Risk of lower groundwater levels in northern Sweden with warmer climates
When winters become warmer in northern Sweden, there is a risk that groundwater levels will fall, despite heavy rainfall. The villain in this story is lingering ground frost that prevents snowmelt and rain from filling underground reservoirs. It shows a new dissertation from the University of Gothenburg.
Precipitation in most of Sweden is sufficient to keep groundwater stocks in balance. However, the effects of climate change in recent decades, with dry summers and mild weather during midwinter, risk affecting groundwater negatively, especially in northern Sweden.
“When the winter months are warmer, a lot of snow melts while the ground is still frozen. This means that the groundwater reservoirs do not fill up as much as before. The water flows on top of the frozen ground into lakes and streams instead of infiltrating underground,” says Michelle Nygren, doctoral student in geology at the University of Gothenburg.
More mild weather days
Michelle Nygren has analyzed groundwater levels, precipitation and temperature in Sweden and Finland, among other places, in recent decades, and she sees a clear increase in the number of mild weather days during the winter months of December – February. This trend is particularly evident in southern Finland. Winters were on average colder in the 1980s, which resulted in a greater proportion of precipitation in the form of snow, followed by more snowmelt later in the spring. When the frost thawed, more of the meltwater could penetrate into the ground and replenish groundwater levels. The growing season also began later, which contributed to a smaller amount of meltwater being taken up by vegetation.
“Slow snowmelt is best for groundwater replenishment. Climate-driven change is most evident north of Stockholm and in Finland, which increases the risk of lower groundwater reservoirs. When the summers get hotter, rain during the summer months is not enough to fill the groundwater reservoirs. The water evaporates or is absorbed more by plants. ”
Increased risk of forest fires
She points out that this leads to an increased risk of forest fires, as the moisture levels in the soil decrease due to lower groundwater levels. There is an increased need to irrigate dry arable land, which costs a lot of money. In southern Sweden, the effects of a warming climate on groundwater vary. Because there is frost, precipitation during the winter months can seep through the soil and fill the groundwater reservoirs. This is insufficient in the eastern parts of southern Sweden and Gotland, which receive too little precipitation in general. There, increasingly hot summers can lead to problems with drought and wells drying out.
“We risk overuse when we pump groundwater. This is especially true for smaller groundwater reservoirs, which respond quickly to weather. Larger reservoirs are more robust and can withstand a year of drought from time to time, but take longer to recover after many years of drought. “
The IPCC reports indicate that the climate is getting warmer and Michelle believes that in 100 years the amount of frost will probably have decreased so much in northern Sweden that the groundwater problems will also decrease. But what will do until then?
– We have enough water in Scandinavia, but it can be very expensive for society because the costs of water purification increase. Agriculture may need to switch to other crops. Like the Swedish Board of Agriculture, I believe that we need to keep more water in reservoirs or reuse wastewater. Groundwater is important for our water supply, and we need more studies of the effects of climate change. ”