Linking hydroclimate indices to projected warming temperature and increased precipitation under CMIP6 for a sub-arctic basin

Oulujoki River basin- Inland sub-Arctic. Understanding the impact of projected accelerated warming and increasing precipitation in the Arctic and sub-Arctic is crucial. This study examines how these changes will reshape the hydroclimatic dynamics of the inland sub-Arctic river basin, using cold climate and precipitation indices derived from statistically downscaled General Circulation Models. The results show an increase in precipitation indices, with mid-century primarily dominated by scenarios SSP1–2.6 and SSP3–7.0. Under SSP5–8.5, precipitation magnitude and intensity steadily rise throughout the century. The projected increase in precipitation magnitudes, intensity, and extreme events are highly correlated with the increasing spring and summer precipitation, linking intensified and heavy precipitation events during these seasons under all future scenarios. Cold climate indices are projected to decrease with a shortened frost season by 3.3 months, advance in spring freshet by 1.5 months under SSP5–8.5, and a drastic decline in cold spell duration index in all scenarios, indicating a lack of supercooling events. These decreasing indices are strongly correlated with warming temperatures with a Pearson correlation coefficient reaching 0.84 under SSP5–8.5. The findings also highlight the limitations of the CMIP6 ensemble in capturing extreme values, as extreme climate indices were not statistically significant. This study thus contributes to the broader understanding of climate dynamics and their potential impacts on cold regions. • Warming and increased precipitation will alter the hydroclimatic dynamics in the sub-Arctic region. • Cold climate indices decline significantly, correlating with rising temperatures. • Spring and summer will see significant increases in precipitation indices. • CMIP6 ensemble reduces uncertainty range but shows limitations with extreme values.