Evaluation of the main heatwave patterns in the northeast of the Iberian Peninsula using ERA5 and CORDEX models

Heatwaves are expected to increase not only in intensity but also in frequency and duration in the next decades. Most of the studies are focused on the temperature variable, but little is known about their synoptic structure, which is especially important in mid-latitude regions.

In this study, we propose a Principal Sequence Pattern Analysis (PSPA) to classify the main synoptic patterns that define heatwaves in the northeast of the Iberian Peninsula. This is done by finding the most correlated input variables that represent the highest number of variance possible. The database used for this analysis comes from ERA5 reanalysis data covering the 1951-2020 period, in which we have selected three variables: mean sea level pressure (MSLP), geopotential height at 500 hPa (Z500) and maximum daily temperature at 2 meters (TMAX). Once the historical analysis is prepared, the same steps are repeated for CORDEX models (1951-2000) to discuss the performance of these models simulating heatwave periods.

The multivariate analysis has resulted in four synoptic patterns that explain more than 50% of the total variance. The four patterns are divided into two groups, stationary and dynamical. The HWs with highest temperatures in the Metropolitan Area of Barcelona are the prefrontal patters, which are dynamical and undulated at Z500 and undetermined at MSLP, with mean maximum temperatures around 35°C. However, the warmest pattern in inland areas is stationary and stable, generated at Z500 by intense anticyclonic ridges covering the Iberian Peninsula and at MSLP by deep thermal lows. The CORDEX models simulate similar patterns but less defined due to the lack of resolution. Z500 results in an overestimation of the anticyclonic ridges and MSLP shows an underestimation of pressure gradients, simulating more undetermined patterns. However, there are discrepancies between the models, which will result in different future projections in the climate change scenarios.