Monthly hydrological report January 2014

Problems due to ice dams in some areas; lake ice thicknesses rapidly increasing

Ice thickness in the end of January 2014

Precipitation was low in January, and with the exception of Lapland there was only a light snow cover. Discharges in the main watercourses were high due to the mild weather at the turn of the year. During the second week of January heavy frosts caused hanging ice dams in many rivers between southern Finland and Pohjois-Pohjanmaa. These dams were disrupted using explosives and mechanical diggers. The frosts caused freezing over of lakes and development of groundfrost throughout southern and central Finland. Groundwater levels were high in all areas except northern Finland.

Precipitation

Precipitation in January was low almost throughout the country. Rather heavy precipitation occurred during the second week of the month in many areas, but thereafter there was almost none during a period of heavy frost. The lowest precipitation was in Pohjanmaa, below 10 mm, and most areas received 10−35 mm. The highest precipitation figures of about 40 mm were recorded along the southern and south-western coastline.

Snow cover

The beginning of January was snow-free to the south of a line from Oulu to Joensuu, but before the middle of the month the weather became more typically wintry and a light snow cover also developed in the south. In the north the water equivalent of the snow cover increased during the first two weeks of the month by about 20 mm, but thereafter the precipitation was low throughout the country. Only on the very last day of the month did an appreciable amount of snow fall in the southern and south-western coastal zone. By the end of the month the water equivalent in southern and central Finland was below 20 mm, well below the seasonal mean. In northern Finland the snow burden was generally close to the mean. In most parts of Kainuu, Koillismaa and Lapland the water equivalent was 80−130 mm and the heaviest snow covers, even exceeding 200 mm water equivalent, were recorded in north-western Lapland.

Water level and discharge

The mild period which had started during December continued into January, causing melting of snow and increasing water levels and discharges as far north as Oulu. The mild weather rapidly gave way to a period of heavy frost during the second week of January, which caused river discharges to decrease.  Lake water levels also began to decrease due to the heavy frosts in all but the largest lakes. The heavy frosts coupled with initially high discharges resulted in hanging ice dam formation from the south of the country as far north as the river Simojoki. Floods were combatted during January in various parts of the country by detonation of ice dams or opening them with mechanical diggers. Despite these efforts, some waterside cottages and sauna buildings were affected by the rising water levels. The mean January discharge was close to the seasonal mean in the rivers Kemijoki and Tornionjoki, but in the other major watercourses the discharges were clearly above the mean. Lake water levels were high in all areas except Lapland.

The deviation of the level of lake Pielinen from the seasonal mean at the end of January was +70 cm, and corresponding figures in some other Finnish lakes were: Kallavesi +50 cm, Saimaa +41, Keitele +31, Päijänne +44, Pyhäjärvi, Säkylä -1, Längelmävesi +18, Näsijärvi +14, Lappajärvi +74, Lammasjärvi +30, Oulujärvi +69, Lokka-85 and Inari -19 cm. The discharge of the river Pielisjoki was 154% of the mean January discharge during the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 128%, Kymijoki 130, Karjaanjoki 119, Kokemäenjoki 132, Siikajoki 360, Oulujoki 127, Iijoki 212, Kemijoki 94 and Tornionjoki 105%.

Groundwater level

Groundwater levels were 10−30 cm above the seasonal mean in all areas except northern Finland. In northern Lapland the levels were 10−40 cm below the mean. The mild weather in early January caused some level increases, but towards the end of the month the levels turned to a typical winter decrease.

Groundfrost

After the onset of the frosty period in mid-January, groundfrost developed throughout the country. By the end of the month the recorded depths were 20−45 cm in southern and central Finland, i.e. 5−10 cm deeper than normally. In northern Finland the depths of 15−50 cm were 5−20 cm weaker than normally.

Ice cover

 Most of the lakes of southern and central Finland were still without an ice cover at the beginning of January, but the heavy frosts starting on the tenth of the month soon caused freezing of the lakes. Because of the light snow cover the ice layers increased in thickness rather rapidly, with strong blue ice. By the end of the month ice thicknesses in southern and central Finland were 20−40 cm, i.e. 5−15 cm less than the seasonal mean. In the north, lake ice thicknesses varied between 30 cm in Kainuu and 63 cm in lake Kilpisjärvi. These figures were rather close to the seasonal mean. The ice cover over the river Tornionjoki was as heavy as >70 cm, but further south many rivers and streams had rather weak ice covers because of the high flow rates.

Maps, graphs and tables

Published 2014-06-26 at 10:39, updated 2014-06-26 at 10:37