Climate change alters atmospheric chemistry and meteorological conditions in ways that exacerbate surface ozone pollution, with consequences for human health and agriculture. In Austria, where ambitious emission controls have improved air quality in the past, rising temperatures and elevated methane abundances in the context of climate change may counteract these gains. This paper assesses the societal welfare effects of ozone exposure in Austria under future climate scenarios by comparing a medium (RCP4.5) to a high (RCP8.5) emission scenario for 2030 and 2050. We further introduce a novel scenario (RCP8.5+), in which only Austrian ozone precursor emissions are more stringently controlled under a global high-emissions context, to evaluate the effectiveness of national emission controls. Net effects are quantified by integrating market costs – agricultural yield changes and emission control costs assessed in a computable general equilibrium model – with non-market health costs. Results show that in 2030, emission control costs in RCP4.5 exceed the societal welfare benefits of a reduced ozone burden compared to RCP8.5. By 2050, however, benefits outweigh costs with a benefit-cost ratio (BCR) of seven. This shift reflects higher upfront control costs in 2030, which lead to sustained air quality improvements through mid-century. In RCP8.5+, national emission controls yield strong benefits with a BCR of eight. While both scenarios (RCP4.5 and RCP8.5+) reduce yield losses compared to RCP8.5, health benefits dominate the societal welfare gains. These findings underscore the local benefits of national air quality management, highlighting its effectiveness as an abatement strategy for managing ozone risks in a warming climate.

The northern hemisphere stratospheric polar vortex, and thus Arctic column ozone content, is characterized by large interannual variability, driven by the interplay of various chemical and dynamical forcings throughout the winter and spring seasons. The 2023/24 season showed record high March total column ozone, whereas 2010/11 and 2019/20 experienced large springtime Arctic ozone losses due to an exceptionally strong and prolonged polar vortex state. The winter/spring 2015/16 were also remarkable, in that unprecedented cold stratospheric temperatures in January were interrupted by a sudden stratospheric warming event, and the fears of large springtime ozone losses turned out to be unfounded. Our main research question is motivated by these events: To which extent can springtime Arctic ozone columns be predicted from the preceding wintertime observational record? To this end we investigate the suitability of wintertime mean polar cap temperature, PSC proxies and eddy heat flux as predictors of springtime ozone in ERA5 and MERRA2 reanalysis data. Our results show that using these predictors springtime ozone can only be “forecast” with short lead times, and even then with limited accuracy. In contrast expanding the analysis to ozone observations earlier in the season, we find substantially higher predictive skill compared to temperature, PSC proxies or eddy heat flux: this can be understood as ozone reflecting both the chemical and dynamical conditions over the northern polar cap.

The joint occurrence of droughts and heat waves is expected to change with advancing climate change. While drought and heat themselves can already have major impacts on ecosystems and society, their compound occurrence can lead to amplified effects. Previous studies have analyzed changes in the occurrences frequency of compound drought-heat events and found increasing trends in some regions. In this study, we revisit these occurrence trends and additionally analyze the mechanisms that couple drought and heat as well as their changes in space and time. Considering drought as deficit of soil moisture and heat as an extreme temperature, evapotranspiration (ET) is the main physical process connecting both extremes. Therefore, we focus particularly on ET anomalies, because higher-than-normal ET during drought-heat events indicates that heat is inducing drought (heat → drought) as high temperatures lead to high vapor pressure deficit which increases ET that in turn depletes soil moisture. Vice versa, lower-than-normal ET suggests drought is triggering hot temperatures (drought → heat) as low soil moisture limits ET such that more of the incoming radiation is partitioned to sensible heat flux and hence warming the air. To better understand the underlying controls of these ET anomalies, we analyze their drivers by considering anomalies of precipitation, radiation, vapor pressure deficit and Leaf Area Index, which are in turn linked to anomalies in atmospheric circulation. Finally, we compare the relevance of these drivers, and of the drought → heat vs. heat → drought mechanisms in space, and link them with aridity and land cover type. In our analysis, we employ weekly data from the ERA5 reanalysis alongside gridded products derived with machine learning methods which were trained with in-situ observations. We define drought and heat with a percentile based approach filtering the lowest (< 5th percentile) absolute soil moisture values and highest (> 95th percentile) absolute temperatures at each grid cell. Understanding the mechanisms behind compound drought-heat extremes can help improve related forecasts, and to validate and constrain model projections of trends in these events.

Debris flows represent a severe hazard in Alpine regions. The initiation of debris flows is connected to several hydro-meteorological and geomorphological factors. For operational early warning and assessment of climate change impact, knowledge about critical rainfall conditions is needed. For several regions of the European Alps intensity-duration (I-D) thresholds for debris flows have been derived in recent years. In this study we provide triggering rainfall conditions of high temporal and spatial resolution for > 3700 documented torrent processes including debris flows that occurred in Austria between 2003 and 2022. Additionally, we estimate the change in their probability of occurrence in a future climate, based on an ensemble of bias corrected and localized EURO-CORDEX simulations. We find slightly steeper I-D curves for debris flows than for torrent floods and no clear trend indicating substantial influence of antecedent rainfall on the triggering rainfall. For all process types, it is shown that both the probability of occurrence and the areas affected by triggering precipitation events increase substantially in the future, with clear dependences on the emission scenarios (RCPs). The results of this study provide a basis for improved event forecasting in a changing climate.

We utilized the Earth System model SOCOLv4 to assess the impacts of the Hunga Tonga-Hunga Ha’apai eruption comprehensively. To accurately estimate the model's performance in terms of water vapour and aerosol plume transport during the initial year, we conducted a multi-member ensemble of free-running simulations and additional simulations employing atmospheric dynamics specified to the ERA5 reanalysis data. These simulations were compared with satellite and reanalysis products. The free-running ensemble simulations with only SO2 (no additional H2O) emissions showed the importance of the two species interaction for the resulting sulphate aerosol evolution, in agreement with previous studies. Furthermore, our primary free-running ensemble simulations, comparing scenarios with and without the eruption event, unravelled a negative response in polar stratospheric ozone levels and temperature. Importantly, these changes were found to be coupled to polar vortex dynamics confirming a larger ozone hole during the austral winter and spring of 2023.

Assessing the spatio-temporality of risks associated with climate change have become dominant in disaster risk research. However, integrated assessments of spatio-temporal aspects combing hazard, exposure and social vulnerability is still under-researched, especially in the fields extreme heat events and heightened ozone concentrations. Studies frequently tend to concentrate either solely on the hazard dimension, such as heatwaves and ozone exceedances, neglecting their interactions (Feron et al. 2023), or solely on isolated spatio-temporal assessments of social vulnerability and exposure (Santos et al. 2022). Using the recent risk conception of the latest IPCC report, we analyze risk as the cumulative interaction of hazard, exposure and vulnerability for historical trends and near future scenarios.A novel data set allows for an integrated assessment of historic spatio-temporal trends as well as near-future trends using different SSP-RCP combinations (SSP2-4.5 & SSP3-8.5) at census tract level. To assess the combined impact of temperature and ozone extremes, we utilize bias-corrected model fields from high resolution runs of the coupled chemistry-climate model WRF-Chem. Population data was projected until 2050 by combining historical growth rates for selected indicators with national change rates from the Shared Socio-economic Pathways (SSP) database by IIASA (Riahi et al. 2017). Regional variations in national SSP change rates are weighted with regionalized projections for population and age groups, and historic data on income and education from the Eurostat Database.Methodologically, we use the Adjusted Mazziotta-Pareto Index (AMPI) normalization method to overcome the limitations of comparing z-scored values over time as reported by Santos et al. (2022). This has the advantaged that all values across all periods of time are considered in normalization (Mazziota & Pareto 2022). Bases on the integration into a composite indicator, we, first, performed a multivariate analysis of how sub-indicators for hazard, exposure and social vulnerability relate to each other for Austria. Second, we applied global and local Moran’s I statistics to analyze if the spatial patterns have changed in terms of spatial heterogeneity or spatial clustering over time.The paper concludes by highlighting the needs of integrated risk assessments and discusses the potentials and limitations of our assessment approach. Finally, possible benefits of the interdisciplinary and small-scale use of SSP-RCP combinations for a more comprehensive formulation of informed policy guidelines. Feron, S., Cordero, R. R., Damiani, A., Oyola, P., Ansari, T., Pedemonte, J. C., ... & Gallo, V. (2023). Compound climate-pollution extremes in Santiago de Chile. Scientific Reports, 13(1), 6726.Mazziotta, M., & Pareto, A. (2022). Normalization methods for spatio‐temporal analysis of environmental performance: Revisiting the Min–Max method. Environmetrics, 33(5), e2730.Riahi, K., Van Vuuren, D. P., Kriegler, E., Edmonds, J., O’neill, B. C., Fujimori, S., ... & Tavoni, M. (2017). The Shared Socioeconomic Pathways and their energy, land use, and greenhouse gas emissions implications: An overview. Global environmental change, 42, 153-168.Santos, P. P., Zêzere, J. L., Pereira, S., Rocha, J., & Tavares, A. O. (2022). A novel approach to measuring spatiotemporal changes in social vulnerability at the local level in Portugal. International Journal of Disaster Risk Science, 13(6), 842-861.

The January 2022 Hunga Tonga–Hunga Ha’apai (HT) eruption injected sulfur dioxide and unprecedented amounts of water vapour (WV) into the stratosphere. Given the manifold impacts of previous volcanic eruptions, the full implications of these emissions are a topic of active research. This study explores the dynamical implications of the perturbed upper-atmospheric composition using an ensemble simulation with the Earth system model SOCOLv4. The simulations replicate the observed anomalies in the stratospheric and lower-mesospheric chemical composition and reveal a novel pathway linking water-rich volcanic eruptions to surface climate anomalies. We show that in early 2023 the excess WV caused significant negative anomalies in tropical upper-stratospheric and mesospheric ozone and temperature, forcing an atmospheric circulation response that particularly affected the Northern Hemisphere polar vortex (PV). The decreased temperature gradient leads to a weakening of the PV, which propagates downward similarly to sudden stratospheric warmings (SSWs) and drives surface anomalies via stratosphere–troposphere coupling. These results underscore the potential of HT to create favorable conditions for SSWs in subsequent winters as long as the near-stratopause cooling effect of excess WV persists. Our findings highlight the complex interactions between volcanic activity and climate dynamics and offer crucial insights for future climate modelling and attribution.

Solar particle events (SPEs) are short-lived bursts of high-energy particles from the solar atmosphere and are widely recognized as posing significant economic risks to modern society. Most SPEs are relatively weak and have minor impacts on the Earth's environment, but historic records contain much stronger SPEs which have the potential to alter atmospheric chemistry, impacting climate and biological life. The impacts of such strong SPEs would be far more severe when the Earth's protective geomagnetic field is weak, such as during past geomagnetic excursions or reversals. Here, we model the impacts of an extreme SPE under different geomagnetic field strengths, focusing on changes in atmospheric chemistry and surface radiation using the atmosphere-ocean-chemistry-climate model SOCOL3-MPIOM and the radiation transfer model LibRadtran. Under current geomagnetic conditions, an extreme SPE would increase NOx concentrations in the polar stratosphere and mesosphere, causing reductions in extratropical stratospheric ozone lasting for about a year. In contrast, with no geomagnetic field, there would be a substantial increase in NOx throughout the entire atmosphere, resulting in severe stratospheric ozone depletion for several years. The resulting ground-level ultraviolet (UV) radiation would remain elevated for up to 6 y, leading to increases in UV index up to 20 to 25% and solar-induced DNA damage rates by 40 to 50%. The potential evolutionary impacts of past extreme SPEs remain an important question, while the risks they pose to human health in modern conditions continue to be underestimated.

Tropospheric ozone is an air pollutant that poses a public health problem in Europe. Climate change could increase the formation of ozone. Applying past and predicted annual total (all-cause) mortality data and modeled daily ozone concentrations, we performed a nationwide health impact assessment estimating annual ozone-related (attributable) deaths in Austria. Different approaches were compared. Estimates were based on maximal 1-h averages of ozone. Until the decade from 2045 till 2055, more people will die in Austria because of the demographic trends. Therefore, more deaths will also be attributable to ozone. Higher greenhouse gas emission scenarios (e.g. Representative Concentration Pathway RCP8.5 compared to RCP2.6) will lead to more ozone-related deaths, mostly due to the national emission of ozone precursors (a difference of 250-340 cases per year, depending on the model), but to a lesser extent because of global climate change. Increases in attributable deaths will be affected mostly by national, not global mitigation measures. National emission reduction will certainly have a strong and beneficial effect on local atmospheric chemistry, air quality, and public health.

Abstract Climate models robustly project acceleration of the Brewer‐Dobson circulation (BDC) in response to climate change. However, the BDC trends simulated by comprehensive models are poorly constrained by observations, which cannot even determine the sign of potential trends. Additionally, the changing structure of the troposphere and stratosphere has received increasing attention in recent years. The extent to which vertical shifts of the circulation are driving the acceleration is under debate. In this study, we present a novel method that enables the attribution of advective BDC changes to structural changes of the circulation and of the stratosphere itself. Using this method allows studying the advective BDC trends in unprecedented detail and sheds new light into discrepancies between different data sets (reanalyses and models) at the tropopause and in the lower stratosphere. Our findings provide insights into the reliability of model projections of BDC changes and offer new possibilities for observational constraints.

We investigate the performance of two widely used chemistry-transport models (CTMs) with different chemical mechanisms in reproducing the ambient maximum daily 8-h average ozone (MDA8 O _3 ) burden over Central Europe. We explore a base case setup with boundary conditions (BC) for meteorology from the ERA-Interim reanalysis and chemical BC from CAM-Chem as well as effects of alterations in these BC based on global model fields. Our results show that changes in meteorological BC strongly affect the correlation with observations but only marginally affect the model biases, while changes in chemical BC increase model biases while correlation patterns remain largely unchanged. Furthermore, our study highlights that CTM choice (and choice of chemical mechanism) has a similar or even larger impact on MDA8 O _3 levels as the impact of altered BC. In summary, our study calls for a multi-model strategy combining different CTM and BC combinations to explore the bandwidth of MDA8 O _3 distributions and thus uncertainty in hindcasts and future projections, in analogy to climate studies considering ensemble simulations under the same anthropogenic emissions but with slightly different initial conditions.

State-of-the-art chemistry–climate models (CCMs) still show biases compared to ground-level ozone observations, illustrating the difficulties and challenges remaining in the simulation of atmospheric processes governing ozone production and loss. Therefore, CCM output is frequently bias-corrected in studies seeking to explore the health or environmental impacts from changing air quality burdens. Here, we assess four statistical bias correction techniques of varying complexities and their application to surface ozone fields simulated with four CCMs and evaluate their performance against gridded observations in the EU and US. We focus on two time periods (2005–2009 and 2010–2014), where the first period is used for development and training and the second to evaluate the performance of techniques when applied to model projections. We find that all methods are capable of significantly reducing the model bias. However, biases are lowest when we apply more complex approaches such as quantile mapping and delta functions. We also highlight the sensitivity of the correction techniques to individual CCM skill at reproducing the observed distributional change in surface ozone. Ensemble simulations available for one CCM indicate that model ozone biases are likely more sensitive to the process representation embedded in chemical mechanisms than to meteorology.

To estimate the effect of vegetation stress and changes in biogenic volatile organic compound (BVOC) emissions on urban ozone (O3) levels we perform a systematic, observation-based analysis of the relationship between formaldehyde (HCHO) mixing ratios, meteorological parameters, measurement-based drought indicators and O3 over the central European city of Vienna, Austria. In addition, numerical models SURface EXternalisée (SURFEX), Model of Emissions of Gases and Aerosols from Nature (MEGAN) Vers.2.1 and 3 and MOdèle de Chimie A Grande Echelle (MOCAGE) are combined to estimate the soil moisture, the spatial distribution and drought response of isoprene emissions, and the resulting distribution of HCHO in the atmosphere. To analyse the effect of drought during spring and summer we contrast observations during dry and reference years. Our results show that the observed HCHO can be explained using the simulated isoprene emissions as well as observed and simulated vegetation drought responses. HCHO mixing ratios differ strongly between dry and reference seasons. Spring-time precipitation deficits facilitate reduced HCHO mixing ratios due to delayed and weakened plant growth. In consequence also O3 burdens are lowered due to reduced BVOC precursor emissions. These reductions occur despite radiation levels being higher than during the reference year, illustrating the strong potential of spring-time BVOC emissions to modulate urban O3 burdens. Conversely, during summer elevated O3 levels occur during local drought conditions. These are driven by advected isoprene originating from nearby forest areas, which are not affected by drought. Our results regarding elevated summer-time O3 burdens under vegetation heat and drought stress are in good agreement with previous work.

Photolysis of molecular oxygen (O2) sustains the stratospheric ozone layer and is thereby protecting living organisms on Earth by absorbing harmful ultraviolet radiation. In the past, atmospheric O2 levels were not constant, and their variations are thought to be responsible for the extinction of some species due to the thinning of the ozone layer. Over the Phanerozoic Eon (last ∼500 Mio years), the O2 volume mixing ratio ranged between 10% and 35% depending on the level of photosynthetic activity of plants and oceans. Previous estimates, mostly performed by simplified 1-D models, showed different ozone (O3) responses to atmospheric O2 changes within this range, such as monotonically positive or negative correlations, or displaying a maximum in the O3 column around a certain O2 level. Here, we assess the ozone layer sensitivity to atmospheric O2 varying between 5% and 40% with a state-of-the-art 3-D chemistry-climate model (CCM). Our findings show that the O3 layer thickness maximizes around the current mixing ratio of O2, 21% ± 5%, while lower or higher levels of O2 result globally in a reduction of total column O3. At low latitudes, the total column O3 is less sensitive to O2 variations, because of the “self-healing” effect, namely, a vertical dipole in the tropical ozone response. Mid- and high-latitude O3 columns that are largely affected by transport of O3 from the tropics, however, are much more sensitive to O2 with changes up to 20 DU even for small (±5%) O2 perturbations. We show that these variations are largely driven by the radiative impact of O3 on stratospheric temperatures and on the strength of the Brewer-Dobson circulation (BDC), indicating chemistry-radiation-transport feedback. High O2 cases result in an acceleration of the BDC and vice versa, which always works in favor of the negative part of the O3 anomaly dipole in the tropics being more effectively transported to the mid- and high-latitudes than the positive one. Although there are other factors strongly influencing O3/O2 relationship on the Phanerozoic Eon timescales that have not been considered here, our results and the presented mechanism bring useful insights for other studies focusing on the long-term O3/O2 relationship.

&lt;p&gt;Ozone production and loss in surface air is determined by ambient temperature, &amp;#160;chemical conditions and precursor emissions. Despite efforts to abate surface ozone air pollution, the daily maximum 8-hour average ozone target value for the protection of human health &amp;#160;is regularly exceeded at several monitoring sites in Austria especially during the warm seasons.&amp;#160;&lt;/p&gt; &lt;p&gt;Here we investigate projected changes in the surface ozone burden and effects of climate warming and changes in precursor emissions over the next decades in a series of tailored chemistry-transport model (CTM) experiments, performed with WRF-Chem and CAMx. Specifically we contrast changes in ozone air quality in decadal time slices for 2026-2035 and 2046-2055 with the recent past (2007-2016). Our CTM ensemble comprises simulations following the Representative Concentration Pathways (RCPs) 2.6, 4.5 and 8.5. Our results show a persistent large variability in ozone abundances driven by the large intra- and interannual &amp;#160;variability in meteorological conditions. Overall we find general improvements in the surface ozone burden for low emission scenarios (RCP2.6 and RCP4.5) driven by ambitious NOx controls. In contrast under RCP8.5 we find, on the one hand an increase in the frequency of non-attainment days and on the other a shift in the prime ozone season from summer towards spring. These increases are driven by both a climate penalty and changes in the chemical production regime (NOx vs. VOC limitation) and increasing methane and ozone backgrounds. Furthermore, we investigate impacts of projected ozone changes on human health at the municipal level in Austria.&lt;/p&gt;

Rising greenhouse gases (GHG) and decreasing anthropogenic ozone-depleting substances (ODS) are the main drivers of the stratospheric climate evolution in the 21st century. However, the coupling between stratospheric composition, radiation and dynamics is subject to many uncertainties, which is partly because of the simplistic representation of ozone (O 3 ) in many current climate models. Changes in ozone due to heterogeneous chemistry are known to be the largest during springtime in the Arctic, which is also a season with very active stratosphere–troposphere coupling. The focus of this study is to investigate the role of varying ozone levels driven by changing GHG and ODS for the Arctic polar cap stratosphere. We use two state-of-the-art chemistry-climate models with ocean coupling in two configurations (prescribed ozone fields vs. interactive ozone chemistry) for three different scenarios: preindustrial conditions—1 × CO 2 , year 2000 conditions (peak anthropogenic ODS levels) and extreme future conditions—4 × CO 2 . Our results show that in the upper and middle stratosphere CO 2 thermal cooling is the dominant effect determining the temperature response under 4 × CO 2 , and outweighs warming effects of ozone by about a factor of ten. In contrast, in the lower stratosphere, the effects of O 3 warming and CO 2 cooling under 4 × CO 2 are largely offsetting each other. ODS driven variations in O 3 affect both the temperature mean and variability, and are responsible for the tight springtime coupling between composition and dynamics under year 2000 conditions in comparison to simulations under 1 × CO 2 or 4 × CO 2 .

Data from a dual-polarized, solid-state X-band radar and an operational C-band weather radar are used for high-resolution analyses of two hailstorms in the Vienna, Austria, region. The combination of both radars provides rapid-update (1 min) polarimetric data paired with wind field data of a dual-Doppler analysis. This is the first time that such an advanced setup is used to examine severe storm dynamics at the eastern Alpine fringe, where the influence of local topography is particularly challenging for thunderstorm prediction. We investigate two storms transitioning from the pre-Alps into the Vienna basin with different characteristics: 1) A rapidly evolving multicell storm producing large hail (5 cm), with observations of an intense Z(DR) column preceding hail formation and the rapid development of multiple pulses of hail; and 2) a cold pool-driven squall line with small hail, for which we find that the updraft location inhibited the formation of larger hailstones. For both cases, we analyzed the evolution of different Z(DR) column metrics as well as updraft speed and size and found that (i) the 90th percentile of Z(DR) within the Z(DR) column was highest for the cell later producing large hail, (ii) the peak 90th percentile of ZDR preceded large hailfall by 20 min and highest updraft size and speed by 10 min, and (iii) sudden drops of the 90th percentile of Z(H) within the Z(DR) column indicated imminent hailfall. SIGNIFICANCE STATEMENT: Thunderstorm evolution on the transition from complex terrain into the Vienna basin in northeastern Austria varies strongly. In some instances, thunderstorm cells intensify once they reach flat terrain, while in most cases there is a weakening tendency. To improve our process understanding and short-term forecasting methods, we analyze two representative cases of hail-bearing storms transitioning into the Vienna basin. We mainly build our study on data from a new, cost-efficient weather radar, complemented by an operational radar, lightning observations, and ground reports. Our results show which radar variables could be well suited for early detection of intensification, and how they relate to thunderstorm updraft speeds and lightning activity.

Excess reactive nitrogen (Nr), including nitrogen oxides (NO x ) and ammonia (NH 3 ), contributes strongly to fine particulate matter (PM 2.5 ) air pollution in Europe, posing challenges to public health. Designing cost-effective Nr control roadmaps for PM 2.5 mitigation requires considering both mitigation efficiencies and implementation costs. Here we identify optimal Nr control pathways for Europe by integrating emission estimations, air quality modeling, exposure-mortality modeling, Nr control experiments and cost data. We find that phasing out Nr emissions would reduce PM 2.5 by 2.3 ± 1.2 μg·m −3 in Europe, helping many locations achieve the World Health Organization (WHO) guidelines and reducing PM 2.5 -related premature deaths by almost 100 thousand in 2015. Low-ambition NH 3 controls have similar PM 2.5 mitigation efficiencies as NO x in Eastern Europe, but are less effective in Western Europe until reductions exceed 40%. The efficiency for NH 3 controls increases at high-ambition reductions while NO x slightly decreases. When costs are considered, strategies for both regions uniformly shift in favor of NH 3 controls, as NH 3 controls up to 50% remain 5-11 times more cost-effective than NO x per unit PM 2.5 reduction, emphasizing the priority of NH 3 control policies for Europe.