SUMMER 2025 – HEATWAVES AND INCREASING FOREST DAMAGE RISKS
Summer weather conditions were exceptional in Finland
The beginning of summer was cool and rainy, but July brought a drastic change in the weather. Finland experienced the most prolonged heatwave in recorded history, with temperatures exceeding 30°C. Such heat, combined with a lack of rain, has caused the land surface to dry out and raised the risk of forest fires.
Heatwave hits all of Europe
The exceptional heat of summer 2025 was not limited to Finland; but the rest of Europe also suffered from extreme temperatures. For example, in France and Germany, temperatures exceeding 40°C were recorded on multiple days, and wildfires in southern Europe resulted in evacuations. In Spain and Greece, forest damage increased rapidly due to uncontrolled wildfires. On a European scale, this summer once again demonstrated the impact of climate change: more and more countries are struggling with drought, heat, and natural disasters simultaneously.
The situation of the European spruce bark beetle in summer 2025
Long-term drought weakens the defense mechanisms of trees, and the superficial root system of spruces is particularly susceptible to drought. However, the cool and rainy weather of early summer adversely affected the European spruce bark beetle, resulting in their populations remaining more moderate in several regions compared to last year. The 700-degree-day heat sum limit for the first generation of the beetle to mature in the summer was reached in the southern part of the country around mid-July, which was about two weeks later than in the previous year. A second generation of beetles is unlikely to develop this summer, as it would require a heat sum of 1500 degree-days.
Finland experienced a record-breaking heat wave in July 2025.
Future summers – towards increasingly hotter extremes
Heatwaves similar to those experienced in the summer of 2025 are unlikely to be just an exception. Climate scientists predict that as early as the 2030s, Finland could experience more consecutive weeks with temperatures above 30°C, while droughts are expected to intensify. This means that water management, forest fire prevention, and urban cooling measures will become even more critical. In nature, drought and repeated heatwaves can alter the species composition of forests, as drought-sensitive species such as spruces and wetland plants decline. In contrast, heat- and drought-tolerant species are expected to become more common. If current trends continue, Finnish summers for future generations may resemble the current conditions in Central Europe: prolonged heatwaves, dry rivers, and preparation for the forest fire season starting in the spring.
References:
Heatwaves and wildfires highlight urgency of action on extreme heat, 2025, World Meteorological Organization. Cited by 31.7.2025. https://wmo.int/media/news/heatwaves-and-wildfires-coincide-anniversary-of-call-action-extreme-heat.
Kirjanpainajan parveiluseuranta, Metsätuhot, Luonnonvaratieto -karttapalvelu, Luonnonvarakeskus. Cited by 4.8.2025. https://luonnonvaratieto.luke.fi/kartat?panel=metsatuhot. [In Finnish].
Ruosteenoja, K. and Jylhä, K., 2023. Heatwave projections for Finland at different levels of global warming derived from CMIP6 simulations. Geophysica, 58(1).