The study evaluates a 76-year period (1950–2025) of co-occurrence of droughts and heatwaves in Slovenia across 30-year time blocks: 1950–1979, 1980–2009, and 1996–2025. Data from the ERA5 Land reanalysis were used and validated against eight meteorological stations operated by Slovenian Environment Agency (ARSO). The Excess Heat Factor (EHF) was used to define heatwaves, and the Standardized Precipitation Index (SPI) was used for droughts assessments. The compound impact of droughts and heatwaves was determined using the developed Compound Drought Heatwave Index (CDHI). Validation of the ERA5 Land data confirmed the high reliability of the air temperature reanalysis in lowland and urban environments (r = 0.98–0.99), whereas larger deviations occurred in high-mountain areas (Kredarica) due to coarse spatial resolution of ERA5 Land dataset. For precipitation, the reliability of the reanalysis is relatively good (r = 0.84–0.86). During the 1996–2025 period, air temperatures increased significantly, rising by 1.8 °C to 3.3 °C. The number of heatwave days in the same period (1996-2025) increased by 25 to 38 days. Precipitation shows no significant annual trend, with only the month of May standing out with a statistically significant (p < 0,05) increase in rainfall. The CDHI index demonstrates that the areas with the strongest cooccurrence are in western and southwestern Slovenia, with a recurrence frequency of 10% to 20%. The results highlight the necessity of proactive water management.
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