Slovenia: Vulnerabilities

Extreme floods occurred from 4 to 6 August 2023 in Slovenia causing three casualties and total direct and indirect damage, including post-disaster needs, close to EUR 10 billion. This was significant at over 10 % of Slovenia’s annual gross domestic product. The return period of the event (both rainfall and peak discharge values) was in many locations in Slovenia over 250 or even over 500 years. In a network of 26 meteorological stations, 12 h rainfall intensity was higher than 100 mm at 13 stations (26).

The last decade has seen a number of large-scale floods. It has been estimated that floods in the Savinja river basin have caused damage amounting to 20% of Slovenia’s national income. The values of the peaks of maximum flows of the majority of watercourses have grown (21).

Physically speaking, it is sensible to forecast that the higher temperatures and greater instability of the troposphere will increase the probability of intensive rainfall. The model assessment of the impact of an increase in intense rainfall by 20% shows that in this case large watercourses in the Alpine and sub-Alpine worlds would rise by 30%. The risk of floods in the Alpine and sub-Alpine regions is directly escalated by increasing temperature of the atmosphere, since some flood situations in the autumn and spring are mitigated by the transition from rain to snow in regions lying at higher altitudes (21).

Vulnerability to floods is also increasing owing to settling in border flood regions. Vulnerability to floods is projected to increase in the future due to the combined impact of direct anthropogenic factors (change in the outflow properties of watercourses, settlement of border flood regions) and climate change (21).

Particularly worrying in the context of climate change is the already considerable risk of floods. Apart from direct risk to human life and health, floods exert an increased risk and psychological pressure on the population living in the regions at risk (21).

Upper Soča River basin

The impact of projected climate change on the hydrological cycle in the Upper Soča River basin has been estimated based on one global climate model and the IPCC A1B emission scenario, downscaled for local use, and a hydrological model for river flow (25).The Upper Soča River basin is one of the wettest parts of Europe (total annual precipitation: 1,200 - 3,500 mm). The simulated impact was quantified by comparing results of the hydrological modelling for the control period (1971–2000) and different scenario periods (2011–2040, 2041–2070, 2071–2100).

The climate projections show warmer and wetter winters, and hotter and drier summers in the scenario periods. The projected rise in temperature is reflected in the increased actual evapotranspiration, the reduction of snow amount and summer groundwater recharge. Changes of monthly and period average discharges follow the trends of the meteorological variables. Changes in precipitation patterns have a major influence on the projected hydrological cycle and are the most important source of uncertainty. Estimated extreme flows indicated increased hazards related to floods, especially in the near-future scenario period, while in the far future scenario period, distinctive drought conditions are projected. Discharge is projected to increases during winter and decrease during summer months. The duration of low-flow situations becomes longer and shifts towards late autumn in the last scenario periods (25).

Europe: casualties in the past

The annual number of reported flood disasters in Europe increased considerably in 1973-2002 (1). A disaster was defined here as causing the death of at least ten people, or affecting seriously at least 100 people, or requiring immediate emergency assistance. The total number of reported victims was 2626 during the whole period, the most deadly floods occurred in Spain in 1973 (272 victims), in Italy in 1998 (147 victims) and in Russia in 1993 (125 victims) (2).

Throughout the 20th century as a whole flood-related deaths have been either stable or decreasing while economic burdens of flooding and related societal disruptions have become decidedly worse. 20th century flood disaster death tolls have been typically averaging fewer than 250 per year (3).

Europe: flood losses in the past

The reported damages also increased. Three countries had damages in excess of €10 billion (Italy, Spain, Germany), three in excess of 5 billion (United Kingdom, Poland, France) (2).

Expressed in 2006 US$ normalised values, total flood losses over the 1970–2006 period amounted to 140 billion, with an average annual flood loss of 3.8 billion (4). Results show no detectable sign of human-induced climate change in normalised flood losses in Europe. There is evidence that societal change and economic development are the principal factors responsible for the increasing losses from natural disasters to date (5).

Policy makers should not expect an unequivocal answer to questions concerning the linkage between flood-disaster losses and anthropogenic climate change, as this field will very likely remain an important area of research for years to come. Longer time-series of losses are necessary for more conclusive results (6).

Europe: flood frequency trends in the past

In 2012 the IPCC concluded that there is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at a regional scale because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of changes in land use and engineering. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes. There is low confidence (due to limited evidence) that anthropogenic climate change has affected the magnitude or frequency of floods, though it has detectably influenced several components of the hydrological cycle such as precipitation and snowmelt (medium confidence to high confidence), which may impact flood trends (24).

Despite the considerable rise in the number of reported major flood events and economic losses caused by floods in Europe over recent decades, no significant general climate‑related trend in extreme high river flows that induce floods has yet been detected (7).

Hydrological data series do not indicate clear upward trends in the frequency and magnitude of floods in Europe. The direct anthropogenic causes include land use change, river channel modifications and increased activities in areas vulnerable to floods. Thousands of square kilometres of impermeable surfaces have been created, coastal urbanization has been extensive. The overall impact of these changes probably exceeds the impact of trends in meteorological variables in today's Europe (8).

In western and central Europe, annual and monthly mean river flow series appear to have been stationary over the 20th century (9). In mountainous regions of central Europe, however, the main identified trends are an increase in annual river flow due to increases in winter, spring and autumn river flow. In southern parts of Europe, a slightly decreasing trend in annual river flow has been observed (10).

In the Nordic countries, snowmelt floods have occurred earlier because of warmer winters (11). In Portugal, changed precipitation patterns have resulted in larger and more frequent floods during autumn but a decline in the number of floods in winter and spring (12). Comparisons of historic climate variability with flood records suggest, however, that many of the changes observed in recent decades could have resulted from natural climatic variation. Changes in the terrestrial system, such as urbanisation, deforestation, loss of natural floodplain storage, as well as river and flood management have also strongly affected flood occurrence (13).

Europe: projections for the future

IPCC conclusions

In 2012 the IPCC concluded that considerable uncertainty remains in the projections of flood changes, especially regarding their magnitude and frequency. They concluded, therefore, that there is low confidence (due to limited evidence) in future changes in flood magnitude and frequency derived from river discharge simulations. Projected precipitation and temperature changes imply possible changes in floods, although overall there is low confidence in projections of changes in fluvial floods. Confidence is low due to limited evidence and because the causes of regional changes are complex, although there are exceptions to this statement. There is medium confidence (based on physical reasoning) that projected increases in heavy rainfall would contribute to increases in rain-generated local flooding, in some catchments or regions. Earlier spring peak flows in snowmelt- and glacier-fed rivers are very likely, but there is low confidence in their projected magnitude (24).

More frequent flash floods

Although there is as yet no proof that the extreme flood events of recent years are a direct consequence of climate change, they may give an indication of what can be expected: the frequency and intensity of floods in large parts of Europe is projected to increase (14). In particular, flash and urban floods, triggered by local intense precipitation events, are likely to be more frequent throughout Europe (15).

More frequent floods in the winter

Flood hazard will also probably increase during wetter and warmer winters, with more frequent rain and less frequent snow (16). Even in regions where mean river flows will drop significantly, as in the Iberian Peninsula, the projected increase in precipitation intensity and variability may cause more floods.

Reduction spring snowmelt floods

In snow‑dominated regions such as the Alps, the Carpathian Mountains and northern parts of Europe, spring snowmelt floods are projected to decrease due to a shorter snow season and less snow accumulation in warmer winters (17). Earlier snowmelt and reduced summer precipitation will reduce river flows in summer (18), when demand is typically highest.

For the period 2071-2100 the general feature is a decrease of extreme flows in areas where snowmelt floods are dominating in the present climate. The hundred year floods will attenuate by 10-50% in northern Russia, Finland and most mountainous catchments throughout Europe. An increase by similar amount is projected in large areas elsewhere, whereas a mixed pattern is likely in Sweden, Germany and the Iberian Peninsula (2).

Increase flood losses

Losses from river flood disasters in Europe have worsened in recent years and climate change is expected to exacerbate this trend. The PESETA study, for example, estimates that by the 2080s, some 250-400 million Europeans could be affected each year (compared with 200 million in the period between 1961 and 1990). At the same time, annual losses due to river flooding in Europe could rise to €8-15 billion by the end of the century compared with an average of €6 billion today (22).

Large differences across Europe

Annual river flow is projected to decrease in southern and south-eastern Europe and increase in northern and north-eastern Europe (19).

Strong changes are also projected in the seasonality of river flows, with large differences across Europe. Winter and spring river flows are projected to increase in most parts of Europe, except for the most southern and south-eastern regions. In summer and autumn, river flows are projected to decrease in most of Europe, except for northern and north-eastern regions where autumn flows are projected to increase (20). Predicted reductions in summer flow are greatest for southern and south-eastern Europe, in line with the predicted increase in the frequency and severity of drought in this region.

Climate-related changes in flood frequency are complex and dependent on the flood generating mechanism (e.g. heavy rainfall vs spring snowmelt), affected in different ways by climate change. Hence, in the regions where floods can be caused by several possible mechanisms, the net effect of climate change on flood risk is not trivial and a general and ubiquitously valid, flat-rate statement on change in flood risk cannot be made (23).

Flood risk tends to increase over many areas owing to a range of climatic and non-climatic impacts, whose relative importance is site-specific. Flood risk is controlled by a number of non-climatic factors, such as changes in economic and social systems, and in terrestrial systems (hydrological systems and ecosystems). Land-use changes, which induce land-cover changes, control the rainfall-runoff relations in the drainage basin. Deforestation, urbanization and reduction of wetlands diminish the available water-storage capacity and increase the runoff coefficient, leading to growth in the flow amplitude and reduction of the time-to-peak. Furthermore, in many regions, people have been encroaching into, and developing, flood-prone areas, thereby increasing the damage potential. Important factors of relevance to flood risk are population and economy growth, flood protection strategy, flood risk awareness (or flood risk ignorance) behaviour and a compensation culture (23).

Adaptation strategies - Spatial planning

Climate change will bring about a potentially increased risk of flooding. The risk of flooding in Slovenia is already high. Apart from systematic implementation of hydro-technical measures, it will be important to downgrade the penetration of settlements in regions at flood risk, as the costs of technical protection against floods may grow substantially, while exacerbating problems downstream. All this will require more robust planning of specific infrastructural facilities, particularly bridges and road and rail connections. Room must be preserved for inundation areas and high water catchment areas (21).

The expected reduced low flows must be taken into account in the design of the dimensions of wastewater treatment plants and plans for capturing water for industrial needs and irrigation (21).

Adaptation strategies - Contingency planning

Torrential floods represent a particularly serious problem in Slovenia; these emerge in the upper parts of river basins. These situations are characterised by a lack of time for the preparation and implementation of measures, and for the possible evacuation of goods and people. As a consequence, the damage and risk to human life are substantially greater. In order to address this problem successfully, plans have been drawn up for the early warning system to be upgraded. This system is based on meteorological prognostic models with high spatial resolution linked with hydrological models, which makes it possible for the responsible services to engage promptly in a state of increased readiness. To this end, the real-time monitoring of rainfall enabled by meteorological stations and radars can serve as a basis for the implementation of measures (21).

Adaptation strategies - EU Directive on flood risk management

The new EU Directive on flood risk management, which entered into force in November 2006, introduces new instruments to manage risks from flooding, and is thus highly relevant in the context of adaptation to climate change impacts. The Directive introduces a three-step approach (2):

• Member States have to undertake a preliminary assessment of flood risk in river basins and coastal zones.
• Where significant risk is identified, flood hazard maps and flood risk maps have to be developed.
• Flood risk management plans must be developed for these zones. These plans have to include measures that will reduce the potential adverse consequences of flooding for human health, the environment cultural heritage and economic activity, and they should focus on prevention, protection and preparedness.

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Slovenia.

1. Hoyois and Guha-Sapir (2003), In: Anderson (ed.) (2007)
2. Anderson (ed.) (2007)
3. Mitchell (2003)
4. Barredo (2009)
5. Höppe and Pielke Jr. (2006); Schiermeier (2006), both in: Barredo (2009)
6. Höppe and Pielke Jr. (2006), in: Barredo (2009)
7. Becker and Grunewald (2003); Glaser and Stangl (2003); Mudelsee et al.(2003); Kundzewicz et al.(2005); Pinter et al.(2006); Hisdal et al.(2007); Macklin and Rumsby (2007), all in: EEA, JRC and WHO (2008)
8. EEA, JRC and WHO (2008)
9. Wang et al.(2005), in: EEA, JRC and WHO (2008)
10. Milly et al. (2005), in: EEA, JRC and WHO (2008)
11. Hisdal et al. (2007), in: EEA, JRC and WHO (2008)
12. Ramos and Reis (2002), in: EEA, JRC and WHO (2008)
13. Barnolas and Llasat (2007), in: EEA, JRC and WHO (2008)
14. Lehner et al.(2006); Dankers and Feyen (2008b), both in: EEA, JRC and WHO (2008)
15. Christensen and Christensen (2003); Kundzewicz et al.(2006), both in: EEA, JRC and WHO (2008)
16. Palmer and Räisänen (2002), in: EEA, JRC and WHO (2008)
17. Kay et al. (2006); Dankers and Feyen (2008), in: EEA, JRC and WHO (2008)
18. Andréasson, et al. (2004); Jasper et al.(2004); Barnett et al.(2005), all in: EEA (2009)
19. Arnell (2004); Milly et al. (2005); Alcamo et al. (2007); Environment Agency (2008a), all in: EEA (2009)
20. Dankers and Feyen (2008), in: EEA (2009)
21. Republic of Slovenia, Ministry of the Environment, Spatial Planning and Energy (2002)
22. Ciscar et al. (2009), in: Behrens et al. (2010)
23. Kundzewicz (2006)
24. IPCC (2012)
25. Janža (2013)
26. Bezak et al. (2023)