Comment on the results
Based on the equalized values, it can be seen that the average annual precipitation for Sweden was around 600 millimeters until the mid-70s. Since then, the yearly precipitation has increased and is now closer to 700 millimeters.
The average winter precipitation has slowly increased from approximately 100 millimeters since around 1890, to approximately 150 millimeters in present time.
There is a lot that suggests that early precipitation observations underestimated precipitation amounts, especially in the case of snowfall. It is, however, difficult to estimate how great this underestimation has been. In addition, the review with correction or interpolation of suspect or missing precipitation values were probably not as extensive as in the present. For this reason, the time up to 1933 is grayed out in the chart and caution should be exercised in making any climatological conclusions based on this time period.
How is yearly and seasonal precipitation defined?
The yearly precipitation is the total amount of precipitation during all days of the year. The same applies to precipitation during different seasons. Winter (December-February) is given the year that applies to January and February. For example, winter 2021 is the months from December 2020 to February 2021.
The amounts of precipitation refer to an average value for Sweden as a whole.
Why is this indicator important?
Sufficient access to fresh water is vital for humans and nature. Precipitation also has a great economic significance for hydropower and more. However, if the precipitation falls violently or in large quantities, this can cause problems in form of floods and landslides.
It is not only the amount of precipitation per se that is decisive, evaporation must also be taken into account. Evaporation is expected to increase in a warmer climate. Trends in precipitation should therefore be studied together with trends in temperature and water flow.
How has the indicator been calculated?
SMHI has just over 600 stations that measure precipitation. The number has varied over time. At most, SMHI measured precipitation at over 900 locations with a clear increase after the 1930s. The precipitation observations that have been digitized have been used for this indicator.
Precipitation in the future
Precipitation greatly varies from year to year and season to season. In a warmer climate, precipitation is expected to increase on average. This is due to, among other things, the fact that warm air can contain more vaporized water than cold air. The development depends on the extent to which greenhouse gas emissions continue.
Precipitation is expected to increase during all seasons, but mostly in winter. The biggest increase appears to be in northern Sweden. In parts of southern Sweden however, the increase is not as clear during summer and autumn. In addition, a warmer climate will mean increased evaporation which can affect available water.