Monthly hydrological report October 2014

High regional and temporal variation in hydrological parameters

Precipitation in October 2014

Variation in temperature and precipitation was high in October, which was mirrored in the water reserves.  During the second half of the month some snowfalls were recorded throughout the country and smaller lakes in the north froze over. Melting of snow during warmer weather coupled with heavy rainfall increased discharges at the end of the month particularly in Pohjois-Pohjanmaa and southern Lapland. Groundwaters were increasing, but still below the mean.

Precipitation

Precipitation in October was low in southern Finland and in Lapland, where the precipitation sum of 15-30 mm was below half the seasonal mean. By contrast, the precipitation of over 70 mm in central Finland and Pohjois-Pohjanmaa was in some areas over 1.5-fold the mean for October.

Snow

A thin cover of snow was formed in Pohjois-Kainuu, Koillismaa and south-western Lapland before the middle of the month. Towards the end of the month falls of snow were recorded almost throughout the country, but persisted for more than a few days only in northern Finland and parts of Pohjois-Karjala. In Kainuu the water equivalent of the snow cover reached almost 40 mm during the last week of October, but by the very end of the month small amounts of snow persisted only in northernmost Lapland.

Water level and discharge

Autumn precipitation caused lake level increases towards the end of the month particularly in Pohjois-Pohjanmaa and in western and central Finland. The greatest level increases were recorded in unregulated lakes of the southern part of the Iijoki watercourse. In southern Finland and in Lapland the changes in water levels were rather small and some levels even decreased slightly. Lakes of the river Vuoksi watercourse were below the seasonal mean. The lakes of Pirkanmaa and central Finland, which had been low for some time, increased towards the seasonal mean but were still clearly below the mean. Elsewhere, lake levels at the end of the month were close to the seasonal mean. In central Finland and Pohjois-Pohjanmaa the heavy precipitation in October caused discharge increases, which in some places were very high by the end of the month. In other regions, the conditions of low precipitation continued and discharges remained clearly below the seasonal mean. Mean discharges of the major watercourses in October were generally below the mean for October.

The deviation of the level of lake Pielinen from the seasonal mean at the end of October was -39 cm, and corresponding figures in some other lakes were: Kallavesi -17 cm Saimaa -10, Keitele -24, Päijänne -18, Pyhäjärvi, Säkylä -18, Längelmävesi -23, Näsijärvi -5, Lappajärvi +0, Lammasjärvi -20, Oulujärvi -13, Lokka -65 and Inari -14 cm. The mean monthly discharge of the river Pielisjoki was 68% of the mean October discharge during the reference period 1971-2000, and corresponding figures in some other rivers were: Vuoksi 103%, Kymijoki 61, Karjaanjoki 48, Kokemäenjoki 38, Siikajoki 79, Oulujoki 85, Iijoki 112, Kemijoki 88 and Tornionjoki 79%.

Groundwater level

Groundwater levels were increasing in southern and central Finland, but were still 0-30 cm below the seasonal mean due to the dry autumn. Elsewhere, the levels were generally 5-50 cm below the seasonal mean. Groundfrost was recorded in parts of eastern and northern Finland to depths of 0-5 cm.

Surface water temperature and ice cover

Cooling of watercourses occurred at the beginning of October throughout the country in typical fashion for the time of year. After the middle of the month the weather cooled considerably, and so did the waters. Some small watercourses in the north froze over, and frazil ice was recorded along some southern lake shores. During the last week of October the weather became warmer again, particularly in southern and central Finland, and surface water temperatures increased towards the seasonal mean. Surface water temperatures at the end of October were 3-6°C in southern and central Finland and below 4°C in the north. In northern Finland some small watercourses were frozen over by the end of the month, although the ice covers were still very weak. The larger lakes were still unfrozen.

Evaporation

Evaporation from soil layers was very low. Monthly evaporation sums from the larger lakes on the basis of watercourse model calculations were generally 30-60 mm.

Maps, graphs and tables

Published 2015-01-30 at 17:53, updated 2015-01-30 at 17:52