**3. Results**

#### *3.1. Human Transformation of Alpine Water Bodies*

Since the first half of the 19th century, almost all larger running waters in the Austrian Alps have been severely modified by humans due to river straightening and channel narrowing. The main objective for the comprehensive hydraulic works was on land reclamation, improvement of navigation, and log driving. As a consequence, since 1826–1859, 40% of the former surface area of the Alpine running waters have vanished (see Figure 2). Expressed in a simplified manner: on average, rivers and streams have lost 40% of their former active channel width (omitting reductions in channel length due to river straightening). The data clearly show truncated flood retention and conveyance capacities due to the infilling of former channel areas. Surprisingly, stagnant water bodies have slightly increased in surface area. The reason for this can be found in new glacier lakes that have emerged after glacier decline and—most of all—in the construction of large reservoirs for hydro-energy purposes. Due to their storage capacity, the latter can partly help mitigate flood risks in Alpine environments [45]. Figure 2 also reveals the comprehensive areal reduction in ice-covered areas as a consequence of glacier retreat. Glaciers formerly covered 2.6% of the study area; today, they merely form 0.7%. This equals to an areal reduction of 73%. Because glaciers annually and inter-annually buffer precipitation in form of ice, they significantly influence the flow and flood regime of Alpine rivers. The severely reduced glaciated areas indicate significant losses in runoff storage capacity, resulting in increasing surface runoff during precipitation events [46]. Thus, it amplifies the flood risk in downstream valley sections.

#### *3.2. Land Use in Flood-Prone Areas*

#### 3.2.1. Settlement Development

Although the area for running waters and glaciers has been reduced within the time frame of the analysis, settlement areas have expanded. These analyses were conducted for

the catchments of the rivers Rhine, Salzach, and Drava, which include main parts of the Austrian federal states of Vorarlberg, East Tyrol, Salzburg, and Carinthia.

**Figure 2.** Proportions of the Alpine water bodies and glaciers in the Austrian catchments of the rivers Rhine, Salzach, and Drava (%) (left column: 1826–1859, right: 2016).

First, data on the general settlement development (i.e., inside and outside flooding areas) between 1826–1859 and 2016 were analyzed. The results show that development was primarily taking place in areas around the main cities and in larger valleys, such as the Rhine-Valley in Vorarlberg. Settlement expansion did not occur to the same extent in the mountainous regions. A comparison of the amount of settlement area per region historically and currently was made (see Figure 3). Although in the historical context, the percentage of settlement area per region is below 0.5%, in 2016, it increased to 3.6% in Vorarlberg and to approximately 2% in Carinthia and Salzburg. The settlement development therefore varies between the different Alpine regions but has significantly increased throughout the whole study area.

**Figure 3.** Proportion of settlement area per region.

Besides the general settlement development, the amount of space that is affected by flooding is an important variable. The results show that in Vorarlberg, 10 % of the study

area is potentially affected by flooding. In Carinthia, it is 7%, in Salzburg 5%, and in East Tyrol, 3 %. At local level, considerable differences within each federal state can be found, from flood zones covering 97.6% of the surface area of the municipality of Altach to 0.89% in Dünserberg (both located in Vorarlberg). These differences derive from the municipality's location being either in a broad valley or in a very mountainous area. Thus, municipalities were and are affected by flooding in a very different way.

To show the settlement areas exposed to flooding, development inside and outside flood-prone areas was analyzed, as well as the absolute and relative values, which are based on the factor calculated by dividing the current settlement area by the historical area. The results from the historical analysis show that, for the whole study area, 21% of settlement areas were located within flood-prone areas. In 2016, this amounted to 29%; therefore, an increase in development in flood-prone areas can be detected. Differences can be observed when comparing absolute and relative development. The absolute value indicates a higher increase in settlements outside of flooding areas, whereas the relative value is higher for development inside flood-prone areas. On the one hand, this is caused by the limited use of floodplains for development in the 19th century, when adding just a few buildings could result in a high relative value. On the other hand, a shift towards using (former) floodplains for development can be observed.

Besides the temporal aspect of the analysis, the regional differences—based on the municipalities—was explored. According to the absolute numbers, settlement development in flood-prone areas shows a similar dissemination as the general settlement development. Municipalities with a high settlement expansion in flood zones are located in urban areas and the main valleys. Peripheral regions show less development in flood-exposed areas. This demonstrates the link between settlement development in flood-prone areas and the general settlement dynamic within a municipality. Furthermore, a correlation can be found between the number of buildings and infrastructure located in flooding areas and the amount of land potentially affected by flooding within a municipality.

To gain further insight into the spatial distribution of flood damage potential, the amount of settlement area situated in flood-prone areas per municipality was calculated.

Especially in Salzburg and Carinthia, it can be observed that, in more mountainous and peripheral regions, a higher share of settlements is located in flood-prone areas (both in the historical and the current context; see Figure 4).

**Figure 4.** Percentage of settlement area potentially affected by flooding in Carinthia, 2016 (source of borders: Federal Office of Metrology and Surveying (BEV)).

By the results of this exposure analysis, the growing pressure on flood-prone areas and the increase in flood damage potential due to settlement development becomes evident.

#### 3.2.2. Agricultural Land

As settlements are expanding, agricultural land is declining. In the period from 1951 to 2020, the agricultural area in Austria has decreased by 35% (excl. alpine pastures) [43]. Within the last 20 years, agricultural areas have decreased by 14%, from about 3 million ha (year 2000) to 2.6 million ha in 2020 [43]. Figure 5 shows the decline in agricultural land area over the last 20 years, differentiated by Austrian federal states. The significantly higher decline in the Alpine parts of the country is clearly visible. In Carinthia, the southernmost province, the decline in agricultural area was 21%.

**Figure 5.** Decline in agricultural land in Austrian federal states between 2000 and 2020 in % (source of borders: Federal Office of Metrology and Surveying (BEV), Alpine Convention).

In total, 38% of Austria was used for agriculture in 2018, which amounts to 3.2 million ha (including 0.6 million ha of alpine pastures). At municipality level, this share of agricultural area varies greatly, for example, in municipalities in Carinthia, it differs between 1% and 56%. According to the spatial intersection of agriculture with flood-prone areas, 7.7% (246,300 ha) of Austrian agricultural areas are situated within flooding areas. In Carinthia, this share is 8.2%. The spatial distribution of these areas is, of course, not uniform, and the share of agricultural land within flood-prone areas varies greatly by municipality. In Carinthia, for example, in the municipality Villach, it is 62%, in four others, it is approximately 50%, and in 12 municipalities, it is still more than 20% (see Figure A1 in Appendix A).

Looking at agricultural land use in flood-prone areas of Carinthia in detail fodder growing (27.5%), extensive grassland (24.2%), feed grain (20.9%), and intensive grassland (17.4%) are the most predominant of 18 land use categories. Within the entire region of Austria, intensive grassland (23.2%), feed grain (21.5 %), extensive grassland (15.2%), fodder growing (10.4%), and oleaginous fruit (8.3%) are the predominant land use categories. In the Alpine region, there is proportionally more field fodder and extensive grassland, whereas bread crop, oleaginous fruit, and intensive grassland are less present (see Figure A2 in Appendix A).

While the first part was looking at agricultural land in general, in the next step a focus is put on land valuable for food production and the economic value of agriculture. About 42% of Austrian agricultural areas are considered particularly valuable for agricultural use—due to their relevance for regional food supply—by the research project BEAT [41]. In order to define valuable agricultural land, the natural characteristics for agricultural production, the resulting production potential—also under climate change conditions—and the regional distribution at the level of small-scale agricultural production areas were considered.

Intersecting these valuable agricultural areas with flood-prone areas reveals that in Austria, 12% (157,200 ha in total) of the total agricultural production areas designated as valuable are located in flood risk areas, whereby their spatial distribution varies greatly.

Figure 6 shows the small-scale agricultural production areas (areas of similar agricultural production conditions) and the associated share of the total valuable area in the respective production area that lies within flood-prone areas.

Particularly in Alpine regions, a greater proportion of soils identified as important for food security tend to be located in flood-prone areas. Whereas the Austrian average of high value agricultural land situated within flood-prone areas is 12%, Carinthia has a share of 21%. Figure 7 shows the distribution of this share for Carinthian municipalities.

**Figure 7.** High value agricultural area in Carinthia situated in flood risk zones, share of high value area per municipality, 2018 (source of borders: Federal Office of Metrology and Surveying (BEV)).

The economic value of agricultural areas is calculated by multiplying the hectare of agricultural land in flood-prone areas with an average regional Standard Output (SO). Figure 8 shows the production value of agricultural land in flood-prone areas per municipality. Very high in absolute figures is the agricultural production in flood-prone zones, for example, in the municipalities in St. Andrä, Klagenfurt, Wolfsberg, Hermagor-Pressegger See, and Spittal/Drau. In addition to the absolute numbers, the relative share of agricultural production value at risk is equality important for farm enterprises and food production.

For example, in the communities Freistritz an der Gail, Weißenstein, Baldramsdorf, Nötsch im Gailtal, and Spittal/Drau, the relative share is above 60%. The relative value takes the different municipality sizes into account and shows especially high numbers in the south west of Carinthia.

**Figure 8.** Standard output in EUR of agricultural areas (only value of crop production in intersecting areas—without livestock value) situated in flood-prone areas—sum per municipality and share within flood-prone areas, 2020 (source of borders: Federal Office of Metrology and Surveying (BEV)).

In this calculation, only the standard output values of crop production are considered. In order to be able to assess the full economic exposure, it would also be necessary to include animal production, which is, in part, closely intertwined with crop production.
