Frequency Of Extreme High Temperature Events Research Articles

Exponential increases in high-temperature extremes in North America

Global warming in the 21st century will alter the frequency of extreme climatic events, such as high-temperature anomalies and “heat waves”. Observations of extreme high temperatures during recent decades have detected upward trends in their frequency of occurrence, and recent state-of-the-art Global Climate Models (GCMs), e.g., Climate Model Intercomparison Projects (CMIPs), notably CMIP5 and CMIP6, have predicted acceleration of temperature trends and high-temperature events by 2100 under projected greenhouse-gas emission scenarios. Hence, the 21st century is expected to experience substantial shifts in the occurrence of extreme events, where present-day, extreme-but-rare high-temperature events will become common during the summer months. The increasing frequency of extreme heat may affect the health and resiliency of social, biological, and infrastructure systems in many regions worldwide, underscoring the need for accurate and reliable long-term assessments of climatic change across global and regional scales. So far, many investigations of high-temperature extremes have been carried out under end-point scenarios, e.g., by comparing GCM-projected changes in the frequency of high-temperature extremes expected in the late 21st century to the late 20th century. In this study, we use extreme value theory and decades of observations of high-temperature extremes at thousands of meteorological stations across North America to investigate continuous shifts in the frequency of extreme high-temperature events due to projected local warming trends. We find that the odds of exceedance of 50-year extreme high-temperature events increases exponentially with increases in mean local temperature. At a majority of the stations studied here, a local mean temperature increase of 0.5–1 ^{circ }C can double the odds of exceedance of 50-year extreme high-temperature events. Based on time-dependent temperature projections, the odds of exceedance of 50-year extreme high-temperature events doubles approximately every 20 years (or sooner) for sim 96% of the stations. Moreover, we find that, for sim 80% of the stations in North America, investigated here, the 50-year extreme high-temperature events will be exceeded annually before 2100.

Interdecadal Variation of Spring Extreme High-Temperature Events in the Western Tianshan Mountains and Its Relationship with the Tropical SST

This study performed an observational analysis to examine the interdecadal variation in the frequency of extreme high-temperature events (EHEs) during spring over the western Tianshan mountain, China, which were characterized by relatively fewer (more) EHEs during 1983–1996 (2000–2015). A composite analysis indicated that the interdecadal increase in EHEs is closely related to a deep dynamic anomalous Iranian high. Under the control of this high system, the water vapor content decreased over the western Tianshan mountains, and atmospheric circulation was dominated by a descending motion. Both were attributed to the decreased cloud cover, inducing a cloud-forced net solar radiation increase. The short-wave radiation flux and sensible heat flux reaching the surface increased, and the net surface heat flux increased cumulatively, which was conducive to the surface temperature increase and EHE occurrence. The anomalous Iranian high responsible for ECEs occurrence was related to the air-sea interaction over the Atlantic and Indo-Pacific. The latitudinal sea surface temperature (SST) difference between the tropical western Pacific and the western Indian Ocean directly strengthens the Walker circulation and thus enhances the Iranian high. In addition, the anomalous Iranian high was affected by the atmospheric wave trains at middle latitude, which was triggered by the warm anomaly of the Atlantic SST.

Relation of Mid-High-Latitude Eurasian ISO to Ural Blocking Frequency and Their Co-Effect on Extreme Hot Events during Boreal Summer

Based on NCEP reanalysis daily data during 1979–2018, the spatiotemporal evolution of the 10–30-day atmospheric intraseasonal oscillations (ISO) at mid-high-latitude Eurasia and its effect on the Ural blocking frequency are investigated. The co-effect of the blocking and ISO on extreme hot event frequency is also investigated. The ISO exhibits two modes of eastward and westward propagation. During the eastward (westward) propagating mode, the northwest–southeast tilted quadrupole (east–west dipole) quasi-barotropic geopotential height anomaly coupled with the air temperature anomaly at the troposphere propagates southeastward (westward). The phase composite shows that, during both modes, the mid-high-latitude low-frequency Rossby wave trains significantly affect the frequency of the European blocking during the propagating journey. The most frequent European blocking appears in phase 2 during both the eastward- and westward- propagating mode. Compared with the situation without the Ural blocking, the blocking activity results in the positive geopotential height anomalies throughout Europe and north of 60° N in the Ural Mountains and the negative geopotential height anomalies in the south of 60° N in the Ural Mountains and north of the Japan Sea. The occurrence of Ural blocking is conducive to the occurrence of extreme high-temperature events in Europe and the high latitudes of the Ural Mountains, and a reduced frequency of extreme high-temperature events in the mid-latitudes of the Ural Mountains and north of the Japan Sea. Therefore, the Ural blocking activities significantly regulate the effect of the two propagating ISO modes on the extreme hot events over the middle and high latitudes of Eurasia.

Future changes of the extreme high‐temperature events influenced by foehn winds in Niigata, Japan

AbstractThis study quantifies the future changes in extreme high‐temperature events (ETE) influenced by foehn winds in Niigata, Japan, using numerical and sensitivity experiments based on regional climate modelling. Numerical simulations suggest that the contribution of foehn winds to ETEs is approximately 3.5°C in both the baseline (past) and future climate, and hence it remains unaffected by future climate change; however, the frequency of ETEs is influenced by foehn winds may increase by a factor of 1.5. This is due to the fact that the pressure gradient between land and sea (i.e., the pressure gradient driving the sea breezes) is expected to decrease during the daytime in the future, making it easier for foehn winds to reach Niigata; it also suggests that foehn winds, due to their high‐pressure pattern, which is easily affected by the weakening of the sea breezes, may increase in the future. Overall, to evaluate the regional effects of climate change, it is necessary to understand how future changes in local circulation will impact future changes in the regional climate.

Increased Interannual Variability in the Dipole Mode of Extreme High-Temperature Events over East China during Summer after the Early 1990s and Associated Mechanisms

Abstract The dominant mode of the interannual variability in the frequency of extreme high-temperature events (FEHE) during summer over eastern China showed a dipole mode with reversed anomalies of FEHE over northeastern and southern China. This study found that the interannual variability of this dipole mode underwent an interdecadal increase after the early 1990s. The anomalous atmospheric circulation responsible for the FEHE dipole mode was associated with the air–sea interaction over the western tropical Pacific and North Atlantic. Due to the weakened correlation between the SST in the tropical Pacific and in the Indian Ocean after the early 1990s, a meridional atmospheric wave train induced by the anomalous SST around the Maritime Continent (MCSST) was intensified during 1994–2013, which was also contributed by the increased interannual variability of MCSST. However, under the influence of the anomalous SST in the Indian Ocean concurrent with the anomalous MCSST, the meridional wave train was weakened and contributed less to the dipole mode during 1972–93. In addition, the dipole mode was associated with the atmospheric wave trains at middle to high latitudes, which were different during the two periods and related to different air–sea interaction in the North Atlantic. The interannual variability of the dipole mode induced by the associated SST anomalies in the North Atlantic during 1994–2013 was significantly larger than that during 1972–93. Therefore, the interannual variability of the dipole mode was increased after the early 1990s.

Interdecadal Variations in Extreme High–Temperature Events over Southern China in the Early 2000s and the Influence of the Pacific Decadal Oscillation

This study documents a sudden interdecadal variation in the frequency of extreme high–temperature events (FEHE) over southern China during summer in the early 2000s, which is characterized by a relatively small (large) FEHE during 1991–2000 (2003–2018). The composite analysis on the extreme high–temperature events (EHEs) over southern China indicates that the occurrence of EHEs is mainly influenced by increased downward surface net shortwave radiation, which is induced by the cloud–forced radiation anomalies associated with reduced cloud; the reduced cloud is attributed to anomalous descent motion and decreased water vapor content in the troposphere. Compared to the situation during 1991–2000, anomalous descent motion and decreased atmospheric water vapor content occurred over southern China in summer during 2003–2018, providing a more favorable climatic condition for EHEs. This interdecadal variation is associated with the strengthened Pacific Walker circulation after 2003. The Pacific decadal oscillation (PDO) is suggested to be an important driver for the above interdecadal variation, which shifted from a positive phase towards a negative phase after 2003. Numerical experiments demonstrate that a negative phase of PDO may induce a strengthened Walker circulation and anomalous atmospheric descent motion as well as water vapor divergence over Southern China.

Statistical Explanation for Trends in Extreme Summer Temperatures at Phoenix, Arizona

A reanalysis of the same Phoenix daily minimum and maximum temperature data examined by Balling et al. has been performed. As evidenced by substantial increasing trends in both the mean minimum and maximum temperatures, this area has experienced a marked heat island effect in recent decades. Balling et al. found that a statistical model for climate change in which simply a trend in the mean is permitted is inadequate to explain the observed trend in occurrence of extreme maximum temperatures. The present reanalysis establishes that by allowing for the observed decrease in the standard deviation, the tendency to overestimate the frequency of extreme high-temperature events is reduced. Thus, the urban heat island provides a real-world application in which trends in variability need to be taken into account to anticipate changes in the frequency of extreme events.