Climate change and floods

Spring floods are created when a thick layer of snow melts quickly. Climate change is reducing snow cover and bringing us milder winters and warmer springs. What does this mean for spring floods?

Air temperature and precipitation strongly affect the volume of water running into rivers in different seasons. There is usually less runoff in summer and winter, and more in spring and autumn as rivers are swelled by snow melt and autumn rains.

Climate change is altering this situation by increasing the discharge of rivers, especially in winter. Winter flow rates may be multiplied by the end of this century and cause fluvial floods in mid-winter, as has already been seen in Southern and Central Finland.

While spring floods will correspondingly become less severe in many places, they will not disappear altogether, and in Lapland, they may become even more severe over the next few decades as more snow will accumulate during the winter. Predicting floods will in any case be more difficult because of increasing annual and local variations.

Climate change is expected to increase the annual runoff across the country by an average of 3% to 8%. While this does not seem like a large figure, it encompasses considerable temporal and geographical variations. As climate change will bring heavy rains, periods of drought and other extreme climatic phenomena, variations may be greater than today.