Climate variations of heat waves on the Croatian Adriatic coast for the period 1961–2018

An analysis of characteristics of the boreal summer season June-July-August measured daily maximum 2-m air temperatures and associated heat waves (HWs) for 1961–2018 was conducted for three locations on the Croatian Adriatic coast representing its northern (Rijeka), central (Split) and southern (Dubrovnik) extents. Greater values occurred in the second part of the period (1990–2018) than in the first part (1961–1989), including significant (α = 0.01) trends in mean seasonal averages (0.44 to 0.69 °C per decade), extremes, frequencies, duration, and intensity. Exceedances and HWs spanning from 10 June to 24 August were determined in 53 years (out of 58 years) by the 95th and in 9 years by the 99th percentile criteria. Since heat stress often affects health at the beginning of HWs, exceedances of one or more days were all considered regardless of a minimum length or separation. In 30 years, the exceedances occurred at all locations in the same year. There were 122–147 (30–36) HW cases lasting 245–259 (51–54) days for the 95th (99th) thresholds. The maximum event duration was between 9 and 12 (5) days for the 95th (99th) thresholds. During the longest duration event, synoptic conditions were characterized by propagation of a strong and broad ridge of the Azores High extending into southern Europe and by blocking lows from the north. These results show that the Croatian coast, as part of the Mediterranean hot spots , is experiencing a significant increase in warming and associated frequency of HWs, which is likely to continue in the future.