Monthly hydrological report November 2013

Mild and wet weather in southern and central regions

Snow water equivalent in November 2013, Snow water equivalen in November 2013
November was very mild and wet in southern and central Finland. Both water levels and discharges were above the seasonal mean in many areas, and in some coastal rivers even reached figures typical for the spring flood. Groundwater levels were also high as a result of the heavy precipitation. In the north the weather was already wintry and less wet, and in Lapland below-average water levels were recorded. The lakes of Lapland and Kainuu froze over during November. By the end of the month the snow cover was already heavy over parts of Lapland. Groundfrost in November was recorded only in Lapland.

Precipitation

Precipitation during November was high in most parts of the country, particularly in eastern and southern regions. In Lapland, precipitation was close to the seasonal mean. Overall, precipitation figures varied between <20 mm in northern Lapland and >100 mm in the southern coastal zone. In most areas, the recorded precipitation was 40−90 mm.

Snow

At the beginning of November, a snow cover was recorded only in Lapland and Koillismaa. During the course of the month the snow-covered area extended southwards and by the end of November most of the country had a blanket of snow. On the last day of the month the water equivalent of the snow cover in north-western Lapland exceeded 100 mm. Around Kuusamo and in easternmost Lapland the corresponding figures were generally 60−90 mm and in other parts of Lapland and Kainuu 30−60 mm. Further south the amount of snow was much lower.

Water level and discharge

The increase in water levels and discharges which had started in October continued during November, although the increase levelled off or even turned to a decrease in most lakes and rivers during the course of the month. In southern and central Finland the discharges were clearly above the mean for November, and in many coastal rivers typical spring flood levels were recorded. In Lapland, lake water levels decreased almost throughout the month as a result of the wintry weather, and as in the preceding months discharges remained below or at best equalled the seasonal mean. In the river Oulujoki and Kemijoki watercourses, the discharge figures were only half the seasonal mean for November. By the end of the month water levels were clearly below the seasonal mean in many lakes of Lapland. By contrast, in eastern Finland and in Päijät-Häme the levels were in many cases very high. Elsewhere, the recorded water levels varied on both sides of the seasonal mean.

The deviation of the level of lake Pielinen from the seasonal mean at the end of November was +20 cm, and corresponding figures in some other lakes were: Kallavesi +33 cm, Saimaa -1, Keitele -1, Päijänne +17, Pyhäjärvi, Säkylä -10, Längelmävesi -5, Näsijärvi -7, Lappajärvi +21, Lammasjärvi +11, Oulujärvi +4, Lokka -135 and Inari -32 cm. The mean monthly discharge of the river Pielisjoki was 111% of the mean November discharge for the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 95%, Kymijoki 107, Karjaanjoki 94, Kokemäenjoki 86, Siikajoki 156, Oulujoki 45, Iijoki 117, Kemijoki 48 and Tornionjoki 86%.

Groundwater level

In southern and central Finland groundwater levels increased as a result of the heavy precipitation to 0−15 cm above the seasonal mean. In eastern and northern Finland the levels were still 10−60 cm below the mean.

Groundfrost

Groundfrost was recorded in northern and central Lapland to depths of 0−25 cm and in southern Lapland and Pohjanmaa to 0−5 cm.

Surface water temperature and ice cover

In southern and central Finland lake water temperatures during November generally remained above the seasonal mean, although typical cooling occurred in keeping with the season. Some small watercourses began to freeze over in central Finland and in parts of southern Finland towards the end of the month. In Lapland, smaller watercourses had already frozen in October, but the larger water bodies froze over only at the end of November during a period of heavy frost. By the end of the month ice thicknesses in Lapland were generally 15−25 cm, on both sides of the seasonal mean. Further south, the ice covers were still very weak and in southern and central Finland the larger watercourses were still unfrozen.

Maps, graphs and tables

Published 2014-04-04 at 13:39, updated 2014-04-04 at 13:36