Monthly hydrological report March 2014

Spring came early to southern and central Finland

Ice thickness in the end of March 2014

March was mild and precipitation was low. Warm spring weather melted snow, groundfrost and watercourse ice covers in southern and central Finland. Melting of snow caused increased river discharges in some areas, but normal spring flood levels were not reached. Groundwater levels were rather high. Both snow and ice covers were thinner than normally in most areas.

Precipitation

Precipitation during March was 20−40 mm in most parts of the country, although higher figures were recorded in north-western Lapland. In southern and central regions the precipitation was generally well below the seasonal mean. Precipitation came both as snow and as rain in almost all areas.

Snow cover

The snow burden in March was very low in many areas. Average or above-average figures were recorded only in Lapland and Koillismaa. At the beginning and after the middle of the month the whole country was covered in snow for short periods, but otherwise southern, western and central Finland were almost completely free of snow. Warm weather at the beginning of the month melted snow as far north as Lapland, but at the end of March the northern areas were covered with new snow. By the end of the month the water equivalent of the snow cover in Kainuu, southern Lapland and the area around Inari was generally 90−140 mm, elsewhere in Lapland and Koillismaa 150−200 mm. The area below a line from Oulu to Joensuu was almost completely free of snow.

Water level and discharge

In Lapland, both water levels and discharges were rather stable during March, in typical winter fashion, or were slowly decreasing. Further south, the early onset of spring melted snow at the beginning of the month and increased discharges, although not to flood levels. In Pohjanmaa the peak discharges were clearly below the level of spring flooding. Melting of snow and precipitation resulted in level increases in some lakes as far north as Pohjois-Pohjanmaa. Generally, however, the levels continued to decrease or remained stable. Water levels in March were mainly still very high, except in Lapland. Towards the end of the month cold nights and dry, sunny weather checked increases in water levels, and discharges decreased steadily. Due to the early spring, mean river discharges were generally above the seasonal mean except in Lapland.

The deviation of the level of lake Pielinen from the long-term seasonal mean at the end of March was +51 cm, and corresponding figures in some other lakes were: Kallavesi +34, Saimaa +52, Keitele +28, Päijänne +63, Pyhäjärvi, Säkylä +9, Längelmävesi +15, Näsijärvi +36, Lappajärvi +62, Lammasjärvi +24, Oulujärvi +81, Lokka -50 and Inari -11 cm. The monthly discharge of the river Pielisjoki was 143% of the mean for March during the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 130%, Kymijoki 110, Karjaanjoki 62, Kokemäenjoki 95, Siikajoki 316, Oulujoki 123, Iijoki 220, Kemijoki 107 and Tornionjoki 119%.

Groundwater level

Groundwater levels were rather high for the time of year in some areas due to the early spring. In southern and central Finland the levels were as much as 20−50 cm above the seasonal mean. In northern Lapland the groundwaters had remained low after the previous autumn, and the surfaces were still 10−40 cm below the seasonal mean.

Groundfrost

In southern and central Finland groundfrost had melted in many areas, although depths of 0−15 cm were still recorded in some areas. In the north, groundwater depths were 10−50 cm. Maximum groundfrost depths were reached by late January or early February in southern and central Finland, and by February-March further north.

Ice cover

In southern and central Finland lake ice covers began to weaken already at the end of February. During March, they decreased further by 10−15 cm. By the end of the month the ice thicknesses were generally below 25 cm in southern and central Finland, clearly below the seasonal mean. Towards the end of the month, ice thicknesses began to decrease as far north as lake Oulujärvi. In northern parts of central Finland and in Kainuu and Pohjois-Pohjanmaa, the measured ice thicknesses were generally 35−55 cm. In Lapland the ice was still very strong and increasing. In most lakes the ice thickness was 55−70 cm and in lake Kilpisjärvi depths of over 90 cm were recorded. The figures for Lapland were close to or slightly above the seasonal mean.

Maps, graphs and tables

Published 2014-08-04 at 10:38, updated 2014-08-04 at 10:37