In August 2023, Slovenia experienced unprecedented flooding, as heavy rains affected two-thirds of the country, resulting in estimated economic losses of €9.9 billion[1] (of which €350 million were insured[2] ) Prime Minister Robert Golob described the event as Slovenia’s worst natural disaster since gaining independence in 1991. The northwest regions, including Slovene Littoral, Upper Carniola and Carinthia, were particularly hard-hit, suffering considerable damage to roads, bridges, buildings and agriculture.
Slovenia is one of the smallest countries in Europe and since 1980 has accounted for only 1% of Europe’s €650 billion (2022 Euros) in weather-related economic losses.[3] However, on a per-capita basis, the country ranks highest in Europe at €3,452 per person over the same period. This highlights the vulnerability of Slovenia’s population to natural disasters, a situation that is likely to be exacerbated in the future by the expected impacts of climate change on extreme weather.
The economic losses from flooding in 2023 alone exceeded the cumulative inflation-adjusted losses of the past 40 years, making it the country’s most expensive weather event on record. Considering this, we examine how climatic, exposure, land use and construction factors affect flood-related risks and resilience in Slovenia.
Slovenia, located at the eastern end of the European Alps, has over 30,000 kilometers of waterways, many of which are tributaries of the Danube that flow from the western to the eastern parts of the country. Slovenia experiences the frequent passage of weather systems, and the capital, Ljubljana, is the second wettest in Europe with an annual average precipitation of about 1,400 millimeters; however, the first half of 2023 was even wetter than usual. Many parts of the country experienced two to three times the average expected rainfall in July, causing rivers to reach their bank-full capacity.[4]
From a meteorological perspective, the setup was unique for the time of year. A trough of cold Atlantic air passed over Western Europe resulting in a shallow cyclonic system forming over the northern Mediterranean and an embedded weather front sitting over Slovenia for more than 36 hours. This weather pattern (the interaction between a cold Atlantic trough and a cyclonic system) is atypical for midsummer, more closely resembling autumn and winter conditions. Prefrontal and frontal storms resulted in heavy and persistent rainfall throughout the proceeding days, until the cyclone moved eastward and weakened.
Between August 3 and 6, large parts of the northwest of the country received more than 250 millimetres of rainfall (Figure 1), with some areas receiving the majority of this within just 12 hours.
Source: ARSO
This exceeded the average rainfall normally received in these regions during the entire month of August, according to the Slovenian Environment Agency (ARSO). Several monitoring stations estimated that the event represented a rainfall occurrence exceeding a 1-in-250-year return period.[4]
Multiple rivers broke their banks, leading to widespread flooding in 85% of municipalities in the country. Depending on the location, the estimated magnitudes of flow return periods range between 1-in- 100-year to 1-in-500-year events, with all-time records being set at 31 stations. Defenses performed well, and although many were overtopped, only one on the Mura River failed. Over 8,000 homes were flooded, 400 of which were completely destroyed. The intense rainfall also gave rise to well over 1,000 landslides. Between flooding and landslides, 70 bridges were damaged or destroyed and scores of kilometers of roads damaged or closed.[5] In total, seven people are known to have died.
8,000 homes were flooded
400 homes were completely destroyed
1,000 landslides
70 bridges were damaged
Despite the severity of the flooding, a notable success was Slovenia's advanced flood early warning network. This network proved crucial in minimizing casualties, demonstrating the significant impact of timely and effective disaster response mechanisms.[6] Developed as a collaboration between the ARSO and the Danish Hydrological Institute, it features advanced hydrological/hydrodynamic models that integrate real time data, such as water levels, discharge and rainfall.
Central to the network is the HYDROALARM[7] system, which issues public warnings and categorizes the country into 26 regions, each marked with color-coded flood danger levels. Additionally, Slovenia benefits from broader European initiatives, such as the European Flood Awareness System, developed by the European Commission and the European Centre for Medium-Range Weather Forecasts, which contributes to the country’s response efficiency.
Slovenia is situated at the crossroads of major climatic influences: the Mediterranean climate from the southwest, the Alpine climate from the north and the Continental climate from the east. This climatic diversity means that regional processes will likely play a role in shaping strategies for the management of and adaptation to increased flood risks in a warming world.
Regional climate modeling studies suggest that daily precipitation extremes in the wider Mediterranean region will exhibit a strong north-south gradient, with decreases in the south and increases in the north, including in Slovenia.[8] This pattern arises in the models due to the complex interaction of changes in large-scale wind patterns, regional evaporation within the Mediterranean and orographic effects from the Alps.
At the same time, in the Alpine parts of Slovenia, flood risk will be more closely tied to temperature changes. According to the Intergovernmental Panel on Climate Change, mountain regions are warming faster than surrounding areas.[9] With rising temperatures, more precipitation will fall as rain rather than snow, and where snow does accumulate, it will melt faster.
These factors will combine to increase the overall flood risk in these regions. Indeed, paleo flood records reconstructed from lake sediments indicate that over the last 9,000 years warm periods have been characterized by an increase in extreme (>1-in-100 year) flood events in the European Alps.[10]
The climate is not the only factor changing in Alpine countries. Land use has also seen a marked shift over the past two centuries. Scientists at the University of Natural Resources and Life Sciences in Vienna have undertaken a detailed comparison of early 19th century land use against the present day in the Rhine, Salzach and Drava River catchments.[11] Their findings revealed a 40% reduction in river channel areas due to channel straightening and canalization, along with a 95% reduction in wetlands. Other changes in grassland, forest and cultivated areas together with the construction of embankments for infrastructure and flood defenses brought about severe losses in river storage and conveyance capacity.
This reduction in capacity raises water levels and ultimately makes floodwaters travel faster, which increases the height of flood peaks. The situation is also exacerbated by urbanization. In Slovenia, the ongoing trend of urban development in valleys and lower river areas means that around two-thirds of the population will soon be exposed to flood risk.[12]
Extreme flooding will remain a critical concern for Slovenia, a risk amplified by the realities of a warming planet and increasing exposures on flood plains. The record-breaking floods in 2023 highlight the vital importance of resilient construction. A key strategy in addressing this challenge involves repairing and retrofitting existing infrastructure to bolster its resilience, thus ensuring better preparedness for future flooding scenarios. Recognizing this need, the Slovenian government, with the backing of the European Union, has committed to make it so.
If events of this nature increase in frequency, insurability may also be affected, and the government may end up taking more of the strain. In the long run, it might be beneficial to consider alterations in land use and river management as integral components of a comprehensive solution. Additionally, examining how risks from catastrophic events are managed within current financial, corporate and public institutions — and identifying potential improvements — would be a prudent approach to enhance overall preparedness and response strategies.
