Le chef du DHMZ a révélé les applications auxquelles il fait le plus confiance, le temps qu'il fera jusqu'à la fin du mois de juillet et quand une nouvelle vague de chaleur nous menace !

Heatwaves have become increasingly frequent, longer-lasting, and more intense over recent decades, according to data from Croatia's national weather service. The phenomenon is directly linked to the rise in temperatures across landmasses, oceans, and seas worldwide due to climate change. Analysis shows that heatwave frequency has increased two to three times compared to the mid-20th century, while the number of days affected by such events has grown two to five times, depending on geographic and climatic conditions. The average duration of individual heatwaves has extended by one to four days, and their intensity has also risen, daily peak temperatures during these periods have climbed by 1 to 3 degrees Celsius. These effects are evident even in regions previously unaffected, with evidence of expanding influence zones. In Croatia, climate data reveals similar trends. Over the past 30 to 40 years, there has been a marked increase in the number of hot days (where maximum temperature reaches 30°C), very hot days (35°C), warm or tropical nights (minimum temperature above 20°C), and prolonged periods without significant cooling, characterized by the absence of cooler air masses. These patterns align with broader European observations, reinforcing the connection between rising global temperatures and the intensification of extreme weather events. Heatwaves occur under specific synoptic conditions that allow for sustained warming of the air. One of the most common causes is the presence of a stationary anticyclone, which can last several days to weeks. Such systems are marked by clear skies, sinking air (subsidence), and adiabatic heating, leading to high atmospheric pressure, calm winds, and minimal precipitation. This lack of effective heat transfer exacerbates the accumulation of warmth in the atmosphere. Another contributing factor is the so-called “omega block,” a pattern where a powerful anticyclone becomes trapped between two cyclones, creating a near-stationary weather system. In this configuration, the jet stream flows around the blocked area, forming a shape resembling the Greek letter Omega. This results in prolonged periods of stable weather, often culminating in heatwaves. Additionally, the influx of extremely hot Saharan air from Africa plays a role, especially when combined with persistent westerly winds associated with a stationary cyclone over the eastern Atlantic. This allows large quantities of very hot, dry air to cross the Mediterranean and reach Central Europe. The self-amplifying nature of heatwaves is partly due to soil drying and increased plant transpiration. Initially, a significant portion of solar energy is used to evaporate water from the ground and plants. However, as the soil dries, less energy goes into evaporation, and more is directed toward direct heating of the soil, vegetation, and air. This shift from latent to sensible heat leads to further temperature increases, creating a positive feedback loop that intensifies the heatwave. Global warming, driven by increasing concentrations of greenhouse gases, is another key driver. Current global temperatures are approximately 1.5 to 1.8 degrees Celsius higher than pre-industrial levels. As a result, each modern-day heatwave develops within an already warmer atmosphere, making temperature extremes more pronounced. While the physical mechanisms behind heatwave formation remain unchanged, the baseline temperature has risen, resulting in stronger and more frequent occurrences. The duration of heatwaves is also influenced by changes in atmospheric circulation. The Earth’s atmosphere does not flow in simple circular paths but follows wave-like patterns known as Rossby waves. These waves are connected to the jet stream, which continuously moves eastward, causing deviations in weather patterns. Recent shifts in these patterns have contributed to the persistence of heatwaves, as they create conditions that sustain high-pressure systems for longer periods. Meteorological officials in Croatia, including head of the State Hydrometeorological Service Dr. sc. Ivan Güttler, have noted that the frequency and intensity of heatwaves have increased since the 1990s. He explained that while droughts and floods were once considered rare, today’s extreme weather events are becoming more predictable. Heatwaves are now forecastable up to seven days in advance, and public awareness of weather warnings is growing. Güttler emphasized that while some European countries experience record-breaking temperatures, Croatia benefits from the widespread use of air conditioning, reducing the risk of heat-related health impacts. Despite these advancements, challenges persist. For example, heavy rainfall and thunderstorms, particularly in northern Italy, have led to localized flooding and lightning-induced wildfires. These events highlight the complex interplay between rising temperatures and changing precipitation patterns. Güttler also pointed out that larger hailstones, exceeding five centimeters in diameter, are now falling 300 percent more frequently than in the 1950s, posing new risks to infrastructure and agriculture.