Here are the first results we can share from the Skärgårdscentrum Korpoström
–> no strong summer, and no heatwave detected in the water; so far …
These will be updated regularly with the help of the Knattelabbet
To help you compare this year with previous ones, we’ve also included temperature curves from the past four years, measured at Skärgårdscentrum Korpoström.
Some details (as of August 11, 2025):
The heatwave lasted for 27 days (from 16.7.2025 to 11.8.2025)
The maximum intensity was 6.6 °C (on 28.7.2025)
The mean intensity was 4.15 °C
The maximum temperature was 25.2 °C (on 28.7.2025)
The temperature rose very quickly! The average onset rate was about +0.5 °C/day, and the average decline rate was -0.3 °C/day.
To note, similar heatwave intensities have been recorded before, but this year it’s occurring during “peak” summer = which means we are really close to some thermal tolerances of organisms in the Archipelago Sea now.
Shown are recorded temperatures (°C; solid black lines) at the Korpoström pier at 1 m depth. This dataset was analyzed on the occurrences of heatwaves and cold spells after Hobday et al. (2016), based on modelling using 2006 - 2021 climatological values from Seili at the University of Turku (grey solid line). The thresholds for heatwaves (i.e., 90th percentile) and cold-spells (i.e., 10th percentile) are represented as dotted lines. Temperatures above the climatological values, but below the 90th percentile are shown in orange, whereas temperatures above the 90th percentile are shown in red. Temperatures below the climatological trend, but above the 10th percentile are shown in light-blue, whereas temperatures below the 10th percentile are shown in dark-blue.