Summer Heatwaves Trends and Hotspots in the Barcelona Metropolitan Region (1914-2020)

Abstract

Daily maximum, TX, and minimum, TN, temperatures recorded at Fabra Observatory, for the period 1914–2020 (from June to September), have permitted to identify the daytime and nighttime heatwaves, HWs, at Barcelona Metropolitan Region, BMR, along 107 years. Four indices have been computed both for maximum and minimum temperatures heatwaves: the number of events per season, HWN; their maximum duration, HWD; their frequency of occurrence, HWF; and the amplitude of the hottest day event, HWA. Trends in these indices have been obtained and their statistical significance quantified by means of the Mann-Kendall test. For the whole period (1914–2020), positive significant trends have been detected for the four indices corresponding to maximum and minimum temperatures. Nevertheless, when 30-year moving window datasets have been analysed, trends of different signs are obtained. The change in these signs, around 1960s, is outstanding, as well as the behaviour of the heatwaves since year 2000 for TX, and since 1985 for TN, when every year has at least one episode with high duration and amplitude. The convenience of using the four HW indices is evaluated applying a Principal Component Analysis, PCA. Additionally, the spatial distributions of the Modis land surface temperatures, LST, corresponding to some extreme heatwaves, permits the detection of two hotspots in the BMR, one of them for TX and the other for TN. It is also worth mentioning that correlations between Western Mediterranean Oscillation index, WeMOi, and HW episodes are detected, being notable that at the beginning of these episodes WEMOi values are usually lower.