Monthly hydrological report June 2014

Lake waters unusually cool, water levels generally near-average

Precipitation in June 2014

June began with very warm weather, but the end of the month was exceptionally cold. The mean monthly temperature was below the average throughout the country. Considerable regional variation was recorded in monthly precipitation. Watercourse levels generally decreased in typical summer fashion, and by the end of the month varied on both sides of the seasonal mean. Groundwater levels were mainly below the seasonal mean, except in parts of Lapland. Lake water temperatures varied between high and low extremes depending on the prevailing air temperature, but by the end of the month the waters were exceptionally cool.

Precipitation

Precipitation in June varied considerably in different parts of the country. In Pohjanmaa the monthly precipitation was even below 20 mm, whereas in parts of southern Finland and north-western Lapland figures over 100 mm were recorded. Precipitation in the wettest areas was well above the seasonal mean. Along the coast of the Gulf of Bothnia and in northern parts of the river Vuoksi watercourse, precipitation was unusually low.

Water level and discharge

Lake water levels at the beginning of June were decreasing, or began to decrease before the middle of the month, with the exception of some large regulated lakes. During the latter half of the month heavy rainfall caused level increases in many areas, although the level changes were generally not great. River discharges increased temporarily as a result of the rainfall to rather high levels, although for most of the time they remained close to or even below the seasonal mean. In the northern rivers Tenokjoki and Muonionjoki, melting of the last of the snow increased discharges to a second spring flood at the beginning of the month.

By the end of June, water levels in most lakes were close to the seasonal mean, although despite rather heavy precipitation the levels in larger lakes of western Finland were still low after the dry spring. Lakes Pielinen and Inari were also low, whereas the level of lake Saimaa was still above the seasonal mean. Mean discharges of the major watercourses varied on both sides of the seasonal mean.

The deviation of the level of lake Pielinen from the seasonal mean at the end of the month was -24 cm, and corresponding figures in some other Finnish lakes were: Kallavesi -6 cm, Saimaa +29, Keitele -20, Päijänne +4, Pyhäjärvi, Säkylä -9, Längelmävesi -17, Näsijärvi -1, Lappajärvi +0, Lammasjärvi -21, Oulujärvi +15, Lokka -45 and Inari -22 cm. The discharge of the river Pielisjoki was 90% of the mean June discharge during the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 114%, Kymijoki 107, Karjaanjoki 49, Kokemäenjoki 52, Siikajoki 103, Oulujoki 149, Iijoki 62, Kemijoki 83 and Tornionjoki 117%.

Groundwater level

Groundwater levels in southern and central Finland were 0-15 cm below the seasonal mean; in the coastal zone of the Gulf of Bothnia the corresponding deficiency was 15-30 cm. During the period of cool weather and higher precipitation towards the end of June, the decrease in groundwater levels slowed down. In Kainuu and in southern and central Lapland the groundwater levels were 0-30 cm above the seasonal mean. In northern Lapland, below-average levels were still recorded.

Snow and ice cover

By the beginning of June, ice and snow were recorded only in north-western Lapland. Break-up of ice over lake Kilpisjärvi occurred at a typical time around Midsummer. The last of the snow had also melted from this region at the normal time before the middle of the month.

Surface water temperature

Lake waters warmed considerably after the beginning of June, and by the 10th day water temperatures were clearly above the seasonal mean, even reaching 20°C in some lakes of southern and central Finland. In Lapland, water temperatures increased well above the seasonal mean, even slightly earlier than in the south. Thereafter the waters cooled considerably. By Midsummer, the temperatures were unusually cool throughout the country, and were generally below 15°C. The weather remained cool after Midsummer and water temperatures were exceptionally low for the time of year, in many places cooler than ever previously recorded in late June during the 21st century. By the end of the month, lake water temperatures were 14-17°C in southern and central Finland and 5-13°C in Lapland. These temperatures were generally 2-4°C below the seasonal mean.

Maps, graphs and tables

Published 2014-11-18 at 14:45, updated 2014-11-18 at 13:41