Climate-adapted and dimensioning flows

By using existing regional climate scenarios together with hydrological model calculations, SMHI can produce hydrological scenarios. Frequency analysis provides an idea regarding how climate scenarios affect the outcome of the traditional dimensioning documentation.

Why should we take the climate issue into consideration?

Today, design data is used for construction in water through the frequency analysis of existing hydrological measurement series. These measurement series can be up to 100 years or even longer.

The series contain information on what hydrological conditions have been like and dimensioning based on these conditions will consequently apply for a period which has already passed.

An analysis recently carried out of SMHI's meteorological measurement series, where the years 1991-2005 are compared with the meteorological standard normal period 1961-1990, indicates that it has become warmer and in most areas of the country there is even more precipitation.

A result which indicates that the greenhouse effect may have begun to play an increasingly more important role in our climate and which also emphasises the validity of the results from the climate scenarios.

New methodology

Traditional frequency analysis of hydrological measurement series is based on the assumption that the climate is stable and that the future flows have the same statistical characteristics that we have observed and catalogued in our time series.

This means that the results can be questioned if the climate is not stable. Against this background, and the fact that both temperature conditions and precipitation are changing in a future climate, it is important that, when calculating dimensions, consideration should also be given to the system's sensitivity to climate changes.

This is of particular importance if the design is expected to have a service life of 100 years or more.

Climate-adapted design flows are indicated as

  • HHQ 100 - Highest High Tide with a return time of 100 years - based on historic data.
  • Evaluation of future levels (the period 2070-2100) for mean annual river flow and 100-year flood - specified as a percentage of today's levels.