A call-back to the research question is important. That is: For which sub-catchments of the Aare catchment under different flood scenarios can a great amount of financial and personal livelihood damage be expected based on the proportions of the land cover in the respective sub-catchments?
Now, as stated in the analysis, there seems to be a tendency towards strong discharges to take place in the mountainous, high-altitude sub-catchments located mostly in the south of the catchment. It was stated that these are simulations and depending on the weather conditions, strong precipitation events can be expected elsewhere as well. Yet, there must be a tendency that strong precipitation events can be still expected in mountainous areas. This is due to the presence of mountains. With air coming from elsewhere and being pushed against the mountain, it rises and cools down. Thus, the water carrying capacity of the air decreases and the water rains down there.
Next, if compared the peak discharges with the land cover distribution, it can be stated that sub-catchments with little settlement area are most prone big discharge amounts. Thus, most damage towards financial or personal livelihood aspects can be expected there realistically. It can be argued that this could be expected partially due to various reasons. First, as mentioned afore, mountains favour strong precipitation events. Next, the further down the water flows within the entire catchment, the more time and capacity it has to be balanced again, since other rivers coming from other sub-catchment will perhaps not carry so much water due to the event taking place in a small area. This can be illustrated with a simple imaginary equation.
Let us assume that we have 8 starting rivers. At each level 2 of the 8 flow together. Next, from the new 4 again two of those flow together until in a final step where we have 2 rivers left, flow also together into a single final river. Let us also assume that each of the rivers has a discharge of an imaginary amount of 1 (does not matter what size). This would result in the following scenario:
1 + 1 & 1 + 1 & 1 + 1 & 1 + 1 -> 2 + 2 & 2 + 2 -> 4 + 4 -> 8
Let us now double the discharge of the first river, which is underlined, while the rest remains the same. This would result in the following scenario:
2 + 1 & 1 + 1 & 1 + 1 & 1 + 1 -> 3 + 2 & 2 + 2 -> 5 + 4 -> 9
As it is displayed, that first sub-catchment has an increase of 100% discharge. In the final part of the catchment, this results in an increase of only 12.5%.
Through this simple, imagined example it becomes evident that high discharge resilience of rivers grows with time the further downstream it goes.
Consequently, the areas, which are located at the beginning of the discharge net within the catchment which is in the high altitude alpine areas, are least resilient to strong discharge events. This is furthered by the fact that that these areas are frequently shaped like a trough where all discharge accumulates swiftly in a single line. Unfortunately, settlements are frequently located close to those trough water lines due to historic reasons. Thus, the probability of settlements being affected by big river discharges are highest in those regions.
However, as we stated in the analysis part, the proportion of settlement area to the entire land cover of those sub-catchments is mostly rather small. Thus, even though the probability of those settlements being affected is bigger, the amount of settlement and thus the damage potential is lower there.
On the other hand, sub-catchments located in the city belt have a much greater damage potential. This is not solely due to the proportion of settlement area to the entire land cover of the respective sub-catchment. It is more connected to a greater presence of critical infrastructure. This includes transportation axes including freeways and railways, atomic power plants, hospitals just to name a few. Those being damaged by floods would have a much bigger impact on the entirety of the population compared to solely accommodation and business. This is not to be understood as a devaluation of the mountainous, remote regions. It is simply a factual comparison of damage potential. Regarding the probability of high discharge event occurring in the lower lands, those have another advantage compared to the high-altitude regions. A presence of big lakes favours the lowlands in the north. Those, as well as the rivers being fed from multiple sources, have a huge pretention capacity. Thus, the resilience to strong precipitation events and consequently a huge discharge is great.
Nevertheless, this does not mean that the lowland regions are safe from high discharge. As stated afore, the simulations used in this research generate a strong discharge event in only a few regions. If for whatever reason, the number of sub-catchments affected by high discharge increases, the resilience of the lowlands can potentially be broken and huge damage can be caused in such events. On the other hand, while the high-altitude regions are more likely to be affected by high discharge in frequency of events, the length of such events is rather small since the water is capable of flowing downstream faster. In the lowlands, if the bough breaks, the flood event will last way longer since it takes water much longer to flow away in flat areas.
Last but not least, it needs to be stressed that these are simulations. While they hold implications, there is a real uncertainty connected to it. As for instance, in the 300-year event simulation, there seems to be a greater amount of discharge for some catchments while in the 1’000-year event simulation those are much lower. Variation in weather and discharge conditions is real and to be expected.