Summer Heat Waves Research Articles

Pandemic-time mental health surveillance among the French population using survey and routine data

Abstract Alerted by the scientific community about a possible negative impact of the COVID-19 epidemic on population's mental health, Santé publique France (the French public health agency) started a reactive surveillance in March 2020. From a crisis management perspective, the objective was to closely monitor mental health developments during the pandemic and to collect necessary information to implement preventive and protective interventions for the population. The population mental health surveillance was mainly based on two data sources: first, the Coviprev survey, a declarative internet-based survey among the adult population ran weekly and then monthly during the pandemic, and second, the OSCOUR® database, developed after the heat wave of summer 2003 in France, which has been collecting daily emergency department (ED) data for almost 20 years. 94% of French ED visits are collected by the system. The main indicators monitored were mood disorders, anxiety disorders, suicidal ideation and behaviors. This surveillance confirmed, from the start and throughout the epidemic, the negative impact of the health crisis on the population's mental health and suggested that adolescents (aged 11 to 17 years) and young adults (aged 18 to 24 years) have been more affected than the rest of the population. In comparison to previous years, significant increases of mood disorders and suicidal behaviors were observed in both data sources in the beginning of 2021 and are still observed in 2023 for some indicators. The results of the work carried out showed the importance of a continuous surveillance of mental health during a crisis situation based on reactive data sources which are essential tools for steering preventive responses and advocating for the strengthening of mental health prevention and promotion policies. Strengths and limitations of the implemented surveillance system integrating two different data sources will be discussed.

Above-treeline ecosystems facing drought: lessons from the 2022 European summer heat wave

Abstract. In 2022, a large part of Europe experienced an extremely dry and hot summer. In the Alps, this episode occurred after an unusually low-snowfall winter, which aggravated the dryness of soils. This study examines the impact of this particular year on the canopy greenness of above-treeline ecosystems by comparison with previous heat waves that hit the Alps during the last 2 decades. Normalized difference vegetation index (NDVI) time series derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite were processed to extract the temporal variability in yearly maximum NDVI (NDVImax). The responsiveness of NDVImax to snow cover duration and growing-season weather conditions was evaluated in contrasting hydroclimate regions of the Alps using linear mixed-effect models. The year 2022 was unique in that the summer heat wave led to a widespread negative anomaly of NDVImax. The magnitude of this anomaly was unprecedented in the southwestern, driest part of the Alps, where vegetation activity was found to be particularly responsive to snow cover duration and early summer precipitation. In the colder and wetter regions, all warm to very warm summers before 2022 had led to increased canopy greenness, but the combination of a reduced snow cover and low early summer precipitation counteracted this expected beneficial effect in 2022. This study provides evidence that the control of canopy greenness by temperature and water balance differs markedly across regions of the Alps and that the year 2022 bears witness to a shift toward an increasing importance of moisture availability for regulating plant growth at high elevation. This is viewed as a warning sign of what could become the new norm in the years ahead in the context of increasing frequency and intensity of extreme droughts throughout temperate mountain ecosystems.

Summer heat waves and their mortality risk over a 14-year period in a western region of Iran.

Compared to previous decade, impact of heat waves (HWs) on mortality in recent years needs to be discussed in Iran. We investigated temporal change in added impact of summer HWs on mortality in eight cities of Iran. The pooled length of HWs was compared between 2015-2022 and 2008-2014 using random and fixed-effects of meta-analysis regression model. The temporal change in impact of HWs was evaluated through interaction effect between crossbasis function of HW and year in a two-stage time varying model. In order to pool the reduced coefficients of each period, multivariate meta-regression model, including city-specific temperature and temperature range as heterogenicity factors, was used. In addition to relative risk (RR), attributable fraction (AF) of HW in the two periods was also estimated in each city. In the last years, the frequency of all HWs was higher and the weak HWs were significantly longer. The only significant RR was related to the lowest and low severe HWs which was observed in the second period. In terms of AF, compared to the strong HWs, all weak HWs caused a considerable excess mortality in all cities and second period. The subgroup analysis revealed that the significant impact in the second period was mainly related to females and elderlies. The increased risk and AF due to more frequent and longer HWs (weak HWs) in the last years highlights the need for mitigation strategies in the region. Because of uncertainty in the results of severe HWs, further elaborately investigation of the HWs is need.

Predictability of Northwest Pacific marine heatwaves in summer based on NUIST-CFS1.0 hindcasts

Marine ecosystems in the Northwest Pacific (NWP) are being threatened by marine heatwaves (MHWs), which are abnormally high sea-surface temperature (SST) lasting for more than 5 days. However, there is limited research on the predictability of these MHWs. In this study, we investigate the predictability of NWP MHWs in summer using daily data from the coupled climate forecast system (version 1.0) of the Nanjing University of Information Science and Technology (NUIST-CFS1.0) for the period of 1984–2020. We demonstrate that the NUIST-CFS1.0 hindcasts can predict the spatial pattern of the total MHW days (HWD) over the NWP in summer with a lead time of up to eight months. Moreover, the linear trend and interannual variability can be predicted at lead times of up to nine and three months, respectively. We reveal that the interannual variability of HWD is strongly correlated with the preceding El Niño-Southern Oscillation (ENSO); and its predictability also shows significant interannual variability, with MHWs being more predictable in the decaying years of stronger El Niño events. In the El Niño decaying summers, there is an increase in the occurrence of MHWs; the spatial distribution of HWD can be predicted at lead times of up to 19 months, and its forecasting accuracy is far superior to that of the other years. The occurrence of MHWs during El Niño decaying summers is closely linked to strengthened NWP subtropical anticyclone (NWPSA), which increases solar radiation reaching the ocean surface and suppresses surface evaporation, leading to increased SST and thereby MHWs. The remarkable predictability of the MHWs in the NWP region during El Niño decaying summers can be attributed to the high skill at predicting ENSO and its associated NWPSA anomalies.

Postprandial metabolism of Australian hybrid abalone (Haliotis laevigata × H. rubra) in relation to temperature and dietary protein manipulation

Understanding the physiological responses of abalone to culture conditions and nutritional inputs is paramount to maintain optimal performance under densely stocked farming conditions. High water temperature (>24 °C) is widely accepted as a key contributor to elevated summer mortality. High crude protein levels in modern abalone diets may interact with elevated water temperature to produce detrimental effects on abalone physiological processes but have received scant attention. This study measured the energy used in the digestion, absorption, and assimilation (i.e., specific dynamic action (SDA)) of hybrid abalone (Haliotis laevigata x H. rubra) after four months of acclimation to three protein levels (32, 38 and 44%) at three culture temperatures (12, 17 and 22 °C). Hybrid abalone exhibited significant stepwise increases in meal size as temperature increased from 12 through to 22 °C, contributing to significantly different SDA between the temperature treatments. Resting (standard) aerobic metabolic rate and peak metabolism (peak ṀO2) during SDA both increased with temperature, while SDA duration was lowest at 17 °C. No effect of dietary protein was observed within the temperature treatments for the SDA metrics. Abalone held at 12 °C exhibited significantly higher rates of gonad maturation, particularly among females. When 22 °C-acclimated abalone were exposed to a simulated summer heatwave up to 26 °C, they exhibited similar mortality and metabolic responses across protein treatment groups and there was a trend of steadily decreasing ṀO2 with sustained 26 °C water temperature, probably due to fasting. These results help to inform best farming practices to ensure optimal diet, growth, metabolic performance, and survival of hybrid abalone in the dynamic farm environment.

Ecological gradients in a marine cave revisited 26 years after

Marine caves are unique and vulnerable habitats threatened by multiple global and local pressures. Changes in the sessile epibenthic community of the Grotta Azzurra of Capo Palinuro (Salerno, Italy) during the last 26 years have been evaluated using growth forms and trophic guilds as non-taxonomic descriptors, informative of the structure and the functioning of the cave ecosystem, respectively. Photographic samples were collected in 1992 and 2018 to investigate the stability of the ecosystem response to the three main environmental gradients occurring inside the cave: i) confinement, ii) depth, and iii) light. Benthic communities were well spatially distributed along the three gradients inside the cave according to both the morphology and the feeding strategy of organisms, although the zonation was less marked considering trophic guilds. Gradients persisted and zones remained distinct through time, notwithstanding significant changes in community composition. The trophic organization was preserved throughout the cave, but significant changes in the spatial organization of benthic assemblages were widely observed, mainly due to 3-dimensional growth forms replaced by 2-dimensional (i.e., encrusting) growth forms and by increased sedimentation, thus causing the structural homogenization of the cave community. The outermost and the deepest sectors of the cave experienced higher changes compared to the most confined, blind-ended, sector and to the shallowest depths, which resulted comparatively more stable. From a functional point of view, filter feeders always dominated the communities (even considering their shift from erect to encrusting morphologies) and the few observed changes were due to the reduction of photophilic autotrophs and active ciliate without lophophore and the increase of mixotrophic sponges. As local human pressures remained low through the period considered, the changes observed are likely to be mainly due to global warming, which caused increased sea surface water temperatures and repeated summer heat waves (reported in 1994, 2003, 2008, 2012, and 2015). Regular monitoring programs on marine caves should be promoted to create historical series of data precious to better understand magnitude and pattern of change in the long-term evolution, and to estimate the recovery time of such priority habitats.

Investigation of the Indian summer in the state's popular capital and correlation between IMD and ERA5 dataset during the past five decades (1973–2022)

In this comprehensive study, spanning five decades from 1973 to 2022, the increasing prevalence and duration of heat waves in India, particularly in central and northwest regions, are examined. These heat waves are found to be associated with elevated pressures, anticyclonic flow patterns, clear skies, and diminishing soil moisture. Furthermore, variations in sea surface temperatures (SST) in the tropical Indian Ocean and the central Pacific significantly influence the occurrence of heat waves in India. The study predicts longer and more frequent heat waves as a consequence of the warming tropical Indian Ocean and an increase in El Nino occ-urrences, highlighting the growing heat-related challenges facing the country. Analyses of the present climate using climate models agree with the highest temperature zones that have been observed, emphasizing the importance of radiative heating. This study determines the areas that are most vulnerable to heat waves and regions with the highest temperatures, and it pinpoints the cause as wind flow from these areas, which is induced by favourable atmospheric circulations. The findings of this investigation would have broad applications in both vulnerability and risk evaluation as well as prediction. This study focused on the ERA-Interim and IMD gri-dded data sets in order to evaluate the validity of heatwave detection across several datasets. It looked at particular heatwave dates from March to June in several places and years, included Lucknow in 2016, Delhi in 2019, Jaipur in 2016, and Bhubaneswar in 1988. Among the two datasets, the research showed a statistically substantial agreement, especially during Lucknow's 2016 summer heatwave. However, Bhubaneswar had the lowest correlation, suggesting that the temperature profile in both datasets was identical. With a larger concentration of matched pixels at the mean temperature, Jaipur in 2019 had the best fit. The study's findings were summarized by pointing out the significance of the mid-temperature range from 30°C to 40°C in heatwave identification.

Increasing Trends of Heat Waves and Tropical Nights in Coastal Regions (The Case Study of Lithuania Seaside Cities)

Climate change is leading to an annual increase in extreme conditions. Public health is closely related to weather conditions; hence, climate change becomes a major factor concerning every-day human health conditions. The most common extreme natural phenomenon that affects people’s health is the summer heat wave. During the 21st century, as the air temperature continues to rise, the sea surface temperature (SST) rises along with it, especially along the seacoasts. More massive water bodies, such as seas or larger lagoons, that warm up during the day do not allow the ambient air to cool down quickly, causing the air temperature to often be warmer at night in the coastal area than in the continental part of the continent. Currently, not only an increase in the number of days with heat waves is observed, but also an increase in the number of tropical nights in the coastal zone of the Southeastern Baltic Sea. In this work, heat waves are analyzed in the seaside resorts of Lithuania, where the effects of the Baltic Sea and the Curonian Lagoon are most dominant.

Effects of Climate Change and Urbanization on Vegetation Phenology in the Bucharest Metropolitan Area

Being an essential issue in global warming, the response of urban vegetation to climate change and urbanization has become an increasing concern at both the local and global levels. This study aims to investigate the effect of the urban environment on vegetation phenology for the Bucharest metropolitan area in Romania and to identify the potential climate drivers that influence key phenology in the urban environment. In this study, we comprehensively analyzed the response of urban vegetation phenology shifts due to climate variability and urbanization in the Bucharest metropolitan area from a spatiotemporal perspective during the 2002- 2022 period. Through synergy use of time series of the main climate variables, Air temperature -AT, land surface temperature (LST), and biophysical variables derived from MODIS Terra/Aqua satellite and in-situ data, this study developed a complex statistical and spatial regression analysis. Green space was measured with satellite-derived vegetation indicators Normalized Vegetation Index (NDVI), and Enhanced Vegetation Index (EVI), Net Primary Production (NPP) data, which captures the combined availability of urban parks, street trees, forest, and periurban agricultural areas. Leaf Area Index (LAI) and Photosynthetically active radiation (FPAR) indicators have been used to characterize the effects of meteorological parameters and urbanization impacts on vegetation phenology and their changes. The results show that the response of vegetation phenology to urbanization level and climate parameters variability has a distinct spatiotemporal difference across the urban/periurban gradient. The findings of this study show that the land surface temperature anomalies associated with urbanization-induced climate warming, especially during strong summer heat waves and under urban heat islands alter urban vegetation biophysical properties, directly impacting its phenology shifts. At the metropolitan scale, the urban thermal environment directly impacts vegetation phenology patterns. The quantitative findings of this study are of great importance for understanding the complex impacts of urbanization and climate changes on vegetation phenology and for developing models to predict vegetation phenological changes under future urbanization.

Influence of greenery configuration on summer thermal environment of outdoor recreational space in elderly care centers

Greenery can improve the outdoor thermal environment in elderly care centers during heat wave in summer. However, it lacks quantitative results and rules. This study investigated the summer outdoor thermal environment of four representative elderly care centers in Tianjin to establish the thermal demand of seniors. The different thermal effects of greenery types (GTs) were revealed in elderly care centers. To improve the quality of the outdoor recreational space, this study utilized numerical simulation to quantitatively establish the influence of tree-shrub coverage rate (TSCR) on the thermal comfort of seniors. The results showed that the thermal neutral physiologically equivalent temperature (PET) of elderly people was 27.0 °C in summer, and the thermal acceptance range of PET was 23.6–36.8 °C. Shrubs overall could significantly increase the tree's ability to improve the outdoor thermal environment. Furthermore, this study proposed different TSCR strategies. TSCR of the elderly care center should be greater than 31.5% to obtain great thermal acceptance for the elderly in summer; when the TSCR of the elderly care center could not reach 31.5% due to the reality, TSCR = 10.0% was the efficient strategy to improve outdoor thermal comfort. This research provided a scientific reference for the greenery configuration plan of elderly care centers in summer.

Heat-evolved microalgal symbionts increase thermal bleaching tolerance of coral juveniles without a trade-off against growth

Global climate change is threatening the persistence of coral reefs as associated summer heatwaves trigger the loss of microalgal endosymbionts (Symbiodiniaceae) from the coral tissues, or coral bleaching. We infected aposymbiotic juveniles of the coral Acropora tenuis with either wildtype (WT10) or heat-evolved (SS1 or SS8) Symbiodiniaceae strains Cladocopium proliferum (formerly referred to as Cladocopium goreaui and Cladocopium C1acro). After 10 months at 27 °C, SS8-juveniles were 2 × larger than SS1- or WT10-juveniles. In response to a simulated heatwave (31 °C for 41 days), the WT10-juveniles bleached and showed a decline in respiration while cell densities and respiration in both SS-juvenile groups remained unchanged compared to the controls. These results reveal that some heat-evolved strains can increase the bleaching tolerance of juvenile corals without a trade-off against growth. This response is opposite to the lower nutrient provisioning often reported for naturally thermotolerant Symbiodiniaceae (e.g. genus Durusdinium), thereby offering enhanced fitness to the host without the ecological consequences of diminished growth.

High-resolution data reveal a surge of biomass loss from temperate and Atlantic pine forests, contextualizing the 2022 fire season distinctiveness in France

Abstract. The frequency and intensity of summer droughts and heat waves in Western Europe have been increasing, raising concerns about the emergence of fire hazard in less fire-prone areas. This exposure of old-growth forests hosting unadapted tree species may cause disproportionately large biomass losses compared to those observed in frequently burned Mediterranean ecosystems. Therefore, analyzing fire seasons from the perspective of exposed burned areas alone is insufficient; we must also consider impacts on biomass loss. In this study, we focus on the exceptional 2022 summer fire season in France and use very high-resolution (10 m) satellite data to calculate the burned area, tree height at the national level, and subsequent ecological impact based on biomass loss during fires. Our high-resolution semi-automated detection estimated 42 520 ha of burned area, compared to the 66 393 ha estimated by the European automated remote sensing detection system (EFFIS), including 48 330 ha actually occurring in forests. We show that Mediterranean forests had a lower biomass loss than in previous years, whereas there was a drastic increase in burned area and biomass loss over the Atlantic pine forests and temperate forests. High biomass losses in the Atlantic pine forests were driven by the large burned area (28 600 ha in 2022 vs. 494 ha yr−1 in 2006–2021 period) but mitigated by a low exposed tree biomass mostly located on intensive management areas. Conversely, biomass loss in temperate forests was abnormally high due to both a 15-fold increase in burned area compared to previous years (3300 ha in 2022 vs. 216 ha in the 2006–2021 period) and a high tree biomass of the forests which burned. Overall, the biomass loss (i.e., wood biomass dry weight) was 0.25 Mt in Mediterranean forests and shrublands, 1.74 Mt in the Atlantic pine forest, and 0.57 Mt in temperate forests, amounting to a total loss of 2.553 Mt, equivalent to a 17 % increase of the average natural mortality of all French forests, as reported by the national inventory. A comparison of biomass loss between our estimates and global biomass/burned areas data indicates that higher resolution improves the identification of small fire patches, reduces the commission errors with a more accurate delineation of the perimeter of each fire, and increases the biomass affected. This study paves the way for the development of low-latency, high-accuracy assessment of biomass losses and fire patch contours to deliver a more informative impact-based characterization of each fire year.

Development and hygrothermal performance analysis of a novel eco-friendly insulating wall under various climatic conditions

This work proposes the development, characterization and modelling of new eco-friendly building walls integrating stabilized forms of phase change materials. The aim is to enhance the hygrothermal and energy performances of buildings by improving their management of thermal energy throughout the year and meeting users’ thermal comfort requirements. These are essential axes to help decarbonize heating and cooling, to rehabilitate buildings and to contribute to the energy transition. The experimental and numerical hygrothermal performances of two different building walls are assessed and compared under realistic weather conditions. The maximum temperature inside the wall is reduced by 2 °C for the phase change material hemp concrete compared to the reference hemp concrete in a context of typical summer heatwaves day. Both phase change material hemp concrete and reference hemp concrete showed good moisture regulation capability by dampening cyclic variations in outdoor humidity. The developed numerical model exhibited a good agreement with the experimental results with a maximum root mean square error between experimental and numerical results of about 0.6 °C and 6% for temperature and relative humidity, respectively.

Increasing impacts of summer extreme precipitation and heatwaves in eastern China

Increasing impacts of summer extreme precipitation and heatwaves in eastern China

Impact of Pacific–Japan pattern on temperature and heatwave events in summer over Taiwan

AbstractThe prediction of heatwave events is vital to provide information on possible hazards caused by extremely high temperature. The Pacific–Japan (PJ) pattern is a significant climate variability that controls the summer climate over East Asia. Previous studies have reported that the meridional propagating wave structure associated with the PJ pattern can modulate summer temperature and heatwave characteristics over northeast Asian countries, such as Korea and Japan. Nevertheless, its impacts on the subtropical regions, including Taiwan, a mountainous subtropical island with an approximate population of 24 million, is not yet fully understood. In this study, we investigate the impacts of the PJ pattern on the summer temperature and heatwave characteristics in Taiwan on the interannual timescale using long‐term station‐based temperature and rainfall dataset. We found an island‐wide increase in temperature during the positive phase of the PJ pattern, which is characterized by an anticyclonic anomalous circulation over Taiwan. Meanwhile, the averaged effective area and frequency of heatwave extremes over Taiwan have increased significantly, indicating an increase of exposure to heatwaves. Our examinations of large‐scale environment suggest that the adiabatic warming due to subsidence anomaly associated with the anticyclone over Taiwan is primary contributor of surface warming, which is balanced by diabatic cooling and meridional advective cooling on a seasonal timescale. Our study consolidated the links between the PJ pattern as a climate driver, hot summers and increased summer heatwave events over Taiwan. By combining with the seasonal prediction systems and early warning systems, such understanding can help sectors that are vulnerable to heat stress to prepare for potential hazards.

Framework to assess climate change impact on heating and cooling energy demands in building stock: A case study of Belgium in 2050 and 2100

Climate change has a broad impact on different aspects of energy use in buildings. This study explores potential changes in future heating and cooling energy demands. Increasing comfort expectations resulting from events like the extraordinary summer heatwaves in Europe are accelerating this trend to develop future scenarios for a better understanding of the relationship between future climate changes and the cooling need. This study used future weather data to estimate the heating and cooling energy demands in the Belgian building stock by 2050 and 2100 under base and business-as-usual scenarios using a dynamic building simulation model. The study showed that heating energy demand in the base scenario is expected to decrease by 8% to 13% in the 2050s and 13% to 22% in the 2090s compared to the 2010s. Additionally, the cooling energy demand is expected to increase by 39% to 65% in the 2050s and by 61% to 123% in the 2090s compared to the 2010s. Retrofit strategies applied to different building types contribute to lower the increase in cooling energy demand in the business-as-usual scenario compared to the base scenario. The cooling energy demand for an average building in the business-as-usual scenario is expected to increase with a range of 25% to 71% in the 2050s compared to 45% to 92% in the base scenario and 77% to 154% in the 2090s compared to 72% to 198% in the base scenario compared to the 2010s. The findings of the study provide insights to mitigate the impacts of climate change on heating and cooling energy demands.

Projection of Future Heatwaves in the Pearl River Delta through CMIP6-WRF Dynamical Downscaling

Abstract Recent worldwide heatwaves have shattered temperature records in many regions. In this study, we applied a dynamical downscaling method on the high-resolution version of the Max Planck Institute Earth System Model (MPI-ESM-1-2-HR) to obtain projections of the summer thermal environments and heatwaves in the Pearl River Delta (PRD) considering three shared socioeconomic pathways (SSP1-2.6, SSP2-4.5, and SSP5-8.5) in the middle and late twenty-first century. Results indicated that relative to the temperatures in the 2010s, the mean increases in the summer (June–September) daytime and nighttime temperatures in the 2040s will be 0.7°–0.8°C and 0.9°–1.1°C, respectively. In the 2090s, the mean difference will be 0.5°–3.1°C and 0.7°–3.4°C, respectively. SSP1-2.6 is the only scenario in which the temperatures in the 2090s are expected to be lower than those in the 2040s. When compared with those in the 2010s, hot extremes are expected to be more frequent, intense, extensive, and longer-lasting in the future in the SSP2-4.5 and SSP5-8.5 scenarios. In the 2010s, a heatwave occurred in the PRD lasted for 6 days on average, with a mean daily maximum temperature of 34.4°C. In the 2040s, the heatwave duration and intensity are expected to increase by 2–3 days and 0.2°–0.4°C in all three scenarios. In the 2090s, these values will become 23 days and 36.0°C in SSP5-8.5. Moreover, a 10-yr extreme high temperature in the 2010s is expected to occur at a monthly frequency from June to September in the 2090s. Significance Statement Pearl River Delta (PRD) has been experiencing record-shattering heatwaves in recent years. This study aims to investigate the future trends of summer heatwaves in the PRD by modeling three future scenarios including a sustainable scenario, an intermediate scenario, and a worst-case scenario. Except for the sustainable scenario, summer temperatures in the intermediate and worst-case scenarios will keep increasing, and heatwaves will become more frequent, intense, extensive, and longer-lasting. In the worst-case scenario, extreme heat events that occurred once in 10 years in the 2010s will shorten to once a month in the 2090s. A better understanding of heatwave trends will benefit implementing climate mitigation methods, urban planning, and improving social infrastructure.

The summer heatwave in 2022 and its role in changing permafrost and periglacial conditions at a historic mountain pass in the Eastern Alps (Hochtor, Hohe Tauern Range, Austria).

Air temperatures in Europe in 2022 had been the highest on record for the meteorological summer season [June, July and August (JJA)], with +1.3°C above the 1991-2020 average. We studied the effects of recent warming on permafrost and periglacial conditions at a historical mountain pass in the Eastern Alps (Hochtor, 2,576 m asl, 47.08°N, 12.84°E). We used ground temperature data (2010-2022), repeated electrical resistivity tomography measurements (2019, 2022) and auxiliary data dating back to Roman times. We quantified permafrost conditions, evaluated frost-related weathering and slope processes and assessed the impact of atmospheric warming on it. Results show that summer ground surface temperatures increased by 2.5°C between 1891-1920 and 1991-2020, whereas frost-related weathering and periglacial processes decreased. The summers of 2003, 2015, 2019 and 2022 were the four warmest ones in 1887-2022. Hochtor changed in 2010-2022 from an active permafrost site to an inactive one with supra-permafrost talik. A general three-layer structure was quantified for all three ERT profiles measured. The middle, 5-10m thick layer is ice-poor permafrost detected in 2019, whose existence, although smaller, was confirmed in 2022. Resistivity decreased at the three profiles by 3.9% to 5.2% per year, suggesting permafrost degradation. We interpret the resistivity changes between the summers of 2019 and 2022 as a long-term signal of permafrost degradation and not as the single effect of the summer heatwave in 2022. As our data show how rapidly permafrost degrades and as we face an even warmer climate for the remaining part of the 21st century, we expect that near-surface permafrost at the Hochtor site will soon be history.

Season-dependent heatwave mechanisms: A study of southern China

Heatwaves are among the deadliest weather-related disasters. They are not only seen in summer but also may appear in spring and autumn, especially under climate warming. Although the mechanisms of summertime heatwaves have been extensively studied, how they differ from spring and autumn seasons and possibly season-dependent mechanisms of heatwaves are poorly understood. Here we examine the specific processes associated with spring, summer, and autumn heatwaves in southern China during 1961–2020. We show that heatwaves in all three seasons are intensifying in frequency, duration, and intensity, and they exhibit distinctly season-dependent circulation changes. Summer heatwaves are characterized by a warm-core high-pressure structure, while spring and autumn heatwaves exhibit a warm low pattern. Summer heatwaves are mainly triggered by the westward (eastward) extension of the western North Pacific subtropical high (South Asian high), and are accompanied by anomalous lower-level anticyclone and positive pressure anomalies. In contrast, spring and autumn heatwaves coincide with lower-than-normal pressure and anomalous southwesterly over East Asia, indicative of a weakening of the East Asian winter monsoon circulation and the Siberian high. Their developments are linked to the eastward movement of an upper-tropospheric wave-like pattern over the mid-latitudes. It is also found that autumn heatwaves are largely contributed by local preceding soil moisture deficit, in comparison to spring and summer heatwaves. Our findings contribute to a better understanding of the heatwave characteristics in different seasons and provide insights into their mitigation strategies.

The Cold Waters in the Port of Genoa (NW Mediterranean Sea) during the Marine Heatwave in Summer 2022

Extreme weather phenomena have become more frequent and intense in recent decades in the context of climate change, and these include heat waves that affect both the atmosphere and seawater masses. In 2022, a summer marine heatwave (MHW) affected the entire Mediterranean Sea, and temperatures up to 5 °C above seasonal mean were reached in the Ligurian Sea in the NW part of the Mediterranean basin. In this scenario, the waters of the Port of Genoa (at the northern apex of the Ligurian Sea) distinguished themselves by maintaining lower temperatures than those of the open sea (a maximum gradient of −6.1 °C on 9 August 2022) after the passage of a fast-moving storm. In this study, the weather and sea parameters of the period (June–December 2022) are analysed to determine the phenomenon that caused the drop in temperatures in the water masses of the Port of Genoa. The sudden cooling of the water masses inside the port was caused by a heavy rainfall event in early August. Moreover, the isolation of the port water masses due to the weak dynamics of the period kept them stationary and locked inside the port. Seawater temperatures inside the port slowly rose again after the event, remaining cooler than outside temperatures throughout August (−0.3 °C on 31 August), reaching and exceeding outside temperatures on 3 September (26.4 °C), and remaining warmer until 3 November 2022 (21.5 °C).