Past and future climate trends focused on synoptic patterns in the northeast of the Iberian Peninsula

Based on a centenary meteorological observatory, the mean temperature and frequency of heat waves at the city of Barcelona is increasing due to global warming. The number of heat wave episodes by climatic periods of 30 years, with a specific percentile 95 (P95) of summer maximum temperature, has been increased from 23 (1951-1980) with a P95 of 31˚C to 59 days (1991-2020) with a P95 of 32.8˚C.  Therefore, it is necessary to analyse weather circulation to understand the reason and predict the possible future impacts. In this study, heat wave events for 1951-2020 have been analysed with ERA5 data, in order to classify the different synoptic patterns and each evolution. It is possible to get climate trends from past reanalysis data, but it is also interesting to predict future possibilities. Most of the previous research is focused on temperature and precipitation while the target of this study is the mesoscale and synoptic circulation. For this reason, Coordinated Regional Climate Downscaling Experiment (CORDEX) data at 0.11˚ grid mesh has been used to analyse the future scenarios compared to the historical simulations of the same source. More specifically, for this study, it was necessary to download mean sea level pressure (MSLP) and 500hPa geopotential height (GHP) data. Due to the big amount of information, it has been applied a statistical method called Principal Component Analysis (PCA) to simplify and reduce the dimensions of the sample. Afterwards, working on a cluster analysis has been necessary to classify the simplified data. The synoptic patterns remain relatively constant throughout the last climatic periods according to ERA5, being the synoptic type “Shallow Cyclone or Undetermined pressure gradient” the recurrent type to cause heat wave periods in summer. CORDEX data shows more dynamism in comparison to ERA5 reanalysis and expects to remain similar until 2100. Northwest and north advections are expected to increase by 7.3% and 6.6% respectively and lows or cyclones are expected to decrease by 8.3% according to RCP4.5 scenarios.