Monthly hydrological report June 2011

Warm water for swimming; water levels in the eastern Lake District still low.

Precipitation during the latter half of June was high, particularly in western Lapland and northern Ostrobothnia. Rainfall increased both discharges and water levels, although in the larger lakes of central and eastern Finland water levels were still low. Surface water temperatures were generally above the mean, although heavy rainfall and winds after the middle of the month caused some cooling. Water temperatures at the end of June reached 24°C in parts of central Finland and were a few degrees above the seasonal mean elsewhere. Groundwater levels were low, particularly in eastern Finland. Considerable variation was recorded in evaporation.

Precipitation

The monthly precipitation sum was clearly above the seasonal mean in many regions. The heaviest rainfall was in western Lapland and Pohjois-Pohjanmaa, where in wide areas precipitation of up to 40–65 mm on some days corresponded to typical figures for the whole month. The monthly precipitation varied between 50 mm in south-western Finland to 150 mm in northern Lapland. The heaviest rainfall occurred during the second half of the month.

Water level and discharge

The heavy precipitation during the second half of June increased discharges particularly in western Lapland and Pohjois-Pohjanmaa. In the river Tornionjoki watercourse, discharges even exceeded those recorded during the spring flood and in the river Iijoki the June discharges equalled those of the spring. At the end of the month, after the period of heavy rainfall, discharges again began to decrease. The effects of the precipitation were also seen in rising lake levels, which generally decrease during June. The rainfall increased water levels in most parts of the country close to the seasonal mean, but in many of the larger lakes of central and eastern Finland the levels were still very low; for example the level deviation in lakes Pyhäselkä and Haukivesi was -45 cm. In Lapland the levels of lakes Lokka and Porttipahta were still unprecedentedly low.

The deviation of the level of lake Pielinen from the seasonal mean at the end of June was -34 cm, and corresponding figures in some other Finnish lakes were: Kallavesi -15 cm, Saimaa -37 cm, Keitele -15 cm, Päijänne -2 cm, Pyhäjärvi cm, Säkylä +3 cm, Längelmävesi -24 cm, Näsijärvi -18 cm, Lappajärvi +15 cm, Lammasjärvi -5 cm, Oulujärvi 0 cm, Lokka -167 cm and Inari -8 cm. The monthly discharge of the river Pielisjoki was 77% of the mean for June during the reference period 1971-2000, and corresponding figures in some other lakes were: Vuoksi 77%, Kymijoki 73%, Karjaanjoki 48%, Kokemäenjoki 63%, Kalajoki 54%, Oulujoki 24%, Iijoki 78%, Kemijoki 73% and Tornionjoki 98%.

Groundwater level

Groundwater levels decreased during June throughout the country as a result of increasing evaporation. Heavy rainfall slowed the level decreases and caused short-term variation in small formations according to the amount of precipitation. Groundwater levels were generally 0–30 cm below the long-term seasonal mean; in eastern Finland the deficit was even greater, 20–50 cm.

Groundfrost

Groundfrost was still recorded in some parts of northern Finland during June.

Evaporation

Evaporation varied considerably during June. At the beginning of the month and during hot weather during the last days of June the evaporation was strong, whereas very low evaporation was recorded in many areas during the cool, rainy weather in between. Evaporation sums measured from Class A pans varied between 50 mm in northern Lapland and over 150 mm in southern and central Finland. In Pohjanmaa and in the Åland Archipelago evaporation was below the mean for June, whereas in many parts of southern and eastern Finland the recorded figures were above the mean. In northern Finland the monthly evaporation sum was close to the seasonal mean. On the basis of model calculations the evaporation from land areas was generally 60–90 mm and from the larger lakes 90–150 mm.

Water temperature

Hot weather at the beginning of June increased water temperatures to 2–6°C above the seasonal mean. During the middle of the month the weather cooled and water temperatures also decreased. Windy and rainy weather around Midsummer mixed and cooled the water layers and temperatures were close to the seasonal mean. Warmer weather at the end of the month again increased water temperatures to 2–6°C above the seasonal mean. Surface water temperatures at the end of the month were 19–26°C in southern and central Finland, Pohjois-Pohjanmaa and Kainuu, and 11–20°C in Lapland. Ice broke up in lake Kilpisjärvi on June 9th, about 1 week ahead of the normal schedule.

Maps, graphs and tables

ISSN-L 0358-6367
ISSN 1799-6899

Published 2011-08-16 at 12:32, updated 2013-07-01 at 12:51