to the east, lies Małe Lake (or Smuszewo, or Kujawki) with which it is connected by a section of the Wapno– Laskownica Canal. Extending westward from Czeszewo Lake are large peatland areas, intersected by drainage ditches and canals, while closed depressions are present in the upland area. Fig. 7 - Annual precipitation at Gołańcz station (1954–2023), with divided into cold (months X–III) and warm seasons (months IV–IX) Fig. 8 - Annual precipitation at Gołańcz station (1954–2023), with divided into cold (months X–III) and warm seasons (months IV–IX) Tab. 3 - Average total precipitation for Gołańcz station by decades for the period 1954–2023 Fig. 9 - Total (1) and direct (2) catchment area of Czeszewo Lake with hydrographic objects: 3) surface waters, 4) wetlands, 5) WapnoLaskownica Canal, 6) main streams, 7) other streams and drainage ditches. Other designations: 8) meadows and grassland, 9) forests, 10) built-up areas. Source: own study based on the Database of Topographic Objects 1:10k (https://geoportal.gov.pl) 54 Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it R. gRaf, L. KaCZMaREK, S. KRÓLEWICZ, W. RĄCZKOWSKI & L. ŻUK The area is characterized by an unfavorable water balance structure. The average annual precipitation here is among the lowest in Poland, amounting to 508 mm for the Gołańcz station for the period 1961-2000, and 511 mm for the years 1954-2023 (see above). Additionally, the region is in a low runoff zone, with runoff levels even below 100 mm, compared to the average runoff for Poland of around 165 mm. The average unit runoff values in the Czeszewo Lake catchment area are about 2 l/s km², compared to the Polish average of 5.5 l/s km². These low values result from very high evaporation in the lake’s catchment area and weak contact between the canal waters and groundwater. The drainage streams in the region are shallowly incised into the upland area, thus usually draining only the shallow and typically poorly endowed aquifers. Additionally, the main stream, the Wapno–Laskownica Canal, has been regulated for the needs of the Wapno mine and the developing agriculture in the region. Research conducted in this area by Sporakowski (1969) already confirmed high evaporation (477 mm) and very low runoff (85 mm) during that period, despite significant drainage works being carried out in the region. This situation results from the constriction in the lake’s ribbon, which hinders flow. Large areas of peatlands and the lake, thus areas of increased local evaporation, undoubtedly contributed to reduced runoff. The effects are deepening water deficits, prolonged periods of low water levels in the lake, and periodic water disappearance in the canal and other smaller streams. According to Gilly’s topographic map, the so-called Special Karte von Sudpreussen (1802-1803), the area around Czeszewo Lake was marked as swamps. Their area was approximately 300 ha at that time (sołowiej, 1975). Measurements from 1955 showed that 2/3 of the swamp areas had been transformed by humans. This process began in the first half of the 19th century when drainage led to a rapid reduction in the lake’s area, by about 1/4 of its original area (Libelt, 1870-1871). The rate of shrinkage of the original basin area, due to sediment filling, significantly accelerated in the last decades of the 20th century. This is evidenced by the reduction in the water surface area from 148.3 ha in 1961 (The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn) to 125 ha in 1989 (Choiński, 1992) (Fig. 10). Generally, it can be stated that in terms of hydrographic changes in the studied area over the last 150-200 years, there has been a lowering of groundwater levels, a reduction in the extent and depth of the lake, and the elimination of post-glacial kettle holes in the upland (most of the ‘kettle holes’ have become peatlands). In the former wetland areas in the immediate vicinity of Czeszewo Lake, small water bodies have formed as a result of peat extraction. In its current form, Czeszewo Lake can be classified as a dimictic stratified lake: max depth 8 m and average depth 3.7 m Fig. 10 - Historical changes in the surface of Czeszewo Lake and surrounding wetlands and peatlands based on maps from the 19th to the 21st century 55 Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it CLIMATE CHANGE AND ARCHAEOLOGICAL HERITAGE: RISK IDENTIFICATION AND MONITORING OF A LAKESHORE ARCHAEOLOGICAL SITE IN SMUSZEWO (POLAND) - A CASE STUDY settlement embankment, both from the lake side and the eastern side. An increase in soil moisture within the embankments was also recorded. In August (August 6th, 2024) and September, the water level in the lake stabilized at 88.30 m above sea level, while from November, it began to rise slowly. The water level in Czeszewo Lake shows clear seasonal changes in the annual cycle (the amplitude of fluctuations exceeds 1 m), as confirmed by hydrological monitoring data conducted in 2024. The dynamics of water level fluctuations in the lake are related to both meteorological conditions and changes in the lake’s water balance structure. The highest level was recorded at the end of winter, and the lowest at the end of autumn (Fig. 11). The winter-spring period is characterized by an increase in water level due to snow-rainfall replenishment. Gradual lowering of the water level, associated with intense evaporation and limited surface water inflow, is observed in the summer-autumn season. However, with the intensification of atmospheric precipitation at the turn of autumn and winter, a slow increase in the water level in the lake occurs. In early autumn 2024, despite the increase in precipitation totals, groundwater runoff and retention caused a further lowering of the water level in the lake, resulting in the extension of the lowest levels until mid-November 2024. Seasonal changes are related to the manner and intensity of reservoir replenishment processes, especially in extreme situations such as floods or droughts, when replenishment is limited or slowed (atmospheric and hydrological droughts). The lake’s response to increased or limited replenishment can be inferred from differences in the lake’s shoreline extent identified based on materials from different periods and interpreting the spread of waterlogged areas in its surroundings. Satellite images and UAV orthophotos clearly identify temporal-spatial changes in the eastern part of Czeszewo Lake (Fig. 12). At the site, changes in land use (from arable land to regularly mowed meadow) can be observed, preventing shoreline vegetation from encroaching on its area. This allows it to remain well visible in the field. Elevated parts of the embankment often have separate mowing treatments, and in these places, the vegetation cover is less dense. Consequently, after some time (up to one month), these surfaces are more prone to erosion by very intense rainfall. All subsequent images show a gradual increase (Choiński, 2007). However, the waters filling the lake basin are continuously mixed by wind action (wavy water surface is often visible in available remote sensing data), making it effectively a polymictic pond-type lake (Kajak 1989; Szybowski & Tonder, 1989). During the peak summer seasons, the maximum temperature differences between the surface and bottom layers do not exceed 5.50°C. There have also been instances where the temperature difference did not exceed 0.20°C (Ziętkowiak & Choiński, 1991; Szymańska, 1993). There is no observed stratification of the lake waters, or it is very short-lived. Frequent, complete mixing of the lake waters means that the lake basin has an active bottom throughout. This increases the lake’s ability to self-purify its waters, although it also hinders the deposition of suspended material in the water. The high intensity of water exchange in the lake (170% per year), involving the entire water mass, is a factor that limits the accumulation of nutrients (Szybowski & Tonder, 1989). Since the 1980s and 1990s, no changes have been observed in the species composition of emergent and submerged plants in Czeszewo Lake. The reduction in the range of some of them was more related to the introduction of intensively feeding silver carp into the lake than to the slow increase in water mineralization (Ziętkowiak et alii, 1995). The polymictic nature of the lake (frequent mixing of water due to wind) prevents long-term stratification, resulting in significant dynamics of the thermal and hydrological regime. Water level fluctuations in the flow-through lake, such as Czeszewo Lake, are related to the seasonal variability of meteorological factors (precipitation and air temperature) and the dynamics of the river network. The character and area of the direct catchment, as well as the morphometry of the lake basin (area and depth), the extent of shoreline vegetation, and the degree of lake overgrowth (development phase), also influence it. Local monitoring of water levels in Czeszewo Lake, conducted since May 2024 as part of the TRIQUETRA project, has shown their dynamic nature (Fig. 11). From January to December 2024, the amplitude of water level fluctuations was 0.96 m, with a maximum of 89.20 m above sea level recorded on February 23rd and a minimum of 88.24 m above sea level noted on January 5th, 2024. The highest water levels in February and March were the result of winter rainfall and snowfall in the preceding months. At the turn of February and March 2024, some of the highest water levels in the lake in recent decades were recorded. Meteorological data confirm that precipitation totals from October 2023 to March 2024 were among the highest since 1954 for the Gołańcz station. From January 5th, 2024, to February 23rd, 2024, the water level in the lake increased by 0.96 m, while from February 23rd, 2024, to August 6, 2024, a systematic decrease of 0.80 m was recorded. This very high-water level (late February and March) was also recorded using UAV aerial photographs (Fig. 2). The UAV image from March 13, 2024, shows the high-water level under the Fig. 11 - Changes in water levels in Czeszewo Lake in 2024-2025 62 R. gRaf, L. KaCZMaREK, S. KRÓLEWICZ, W. RĄCZKOWSKI & L. ŻUK Italian Journal of Engineering Geology and Environment, Special Issue 1 (2025) www.ijege.uniroma1.it improving mapping methodology to increase the accuracy of vulnerability assessments and risk modeling. The current study established preliminary frameworks for overlaying vulnerability zones on potential threat areas, providing insights into spatial risk patterns. The thematic risk profiles generated in this study offer a visualization of multifaceted threats, combining climatic and anthropogenic influences. Further integration of high-resolution remote sensing data, longterm monitoring, and predictive modeling may be necessary to improve risk assessment and develop targeted protection strategies for lakeshore archaeological sites like in Smuszewo and its surrounding environment. ACKNOWLEDGEMENTS This work is based on procedures and tasks implemented within the project “Toolbox for assessing and mitigating Climate Change risks and natural hazards threatening cultural heritage – TRIQUETRA”, which is a Project funded by the EU HE research and innovation programme under GA No. 101094818. https://triquetra-project.eu/ erosion rates and northern areas facing water retention challenges. In the risk assessment of the archaeological site, various levels of data analysis were considered: 1) in the immediate vicinity of the archaeological site, 2) in the river and lake catchment area, and 3) landscape level. These allowed for identifying the main trends in both historical and contemporary dimensions. This does not mean that all aspects have been resolved and discussed. For example, the fundamental assumption about the importance of the lake water level for the preservation of archaeological relics requires a more thorough examination of their preservation state and burial level. This requires additional geophysical research. Additionally, indicating the importance of seasonal precipitation does not yet resolve the issue of the impact of short-term intense rainfall. It is necessary, on the one hand, to monitor the situation and, on the other hand, to model the runoff rate in the catchment under given conditions. 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