Conditional and residual trends of singular hot days in Europe

Abstract

The influence of anthropogenic climate change on both mean and extremely hot temperatures in Europe has been demonstrated in a number of studies. There is a growing consensus that high temperature extremes have increased more rapidly than the regional mean in central Europe, while the difference between extreme and mean trends is not significant in other European regions. However, it is less clear how to quantify the changes in different processes leading to heat extremes. Extremely hot temperatures are associated to a large extent with specific types of atmospheric circulation. Here we investigate how the temperature associated with atmospheric patterns leading to extremely hot days in the present could evolve in the future. We propose a methodology to calculate conditional trends tailored to the circulation patterns of specific days by computing the evolution of the temperature for days with a similar circulation to the day of interest. We also introduce the concept of residual trends, which compare the conditional trends to regional mean temperature trends. We compute these trends for two case studies of the hottest days recorded in two different European regions (corresponding to the heat-waves of summer 2003 and 2010). We use the NCEP reanalysis dataset, an ensemble of CMIP5 models, and a large ensemble of a single coupled model (CESM), in order to account for different sources of uncertainty. We also evaluate how bias correction of climate simulations influences the results.

Towards a compound-event-oriented climate model evaluation: a decomposition of the underlying biases in multivariate fire and heat stress hazards

“…Other types of compound events, e.g. temporal clustering of storms (Bevacqua et al 2020c;Priestley et al, 2017) and simultaneous extreme events in distant regions (Kornhuber et al, 2020) can also lead to large impacts and are therefore relevant for the impact community. A compound-event-oriented evaluation of impacts similar to that proposed here, i.e.…”

“…For example, the risks associated with combined high temperature and high/low relative humidity such as heat stress and fires can manifest in heat-related human fatalities (Raymond et al, 2020) and fire-induced tree mortality (Brando et al, 2014) even if the two contributing variables are not necessarily extreme in a statistical sense. In the future, combinations of climate variables leading to disproportionate impacts will be affected by global warming, and reliable risk assessments are required (Fischer and Knutti, 2013;Russo et al, 2017;Schär, 2016;Raymond et al, 2020;Jézéquel et al, 2020;. Therefore, a better understanding of how climate models represent the joint behaviour of variables behind compound events, such as temperature and relative humidity, is crucial to correctly quantify their associated hazards today and in the future (Zscheischler et al, 2018).…”

Atmospheric Blocking and Weather Extremes over the Euro-Atlantic Sector – A Review

“…Under future climate conditions, blocking is projected to remain the most relevant circulation feature initiating European heat waves (Brunner et al, 2018;Schaller et al, 2018). Despite some indications of a weakening of the midlatitude circulation in summer in recent decades (Coumou et al, 2015;Horton et al, 2015), studies on future changes in the properties of weather systems associated with heat waves (such as blocking persistence) come to diverging conclusions (Plavcova and Kysely, 2013;Brunner et al, 2018;Mann et al, 2018;Schaller et al, 2018;Jézéquel et al, 2020;Huguenin et al, 2020). Whether future changes in blocking dynamics might lead to changes in heat waves beyond their thermodynamic intensification thus remains an important question for future research.…”

A dynamical adjustment perspective on extreme event attribution

“…The second objective of this study is to revisit the attribution of the links between recent changes in atmospheric circulation patterns and the increased occurrence of summer hot temperature extremes over several midlatitude regions (Horton et al, 2015;Jézéquel et al, 2018Jézéquel et al, , 2020. We first apply dynamical adjustment at a daily timescale to all summer days of the 1979-2018 period for both maximum (TX) and minimum temperature (TN).…”