Finland's network of meteorological and climate observation
Finland's longest uninterrupted series of meteorological observation is from Kaisaniemi in Helsinki. Regular meteorological observations form the basis for reliable climate research.
Continuous observations since 1844
Finland's oldest known meteorological observations conducted with measuring instruments date back to the 1700s in Turku. In addition to Turku, meteorological observations were performed at around ten other localities at the time. These series of observations are, however, discontinuous and as the measuring methods are unknown, the majority of meteorological observations dating back to the 18th and early 19th century are not suitable for climate research purposes.
Professor G. G. Hällström initiated meteorological observations in Helsinki in October 1828. Continuous, systematic meteorological observations have been conducted in Kaisaniemi, Helsinki, since 1844. In 1846, the Finnish Society of Sciences and Letters equipped five other meteorological observing stations with up-to-date meteorological observation equipment, and in the 1880s, as many as about 50 stations were operational. After Helsinki, the longest uninterrupted series of meteorological observations originate in Oulu, Kajaani and Kuopio.
The meteorological observation network developed first in the southern and central parts of the country. Lapland's first meteorological observing stations began operating in Inari and Sodankylä in the early 1900s. The number of meteorological observing stations is still higher in the southern and central parts of the country than in the north.
Precipitation observation network developed later
In the early days, meteorological observations mostly consisted of air temperature and barometric pressure. Precipitation observations were only conducted in a few localities. The network of precipitation observation did not expand significantly until 1907, as a special grant was awarded for establishing precipitation observing stations.
Since the amount of precipitation varies a lot depending on time and place, a denser network of stations is required for observing it than temperature. Today, the number of observing stations measuring precipitation is significantly higher than the number of stations observing temperature and other variables, too.
Homogenised time series reveal climate change
Even though the performance of meteorological observations is strictly regulated, long climate time series always include points of discontinuity. An observing station that has been operational for decades, even more than a hundred years, has seen many changes throughout history. Factors causing points of discontinuity in time series include changes in observation equipment and its placement, changes in observation times and mean value calculation methods, and changes in the environment of the observing stations. The location of several observing stations has also changed over time.
For the purpose of climate research, the history of observing stations is closely examined and the aim is to homogenise time series. In other words, the aim is to dissipate from the observations signals due to factors other than actual climate change (e.g. growth of cities). Only a homogenised time series provides reliable material to facilitate research of changes in climate.