Regional and altitudinal aspects in summer heatwave intensification in the Western Carpathians

The current warming of climate has led to an enhancement of the extreme temperature risks threatening various systems. Following that, we analysed the progress of the main type of the temperature-extreme weather events—heatwaves (HWs). We focused on the area of the Western Carpathians (Central Europe), since the Carpathian Mountains are widely recognised as an important biodiversity hot-spot particularly for mountain species in Europe. The HWs were identified for a range of elevations from low to high altitudes including a high mountain station. We used the percentile threshold-based calculation of HW, which in comparison to those using absolute thresholds allows for revealing the possible threats of climate warming extremes at the range of altitudes. We observed the HWs based on the maximum (HWMAX) and average (HWAVG) daily air temperatures in June–August during the period of 30 years (1989–2018) and we characterised them by the strength, frequency, and duration of the longest HW event. The Mann-Kendal trend test of these heatwave characteristics was significantly positive (p < 0.05) at most of stations throughout the region of Western Carpathians. At the high mountain station, particularly the maximum temperature exceedance increased, indicated by significant positive trends of HWMAX in strength (p = 0.02), frequency (p = 0.01), and duration of the longest event (p = 0.02). The majority of the strongest HWs occurring across Europe over the last three decades hit the area of Western Carpathians. More importantly, the area experienced the regional HWs, severity of which was comparable to those of exceptionally strong HWs, although these regional HWs were less important from the large-scale aspect. The greatest intensification of HWs is evident particularly in the last decade, although the longest HWMAX event from 1994 was not exceeded. Our results show potentially enhanced HW-induced stress to organisms as a consequence of the coincidence of HWMAX and HWAVG of the comparable strength during the last decade.