# Impact of High Water Levels in Lake Baikal on Rare Plant Species in the Coastal Zone
## 1 Introduction  
Studies on water-level fluctuations in aquatic systems are currently becoming increasingly important, especially in the context of global climate change. Water-level monitoring has been identified as one of the key objectives of both the World Meteorological Organization (WMO) and the Global Climate Observing System (GCCOS) [1, 2]. The focus of relevant scientific research is on the study of the ecological response of ecosystems to water-level fluctuations [3, 4]. It has been repeatedly noted that changes in the hydrological regime lead to large-scale losses and degradation of coastal ecosystems [5, 6, 7]. The vegetation that grows on the banks of water bodies may be vulnerable to inundation due to water-level fluctuations [8, 9]. Among the hydrological and climatic factors that influence riparian zone vegetation conditions, the duration of inundation and water depth have the greatest effect [10, 11]. Studies have shown that the shoreline zone of reservoirs experiences a decline in the species diversity of plant communities [12, 13], a decrease in plant reproductive function [14], and the invasion of non-native species [15]. The most significant impact on vegetation is seen as a result of reservoir construction [16]. During the process of reservoir filling, significant areas are inundated, leading to the irreversible loss of plant habitats [17]. Following the rise in water level, former valley slopes transition into the zone of reservoir banks transformation. During the initial years of reservoir operation, the shore may widen by several tens or even hundreds of meters. This abrasion process also leads to the degradation and loss of vegetation cover. Subsequently, a new shoreline ecosystem adapted to the reservoir-level regime is formed [18]. Undoubtedly, studies of the impacts of water-level fluctuations on rare species are of great importance. They are among the most vulnerable components of ecosystems, as they have a limited number of populations and are localized within a narrow range. Thus, the conservation of rare plant species and endemics is crucial for maintaining biodiversity and ecosystem resilience [19]. The paper considers threats to rare coastal plant species of a lake of international ecosystem importance. In 1996, Lake Baikal was designated a UNESCO World Heritage Site, thereby underscoring its distinctive attributes and global significance. Its territory also encompasses the Selenga River delta, which is classified as a wetland under the Ramsar Convention [20]. The lake's ecosystem is characterized by an exceptional diversity of rare and endemic animal and plant species. Lake Baikal has been functioning as a water reservoir since the late 1950s, following the regulation of the Angara River [21; 22]. The construction of the Irkutsk HPP dam resulted in a 0.8 m increase in the lake level [23]. This led to a number of negative consequences: changes in the hydrochemical and hydrobiological regime, the flooding of residential houses and infrastructure facilities, the activation of abrasion processes, impacts on flora and fauna, etc. These changes occurred mostly in the Republic of Buryatia, in the eastern part of the lake with predominantly gentle shores [24]. This study focuses on the assessment of potential damage to rare plant species on the southeastern coast of Lake Baikal as a result of a potential water-level rise. Despite the presence of few studies of the level regime of Lake Baikal, covering its various aspects from hydrological modeling to its impact on avitauna [21; 23; 25; 26; 27], there are practically no works devoted to inundation zone modeling at high water levels and the assessment of its impact on coastal vegetation, including rare species. The main provisions of the article are as follows:  
1. The creation of digital elevation models made it possible to carry out the hydrological modeling of inundation zones at extremely high water levels;
2. On the obtained territories, fieldwork was carried out to count the number of rare species subjected to flooding;
3.