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'New normal' mild Finnish winters threaten waterways

Researchers warn that winter runoff from rain-soaked fields is undermining massive investments in waterways protection.

Vettä täynnä oleva Mustionjoki kuohuaa Billnäsin padolla.
High water at the old Billnäs forge in Raseborg. Image: Kari Ikävalko / Yle

Rain in recent days has washed away the thin snow cover in southern Finland, especially coastal areas along the Gulf of Finland. Rivers and other bodies of water are full of water after a rainy autumn.

The situation is in line with forecasts of how Finnish winters are becoming as the climate warms. The ground remains wet, with extensive areas remaining bare in the winter. Large volumes of nutrients flow from sodden, exposed fields into waterways, spurring eutrophication in warmer weather.

Such runoff is difficult to prevent outside of the growing season, when there is little or nothing growing in fields. Environmental researchers warn that such winter discharges are undermining tens of millions of euros of investments in waterways protection.

Valuable fertiliser washes into ditches and rivers

The rate of flow in many rivers is now significantly higher than during a normal year. And the more flow, the more nutrients are moving into lakes and the shallow, brackish Gulf of Finland, which has long suffered from an excessive nutrient load. This means that during the next growing season there may well be more than twice as heavy a nutrient load as during an average year, likely spurring toxic algae blooms, say experts at the Finnish Environment Institute (SYKE).

"The conditions have been exceptional, and their impacts on waterways can't be controlled," says SYKE agronomist Markku Puustinen, referring to the nearly continuous rain in some areas in late 2017.

Exceptionally rainy December

Figures from the Finnish Meteorological Institute (FMI) confirm that December was exceptionally rainy in many areas, as was the whole of last year through much of southern Finland.

Water levels will now remain high far into the winter, even if there is a dry spell, says Puustinen. He says the worst situation in regard to future algae problems is if the ground becomes waterlogged right after the growing season, before it freezes. Then valuable nutrients such as phosphorus flow off fields, particularly those on slopes. In a normal year, most of the precipitation during the winter and early spring comes in the form of snow. Heavy rains in the autumn and early winter are especially harmful when the fields stay bare due to the warming climate.

"The worst-case scenario is that all the efforts we have put into waterways protection come to naught," Puustinen tells Yle.

Big losses in waterways protection and fertiliser

Every year, hundreds of millions of euros are spent on waterways protection in Finland. Environmental officials estimate that one fifth of this may already be going to waste due to climate change, but add that the figure may actually be higher.

Last year Finland received about one fifth more rain than the long-term average. Researchers say that matches forecasts for the future 'new normal'.

The FMI says that despite a cool summer, last year was between 0.5 and 1 degree warmer than the long-term average. Only eastern Lapland saw temperatures close to average.

As the effects of climate change are more pronounced closer to the poles, average annual temperatures are on track to rise by several degrees in Finland over the coming decades.

Overall water levels will not necessarily rise at the same pace, but the changes are expected to bring more heavy rainstorms and winter rainfall.

There have been several years with above-average rain recently. The past year fell short of the 2008 record, but it rained more and more steadily throughout the year.

December brought more than 100 millimetres of rain to many areas. Total rainfall during the year approached one metre in some parts of southern Finland, with Espoo's Nuuksio National Park measuring 945 millimetres of rain. Normally Nuuksio receives about 700 mm.

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