DROUGHT AND HEATWAVES IN GORENJSKA β SORA CATCHMENT, SLOVENIA
Drought intensified by heatwaves in the 2022 growing season
Summer of 2022 in Slovenia was characterised by a persistent lack of precipitation, record high temperatures and several heatwaves, which lead to extreme drynessΒ of the topsoil layer, particularly in the western part of the country. The months-long precipitation deficit, which lasted almost continuously from January until the beginning of September 2022, ranked 2022 one of the driest years meteorologically in Slovenia. At the beginning of the summer, the conditions already indicated drought at the scale of a natural disaster. A series of heatwaves (the number ranging from 1 to 4, depending on the location) that occurred from the second half of June to the end of August, led to a long period of severe heat stress and, in combination with a lack of precipitation and dried-out soils, strongly affected ecosystems. At the end of July, the natural vegetation wasalready showing signs of yellowing and leaf fall typical of autumn. In July, high fire risk was also declared for
the entire country and the most extensive wildfire in Slovenia broke out in its western part. In general, the western and central Slovenia were more affected by topsoil drought, while it was less pronounced in the east of the country. In terms of duration and severity, the topsoil drought in 2022 ranks among the most extreme in Slovenia. It affected 23,570 people in 211 municipalities. The final economic damage was estimated at 148 million euros, exceeding 30 % of normal annual agricultural production, meaning that the 2022 drought was indeed declared a national disaster. In addition to agriculture, natural systems and other key socio-economic sectors, such as energy and river transport were also affected. Groundwater drought was observed as well, resulting in municipalities and utility companies throughout Slovenia advising people to conserve water, and firefighters delivering drinking water to users (including livestock) without access to it, especially to settlements at higher altitudes.
Extreme rainfall in Slovenia from 3rd to 6th August 2023 leading to devastating floods and landslides
The most extensive and destructive floods in Slovenia were the result of the interaction of several different predisposing factors, including the atypical synoptic situation for summer, warm sea surface and saturated soil conditions. These factors were favourable for the onset of the flood event between 3rd and 6th August, when a weather front persisted over Slovenia for almost 36 hours, bringing the normal amount of precipitation for August in some areas in just a few hours. Severe storms with heavy rainfall, hail and strong winds caused several landslides and the strong winds knocked down a considerable number of trees. Record or near-record daily precipitation amounts were measured at several stations in the area of heaviest rainfall on 4th August, including in the southeastern part of the Sora catchment. The amount of precipitation at several stations in the region was estimated at a 200-year return period or higher. From a hydrological perspective, high water thresholds were exceeded at 122 gauging stations on 74 rivers in Slovenia, including the Sora river and its tributaries (FIGURE 1). The unique characteristic of this flood event was that the three largest Slovenian rivers, Sava, Drava and Mura, were all flooding at the same time. Record discharges were measured at 31 gauging stations (3 in the Sora catchment), most of which had a return period of 100 years or more. Numerous roads, water supply, and electrical installations were damaged. Several buildings were flooded or damaged, and 265 landslides were triggered in the municipalities of Ε kofja Loka, Gorenja vas – Poljane, Ε½iri and Ε½elezniki. The final estimate of direct material damage caused by the August floods in Slovenia was 2.98 billion euros.
Extreme rainfall and flash floods in Slovenia on 18th September 2007
On 18th September 2007, the western, north-western and northern parts of Slovenia experienced heavy and abundant precipitation. It led to a rapid increase in river discharges, especially in the BaΕ‘ka grapa area and the wider Cerkno and Ε kofja Loka hills area. Flash floods of the SelΕ‘ka Sora, DavΔa and Kroparica rivers caused severe damage in the area (FIGURE 2). The torrents and rivers in the Karavanke region, the foothills of the Kamnik-Savinja Alps, Kranj and DomΕΎale fields, the Tuhinj Valley, and in the wider Celje region, flooded as well. In the areas with the greatest damage, the discharges exceeded the 100-year return periods. Out of 210 municipalities in Slovenia, 60 reported flood damages, and the total economic flood damage was estimated at 223.7 million euros; highest damage was reported by the municipality of Ε½elezniki in north-west Slovenia. There were six fatalities as a result of the event.
WINTER STORM ELEANOR IN THE SAVOY ALPS β ARLY RIVER CATCHMENT, FRANCE
Winter storm Eleanor in January 2018 Storm
Eleanor was an extratropical cyclone that hit several European countries (from Ireland to Austria) between 2nd and 5th January 2018. In France, with wind speeds of over 130 km/h, intense precipitation and temperature rise leading to rain-on-snow episodes, Eleanor emerged in a context already weakened by other storms that had occurred previously and with water-saturated soils. In the case study area of the Arly river catchment in the Savoy Alps, the event led to a sharp increase in instability phenomena: avalanches, mudflows, rockfall, landslides and torrential flooding (Stoffel and Corona, 2018; Barthelon, 2018). The storm caused extensive damage and traffic disruption in many municipalities. Eleanor was estimated to be the sixth strongest storm in Europe since 1995 with an estimated return period at around 20 years in the current climate and an estimated economic impact of 700 million euros (Vautard et al., 2019).
SHORT-DURATION RAINFALL EXTREMES LEADING TO CASCADING AND COMPOUND MASS MOVEMENTS IN GARMISCH-PARTENKIRCHEN, GERMANY
Episodes of short-duration rainfall extremes in Garmisch Partenkirchen in recent decades, leading to compound and cascading mass movements
The pilot area of Garmisch-Partenkirchen was hit over past years by several episodes of intense precipitation of short duration which led in most cases to gravitational mass movements of different levels of severity. One of the most relevant episodes occurred on 22nd August 2005 when compound hazards, including debris flows and flash flood, were triggered by intense rainfall. On the day of the event, precipitation totals exceeded 100 mm at most weather station sites in the area. In Garmisch the estimated return period of the summer event was of ~ 90 years. More recent summer episodes of intense precipitation of short duration triggering flash floods in the area occurred in 2018, 2020 and 2021.
THE VAIA STORM IN THE EASTERN ALPS β THE CASE OF TRENTINO β SOUTH TYROL (FASSA/FIEMME AND CAREZZA/EGA VALLEYS), ITALY
Large-scale storm in October 2018 with extreme precipitation and wind speed leading to forest damages, floods and gravitational mass movements in the Eastern Alps
Between 27th and 30th October 2018 an exceptional Mediterranean storm named Vaia hit the eastern Alps leading to severe damages in many Alpine regions. Due to the combination of intense precipitation and extremely high wind speed, several windfalls, floods and debris flows were recorded in the Italian Trentino β South Tyrol region, especially in the pilot area centred on the Fiemme and Ega Valleys where the huge number of fallen trees modified the forest landscape substantially. During the first three days of the event, most observation sites in South Tyrol and Trentino registered record values of cumulated precipitation, in some cases exceeding 400 and even 600 mm in a few locations in Trentino (Passo Cereda and Passo Pian delle Fugazze). On 29th October, exceptional wind speeds occurred in combination with rainfall, with the highest values observed between 1,500 and 2,000 m above sea level (a.s.l.) where wind gusts exceeding 120 km/h were recorded.
SHORT-DURATION RAINFALL EXTREMES LEADING TO GRAVITATIONAL MASS MOVEMENTS IN A TRANSBOUNDARY ITALIAN-AUSTRIAN AREA β WIPPTAL AND STUBAITAL, ITALY & AUSTRIA
Summer episodes of short-duration rainfall extremes in Wipptal (it) and Stubaital (at) in 2021 and 2022, leading to debris flows and other mass movement types
The Italian-Austria cross-boundary pilot area of Wipptal (IT) and Stubaital (AT) was hit over past years by several episodes of intense precipitation of short duration during the summer months. These events led in most cases to flood and gravitational mass movements of different levels of severity. An impactful event occurred on 16th August 2021 in the Wipptal area, when thunderstorms with heavy rain, exceeding 80 mm per day, caused a debris flow and, as a cascading effect, flooding with damage to buildings and infrastructure. In Stubaital, a heavy precipitation episode occurred on 22nd July 2022 with more than 100 mm per day recorded by local weather stations and triggered several debris flows damaging infrastructure and blocking several roads.
