Monthly hydrological report June 2013

Lake waters exceptionally warm, water levels generally decreasing

Surface water temperature in June 2013


June was exceptionally warm and in many places precipitation was high. Lake water levels were generally decreasing and river discharges were low. Occasional heavy precipitation increased the discharges in some small rivers, culminating in Pohjanmaa at the end of the month. Groundwater levels were decreasing throughout the country. Surface water temperatures were exceptionally high on two occasions during the month, and record high mean monthly temperatures were recorded in many parts of southern and central Finland.

Precipitation

Precipitation in June was above the seasonal mean in many areas. The heaviest rainfall was recorded in western Finland, Koillismaa and western Lapland. These areas received 100−160 mm of rainfall, in some cases over twofold the seasonal mean. The lowest rainfall, below 30 mm, was recorded in northern Lapland, and corresponding figures in the southern and south-western coastal zone were below 50 mm.

Water level and discharge

Lake water levels were generally decreasing in June and river discharges were typically low, but heavy precipitation caused transitory level increases in some areas. Very heavy rainfall in Pohjanmaa during the last week of the month caused a clear increase in discharges, and some increases were also recorded in regions of Lapland with heavy incident rainfall. Of the larger lakes, the level of lake Päijänne increased during June. The levels of lakes Saimaa and Pielinen turned to a decrease earlier than normally due to low precipitation. By the end of the month, lake water levels were generally close to or below the seasonal mean; in lakes Pielinen and Kallavesi deficits of 40 and 20 cm were recorded. The level of lake Saimaa, which had been above the mean for over one year, was still 20 cm high, but the deviation from the seasonal mean was continuously decreasing. The mean discharges of the main watercourses were generally well below their seasonal means, and the smaller coastal rivers also had low discharges.

The deviation of the level of lake Pielinen from the seasonal mean at the end of June was -38 cm, and corresponding figures in some other lakes were: Kallavesi -19 cm, Saimaa +21, Keitele -8, Päijänne +6, Pyhäjärvi, Säkylä -1, Längelmävesi -9, Näsijärvi +5, Lappajärvi +11, Lammasjärvi -34, Oulujärvi -4, Lokka -63 and Inari -11 cm. The monthly discharge of the river Pielisjoki was 80% of the mean for the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 102%, Kymijoki 88, Karjaanjoki 72, Kokemäenjoki 58, Siikajoki 38, Oulujoki 51, Iijoki 60, Kemijoki 64 and Tornionjoki 85%.

Groundwater level

Groundwater levels were decreasing throughout the country. In southern and central Finland the levels were 0−25 cm below the seasonal mean and in northern Finland the deficit was 0−10 cm.

Groundfrost

Groundfrost persisted in June in parts of Lapland.

Evaporation

Monthly evaporation measured with Class A pans varied between 60 and 120 mm. The evaporation sums were below the seasonal mean in many regions. The highest precipitation was recorded during warm weather at the beginning and the end of the month. On the basis of model calculations, evaporation from land areas was generally 40−80 mm and from the larger lakes 80−120 mm.

Surface water temperature

Surface water temperatures increased at the beginning of June to unprecedentedly high values, in southern and central Finland even to 22ºC. After the tenth of the month, these high temperatures decreased markedly due to a change in the weather type. Thereafter the recorded temperatures were rather close to the seasonal mean, until warm weather after Midsummer again increased water temperatures clearly above the mean. Surface water temperatures at the end of the month were generally 18−24ºC in southern and central Finland and in Kainuu and 10−20ºC in Lapland. These figures were generally above the seasonal mean. The mean surface temperatures for June were higher than ever previously recorded in many lakes of southern and central Finland.

Ice thickness

The ice cover of lake Kilpisjärvi broke up at the beginning of June, about 2 weeks ahead of the normal schedule.

Maps, graphs and tables

Published 2013-10-28 at 13:36, updated 2013-10-28 at 13:35