Monthly hydrological report February 2014

Exceptionally light snow cover in southern and central Finland; ice and groundfrost also shallow

Snow water equivalen in February 2014

February was very mild. Precipitation varied on both sides of the seasonal mean. In southern and central Finland snow depths were exceptionally low, even setting new records in some places. Melting of snow caused an atypical increase in discharges and water levels in southern and western regions. Groundwater levels varied on both sides of the seasonal mean. Ice and groundfrost were both very weak in southern and central Finland. Groundfrost layers were also thin in Lapland, although the amounts of snow and ice were high.

Precipitation

Precipitation in February was low in most areas, 20−40 mm. In northern Lapland the recorded precipitation was even below 20 mm. In Kainuu, Pohjois-Pohjanmaa and southern Lapland the precipitation of over 40 mm was somewhat above the seasonal mean. Some of the precipitation came as rain, even in Lapland.

Snow cover

Some snowfalls occurred at the beginning of the month throughout the country, but before the middle of February the mild weather caused melting of snow in southern and western Finland. Elsewhere the water equivalent of the snow cover continued to increase, until during the last week of the month melting of snow extended as far north as southernmost Lapland. By the end of February southern and western Finland were mainly without a snow cover, and elsewhere below a line from Raahe to Joensuu the water equivalent of the snow was below 20 mm. Further north the snow cover was more substantial; in most parts of Kainuu and Lapland the measured water equivalents were 100−150 mm and in Koillismaa, north-western Lapland and parts of western Lapland there was considerably more snow. In parts of northern Finland the snow cover was in fact heavier than normally in February, whereas in southern and central regions the cover was unusually light. For example in the drainage basins of the Vuoksi, Kymijoki, Kokemäenjoki and Kyrönjoki watercourses the snow cover at the end of February was lighter than ever previously recorded since the beginning of the observation series extending back to 1947.

Water level and discharge

Water levels were low and discharges decreasing at the beginning of February, but melting of snow caused increases in river discharges and water levels in southern and central Finland before the middle of the month, and as far north as the river Simojoki somewhat later. Flood levels were not reached, although the recorded levels were in many places exceptionally high for the time of year. Melt waters even increased the levels of some smaller lakes, but in larger lakes the levels continued to decrease during the end of the month. In most of Lapland apart from the southernmost belt, both water levels and discharges were typically low for the time of year throughout the month. Lake surfaces in Lapland were mainly close to the long-term seasonal mean, but elsewhere they were generally very high. Mean monthly discharges were also high in most of the major watercourses.

The deviation of the level of lake Pielinen from the seasonal mean at the end of February was +51 cm, and corresponding figures in some other lakes were: Kallavesi +25 cm, Saimaa +51, Keitele +30, Päijänne +51, Pyhäjärvi, Säkylä +1, Längelmävesi +17, Näsijärvi +21, Lappajärvi +64, Lammasjärvi +18, Oulujärvi +65, Lokka -71 and Inari -18 cm. The discharge of the river Pielisjoki was 162% of the mean February discharge during the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 132%, Kymijoki 124, Karjaanjoki 84, Kokemäenjoki 100, Siikajoki 149, Oulujoki 124, Iijoki 131, Kemijoki 94 and Tornionjoki 110%.

Groundwater level

Groundwater levels in southern and western Finland were close to the seasonal mean. In central and eastern Finland as far north as southern Lapland the levels were 5−30 cm above the seasonal mean, whereas in northernmost parts of the country they were 10−30 cm below the mean. In some very large groundwater formations groundwater levels had increased to 10−40 cm above the mean.

Groundfrost

Groundfrost in southern and central Finland extended to 5−20 cm, which was 5−15 cm below the seasonal mean. In the north, the recorded depths of 10−50 cm were 10−50 cm below the mean.

Ice cover

In southern and central Finland lake ice did not increase in thickness during February, whereas in Lapland the ice continued develop. In the southern half of the country the ice began to melt towards the end of the month, which was exceptionally early. By the end of the month the ice thicknesses in southern and western Finland were generally 20−30 cm, i.e. 15−25 cm less than the seasonal mean. In central and eastern regions the ice thicknesses were 25−45 cm and in the north they were 40−75 cm. These figures were close to the seasonal mean, in some cases above the mean.

 

Maps, graphs and tables

Published 2014-08-04 at 10:29, updated 2014-08-04 at 10:18