Monthly hydrological report February 2013

Snow burdens on both sides of the seasonal mean; ice and groundfrost rather weak

Water-equivalent-of-snow-february2013

February was mild and precipitation was low. The snow burden varied on both sides of the seasonal mean, but exceptional deviations were not recorded. Watercourse and groundwater levels were decreasing in typical winter fashion. Depths of groundfrost and ice covers did not increase due to the rather weak frosts, and by the end of the month both ice covers and groundfrost were low for the time of year in most parts of the country.

Precipitation

Precipitation during February was below the seasonal mean, with monthly sums generally in the range of 10−30 mm. The lowest precipitation, below 10 mm, was recorded in Inari. The highest, even exceeding 30 mm, was in the area around the capital city and in north-western Lapland. The precipitation came generally as snow in all parts of the country.

Snow cover

The water equivalent of the snow cover, i.e. the snow burden, increased during February particularly in southern and central Finland as a result of falls of snow during the first half of the month. Thereafter there was very little new snow. Some mild days at the very end of the month caused only slight melting of snow. In the north, the increase in the snow water equivalent was slow but continuous throughout the month. Although the snow burden was not exceptional in any regions, one roof collapse causing accidental death did occur at a riding stable in the municipality of Laukaa in the middle of February. At the end of the month the mean water equivalent of the snow cover measured in the field was 40−80 kg/m2 along the western coast and 80−110 kg/m2 elsewhere in southern and central Finland as far north as Oulu. In south-eastern Finland the snow burden was higher, 100−130 kg/m2, in southern Lapland and Koillismaa 100−150 kg/m2 and elsewhere in Lapland generally over 130 kg/m2. The snow covers were above the seasonal mean in southern Finland and in northern Lapland; in the east and particularly in Kainuu they were clearly below the mean.

Water level and discharge

Lake water levels decreased during February almost throughout the country in typical winter fashion. In unregulated lakes the level changes were rather small, whereas in many regulated lakes the levels were decreased considerably. Water levels were generally close to the seasonal mean, although those of some of the larger lakes were still high. Due to the extra regulatory flow to lake Saimaa, the level of lake Pielinen at the end of February was almost normal. The mean discharges of the major watercourses were close to or above the seasonal mean after the rather wet end of the previous year. The discharges of the smaller coastal rivers were generally close to the seasonal mean.

The deviation of the level of lake Pielinen from the seasonal mean at the end of February was +4 cm, and corresponding figures in some other lakes were: Kallavesi +5 cm, Saimaa +61, Keitele +20, Päijänne +26, Pyhäjärvi, Säkylä -4, Längelmävesi +12, Näsijärvi -4, Lappajärvi +19, Lammasjärvi -3, Oulujärvi +32, Lokka -19 and Inari +25 cm. The mean monthly discharge of the river Pielisjoki was 141% of the mean February discharge during the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 132%, Kymijoki 125, Karjaanjoki 96, Kokemäenjoki 102, Siikajoki 76, Oulujoki 110, Iijoki 121, Kemijoki 120 and Tornionjoki 121%.

Groundwater level

Groundwater levels generally decreased during February in typical winter fashion. In most parts of the country the levels were still 10−20 cm above the seasonal mean.

Groundfrost

Only minor changes in groundfrost depth were recorded during February. In the south, groundfrost depths were generally 0−30 cm, i.e. 10−20 cm weaker than normally. In central Finland the depths were 10−35 cm, about 10 cm below the seasonal mean. In the north, measured groundfrost depths of 20−80 cm were close to the seasonal mean, but in most of Lapland the depths were 20−30 cm below the mean.

Ice thickness

Lake ice thicknesses showed rather little change during February. There was almost no formation of black ice because of the lack of periods of heavy frost. In some southern regions ice thicknesses even decreased by a few centimetres. Depths of snow ice increased in some lakes, and its proportion of the overall ice cover was in many cases rather high. Total ice thicknesses at the end of the month were 30−55 cm in southern and central Finland and 45−60 cm in the north. Lake Kilpisjärvi had an ice thickness of 80 cm at the end of the month. The recorded ice thicknesses were generally below the seasonal mean almost throughout the country.

Maps, graphs and tables

ISSN-L 0358-6367
ISSN 1799-6899

Published 2013-05-20 at 13:00, updated 2013-07-01 at 12:54