Trends in tropical nights and their effects on mortality in Switzerland across 50 years

Increasing temperatures and more frequent and severe heat waves in Switzerland are leading to a larger heat-related health burden. Additionally, high nighttime temperatures or tropical nights (TNs) also affect the well-being of the population. We aimed to assess the spatiotemporal patterns in the frequency and the exposed population to TNs, and its mortality effect in Switzerland. We identified the TNs (minimum nighttime temperature >20˚C) in each district in Switzerland using population-weighted hourly temperature series (ERA5- Land reanalysis data set) between 1970–2019. We assessed the change in the frequency of TNs and the exposed population per district and decade through a spatiotemporal analysis. We then performed a case time series analysis to estimate the TN-mortality association (controlled for the daily mean temperature) by canton and for the main 8 cities using data on all-cause mortality at the district level between 1980–2018. We found an overall increase in the annual frequency of TN (from 90 to 2113 TNs per decade) and the population exposed (from 3.7 million to over 157 million population-TN per decade) in Switzerland between 1970–2019, mainly in the cities of Lausanne, Geneva, Basel, Lugano, and Zurich, and during the last two decades. The TN-mortality association was highly heterogeneous across cantons and cities. In particular, TNs were associated with an increase of 22–37% in the risk of mortality in the cantons of Vaud (Relative risk: 1.37 (95%CI:1.19–1.59)), Zurich (1.33 (0.99–1.79)), Lucerne (1.33 (0.95–1.87)) and Solothurn (1.22 (0.88–1.69)), while a negative association was observed in Ticino (0.51 (0.37–0.7)), Basel-Land (0.4 (0.24–0.65)) and Thurgau (0.65 (0.5–0.85)), and a null association in the remaining cantons. Our findings indicate that TNs are a relevant health hazard for a large part of the Swiss population leading to potentially larger impacts in the future due to climate change and increasing urbanization

Suicides and ambient temperature in Switzerland: A nationwide time-series analysis.

AIM OF THE STUDY Previous literature suggests that ambient temperature may play a role in increasing the risk of suicide. Although in Switzerland suicides are an important cause of death, limited research exists on risk factors for suicidal behaviour, including ambient temperature. We aimed to assess the short-term association between ambient temperature and suicide risk in Switzerland between 1995 and 2016, and the differences by region, individual characteristics and method of suicide. METHODS We collected daily data on suicides and mean temperatures in each canton of Switzerland. We used a two-stage approach, consisting of a case time series analysis using conditional quasi-Poisson and distributed lag non-linear models followed by a multivariate meta-regression analysis. We conducted subgroup analyses by sex, age (65 years) and method of suicide (violent or nonviolent). RESULTS Between 1995 and 2016, there were a total of 24,067 suicides in Switzerland. Overall, we found a positive and non-linear temperature-suicide association in all regions. On average, the risk of suicide increased by 34% (1.34 relative risk [95% confidence interval: 1.19-1.52]) from the 10th to the 99th temperature percentile in Switzerland (lag period of 0-2 days). Indications of larger risks were mostly found in females, younger individuals (<35 years) and with nonviolent methods. Regional risks ranged from 24% (East region) to 55% (North-West region). CONCLUSIONS Our findings suggest that increasing temperatures could be considered a risk factor for suicidal behaviour in Switzerland. Knowledge of the profile of people committing suicide could help us to understand the mechanisms behind this association and thus support policymakers in suicide prevention

Exploring vulnerability to heat and cold across urban and rural populations in Switzerland

Heat- and cold-related mortality risks are highly variable across different geographies, suggesting a differential distribution of vulnerability factors between and within countries, which could partly be driven by urban-to-rural disparities. Identifying these drivers of risk is crucial to characterize local vulnerability and design tailored public health interventions to improve adaptation of populations to climate change. We aimed to assess how heat- and cold-mortality risks change across urban, peri-urban and rural areas in Switzerland and to identify and compare the factors associated with increased vulnerability within and between different area typologies. We estimated the heat- and cold-related mortality association using the case time-series design and distributed lag non-linear models over daily mean temperature and all-cause mortality series between 1990-2017 in each municipality in Switzerland. Then, through multivariate meta-regression, we derived pooled heat and cold-mortality associations by typology (i.e. urban/rural/peri-urban) and assessed potential vulnerability factors among a wealth of demographic, socioeconomic, topographic, climatic, land use and other environmental data. Urban clusters reported larger pooled heat-related mortality risk (at 99th percentile, vs. temperature of minimum mortality (MMT)) (relative risk=1.17(95%CI:1.10;1.24, vs peri-urban 1.03(1.00;1.06), and rural 1.03 (0.99;1.08)), but similar cold-mortality risk (at 1st percentile, vs. MMT) (1.35(1.28;1.43), vs rural 1.28(1.14;1.44) and peri-urban 1.39 (1.27-1.53)) clusters. We found different sets of vulnerability factors explaining the differential risk patterns across typologies. In urban clusters, mainly environmental factors (i.e. PM2.5) drove differences in heat-mortality association, while for peri-urban/rural clusters socio-economic variables were also important. For cold, socio-economic variables drove changes in vulnerability across all typologies, while environmental factors and ageing were other important drivers of larger vulnerability in peri-urban/rural clusters, with heterogeneity in the direction of the association. Our findings suggest that urban populations in Switzerland may be more vulnerable to heat, compared to rural locations, and different sets of vulnerability factors may drive these associations in each typology. Thus, future public health adaptation strategies should consider local and more tailored interventions rather than a one-size fits all approach. size fits all approach

Nationwide Analysis of the Heat- and Cold-Related Mortality Trends in Switzerland between 1969 and 2017: The Role of Population Aging.

BACKGROUND: Because older adults are particularly vulnerable to nonoptimal temperatures, it is expected that the progressive population aging will amplify the health burden attributable to heat and cold due to climate change in future decades. However, limited evidence exists on the contribution of population aging on historical temperature-mortality trends. OBJECTIVES: We aimed to a) assess trends in heat- and cold-related mortality in Switzerland between 1969 and 2017 and b) to quantify the contribution of population aging to the observed patterns. METHODS: We collected daily time series of all-cause mortality by age group (<65, 65-79, and 80 y and older) and mean temperature for each Swiss municipality (1969-2017). We performed a two-stage time-series analysis with distributed lag nonlinear models and multivariate longitudinal meta-regression to obtain temperature-mortality associations by canton, decade, and age group. We then calculated the corresponding excess mortality attributable to nonoptimal temperatures and compared it to the estimates obtained in a hypothetical scenario of no population aging. RESULTS: Between 1969 and 2017, heat- and cold-related mortality represented 0.28% [95% confidence interval (CI): 0.18, 0.37] and 8.91% (95% CI: 7.46, 10.21) of total mortality, which corresponded to 2.4 and 77 deaths per 100,000 people annually, respectively. Although mortality rates for heat slightly increased over time, annual number of deaths substantially raised up from 74 (12;125) to 181 (39;307) between 1969-78 and 2009-17, mostly driven by the ≥80-y-old age group. Cold-related mortality rates decreased across all ages, but annual cold-related deaths still increased among the ≥80, due to the increase in the population at risk. We estimated that heat- and cold-related deaths would have been 52.7% and 44.6% lower, respectively, in the most recent decade in the absence of population aging. DISCUSSION: Our findings suggest that a substantial proportion of historical temperature-related impacts can be attributed to population aging. We found that population aging has attenuated the decrease in cold-related mortality and amplified heat-related mortality. https://doi.org/10.1289/EHP9835

Impact of population aging on future temperature-related mortality at different global warming levels.

Older adults are generally amongst the most vulnerable to heat and cold. While temperature-related health impacts are projected to increase with global warming, the influence of population aging on these trends remains unclear. Here we show that at 1.5 °C, 2 °C, and 3 °C of global warming, heat-related mortality in 800 locations across 50 countries/areas will increase by 0.5%, 1.0%, and 2.5%, respectively; among which 1 in 5 to 1 in 4 heat-related deaths can be attributed to population aging. Despite a projected decrease in cold-related mortality due to progressive warming alone, population aging will mostly counteract this trend, leading to a net increase in cold-related mortality by 0.1%-0.4% at 1.5-3 °C global warming. Our findings indicate that population aging constitutes a crucial driver for future heat- and cold-related deaths, with increasing mortality burden for both heat and cold due to the aging population

Comparison of weather station and climate reanalysis data for modelling temperature-related mortality

Multi-Country Multi-City (MCC) Collaborative Research Network: Barrak Alahmad, Rosana Abrutzky, Paulo Hilario Nascimento Saldiva, Patricia Matus Correa, Nicolás Valdés Orteg, Haidong Kan, Samuel Osorio, Ene Indermitte, Jouni J K Jaakkola, Niilo Ryti, Alexandra Schneider, Veronika Huber, Klea Katsouyanni, Antonis Analitis, Alireza Entezari, Fatemeh Mayvaneh, Paola Michelozzi, Francesca de'Donato, Masahiro Hashizume, Yoonhee Kim, Magali Hurtado Diaz, César De la Cruz Valencia, Ala Overcenco, Danny Houthuijs, Caroline Ameling, Shilpa Rao, Xerxes Seposo, Baltazar Nunes, Iulian-Horia Holobaca, Ho Kim, Whanhee Lee, Carmen Íñiguez, Bertil Forsberg, Christofer Åström, Martina S Ragettli, Yue-Liang Leon Guo, Bing-Yu Chen, Valentina Colistro, Antonella Zanobetti, Joel Schwartz, Tran Ngoc Dang, Do Van DungErratum in: Author Correction: Sci Rep. 2022 May 13;12(1):7960. doi: 10.1038/s41598-022-11769-6. https://www.nature.com/articles/s41598-022-11769-6Epidemiological analyses of health risks associated with non-optimal temperature are traditionally based on ground observations from weather stations that offer limited spatial and temporal coverage. Climate reanalysis represents an alternative option that provide complete spatio-temporal exposure coverage, and yet are to be systematically explored for their suitability in assessing temperature-related health risks at a global scale. Here we provide the first comprehensive analysis over multiple regions to assess the suitability of the most recent generation of reanalysis datasets for health impact assessments and evaluate their comparative performance against traditional station-based data. Our findings show that reanalysis temperature from the last ERA5 products generally compare well to station observations, with similar non-optimal temperature-related risk estimates. However, the analysis offers some indication of lower performance in tropical regions, with a likely underestimation of heat-related excess mortality. Reanalysis data represent a valid alternative source of exposure variables in epidemiological analyses of temperature-related risk.The study was primarily supported by Grants from the European Commission’s Joint Research Centre Seville (Research Contract ID: JRC/SVQ/2020/MVP/1654), Medical Research Council-UK (Grant ID: MR/R013349/1), Natural Environment Research Council UK (Grant ID: NE/R009384/1), European Union’s Horizon 2020 Project Exhaustion (Grant ID: 820655). The following individual Grants also supported this work: J.K and A.U were supported by the Czech Science Foundation, project 20-28560S. A.T was supported by MCIN/AEI/10.13039/501100011033, Grant CEX2018-000794-S. V.H was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant agreement No 101032087.info:eu-repo/semantics/publishedVersio

Comparison of weather station and climate reanalysis data for modelling temperature-related mortality.

Epidemiological analyses of health risks associated with non-optimal temperature are traditionally based on ground observations from weather stations that offer limited spatial and temporal coverage. Climate reanalysis represents an alternative option that provide complete spatio-temporal exposure coverage, and yet are to be systematically explored for their suitability in assessing temperature-related health risks at a global scale. Here we provide the first comprehensive analysis over multiple regions to assess the suitability of the most recent generation of reanalysis datasets for health impact assessments and evaluate their comparative performance against traditional station-based data. Our findings show that reanalysis temperature from the last ERA5 products generally compare well to station observations, with similar non-optimal temperature-related risk estimates. However, the analysis offers some indication of lower performance in tropical regions, with a likely underestimation of heat-related excess mortality. Reanalysis data represent a valid alternative source of exposure variables in epidemiological analyses of temperature-related risk

Climate Change and Health Impacts.

There is a well-established relationship between exposure to non-optimal temperatures and a wide range of adverse health outcomes. At present, non-optimal temperatures contribute to 9.4% of total mortality, the equivalent of 74 deaths per 100,000 people annually, with the majority of these deaths being a result from cold exposure (8.5%) compared to heat (0.9%), which is larger than the global mortality burden related to air pollution (7.6%). Evidence suggests that under various climate scenarios heat-related mortality is projected to further increase and is likely to overtake cold-related mortality in some places. Even with full implementation of the Paris agreement and reaching net-zero carbon emissions by 2050, the inherent inertia the climate system will continue to increase temperatures for several more decades after, yielding a substantial additional health burden. Moreover, the projected future heat- and cold-related mortality does not solely depend on the specific climate trajectory that is being followed, also adaptation by populations and changes in population dynamics have the potential to vastly modify the future mortality burden related, which have shown to be highly heterogeneous across regions. As current mitigation policies show a large degree of misalignment with the Paris agreement that aims to keep global warming well below 2.0°C, besides mitigation strategies, accelerated adaptation to non-optimal temperature is essential to reduce the future heat-related mortality burden. Prior to this Ph.D. little was known regarding changes in the heat- and cold-related mortality over long temporal periods, the role of changes in population dynamics, vulnerability and adaptation factors and lastly the possible mortality impacts under various climate change and population scenarios in Switzerland. Therefore, the primary objective is to explore the impacts of heat- and cold in Switzerland, identify adaptation factors, to project future mortality under various climate and population scenarios and to quantify the additional contribution of human induced climate change on the overall heat-related mortality burden, to ultimately help equip policy makers with the tools necessary to create resilient populations against a changing climate. The main body of the thesis consists of eleven publications, of which four studies that are first-author contributions (three published, one submitted), four second-author studies (two published, two submitted) and finally three co-authored studies (two published, one submitted). First, to date, most studies aiming to explore the temperature-mortality association have used weather stations to approximate the exposure of populations to temperature, although this is known to come with substantial limitations. Therefore we aimed to explore whether spatially resolved climate data was at least an equally good predictor for mortality in Switzerland and 39 other countries. In this thesis, we observed that despite a small biases in the absolute temperature observations, newly developed reanalysis data generally compare well to weather stations, as these yielded very similar temperature-mortality association and impacts. Moreover, these findings imply that spatially resolved weather data can now be used to explore the effect of temperature-mortality at very high resolution, in rural regions, on a global scale and in regions with no temperature monitor stations available. However, the analyses provide some indication of lower performance in tropical regions, therefore some caution is required. As we have shown that reanalysis data can be used to study the temperature-mortality association and impacts across the world at high resolution, we aimed on leverage on this exposure data to analyse 49 years of temperaturemortality trends in Switzerland, while also exploring the role of population ageing. This is particularly relevant as older adults are considered particularly vulnerable to non-optimal temperature and as it is expected that progressive ageing will amplify the total non-optimal related mortality. We observed that although the vulnerability remained largely similar over time in Switzerland, the annual number of deaths attributable to heat has more than tripled over the past 50 years. Similarly, the overall cold-related vulnerability substantially decreased, while the attributable number of deaths for cold-mortality has remained constant. This implies that although vulnerability has decreased over time, the increase in overall societal impacts can be attributed to a larger pool of susceptible people, which is driven by population ageing and population development. Thus population ageing was found to attenuate the decrease in cold-related mortality, while it amplified the heat-related mortality impacts, which has significant implications for modelling the projected temperature-mortality burden under different scenarios of climate change. Then, besides temperature being associated with substantial mortality in Switzerland, also tropical nights have shown additive effect on mortality across various in Switzerland. Finally, mental health hospital admissions and suicides have been associated with increases in temperature despite recent public health efforts. Additionally, besides exploring temporal changes in the temperature-mortality impacts, we also aimed to spatially study temperature-vulnerability, which is particularly relevant as studies have hypothesised that large differences in vulnerability exists between urban and rural regions. Moreover, being able to identify the most vulnerable regions at risk for temperature-related mortality in Switzerland, we have the potential to better understand drivers of vulnerability to foster resilient population for the future impacts of a changing climate. Our findings suggest larger temperature vulnerability in urban clusters, particularly for heat compared to rural regions, while cold related vulnerability was similar across typologies. More importantly, this thesis has shown that drivers of temperature-vulnerability can considerably vary by urban-rural typology in Switzerland. In urban regions mainly environmental factors modified the temperature-mortality relationship, while in peri-urban and rural regions, also social factors could explain vulnerability. Climate change and population ageing are constituting a double burden when it comes to temperature-related mortality impacts due to increased exposure to extreme heat and vulnerability. As evidence is limited on the projected synergistic impacts of climate change and population development, we aimed to project heat- and cold-related mortality under various climate change scenarios and population development combined across Switzerland and across 43 countries using over 130 million deathrecords. Our findings suggest that both heat- and cold-related mortality will substantially increase under all scenarios of climate change and population development under all degrees of warming. Moreover, population development will reverse the reduction in cold-related mortality despite a warming climate, and further exacerbate heat-related mortality, leading to a substantial netincrease of the total non-optimal temperature-mortality across the globe, with heterogeneous impacts between regions. Finally, with a changing climate, extremely hot summers will likely increase in frequency. However, although most studies estimate the heat-related mortality in such summer, to date few studies have aimed to disentangle heat-related mortality from the influence of human induced anthropogenic climate change. Therefore, in this thesis we aimed to quantify the contribution of human-induced climate change to the observed mortality due to heat in Switzerland during the summer of 2022. We observed that the extreme heat during the summer of 2022 amounted to more than 600 heat-related deaths in Switzerland, of which more than 60% can directly be attributed to human induced climate change. This PhD project is the first of it’s kind to study the temperature and health impacts in full depth and breath in Switzerland. We have contributed on the global knowledge regarding long term temperature-mortality impacts and understanding the dynamics of demographic changes over time in relation to temperature vulnerability. Then, we have generated new hypotheses that vulnerability largely varies between countries, regions and cities and that different drivers lay the foundation for adaptation, meaning that local adaptation strategies are required. Furthermore, we have improved the epidemiological methodology regarding climate projections and future health impacts by showing that incorporating Shared Socioeconomic Pathways and different demographic baseline assumptions in the models, can vastly modify the measure of impact generated. Finally, we have shown that already today a large part of the heat-related mortality burden can directly be attributed to human induced climate change. Based on the observed results and the remaining uncertainty in climate change epidemiology, current efforts should first be aimed at expanding scientific knowledge regarding climate change and temperaturerelated impacts to a truly global coverage as most countries still remain understudied to get a better picture of regions that will most be affected. Then, causality of study designs applied in climate epidemiology should be improved to have an impact also beyond the field of epidemiology, such as in climate litigation. Finally current efforts should be targeted at understanding the complexity of adaptation and implementation of these, as the most recent summer have been the hottest ever experienced by humankind, however will remain the coolest in the years that are yet to come