## 2 Study Area and Flood Events
### The 2020 Flood  
In the late night of 8 August 2020, an almost stationary mesoscale convective system (MSC) developed over central Greece and the Aegean Sea. The system produced high-intensity rainfall over the complex topography of the island of Euboea that lasted until the early morning hours of 9 August (approximately 8 h) due to the MCS's feedback processes, eventually recording 300 mm in the Steni meteorological station (Figure 3) [22] and smaller amounts in neighboring stations. The ensuing flood caused severe damages clustered mainly in four catchments in central Evia draining westward and catastrophic impacts within the catchment of the Lilas River (Figure 2). Especially near the river's outlet, the flood induced severe effects on properties and infrastructure (mostly bridges), agricultural land, businesses, and daily socioeconomic activities. Due to the adverse conditions introduced by the flood, five fatalities were recorded [22]. The flood event caused extensive and multifaceted impacts, severely affecting several elements of the built environment. Residential and commercial properties suffered the most, with underground spaces with several uses filled with flood waters, gardens submerged, and outdoor facilities rendered unusable. In more severe cases, structural failures were reported in critical infrastructures, including roads and bridges. Roadways were inundated, and bridges suffered structural damage, including partial or total collapse due to erosion and undercutting phenomena in piers [22; 23]. This type of flood-related damage resulted in temporary traffic and transportation disruption, isolation of large areas for several days, and complications to the emergency response actions, including SAR operations and recovery efforts [23]. These disruptions highlighted the inadequacy of existing infrastructure in withstanding such intense hydrological events and the cascading effects such failures can have on local communities. The event also had a profound impact on the geomorphology of the affected areas (Figure 6). Intense erosion was observed along the riverbed of the Lilas River (Figure 6a,b), locally altering its natural course, reducing its capacity to handle water flows in the future, and severely affecting bridges (Figure 6c,d). The coastline was similarly affected, with substantial erosion reshaping the landscape (Figure 6e,f) and threatening coastal ecosystems. Agricultural lands suffered immense losses, with fertile soils washed away, reducing the productivity of the land and posing challenges for local farmers. Floodwaters inundated farmlands, destroying crops and washing vegetation away [22; 23]. Large trees, which play a critical role in stabilizing soil and providing habitat for wildlife, were uprooted, further contributing to the ecological imbalance and exacerbating the risk of future erosion. The floodwaters also caused widespread displacement of mobile objects, ranging from small, lightweight items, like personal belongings, to heavy equipment, such as large trucks. The strength of the currents illustrated the sheer power of the floodwaters, carrying away vehicles and machinery that are critical for both individual livelihoods and broader community functioning. The loss of such equipment not only inflicted financial strain on the affected individuals but also hampered recovery efforts, as heavy machinery is often essential for clearing debris and repairing infrastructure in the aftermath of such events. Collectively, the damages highlighted the interconnected nature of the impacts, where failures in one domain, such as infrastructure, can amplify losses in others, including agriculture and transportation. The event underscores the need for a comprehensive, multidisciplinary approach to flood risk management. It is important to note that the 2020 Lilas flash flood occurred during the COVID-19 pandemic, particularly at the beginning of the second pandemic wave in early August.