Analysis of synoptic weather patterns of heatwave events

Abstract

Heatwaves (HWs) are expected to increase both in duration and intensity in the next decades, but little is known about their synoptic and mesoscalar behavior, which is especially important in mid-latitude regions. Most climate research has focused on temperature analysis to characterize HWs. We propose that a combination of temperature and synoptic patterns is a better way to define and understand HWs because including atmospheric circulation patterns provides information about different HW structures that can irregularly affect the territory, and illustrate this approach at the regional and urban scales using the Iberian Peninsula and the Metropolitan Area of Barcelona as case studies. We first select HW events from 1950 to 2020 and apply a multivariate analysis to identify synoptic patterns based on mean sea level pressure, geopotential height at 500 hPa, and maximum daily 2 m temperature. The results indicate that four synoptic patterns reproduce at least 50% of the variance in HWs, namely, “stationary and stable”, “dynamic and advective”, “stationary and advective”, and “dynamic, advective and undulated”. Next, we apply the analysis to the Representative Concentration Pathway future scenarios (RCPs) 4.5 and 8.5 from the Coordinated Regional Climate Downscaling Experiment (CORDEX) to determine how these synoptic trends can change in the future. The analysis shows that the four synoptic patterns continue to explain 55 to 60% of the variance in HWs. Future HW events will be characterized by an increase in geopotential height at 500 hPa due to the northward shift of the anticyclonic ridge. This is especially true for RCP8.5, which simulates business as usual incrementing fossil fuel use and additionally shows an increase in atmospheric dynamism in north advections from all directions in comparison with RCP4.5. These findings point to the importance of considering the geopotential height in HW prediction, as well as the direction of advections.

Heatwave Duration and Heating Rate in a Non‐Stationary Climate: Spatiotemporal Pattern and Key Drivers

“…Due to a lack of confidence regarding the appropriate selection of threshold for heatwaves definition, this study advances previous studies (i.e., Chambers, 2020;Diniz et al, 2020;Khaliq et al, 2005;Ma et al, 2015;Ventura et al, 2023;Zhi et al, 2021) by presenting an applicable framework to explore the heatwave odds with different durations by applying appropriate threshold for each specific site. Whereas a wide range of absolute (fixed) temperature or daily percentiles (i.e., the 90th, 95th, and 99th) have been applied to quantify the heatwaves, such indices have failed to consider local factors, including the latitude, longitude, altitude, distance to the ocean, land cover, and urbanization directly affect the key features of heatwaves characteristics.…”

Observed long-term changes in extreme temperature and precipitation indices in Spain (1951-2020)

“…Although this is a topic of broad and current interest within the climate change community, most of the studies in Spain focused on particular aspects of precipitation or temperature and often in specific regions (e.g., Páscoa et al 2021;Meseguer-Ruiz et al 2021;Miró et al 2023;Ventura et al 2023). Thus, there is a need to provide local information for the whole country in terms of how the extremes have changed in recent years, considering their frequency, intensity, and persistence in a unified framework.…”

Characterization of the marine‐air intrusion Marinada in the eastern Ebro sub‐basin

“…The fact indicates the persistence of the synoptic situation, either with westerly flows or related to the presence of a thermal low in the centre of the Ebro Valley. Recent results from Ventura et al (2023) show that during summer (JJA for 1951–2020) nearly 50% of the days the synoptical situation is dominated by weak pressure gradient conditions and about 25% is influenced by anticyclonic situations. These synoptical features favour the presence of thermally‐driven circulations in the region, in agreement with results from Table 2.…”