Extreme climate events such as heat waves cause enormous stress on human health and ecosystems and economic losses in agriculture, energy, or water management activities. In particular, the combined effect of above-normal nighttime temperatures and high humidity poses a high risk to human health. This is related to the thermal discomfort which prevents the human body’s recovery from daytime high-heat exposure. Seasonal forecasts of the nighttime heat waves might be used as a tool to anticipate these risks and to better manage their social and economic impacts. However, the ability of the seasonal forecast systems to predict these extreme events has not been explored so far. This work provides insight into the potential of four seasonal forecasting systems (CMCC Seasonal Prediction System 3.5, DWD System 2.1, ECMWF SEAS5, and Météo-France System 7) to provide skillful and reliable predictions of the nighttime heat waves in Europe during the boreal summer season. Different potential proxies for the assessment of nighttime heat waves have been considered: nighttime apparent temperature computed from temperature and humidity at night, the temperature at night, or daily minimum temperature. There are different indices that can be used to investigate extreme temperatures, but the one chosen in this study is very suitable for seasonal forecast analysis because it is invariant to the mean biases and provides an integrated view of the nighttime heat waves for the entire season with information on their duration, frequency, and intensity. The forecast quality assessment has revealed that state-of-the-art seasonal forecast systems are able to provide useful information on the nighttime heat waves in Southern Europe, which is a particularly vulnerable region where timely climate information can benefit the decision-making processes. 

How to cite: Torralba, V., Materia, S., Cavicchia, L., Álvarez-Castro, M. C., Scoccimarro, E., and Gualdi, S.: Seasonal forecasts of the nighttime heat waves in Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8146, https://doi.org/10.5194/egusphere-egu23-8146, 2023.

Extreme heat under the warming environment has direct societal implications for developing and highly urbanized populations. Previous studies have shown that extreme wet-bulb temperature, a multivariate measure of temperature-humidity, has led to anomalously high convective inhibition and increased precipitation intensity over the tropics. However, little is known about the linkage of humid heat stress characteristics, such as duration and peak heat stress, versus the sub-daily precipitation extremes over urban and periurban locations in the tropics. Leveraging ground-based meteorological records of around five decades from the 27 hydrometric observatories of the India Meteorological Department, I investigate the compound occurrence of humid heat stress versus sub-daily precipitation extremes across the Indian subcontinent (4 - 40° latitude and 65 - 100° longitude). Here heatwaves are identified when three or more consecutive days of extreme wet-bulb temperature, T_w, is above the 90^th percentile daily variable threshold for each day of the year.  I show the impact of heat stress and its duration on sub-daily precipitation extremes using a novel conditional probabilistic approach. The risk of sub-daily precipitation extremes at each urbanized location is modelled considering the nonstationarity of underlying drivers. The relative timings between each driver and duration overlap between heatwaves and above-average precipitation extremes (wet spells) are also shown. The results show that the extremal upper dependence between peak T_w and sub-daily precipitation extremes are significantly positive and lies in the range of 0.12 to ≥0.20 across the central northeast region that housed part of the Indo-Gangetic Plains. More than 40% of sites report the most coinciding occurrence of humid-heat stress versus sub-daily precipitation extreme, where each of these drivers readily overlapped each other with a lag time of fewer than two days. Further, I show that considering the magnitude of heat stress as a 10-year return period, even a moderate increase in duration will increase the probability of sub-daily precipitation extremes by a range of 1.7 to 20%, with a notable increase across coastal cities. These results are supported by the physically consistent theory suggesting an increase in sub-daily rainfall extremes in response to climate warming over lands of the tropics because of the combination of “positive thermodynamic” and “dynamic contributions.” The observational evidence of increased sub-daily precipitation extremes in response to humid heat stress would help stakeholders and international organizations build resilient strategies to mitigate the impacts of such consecutive hazards.

How to cite: Ganguli, P.: Observational Evidence Reveals Growing Spatial Scales of Compound Occurrence of Humid Heat Stress-Extreme Rainfall in India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-509, https://doi.org/10.5194/egusphere-egu23-509, 2023.

Heat waves can be one of the most dangerous climatic hazards affecting the planet; having dramatic impacts on the health of humans and natural ecosystems as well as on anthropogenic activities, infrastructures and economy. Based on climatic conditions in West Africa, the urban centers of the region appear to be vulnerable to heat waves. The goals of this work is firstly to assess the potential uncertainties encountered in heat waves detection; and secondly analyze their recent trend in West Africa cities during the period 1993-2020. This is done using two state-of-the-art reanalysis products, namely ERA5 and MERRA, as well as two local station datasets, namely Yoff Dakar in Senegal and Aéroport Félix Houphouët Boigny Abidjan in Ivory Coast. An estimate of station data from reanalyses is processed using an interpolation technique : the nearest neighbor to the station with a land sea mask >=0.5; the interpolated temperatures from local station in Dakar and Abidjan, show slightly better correlation with ERA5 than MERRA. Three types of uncertainties are discussed: the first type of uncertainty is related to the reanalyses themselves, the second is related to the sensitivity of heat waves frequency and duration to the threshold values used to monitor them; and the last one is linked to the choice of indicators and the methodology used to define heat waves. Three sorts of heat waves have been analyzed, namely those occurring during daytime, nighttime and both daytime and nighttime concomitantly. Four indicators have been used to analyze heat waves based on 2-m temperature, humidity, 10-m wind or a combination of these. We found that humidity plays an important role in nighttime events; concomitant events detected with wet-bulb temperature are more frequent and located over the north Sahel. For all indicators, we identified 6 years with a significantly higher frequency of events (1998, 2005, 2010, 2016, 2019 and 2020) possibly due to higher sea surface temperatures in the equatorial Atlantic ocean corresponding to El Nino events for some years. A significant increase in the frequency, duration and intensity of heat waves in the cities has been observed during the last decade(2012-2020); this is thought to be a consequence of climate change acting on extreme events

How to cite: Ngoungue Langue, C. G., Lavaysse, C., Vrac, M., and Flamant, C.: Heat waves monitoring over West African cities: uncertainties, characterization and recent trends, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3460, https://doi.org/10.5194/egusphere-egu23-3460, 2023.

Extreme values of wet bulb temperature are often used as indicators of heat stress for humans and other animals. However, humid heat extremes are fundamentally compound events, and a given wet bulb temperature can be generated by various combinations of temperature and humidity. Differentiating between extreme humid heat driven by anomalous temperature versus anomalous humidity is essential to identifying these extremes’ distinct physical drivers and preparing for their individual impacts. Extreme dry heat tends to occur due to processes such as blocking events and land surface feedbacks, and it has the potential to prime regions for wildfires and crop damage. In contrast, extreme humid heat depends more on strong moisture fluxes and vertical stability to moist convection, and it poses high risk for human health through its influence over heat stress.

Here we explore the variety of combinations of temperature and humidity contributing to heat extremes across the globe. In addition to using traditional metrics, we derive a novel thermodynamic state variable named “stickiness.” Directly analogous to oceanographic spice (which quantifies the relative contributions of temperature and salinity to a given seawater density), stickiness quantifies the relative contributions of temperature and specific humidity to a given wet bulb temperature.

Consistent across metrics, we find that extreme humid heat — that is, the occurrence of wet bulb temperatures sufficiently high to impact human health — tends to occur in the presence of anomalously high humidity. Although theoretically humid heat extremes can be achieved at low humidities if temperature is high enough, this tends not to happen in practice. Using stickiness allows for the direct evaluation of the spatial and temporal variability in the temperature- and humidity-dependence of humid heat events, a task that is more complicated and subjective using traditional variables. We identify locations with high variability in stickiness: these include the Persian Gulf, the western United States, and southeast Australia. These locations are key areas where the predictive skill for heat stress-related mortality may improve by considering fluctuations in atmospheric humidity in addition to dry bulb temperature.

How to cite: Ivanovich, C., Raymond, C., Horton, R., and Sobel, A.: Stickiness: A New Variable to Characterize the Temperature and Humidity Contributions toward Extreme Humid Heat, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10533, https://doi.org/10.5194/egusphere-egu23-10533, 2023.

Africa is particularly vulnerable to present day and future temperature extremes due to its (sub)tropical location, its growing population and the challenges of adapting to extreme heat in many of its regions. Globally, the vast majority of past research on the drivers of heatwaves is focused on dry bulb temperature extremes. The drivers of humid heat extremes vary by location and there is limited understanding of the drivers in all parts of the world, but particularly over Africa. Previous published research by the authors showed increased humidity, cloud, rainfall and/or evaporation drive events over most of Africa. However, across the central African equatorial belt, where absolute values of wet bulb temperature are highest, humid heat extremes are driven by both increased temperature and humidity, and cloud and rainfall anomalies are less important. Here we use ERA5 reanalysis to identify multi-day, large-scale humid heat events over different regions of Africa and quantify the roles of moisture transport, cloud, rainfall and atmospheric circulation. We compare and contrast the different sub-tropical and tropical climatic regions of Africa and present a detailed case study of coastal East Africa. East Africa is of particular interest due to its high climatological wet bulb temperatures, its high population, and its coastal location where the land-sea breeze may be a key control on humid heat extremes. We identify the time of day and locations in coastal East Africa that experience the highest daily maximum wet bulb temperatures and discuss the controlling factors.

How to cite: Birch, C., Keane, R., and Marsham, J.: Varying drivers of humid heat extremes over Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3523, https://doi.org/10.5194/egusphere-egu23-3523, 2023.

In 2018, a severe and long-lasting heatwave in East Asia resulted in significant socio-economic damage. To possibly reduce losses, it is necessary to understand the mechanisms of heatwaves and increase their predictability. In this study, we identify the patterns of geopotential height responsible for the 2018 East Asian heatwave from ERA5 observation and compare them with simulations using Global Seasonal Forecasting System version 6 (GloSea6). The K-means clustering analysis reveals an anomalous high-pressure pattern in Eastern Europe, which is mainly associated with the 2018 East Asian heatwave. GloSea6 experiments were then conducted with various initial conditions. Notably, GloSea6 runs reproducing the observed high-pressure anomaly in Eastern Europe shows a good prediction of the 2018 East Asian heatwave. Sensitivity experiments further highlight the lack of soil moisture in Eastern Europe seems to be a key factor for the anomalous high-pressure pattern there, resulting in the 2018 East Asian heatwave. Our results imply that model- and observation-consistent representations of soil moisture in Eastern Europe are required to reduce the uncertainty in predicting the East Asian heatwaves.

This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMI2020-01212. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No. 2022R1A2C1008858).

How to cite: Kang, J., Wie, J., Lee, S.-M., Lee, J., Kim, B.-J., Yun, S., and Moon, B.-K.: Effect of anomalous high-pressure in Eastern Europe on the prediction of 2018 East Asian heatwave, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5468, https://doi.org/10.5194/egusphere-egu23-5468, 2023.

Heatwaves are weather hazards which can influence societal and natural systems. Recently, heatwaves have increased in frequency, duration, and intensity, and this trend is projected to continue as a consequence of climate change. This has triggered extensive research aiming at a better understanding of their impacts and underlying processes. However, the study of heatwaves is hampered by the lack of a common definition, which limits comparability between studies. This applies in particular to the considered time scale. 

Here, we determine impact-relevant temporal scales of heatwaves. For this purpose we characterise societal metrics related to health (heat-related hospitalizations, mortality) as well as public attention (Google trends, news articles) in Germany. We calculate country-averaged temperatures and select the warmest periods of varying durations between 1 and 90 days. For each time scale, the societal response is assessed to find the heat wave durations with the most pronounced impacts. This way, we yield impact-relevant heat wave durations for Germany. The results differ slightly between the considered societal metrics but indicate overall that heat waves are most relevant at weekly to monthly time scales. Finally, we also compare impact-relevant heat wave durations between moderate and extreme heat waves, as well as between heat waves occurring individually or jointly with droughts.

Our methodology can be extended to other societal indices, countries, and hazard types to form more meaningful definitions of climate extremes in order to guide future research on these events.  An improved understanding of weather and climate hazards with their impacts on society, economy and environmental systems will support better communication for preparation, response, and future adaptation.

How to cite: De Polt, K., Ward, P. J., de Ruiter, M., Bogdanovich, E., Reichstein, M., Frank, D., and Orth, R.: Quantifying impact-relevant heatwave durations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12382, https://doi.org/10.5194/egusphere-egu23-12382, 2023.

Since 2000, numerous people have suffered from heat-related illness and even died of the heatwave, and more than thousands of people in Korea share the similar pain and loss since 2010. The extremely high temperature and humid are known to be responsible for illness and death; however, the spatial correlation between highest temperature and occurrence of heat-related illness seems relatively low according to the previous studies. There can be many reasons for this, one of which is social aspect. Another reason of the varying probability of occurrence can be the duration of the temperature. Therefore, in this paper, in order to analyze the impacts of persistent high temperatures on the occurrence of heatwave disease, we analyzed the number of days of heatwave days and tropical night days immediately preceding the date of the onset of heat-related illness. This research was supported by a grant(2020-MOIS35-002) of Policy-linked Technology Development Program on Natural Disaster Prevention and Mitigation funded by Ministry of Interior and Safety(MOIS, Korea).

How to cite: Baek, J., Lee, S., and Um, J. A.: Impact of Persistent Heatwave on Heat-Related Illness, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2554, https://doi.org/10.5194/egusphere-egu23-2554, 2023.

Current climate change projections show that the probability of occurrence and the magnitude of heat-wave events are increasing worldwide. These events have to be considered as higher risks for territories and ecosystems, especially where vulnerability is high. The occurrence of heat waves translates into several potential damages such as an increase in fatalities and production losses, degradation of natural and cultural heritages, or the triggering of other hazards such as wildfires. The overlap of all these consequences may lead to both relevant economic losses and additional CO₂ emissions affecting our resilience and exacerbating in turn climate change.
In this context, we propose a novel framework for the assessment of risks resulting from heat waves with the aim of quantifying the main contributions to economic losses and CO₂ emissions. This framework follows the conceptual definition of risk provided by the Intergovernmental Panel on Climate Change (IPCC) as the product of hazard, exposure, and vulnerability components. The newly-proposed formulation of these components includes the concept of Nature-Based Solutions (NBS) as strategies carried out to enhance our adaptive capacity in a sustainable and cost-effective way. Since NBS consist of natural features that are also exposed to heat waves, the entire life cycle of NBS is considered (i.e., the implementation, maintenance, and possible restorations). The proposed framework stands as a tool for assessing the local impacts of already-implemented or designed NBS in the current and future climate scenarios.

How to cite: Brogno, L., Barbano, F., Leo, L. S., and Di Sabatino, S.: A Novel Framework for the Assessment of Heat-Wave Risks and Nature-Based Solutions (NBS) Impacts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7995, https://doi.org/10.5194/egusphere-egu23-7995, 2023.

Heatwave episodes have severe consequences in the forms of excess mortality in many regions around the world, shortage of agricultural products, drastic changes in ecosystem function and health risks. Due to the global mean temperature rising, the acceleration of extreme temperature disturbing highly at the local scale level, particularly in urban areas. From an economic growth point of view, Major cities are contributing in terms of GDP more. Heatwaves have impacted European GDP significantly in recent years. Our work is to find the number of frequent heat wave days affecting cities which are contributing to the growth of the economy in terms of GDP and density of population wise in Europe over the near future, mid future and long future using the Apriori algorithm. The features of the heat wave and their attributes have been defined according to the criteria explained in ETCCDI. The dataset that contains heat wave days in Europe derived from EURO-CORDEX climate projections is used in this work.

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How to cite: Ramadoss, M., Kadow, C., Thirunavukkarasu, M., Chellathurai, S., Begum, S., Duraisamy, N., Bhadushah, A., and Rasheed, A.: Using Apriori Algorithm to Find the Number of Frequent Heat Wave Days Affecting Cities in Europe Over the Future Period, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4145, https://doi.org/10.5194/egusphere-egu23-4145, 2023.