Monthly hydrological report in March 1999
Hydrological conditions in Finland in March were normal for the time of year. Precipitation was slightly above the seasonal mean. Snow and groundfrost extended throughout the country and watercourses were covered with a thick but structurally rather
weak layer of ice. Water levels were still above the seasonal mean in many large lakes. The spring season began to develop rapidly towards the end of the month as a result of a period of warm weather.
Precipitation during March was above the seasonal mean in southwestern Finland (40-50 mm) and in Lapland (30-40 mm). Elsewhere the recorded precipitation was close to or below the seasonal mean (20-30 mm). Most of the precipitation came as snow, but
some rainfalls also occurred towards the end of the month.
The snow cover increased at the beginning of March and into the middle of the month. The water equivalent of the snow cover by mid-March was 100-130 mm in southern and central Finland, i.e. 100-130% of the seasonal mean. In other areas amounts of snow
were somewhat below the mean. The highest absolute amount of snow was recorded as usual in the counties of Oulu and Lapland towards the end of the month, with accumulations of 130-170 mm in areas with highest precipitation. At the very end of the month
the snow compressed rapidly and began to melt. In the extreme south-west of the country the ground became bare in some places.
Water levels in watercourses decreased in typical fashion for the winter season. The spring increase in water levels began in some southern watercourses on the very last day of the month. In most lakes, water levels were still above the seasonal mean.
The level deviations of some important Finnish lakes at the end of the month were: Pielinen +29 cm, Kallavesi -3, Saimaa +47, Keitele +8, Päijänne -2, Pyhäjärvi, Säkylä +13, Längelmävesi +18, Näsijärvi -14, Lestijärvi +14, Lammasjärvi +1, Oulujärvi +34,
Ounasjärvi +3, Lokka +37 and Inari +15 cm.
Discharges of some Finnish rivers compared with the mean March discharge figures for the reference period 1961-1990 were: Pielisjoki 128%, Vuoksi 118, Kymi joki 114, Paimionjoki 78, Kokemäenjoki 109, Kalajoki 57, Oulujoki 98, Iijoki 107, Kemijoki 138
and Tornionjoki 103%. Discharges in small rivers of southern Finland began to increase rapidly during the last days of the month.
Groundwater levels generally deceased but remained close to the seasonal mean. Somewhat above-average levels were recorded in some observation stations in Lapland. The groundwater table began to increase towards the end of the month in the south of the
country. Groundfrost layers were somewhat thinner than normal in the south and west but were thicker than normal in the east. In southern and western Finland the recorded groundfrost depths were 0-20 cm, in the east 20-40 cm, in the county of Oulu 40-80
cm and in Lapland 80..140 cm, except that in north-western Lapland the groundfrost extended only to 20-40 cm.
Lake ice was thicker than normal in southern and central Finland. However, the overall ice cover was composed of several structurally different layers: a thin layer of blue ice was overlayed in many cases with water, above which was a layer of rather
weak snow ice. The following total ice thicknesses were recorded at the end of the month: Simpeleenjärvi 68 cm, Päijänne, Tehinselkä 48, Sääksjärvi 61, Pääjärvi (in central Finland) 56, Oulujärvi 56, Unari 66 and Inari (in the open) 60 cm.