Published on: 24.1.2022
Information produced by Finnish Environment Institute
Snow and soil frost affect groundwater resources
When rainwater is infiltrated into the ground, it replenishes groundwater reserves. But what happens to groundwater in winter when precipitation falls as snow and the soil is frozen?
Groundwater levels vary regularly with the seasons. During the winter, the groundwater level goes down. This drop is particularly strong in Lapland but also noticeable in Southern Finland. The groundwater level starts rising again in spring.
The decrease in groundwater levels in winter is caused by snow and soil frost. If precipitation falls as snow and the snow stays on the ground, even the heaviest fall will not replenish groundwater reserves. Soil frost also stops any rainwater and meltwaters from being infiltrated into the ground.
The groundwater level really starts rising only once the soil frost has melted. This usually occurs in May in Lapland, but often as early as March in Southwest Finland. The groundwater level goes up rapidly in spring, as the melting snow produces large volumes of water.
At present, climate change is affecting groundwaters. With winters becoming warmer, a larger share of winter precipitation falls as rain. If there is any soil frost at all, it melts earlier in the spring, and the groundwater level stays relatively high all winter. This is already happening in Southern and Western Finland.