55 Risks and vulnerabilities In order of priority, the risks/vulnerabilities affecting warehouses are: 1) fire: history teaches us that fire has always been the main enemy of wooden warehouses: in presence of wind, the fire can spread from one warehouse to another,affecting the entire structure, from foundations to roof, and damage of wood is irreversible. 2) flood: considering the position of the houses, by the river, with their foundations directly under the water resting on a “quick clay”, the risk of flood occurs whenever the water level of the river rises (due to long periods of rain or due to the melting snow) and, for this reason, the static capacity of the structure is lost. Due to climate change, the risk of floods is now increasing, as it is increasingly frequent the occurrence of extreme weather events. 3) biological infestation: one of the main consequences of elevated moisture/liquid water content (in general high humidity values) is the biological contamination by microorganisms, insects, and other invasive species. Damp wood is vulnerable to attack by mould, bacteria, and pests, whose life cycle is as fast as the conditions are suitable for their growth. The result of climate change is a warmer and more humid climate with the consequent acceleration in biological growth and a higher risk for infestation of structural wood (organic material). 4) exposure to weather: the external surface of the warehouses -roof and facades- in addition to the foundations is obviously subject to the continuous action of external atmospheric agents. The rain, whose direction and force are due to the action of the wind, can be more or less intense. The most exposed portions of wood will be more humid with all the consequent problems related to the water/moisture content inside the structure of the organic material. Climate change (stronger wind and heavy rainfalls/snowstorms) can make the situation worse. In addition, sunlight exposure depends mainly on the season of the year (different inclination of the light rays with respect to the earth's surface) and on the presence or absence of clouds in the air which represent a screen that attenuates the energy carried by the light rays, therefore their intensity. The irradiation of a surface consists in a transfer of heat and therefore in a heating of the irradiated material, in the case of wood the consequences are physical-mechanical stressors (deformations, fractures, cracks, loss of stability). Climate change action consists of an increase in sunlight intensity, thus in the wood decay. 5a) freeze-thaw cycles: Trondheim climate shows severe variations in temperature throughout the year. The problem of freeze-thaw cycles occurs whenever the temperature falls below 0°C (or much below in the presence of salts dissolved in the water) and goes back above 0°C (or above the temperature of transition between liquid water and ice). The consequences of the cycles are minimal if the cycles occur with low frequency over time but become alarming if the freeze-
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