Climate indicators – length of vegetation period

The length of the vegetation period or of the growing season is important and affects e.g. farming and gardening.

The vegetation period is usually defined as the part of the year where the daily average temperature exceeds a certain limit. The temperature limit depends on the type of plant but is usually between +3°C and +5°C. We have used +5°C as the limit, which means that the vegetation period starts halfway through spring and ends halfway through autumn.

For an individual year with large temperature variations from day to day, it can be very difficult to specify an exact point in time where the daily average temperature consistently exceeds a particular value. An average of the daily average temperatures over 10 years gives a significantly smoother temperature pattern, and has been used for this climate indicator. The first bar in the diagram shows the situation for the 10-year period 1961-1970, the second shows the period 1962-1971, and so on until the period 2005-2014.

Length of vegetation period

The diagram for southern Sweden is based on 20 stations in Götaland and southern Svealand. The diagram for northern Sweden is based on 16 stations in northern Svealand and Norrland.

10-year moving averages for the length of the vegetation period in southern Sweden.
10-year moving averages for the length of the vegetation period in southern Sweden.
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10-year moving averages for the length of the vegetation period in northern Sweden.
10-year moving averages for the length of the vegetation period in northern Sweden.
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In northern Sweden the length of the vegetation period has increased by about two weeks over the past 40 years. The length of the vegetation period has also increased in southern Sweden, but not as much. In southern Sweden the increase is concentrated to the last decade.

Start of vegetation period

10-year moving averages for the vegetation period start date in southern Sweden
10-year moving averages for the vegetation period start date in southern Sweden. The red and blue bars show an earlier or later start then the average start date for the period 1961-1990.
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10-year moving averages for the vegetation period start date in northern Sweden. The red and blue bars show an earlier or later start then the average start date for the period 1961-1990.
10-year moving averages for the vegetation period start date in northern Sweden. The red and blue bars show an earlier or later start then the average start date for the period 1961-1990.
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There has been a clear change in the start date since the 1960-ties. But the change has occured differetly in southern and northern Sweden.

End of vegetation period

10-year moving averages for the vegetation period end date for southern Sweden. The red and blue bars show an earlier or later end then the average end date for the period 1961-1990.
10-year moving averages for the vegetation period end date for southern Sweden. The red and blue bars show an earlier or later end then the average end date for the period 1961-1990.
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10-year moving averages for the vegetation period end date for northern Sweden. The red and blue bars show an earlier or later end then the average end date for the period 1961-1990.
10-year moving averages for the vegetation period end date for northern Sweden. The red and blue bars show an earlier or later end then the average end date for the period 1961-1990.
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The vegetation period in the future

The vegetation period is expected to become longer. By the end of the century the vegetation period will be 30-100 days longer than during the period 1961-1990, depending on which scenario is used.

The change is calculated to be greater in southern Sweden and less in northern Sweden. All the climate model simulations show a longer vegetation period. The vegetation period is expected to become longer by about the same number of days in the spring and the autumn.

[More about the vegetation period in the future.]