Extreme Heat Waves Research Articles

The synergistic effects of urbanization and an extreme heatwave event on urban thermal environment in Paris

In late July 2019, an extreme heatwave swept across the European regions. This study focused on examining the collective impacts of urbanization and this extreme heatwave on Paris's thermal environment. To achieve this, high-resolution simulations were performed using the urbanized version of the Weather Research and Forecasting (WRF) model. The inclusion of enhanced urban canopy parameters and improved spatial resolutions significantly improved the near-surface meteorological variables and the spatial-temporal patterns of the urban heat island in Paris. The impervious surface sensitivity study revealed that during the full-day sunlight conditions and low wind scenarios that characterized the extreme heatwave, the urban underlayer contributed to a 0.4 °C rise in daytime temperature and 1 °C increase during nighttime hours in the downtown area. Among the various representative Local Climate Zones (LCZ) types in Paris, namely compact mid-rise, large low-rise, and sparsely built, the contributions to temperature increase were about 0.3 °C (0.7 °C), 0.3 °C (0.5 °C), and 0.3 °C (0.6 °C) for daytime (nighttime) temperatures, respectively. The surface energy budget analysis further indicated that the augmented heat storage within urban impervious surfaces is one of the main causes of the enhanced urban heat island effect, particularly during the nighttime periods during heatwaves.

Frequency analysis of extreme air temperature events in an urban center in the Brazilian savanna

The increase in the planet's average air temperature in recent years has influenced the pattern of natural climatic phenomenons, with levels outside the normal range, the occurrence of prolonged dry periods, torrential rains and heat waves. Due to the climate crisis, extreme events have become increasingly frequent and more intense. With that in view, the aim of this article was to analyze the frequency of occurrence of extreme air temperature events between 2003 and 2023 in Cuiabá-MT-Brazil, as well as to understand the relationship between these extreme heat wave events and the occurrence and intensity of ENOS events. To this purpose, extreme events were analyzed using daily maximum air temperature data for the period from January 1, 2003 to October 31, 2023 obtained from the automated station of the National Meteorological Institute (INMET) located in Cuiabá - MT (CÓDA907), and ONI (Oceanic Niño Index) data. The results showed a significant increase of 86% in the occurrence of extreme events in 2020, compared to 2007, the year with the lowest number of occurrences. Therefore, it is extremely important that issues such as climate emergency, climate change and climate resilience are discussed as a means of public policy, preventing these increases from becoming even worse in frequency and/or intensity.

Global vegetation, moisture, thermal and climate interactions intensify compound extreme events

Compound extreme events, encompassing drought, vegetation stress, wildfire severity, and heatwave intensity (CDVWHS), pose significant threats to societal, environmental, and health systems. Understanding the intricate relationships governing CDVWHS evolution and their interaction with climate teleconnections is crucial for effective climate adaptation strategies. This study leverages remote sensing, reanalysis data, and climate models to analyze CDVWHS during historical (1982–2014), near-future (2028–2060), and far-future (2068–2100) periods under two Shared Socioeconomic Pathways (SSP; 245 and 585). Our results show that reduced vegetation health, unfavorable temperature conditions, and low moisture conditions have negligible effects on vegetation density. However, they worsen the intensity of heatwaves and increase the risk of wildfires. Wildfires can persist when thermal conditions are poor despite favorable moisture levels. For example, despite adequate moisture availability, we link the 2012 Siberian wildfire in the Ob basin to anomalous negative thermal conditions and concurrent unfavorable thermal-moisture conditions. In contrast, the Amazon experiences extreme and exceptional drought associated with unfavorable moisture conditions in the same year. A comparative analysis of Siberian and North American fires reveals distinct burned area anomalies due to variations in vegetation density and wildfire fuel. The North American fires have lower positive anomalies in burned areas because of negative anomalous vegetation density, which reduced the amount of wildfire fuel. Furthermore, we examine basin-specific variability in climate teleconnections related to compound CDVWHS, revealing the primary modes of variability and evolution of CDVWHS through climate teleconnection patterns. Moreover, a substantial increase in the magnitude of heatwave severity emerges between the near and far future under SSP 585. This study underscores the urgency for targeted actions to enhance ecosystem resilience and safeguard vulnerable communities from CDVWHS impacts. Identifying CDVWHS hotspots and comprehending their complex relationships with environmental factors are essential for developing effective adaptation strategies in a changing climate.

Changes in the parameters of extreme temperature events in the western part of the Russian Arctic according to ERA5 and MERRA-2 reanalyses in 1980–2022

The air temperature in the Arctic zone of Russia is increasing at a rate of 0.71 °C per decade, which is three times faster than the global average. The warming of climate is accompanied by an increase in its extremeness, which leads to an increase in the number of dangerous hydrometeorological phenomena. The most significant changes occurred in the statistics of large-scale summer heat waves in European Russia. One of the most important goals in studying current climate changes is to study the frequency of extreme hydrometeorological phenomena, in particular, heat or cold waves. In this paper, we investigate the average daily anomalies relative to the annual variation of air temperature at a height of 2 meters from the surface in the region of the western part of the Russian Arctic (60°–75° N, 30°–85° E), according to ERA5 and MERRA-2 atmospheric reanalyses for the period 1980–2022. Their root-mean-square deviations and the distribution of their average number per year are calculated. We have plotted the fields of average values and the rate of changes in the amplitude, duration and number of anomalous temperature events which exceed two standard deviations in the study region. Areas of increase and decrease in the amplitude, duration and number of extreme events, both with positive and negative temperature anomalies, are displayed. In general, it can be concluded that, on average, the amplitudes of positive extreme air temperature anomalies in the study area slightly increase. The duration of positive extreme anomalies is growing everywhere at a rate of 0.2 days per 10 years. The duration of negative extreme anomalies slightly decreases. The number of events with negative extreme anomalies has been decreasing at a rate of –0.5 to –3 events per year for 10 years, while the number of events with positive extreme anomalies has been increasing from 0.1 to 1 events per year for 10 years.The results obtained significantly expand our knowledge of the spatiotemporal features of the ongoing changes in the extreme climate of the western part of the Russian Arctic, which is of paramount importance for the analysis and forecasting of the development of natural and socio-economic systems in the region under study.

Seabirds boost coral reef resilience.

Global climate change threatens tropical coral reefs, yet local management can influence resilience. While increasing anthropogenic nutrients reduce coral resistance and recovery, it is unknown how the loss, or restoration, of natural nutrient flows affects reef recovery. Here, we test how natural seabird-derived nutrient subsidies, which are threatened by invasive rats, influence the mechanisms and patterns of reef recovery following an extreme marine heatwave using multiyear field experiments, repeated surveys, and Bayesian modeling. Corals transplanted from rat to seabird islands quickly assimilated seabird-derived nutrients, fully acclimating to new nutrient conditions within 3 years. Increased seabird-derived nutrients, in turn, caused a doubling of coral growth rates both within individuals and across entire reefs. Seabirds were also associated with faster recovery time of Acropora coral cover (<4 years) and more dynamic recovery trajectories of entire benthic communities. We conclude that restoring seabird populations and associated nutrient pathways may foster greater coral reef resilience through enhanced growth and recovery rates of corals.

Simulation of Temperature Extremes Over West Africa With MPAS

AbstractA large ensemble of 51 simulations with the Model for Prediction Across Scales (MPAS) has been applied to assess its ability to reproduce extreme temperatures and heat waves in the area of West Africa. With its global approach the model avoids transition errors influencing the performance of limited area climate models. The MPAS simulations were driven with sea surface temperature (SST) and sea ice extent as the only boundary condition. The results reveal moderate cold biases in the range from −0.6° to −0.9°C for the daily mean temperature and −1.2° to −2.0°C for the area mean of the daily maximum temperature. The bias in the number of tropical nights ranges from +3 to −10 days. An underestimation by up to 50% is also present regarding the number of summer days. The heat wave duration index is underestimated regionally by 10%–60%. MPAS simulations are generally closer to the reanalysis results than they are to the observational reference. The results from long term runs and from short term runs with selected SST years are similar. Shortcomings in the reproduction of the temperature and precipitation indices found in the present investigation indicate that the global MPAS approach does provide a fidelity similar to that of the regional climate models.

Nexus between heat wave, food security and human health (HFH): Developing a framework for livelihood resilience in Bangladesh

Bangladesh has been severely affected by the extreme heatwave that is affecting most of Asia. Extreme climate events, particularly heatwave impacts on the food system, pose risks to human health in Bangladesh, explicitly in the north-west part of the country. The association between the heatwave, food security and health are narrowly described in the existing literature, resulting in a research lacuna related diverse component of food system that are particularly vulnerable to the heatwave. The current study therefore aims to develop a framework for understanding the nexus between heatwave, food security, and human health, which will ultimately help to improve livelihood resilience in Bangladesh. A comprehensive literature review was conducted to examine the link between heat waves, food security including human health (HFH) to explore the vulnerabilities in the food system in Rajshahi, Bangladesh. Additionally, the current study conducted a case study on the tribal community (e.g., Santals) of Rajshahi to understand heatwave, food security and health nexus. There is evidence that critical activities in the food system are prone to risk to heat waves. It is complex how heatwaves propagate along the food system and impact elucidative dimensions of food security to impact human health impacts. Different types of disruption related to heatwave can indirectly affect human health by compromising food security, a critical factor of health. The case study of the current investigation reveals that human health can also be affected by the physical impact of the heat wave on the food system, particularly with regard to diet-related impacts and food-borne diseases within the tribal community. In the study, we propose to offer a novel analytical framework to examine and respond to the relationship between heat waves, food security and human health. The investigation provide a benchmark to policymakers, academia, and relevant stakeholders to examine and understand current and future heatwave risks and to develop adaptation strategies to build livelihood resilience in Bangladesh explicitly for tribal community.

High Resolution WRF Modelling of Extreme Heat Events and Mapping of the Urban Heat Island Characteristics in Athens, Greece

In recent decades, large-scale urbanisation has developed rapidly, resulting in significant changes in the local and regional environment and climate. Large metropolitan areas worldwide induce significant changes in local atmospheric circulation and boundary layer meteorology by modifying the underlying surface characteristics and through the emission of anthropogenic heat and pollutants into the atmosphere. We investigate the urban heat island (UHI) characteristics in the city of Athens, Greece, which is one of Europe’s largest metropolitan complexes with a population of approximately 3.7 million inhabitants. The UHI effect is intense due to the city’s size, dense construction, high incident solar radiation, and almost complete lack of natural vegetation, with previous studies suggesting a temperature rise of 4 °C on average in the city centre compared to summer background conditions. We used high-resolution WRF simulations (1-km horizontal grid) driven with ERA5 reanalysis data to produce surface temperature maps in the city of Athens and the surrounding areas (Region of Attiki) during the summer period of 1 July–20 August 2021. Different model parameterizations were tested, both with respect to urban characteristics and physical parameters. The daily minimum and maximum temperatures (Tmin and Tmax) derived from the model were validated against observational data from a dense network of weather stations covering metropolitan Athens and surrounding locations. We further investigate the influence of different meteorological conditions on the UHI gradients as produced by the model and the observational dataset, including the extreme heat wave of 28 July–5 August 2021, during which persistent maximum temperatures of &gt;40 °C were recorded for nine consecutive days. The results indicate a strong correlation between WRF output and recorded minimum and maximum temperatures throughout the test period (R ranges from 0.80 to 0.93), with an average mean absolute bias (MAB) of 1.5 °C, and reveal the intensity and spatiotemporal variability of the UHI phenomenon in the city of Athens, with UHI magnitude reaching 8–9 °C at times. Our work aims to maximise the potential of using high-resolution WRF modelling for simulating extreme heat events and mapping the UHI effect in large metropolitan complexes.

Teleconnections link to summer heat extremes in the south-central U.S.: Insights from CMIP5 and CMIP6 simulations

This study examines the relationship between teleconnections, which represent quasiperiodic modes of large-scale atmospheric and oceanic variability, and extreme heatwaves in the south-central (SC) U.S. region, aiming to understand multiyear variability in the heat extremes. Observational data and model simulations reveal that soil water has a stronger influence on surface air temperature in the SC region than individual teleconnections, though not as strong as their combined influence. Particularly, the Pacific North America (PNA), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO) teleconnections have a substantial impact on surface air temperature in the region through anomalous anticyclonic circulation, during their negative phases. The wave-activity flux analysis shows that the wave train associated with the PNA teleconnection originates from the extratropical North Pacific Ocean, likely influenced by sea surface temperature (SST) forcing. Similarly, the wave packet linked to the PDO pattern originates from the central Pacific Ocean in the middle latitudes. In contrast, the wave train related to the NAO pattern exhibits little connection to SST forcing, originating from Greenland and propagating across Europe, Russia, the North Pacific, and North America. While climate models generally capture the PNA and PDO wave trains, they struggle to accurately simulate the NAO wave train across the North Pacific Ocean towards North America. This indicates the current generation of climate models face challenges in representing the complex dynamics underlying the NAO wave train.

Spatial characterization of global heat waves using satellite-based land surface temperature

The warming world greatly suffers the increase of frequency, severity and duration of heat wave events, which would cause the significant societal and environmental damages and implications from local to global scales. In order to eliminate the limitations of site observations in accurate spatial extent identification and large scale monitoring, this study tried to investigate global heat waves in 2018 using spatial datasets of land surface temperature (LST) derived from AQUA TIR sensors. A 15-year daily maximum LST dataset was used to identify the hot days and heat wave events using the relative threshold method based on the probability density function analysis of LST sequences, then they were adopted in analyzing spatial patterns of duration, frequency and intensity of heat wave events using heat wave numbers (HWN), the frequency of the appeared heat wave days (HWF) and the amplitude of heat wave impacts (HWA) indices, respectively. Our results indicated that more heat wave events and longer heat wave duration happened in low and middle latitudes under the warmer land surface in 2018 than last decade, especially many heat wave events occurred in the environmentally fragile regions and the dense population area. Urban regions achieved the largest HWA by 45.5 ± 6.9℃. Both annual HWF and HWN highlighted seven hot spot regions influenced by heat waves, and most of them distributed around the latitude 30°N and the latitude 30°S. Extreme heat wave of hot spot regions in the Southern Hemisphere mainly happened in winter and spring in contrast to that in North Hemisphere appeared in summer and autumn. Dry climate could contribute to the occurrence of heat waves, and heat wave indices variations also implied the compound consequences between heat waves and drought. Our findings demonstrate that remote sensing datasets are capable of providing the continuous whole-Earth coverage of heat wave changes, and they would play more important roles in preventing or mitigating the impacts of extreme heat events on people and natural environment.

Do abrupt cryosphere events in High Mountain Asia indicate earlier tipping point than expected?

Tipping points of about 16 elements have been identified in Earth system, yet cryospheric tipping point of specific Alpine region has not been studied. Here we analyzed three tipping elements (mountain glacier, snow cover, and permafrost) identified in recent years, evidenced by the facts of frequent occurrence of abrupt massive collapse of glacier mass and the widespread thermakarst of permafrost. Since 2015, strikingly abrupt cryosphere events (ACEs) have been consistently observed over a large range of High Mountain Asia (HMA). Those events were unprecedentedly significant in history, leading to collapses of glaciers following by disconnection of glacier tongue from accumulation basin and recession of thermakarst towards higher elevation. Strong decreasing of snow depth in 2022 was also observed since 2021/2022 winter, coinciding with extreme warming of the year. The widespread high warming rates in the last two decades over HMA might have triggered above ACEs. The dynamic thresholds of ACEs depend largely on high temperature, especially extreme heat wave, for both glaciers and permafrost, closely related to meltwater as a key factor for reaching initial conditions of abrupt changes, suggesting HMA cryosphere is a tipping element under the global warming level of 1.1 °C. The ACEs can cause tremendous damage to local ecosystem and socioeconomy, measures to mitigate risks should be taken when the tipping points are reached.

Understanding the Magnification of Heatwaves over Spain: Relevant changes in the most extreme events

Heatwaves (HW) are a growing climate change-related risk affecting people's lives every year. A consensus exists about the magnification of this phenomena under climate change; however, less is known about their regional-to-local evolution characteristics' undermining appropriate policy and preparedness actions.This study investigates, from 1951 to 2019, regional changes in the occurrence and characteristics of HWs over peninsular Spain and the Balearic Islands (PSBI), highly exposed to climate change. State-of-the-art high-resolution observations provided by the SPAIN02 gridded data set are used for this purpose. Our results show an indisputable magnification of the HW phenomena but with relevant regional differences in the evolution of their characteristics. HWs occur two times more frequently inland, while most intense events take place in coastal areas. More extreme HWs in terms of frequency, maximum intensity, duration, and spatial extent are identified, rather than a progressive intensification in time affecting all HWs population. In the last decades, high frequencies are 8 times more likely, unprecedented high intensities are registered, the yearly maximum spatial extent is larger than ever and the probability to have a long-duration event has doubled. All of this is in the context of a longer HW season, increasing at a rate of about 4 days/decade, particularly in its onset. About 75% of the most severe and impactful HWs occurred after 1985. The most severe HWs, generally, are found not to be the most harmful to human health. This study highlights the importance of detailed knowledge of the spatiotemporal characteristics of HWs to accurately inform local practice for the effective design and implementation of adaptation plans.

Zonally asymmetric component of summer surface temperature trends caused by intraseasonal time-scale processes

Recent years have witnessed extreme heatwaves in Europe and western North America. This study shows that these regions stand out in the zonally asymmetric component of the long-term trend of boreal summer surface temperature, and that intraseasonal timescale processes play an important role in shaping the zonally asymmetric trend pattern. However, these two regions have warmed by different mechanisms. Over Europe, the warming is mostly caused by the positive trend of the net (downward minus upward) surface shortwave radiation weighted by its intraseasonal timescale connection with the skin temperature. The long-term warming in western North America has been caused by the declining surface latent heat flux (weakened evaporative cooling) weighted by its intraseasonal connection with the skin temperature. These mechanisms are consistent with those identified in earlier studies of individual extreme events in the two regions, indicating that part of the long trends are a manifestation of extreme events. The overall findings indicate that to make accurate projections of regional climate change using climate model simulations, it is critical to ensure that the models also accurately simulate intraseasonal variability.

Cool roof strategies for urban thermal resilience to extreme heatwaves in tropical cities

Extreme heatwaves in tropical cities represent a significant short-term weather challenge, directly impacting urban heat, exacerbating human discomfort, and increasing energy demands. To alleviate this, meteorological adjustments utilizing reflective roofing technologies, such as cool roofs, can effectively mitigate heatwave-induced excess heat and enhance thermal comfort. This study assessed the effectiveness of cool roofs in cooling urban areas following heatwaves in Kolkata, India, using comprehensive city-scale simulations. The study presumed that the existing roofing materials, with a reflectivity of 0.15 and emissivity of 0.85, indicated the unmitigated condition. These materials were replaced with third-generation cool roof materials featuring a reflectivity of 0.80 and emissivity of 0.85, leading to a substantial improvement in urban meteorology and thermal comfort compared to the unmitigated state. Notably, during heatwave episodes, the most significant computed reductions in energy flux were 181.3 Wm−2, 16.6 Wm−2, 56.3 Wm−2, and 251.9 Wm−2 for sensible heat, latent heat, ground storage, and net inflow radiation, respectively. Consequently, this led to decreases of 2.3 °C, 6.1 °C, 21.8 °C, and 1.9 °C in urban thermal parameters during peak hours (14:00 LT) for ambient temperature, surface temperature, roof surface temperature, and urban canopy temperature, respectively. The maximum drops in the planetary boundary layer (PBL) were 130.6 m, 1978.5 m, and 1010.3 m for 6:00 LT, 14:00 LT, and 18:00 LT, with an average of 870.3 m. Cool roofs demonstrated their potential to minimize thermal stress during heatwave periods, showcasing a maximum drop in the heat stress index (HSI) of up to 1.5 °C in the morning. Furthermore, outdoor thermal comfort could be significantly enhanced by lowering the universal thermal comfort index (UTCI) at the near surface, resulting in reductions of up to 1.8 °C during peak hours. On average, there was a reduction in UTCI between day and night of approximately 1.2 °C and 0.7 °C in densely populated urban areas. Additionally, the study evaluated 32 case studies that focused on cool roof strategies, revealing remarkably consistent findings that suggest a plausible justification. These findings provide a valuable framework for urban planners and policymakers considering the integration of cool roofs-based heat reduction technology at the city scale.

Ensembles of climate simulations to anticipate worst case heatwaves during the Paris 2024 Olympics

The Summer Olympic Games in 2024 will take place during the apex of the temperature seasonal cycle in the Paris Area. The mid-latitudes of the Northern hemisphere have witnessed a few intense heatwaves since the 2003 event. Those heatwaves have had environmental and health impacts, which often came as surprises. In this paper, we search for the most extreme heatwaves in Ile-de-France that are physically plausible, under climate change scenarios, for the decades around 2024. We circumvent the sampling limitation by applying a rare event algorithm on CMIP6 data to evaluate the range of such extremes. We find that the 2003 record can be exceeded by more than 4 °C in Ile-de-France before 2050, with a combination of prevailing anticyclonic conditions and cut-off lows. This study intends to raise awareness of those unprecedented events, against which our societies are ill-prepared, in spite of adaptation measures designed from previous events. Those results could be extended to other areas of the world.

Size-dependent thermal limits in Australian hybrid abalone: implications for productivity shifts with ocean warming

Ocean warming and extreme heatwaves threaten marine species supporting commercial fisheries and aquaculture. Predicting the responses of these industries to chronic and acute warming depends on understanding which life stages are most vulnerable, the potential for stocks to adapt to changing thermal environments, and the availability of thermally adapted genotypes to help enhance stock resilience through strategic interventions. Here, we shed light on some of these knowledge gaps by quantifying the critical thermal maximum (CTmax) of ~ 10–210 g hybrid abalone (Haliotis rubra × H. laevigata) from two farms representing contrasting thermal environments from south-eastern Australia. CTmax was not dependent on body size or provenance (farm) when heating rates were rapid (1 °C per h), but a significant relationship between CTmax and body size was observed when heating rates were slower and more ecologically realistic (1 °C per 12 h). Histological analyses revealed a negative relationship between CTmax and the stage of gonadal development when abalone were exposed to chronic thermal stress conditions. These results suggest that marine heatwaves and ongoing ocean warming might favour smaller, less fecund animals in natural and farm settings. This could potentially impact future harvestable biomass, recruitment and population dynamics in wild-capture fisheries, and production of larger, high-value animals in farm settings. This study adds to a growing body of literature pointing to complex and often negative effects of climate change on commercial fisheries, and the potential need for interventions aimed at bolstering fisheries resilience against the effects of ocean warming.

Glo3DHydroClimEventSet(v1.0): A global‐scale event set of hydroclimatic extremes detected with the 3D DBSCAN‐based workflow (1951–2022)

AbstractThe emergency of global‐scale hydroclimatic extremes (i.e., meteorological droughts, extreme precipitations, heat waves and cold surges) and associated compound events has recently drawn much attention. A global‐scale unified and comprehensive event set with accurate information on spatiotemporal evolutions is necessary for better mechanism understanding and reliable predictions in sequential studies. Accordingly, this manuscript describes the first‐generation global event‐based database of hydroclimatic extremes produced with the newly proposed 3D (longitude–latitude–time) DBSCAN‐based workflow of event detection. The short name of this database is Glo3DHydroClimEventSet(v1.0), which is obtained from the FigsharePlus webpage (https://doi.org/10.25452/figshare.plus.23564517). The 1951–2022 ERA5‐based multiscale and multi‐threshold daily running datasets of precipitation and near‐surface air temperature are calculated and employed as the input data. A comprehensive event set of hydroclimate extremes is the output of the 3D DBSCAN‐based workflow. From perspectives of spatiotemporal evolutions, this event‐based database is also measured and attached with metric information. For case‐based validation, some recently reported hydroclimatic extremes (e.g., the 2020 summertime flood‐inducing Yangtze River extreme precipitation event) are employed and accurately detected in the Glo3DHydroClimEventSet(v1.0) database. Meanwhile, global‐scale spatiotemporal distributions are preliminarily analysed. For example, global‐scale event counts of extreme heatwaves displayed an increasing tendency since 2005, with a rapid increase after 2010. To sum up, this Glo3DHydroClimEventSet(v1.0) database may facilitate new scientific achievements concerning event‐based hydroclimatic extremes, especially in communities of atmosphere, hydrology, natural hazards and associated socioeconomics.

Trends, forecasting and adaptation strategies of climate change in the middle and west regions of Iraq

Climate change has placed considerable pressure on the residential environment, agricultural, and water supplies in different areas of the world, especially arid places such as Iraq. Iraq is one of the five most vulnerable countries in the world to climate change, where it has been encountering extremes heat waves during the most recent decades resulted in drought, desertification, and rivers dried up, which led to thousands of hectares to turn dry and yellow. This study aims to investigate the trends of climate change in the middle and western regions of Iraq and future expectations. The daily maximum temperature, minimum temperature, and precipitation are downscaled using the Long Ashton Research Station Weather Generator (LARS-WG) model. Five General Circulation Models (GCMs) from Coupled Model Intercomparison Project Phase 5 (CMIP5) are employed for three future periods: the near future (2021–2040), medium future (2051–2070), and far future (2081–2100), based on two scenarios of the Representative Concentration Pathways (RCP4.5 and RCP8.5) for four selected meteorological stations representing the study area. The outcomes of the calibration and validation of the model supported its skill and reliability to downscale precipitation and temperature time series for statistical indices (R2, RMSE and MBE) ranging between (0.894–0.998), (0.1270–1.9274) and (− 0.6158 to 0.0008), respectively. The results showed that the average minimum and maximum annual temperatures will increase at all selected stations across the three future periods by between 0.94 and 4.98 °C by the end of the twenty-first century. Annual changes in precipitation tend generally towards increase for the study area by average (6.09–14.31%) for RCP4.5 and (11.25–20.97%) for RCP8.5 Compared to the historical data (1990–2020). These findings can contribute to become more acquainted with the effects of climate change on the environment and encourage managers and planners to come up with plans for mitigating and adapting to these effects. They can also serve as a guide for future management of water and agricultural resources in the study region.

Intensification of heatwaves in Central Asia from 1981 to 2020 – Role of soil moisture reduction

Heatwaves pose increasing threats on water resources for ecosystems and human consumption especially in arid region, such as Central Asia (CA). As the hinterland of Eurasia, water scarcity and land degradation in CA have increased its vulnerability to heatwaves. While the frequency of heatwaves has been examined, more heatwave metrics such as timing are less known, possible influences of soil moisture on heatwave changes in this region are not fully understood. Using reanalysis and observational datasets, here we examine the spatial–temporal changes of heatwaves in CA during 1981–2020 and the role of various associated factors including soil moisture. The results show that the extreme heatwaves occurred more frequently in northwestern Kazakhstan. Temporally, heatwaves have been intensifying with significant increases in frequency (0.10 events/year), intensity (0.81 °C/year), and duration (0.08 days/year) since the 1980 s, and these trends have accelerated since 1997. The first yearly heatwave event tended to occur earlier in more recent decades, indicating an advanced heatwave season. We also found that the heatwave occurrences were significantly correlated with hydro-meteorological factors. In northwestern of CA, extreme heatwaves are exacerbated by a rapid decrease in soil moisture resulting from reduced precipitation and increased solar net radiation in this area. Our findings provide a scientific basis for understanding the mechanisms and predictions of heatwave in arid regions from the climate change perspective.

Contributions of Local Land‒Atmosphere Coupling and Mesoscale Atmospheric Circulation to the 2013 Extreme Flash Drought and Heatwave Compound Event Over Southwest China

AbstractThe flash drought and heat wave compound event of the 2013 summer in Southwest China was exceptional, with profound socio‒economic impacts. Existing studies have captured the signal of this compound event; however, its causes are still poorly understood. In this study, we utilized a high‐resolution index to examine the life cycle of this compound event from 1980 to 2020 and quantified the relative contributions of land‒atmosphere coupling and mesoscale atmospheric circulation using the air parcel backward tracking method. It was found that the dry soil caused by the precipitation deficit further inhibited precipitation and caused the soil to become even drier, which then led to the development of the flash drought. The dry soil induced a substantial increase in the land‒atmosphere sensible heat flux and a rise in the near‐surface air temperature. During this process, the strength of land‒atmosphere coupling was 2.5 standard deviations higher than the mean value of the climate, playing an integral role in the near‐surface air temperature increase, accounting for 55.9% of the maximum temperature changes. The mesoscale atmospheric circulation contributed 44.1%, of which horizontal advection accounted for 41.1%, while vertical advection only accounted for 3.0%. The western Pacific subtropical high expanded westward, accompanied by the northward‐moving westerly jet stream, which prevented cold air from accessing the Southwest China, and abnormal subsidence interfered with precipitation formation. Furthermore, the control of an abnormally high‐pressure system over the region led to a decrease in cloud cover, allowing more surface incident solar radiation and contributing to the increase in the near‐surface air temperature.