Evaluating approaches to identify winter heat wave events and their hydrological impacts in Sweden

While warm season heat waves are extensively studied, winter heat waves, which are extended periods of above-average temperature during winter months, largely remain overlooked. These events can disrupt typical water availability patterns and degrade water quality, particularly in regions already facing environmental stress.

The identification of heat waves varies depending on the context and objective. For example, variable percentile thresholds are used to study heat wave mechanisms, while fixed temperature thresholds are often applied to assess their ecological impact. In the context of biogeochemical processes that govern contaminant retention and mobilization, variations in surface and groundwater flow can be particularly important.

We analyzed the CAMELS‐SE dataset, which includes long-term observations of daily temperature, precipitation and streamflow from 1961 to 2020 across 50 sites in Sweden, along with local groundwater measurements, to identify and quantify heat-wave events using various approaches, and explore their correlation with observed surface and groundwater flow variability.

The main objective of the study is to determine the timing, duration, frequency, and magnitude of winter heat waves in Sweden, and to assess trends in surface and groundwater flows associated with these events. We also explore whether certain specific geographical regions in Sweden are more vulnerable to the effects of winter heat waves.