Assessment of Long-Term Climatic, Hydrological, and River Ice Dynamics in River Oulankajoki

This study examines long-term climatic and hydrological trends in River Oulankajoki, in Finland. The aim is to understand the impacts of changing climate conditions on river systems. Using 57 years (1966–2023) of daily air temperature and snow depth data from the Finnish Meteorological Institute (FMI) and hydrological observations from the Finnish Environment Institute (SYKE), the analysis incorporates longwave (LW) and shortwave (SW) radiation data from ERA5, accessed through Google Earth Engine (GEE). The Mann-Kendall trend test was employed to detect significant temporal changes, that reveals a significant decreasing trend in both air temperature values and discharge Phase Change Timing (i.e., PCT) over the study period. The results show that the river ice break-up timing has been shifting about 3-weeks in time, meaning that the break-up season occurs earlier than 57 years ago. These changes indicate potential shifts in regional climate dynamics, likely influenced by global climate change. Correlation heatmaps showed strong positive relationships between air temperature (AT) and river ice Break-Up Days (i.e., BUDs).