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Extreme weather Synne in December 2015. Photo: John Haga

It will become wetter

When the temperature increases, the air can hold more water, and more water will also fall. And more will fall in one go when it first starts to rain.

The rainfall in Norway has increased by about 20 percent since 1900, and preliminary estimates suggest that it is going to increase by another 10 to 20 percent by the end of the century.  How large the increase will be depends on how much we pollute (see the figure at the top of the page).

At the same time we know that current models are conservative and have not captured the historical increase. The precipitation may therefore increase even more than current calculations suggest.

Short-term precipitation will increase most

There will often be days with heavy rainfall, and it is the short-term precipitation that will increase the most. This is precipitation that occurs for periods shorter than one day. In Oslo the hours of precipitation in the course of one year have increased by approx 60 percent in 50 years. The increase has been especially pronounced in southern and eastern Norway from 1968 until 2014.

Historical measurements show that the precipitation increase is the result of more days of precipitation than before, but also that there will be more rainfall on the days it rains. The intensity has especially increased in Western Norway, and this may be partly linked to low pressure systems coming in from the sea.

It is the intense precipitation events in a short time that create some of the biggest problems, such as stormwater and flooding in cities and major damage to buildings, roads and train lines.

Climate change will also increase the risk of summer drought, particularly in southern and south-eastern Norway.

Poorer water quality

Extreme precipitation can lead to poorer water quality. With considerable precipitation, there is greater risk that drinking water sources will be contaminated by sewage leaks or run-off from areas with livestock operations.

An example of this is an episode in Bergen in the autumn of 2004, where the parasite Giardia ended up in drinking water and leading to at least 2,500 people becoming sick.

Fungal growth risk

A wetter and warmer climate increases the risk of fungal growth, which will be negative for both health and the economy. At present, more than 600,000 Norwegian houses are at high risk of moisture and water damage. By 2100 the figure may have risen to 2.4 million. It is therefore important in the future to build houses and buildings that can withstand a more humid climate.