National and regional story (Slovenia) - The Slovenian Alps tomorrow – extreme weather events and disappearing glaciers

Geography and climate

The interaction of three major climate systems (Continental, Alpine and sub-Mediterranean) influences the precipitation regime in the territory of the Slovenian Alps. The spatial variability of precipitation is high – annual precipitation varies from 1100 mm in the coastal parts of river basins to more than 3500 mm in the Julian Alps, where maximum Alpine precipitation has been detected. The spatial distribution of precipitation is highly influenced by the complex terrain. Due to an orographic effect, the Julian Alps and the Dinaric barrier receive the most precipitation. This distribution is a consequence of the fact that the largest amount of precipitation falls during conditions of wet southwesterly winds blowing perpendicularly to the high Dinaric-Alpine orographical barrier.

In the Alpine region the most pronounced precipitation maximum occurs in autumn. Precipitation measurements are generally underestimated, especially in high and exposed mountainous regions. Apart from averages, another important aspect involves extreme weather events, as they constitute an integral part of the natural climate. Due to pronounced variability and, by definition, the rare occurrence of weather and climate extremes, it is difficult to assess trends and long-term variations. The time between two occurrences of a particular extreme event in a certain area may extend over a period of several years. The greatest daily quantities of precipitation, even above 400 mm, have been recorded in the region of Posočje (Upper Soča river basin). During the warm part of the year, there are also frequent strong showers, and the estimation is that precipitation exceeding 100 mm in one hour is possible. All extreme events observed to date will continue to occur in the future. Along with the expected impact of climate change on extreme weather we will most likely experience an increase in both intensity and frequency.

We also need to take into account the possible synergistic effects of various components of the climate system and the environment. Extremes have always represented a threat to society and the environment. In such a varied climate as ours, extremes have various impacts and their consequences involve different aspects. Torrents and floods are a direct result of heavy precipitation, which may cause a series of other harmful events such as soil erosion, landslides and material deposits onto fields and pastures.

Although on average there is enough annual precipitation, we have experienced severe summer droughts in Slovenia four times during the last 15 years – till now never in the Upper Soča river basin, but the Upper Sava Valley was affected during the summer of 2003. Even if mountains are not threathened by drought, summer droughts may be experienced in the lower part of river basins.

One of the important features to be considered in planning for adaptation is the fact that a significant part of the Alps belongs to the national nature protected area, and therefore land use changes and interventions that would corrupt the natural environment are heavily restricted. Additional territory belongs to Natura 2000 and is also subject to certain constraints regarding land use and human-induced changes in the environment.

Climate change and scenarios

Changing climate conditions such as rising temperatures will influence the availability and consumption of water, evaporation is expected to increase and the precipitation regime is expected to change. Snow cover in the mountains could melt sooner in the season, and lower altitudes could get less snow due to a change in the ratio between solid and liquid precipitation. Therefore, the river regime might also change from a snow-rain to a rain-snow regime. But climate change will also induce other environmental changes (e.g. erosion, vegetation, soil and water pollution).

Extreme events represent a major burden on the environment, and so climatic analyses of such events are necessary for assessing the damage and for all spatial interventions (threat risk, planning etc.). Regular monitoring and analysis of extreme events is important for establishing climatic changes, since with such monitoring we also monitor the frequency and intensity of these events. At the same time, data on the intensity of extreme events provide the necessary basis for assessing the damage that such events can cause.

Normally, extreme events that cause damage receive greater attention, but it is not necessary for any meteorological variable to achieve an extreme value. How a specific extreme weather event affects the environment therefore depends on a range of factors: the adaptability of the environment, the time in which the event occurs, the weather in the previous period, etc. An increase in the intensity and frequency of extreme events is considered to be closely related to climate change.

Finally, it might seem that the region under consideration is particularly endangered by extreme weather events, but fortunately they are quite rare and reach a destructive force only in a very limited area. Nevertheless, this might change in the not too distant future.

At present, precipitation trends in the Julian Alps in the Soča river basin do not show a decrease everywhere in the Alps as predicted by climate change scenarios. In the Upper Sava Valley there is a decreasing precipitation trend. Also in the lower part of river basins, a decreasing precipitation trend has already been detected, and water consumption may increase in the future, not only due to increasing mean temperature and increasing sunshine duration, but also due to human activities and changes in water use. More important than annual trends are seasonal trends. In the Alpine area, like everywhere in Slovenia, precipitation shows an increasing trend in autumn.