Monthly hydrological report June 2012

High water levels in the eastern Lake District

June was cooler than normally and precipitation was high. Levels of the larger lakes continued to increase, although generally the levels were decreasing. Watercourse discharges were mainly above the seasonal mean and groundwater levels were high in most regions. Due to the cool and wet weather, evaporation was rather low. Surface water temperatures were close to or below the seasonal mean.

Precipitation

Precipitation during June was heavy; 40–80 mm along the western coast and in north-western Lapland and elsewhere generally 80–130 mm. The highest rainfall was in Pohjois-Karjala, in some cases even exceeding 130 mm. In parts of eastern, south-western and northern Finland the recorded precipitation figures were almost twofold the seasonal mean. The lowest precipitation, below 60 mm, was recorded in Etelä-Pohjanmaa. The whole first half of the year was characterised by high precipitation particularly in the Vuoksi and Kymijoki river basins.

Water level and discharge

Lake water levels were generally decreasing during June, but heavy rainfall caused temporary increases in some small lakes. In the largest lakes, e.g. Saimaa, Päijänne and Inari the level increase continued until the end of the month. In southern, western and northern Finland water levels at the end of June were generally close to the seasonal mean but in many lakes in eastern and central regions the levels were exceptionally high. Except for some rivers in south-western and western coastal regions and in Lapland, the discharges of the major river watercourses were above the seasonal mean.

The deviation of the level of lake Pielinen from the seasonal mean at the end of June was +40 cm, and corresponding figures in some other major watercourses were: Kallavesi +14, Saimaa +37, Keitele +29, Päijänne +26, Pyhäjärvi, Säkylä +4, Längelmävesi +9, Näsijärvi -16, Lappajärvi +10, Lammasjärvi -4, Oulujärvi +32, Lokka -18 and Inari +13 cm. The discharge of the river Pielisjoki was 127% of the mean June discharge during the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 115%, Kymijoki 146, Karjaanjoki 108, Kokemäenjoki 122, Kalajoki 104, Oulujoki 177, Iijoki 92, Kemijoki 86 and Tornionjoki 115%.

Groundwater level

Groundwater levels in smaller formations throughout the country were decreasing, but were still generally 5–15 cm above the seasonal mean. In larger formations replenishment is somewhat delayed after rainfall and the levels were therefore still increasing.

Evaporation

June was rather cool and in most areas precipitation was high, and therefore evaporation was clearly below the seasonal mean. Evaporation as measured from Class A pans varied between 40 mm in northern Lapland and 110 mm in central Finland. These figures were generally almost 30 mm below the mean for June. The deviation from the mean was greatest in Pohjanmaa, even exceeding 50 mm. On the basis of watercourse model calculations evaporation from land areas during June was generally 40–80 mm and the corresponding figures for the larger lakes were 80–130 mm.

Surface water temperature

Surface water temperatures at the beginning of the month were generally close to the seasonal mean. In mid-June the temperatures slightly exceeded the mean, but by Midsummer and at the end of the month they were again at or below the mean. In some large and deep lakes changes in wind direction caused a rapid decrease in surface temperatures, when cold benthic waters were brought up to the surface. At some observation sites temperature decreases of up to 5˚C were recorded in a single day. Surface water temperatures at the end of June were 14–19˚C in southern and central Finland and 6–14˚C in the north. These temperatures were somewhat below the seasonal mean. Break-up of ice occurred in Lake Kilpisjärvi at the normal time just before Midsummer (June 19th).

Maps, graphs and tables

ISSN-L 0358-6367
ISSN 1799-6899

Published 2012-08-24 at 10:43, updated 2013-07-01 at 12:13