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Extreme Temperature Event (extreme + temperature_event)

Distribution by Scientific Domains
Life Sciences57%
Earth and Environmental Science42%

Selected Abstracts

Disentangling effects of an experimentally imposed extreme temperature event and naturally associated desiccation on Arctic tundra

FUNCTIONAL ECOLOGY, Issue 6 2006
F. L. MARCHAND
Summary 1Climate projections suggest that extreme events will increase in frequency during this century. As tundra is recognized to be among the most vulnerable biomes, we exposed patches of arctic tundra vegetation to an experimental heatwave (by infrared irradiation), followed by a recovery period. The heating increased the surface temperature with an average of 7·6 °C during 13 days, which slightly exceeded the longest climatic episode with such a temperature deviation since 1961. 2The heatwave decreased stomatal conductance (gs) and PSII maximum efficiency (Fv/Fm), although there were differences in response among the four target species. Salix arctica Pall. (shrub) was affected during the heatwave and could not recover. In Carex bigelowii Tor. ex Schwein (sedge) and Pyrola grandiflora Radius (forb), on the other hand, the effects on gs and Fv/Fm became clear, particularly in the aftermath of the heatwave, whereas Polygonum viviparum L. (forb) was never stressed. 3Effects of the heat on gs were mainly indirect, through increased desiccation, whereas effects on Fv/Fm were more related to leaf temperature (although not in all species). The observed changes can therefore probably be ascribed to a combination of heat and drought causing dysfunctions that ultimately led to senescence. 4Two conclusions of this study, species-specific responses and increased leaf mortality, indicate that more frequent extreme temperature events accompanied by desiccation might alter/endanger tundra communities in a future climate. Predictions of global change effects on arctic ecosystems should therefore take into account the impact of extremes. [source]

Performance of High Arctic tundra plants improved during but deteriorated after exposure to a simulated extreme temperature event

GLOBAL CHANGE BIOLOGY, Issue 12 2005
Fleur L. Marchand
Abstract Arctic ecosystems are known to be extremely vulnerable to climate change. As the Intergovernmental Panel on Climate Change scenarios project extreme climate events to increase in frequency and severity, we exposed High Arctic tundra plots during 8 days in summer to a temperature rise of approximately 9°C, induced by infrared irradiation, followed by a recovery period. Increased plant growth rates during the heat wave, increased green cover at the end of the heat wave and higher chlorophyll concentrations of all four predominating species (Salix arctica Pall., Arctagrostis latifolia Griseb., Carex bigelowii Torr. ex Schwein and Polygonum viviparum L.) after the recovery period, indicated stimulation of vegetative growth. Improved plant performance during the heat wave was confirmed at plant level by higher leaf photochemical efficiency (Fv/Fm) and at ecosystem level by increased gross canopy photosynthesis. However, in the aftermath of the temperature extreme, the heated plants were more stressed than the unheated plants, probably because they acclimated to warmer conditions and experienced the return to (low) ambient as stressful. We also calculated the impact of the heat wave on the carbon balance of this tundra ecosystem. Below- and aboveground respiration were stimulated by the instantaneous warmer soil and canopy, respectively, outweighing the increased gross photosynthesis. As a result, during the heat wave, the heated plots were a smaller sink compared with their unheated counterparts, whereas afterwards the balance was not affected. If other High Arctic tundra ecosystems react similarly, more frequent extreme temperature events in a future climate may shift this biome towards a source. It is uncertain, however, whether these short-term effects will hold when C exchange rates acclimate to higher average temperatures. [source]

Variability of extreme temperature events in south,central Europe during the 20th century and its relationship with large-scale circulation

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2003
Peter Domonkos
Abstract The variability of winter extreme low-temperature events and summer extreme high-temperature events was investigated using daily temperature series (1901,98) from 11 sites in central and southern Europe. An extreme temperature event (EXTE) is defined by various threshold values of daily temperature or daily temperature anomaly. Systematic changes in the frequencies of EXTEs are investigated by the Mann,Kendall test and a method based on the Wilcoxon test. The catalogue of macrocirculation types over central Europe (the Hess,Brezowsky classification) is applied to investigate the connections between EXTEs and large-scale circulation. Circulation classes (HBC) are defined, and mostly spatial averages of EXTEs are examined. There were large long-term fluctuations in the frequencies of both winter extreme cold events (EXCEs) and summer extreme warm events (EXWEs) during the 20th century. The systematic changes referring to the entire period indicate a slight warming tendency, but only a few of the changes, mostly in the northernmost sites, are statistically significant. Strong connections are present between the frequencies of EXTEs and the large-scale circulation on various time scales, particularly for EXCEs. The spatial differences of EXTE fluctuations and EXTE,HBC connections are small within the study area. Northerlies and easterlies, as well as meridional and anticyclonic situations, are favourable for EXCEs, whereas southerlies and persistent anticyclonic situations are favourable for EXWE occurrences. In the latest decades, a decline in the frequency of EXCEs and a sharp increase in the frequency of EXWEs happened, and the residence times of the circulation patterns over central Europe became longer both in winter and summer. Copyright © 2003 Royal Meteorological Society [source]

Lack of Interaction between Extreme High-Temperature Events at Vegetative and Reproductive Growth Stages in Wheat

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 3 2003
B. Wollenweber
Abstract Increased climatic variability and more frequent episodes of extreme conditions may result in crops being exposed to more than one extreme temperature event in a single growing season and could decrease crop yields to the same extent as changes in mean temperature. The developmental stage of the crop exposed to increased temperatures will determine the severity of possible damage experienced by the plant. It is not known whether or not the damaging effects of heat episodes occurring at different phenological stages are additive. In the present study, the interaction of high-temperature events applied at the stages of double ridges and anthesis in Triticum aestivum (L.) cv. Chablis was investigated. Biomass accumulation of control plants and that of plants experiencing high temperatures during the double-ridge stage were similar and were reduced by 40 % when plants were subjected to a heat event at anthesis. Grain number on the main and side tillers declined by 41 %, and individual grain weight declined by 45 % with heat stress applied at the double-ridge stage and anthesis or at anthesis alone. The harvest index was reduced from 0.53 to 0.33. Nitrogen contents in leaves were reduced by 10 % at the double-ridge stage and by 25 % at anthesis. The maximum rates of CO2 assimilation increased with heat stress at the double-ridge stage and higher rates were maintained throughout the growing season. The results clearly indicate that an extreme heat event at the double-ridge stage does not affect subsequent growth or the response of wheat to heat stress at anthesis. [source]

Disentangling effects of an experimentally imposed extreme temperature event and naturally associated desiccation on Arctic tundra

FUNCTIONAL ECOLOGY, Issue 6 2006
F. L. MARCHAND
Summary 1Climate projections suggest that extreme events will increase in frequency during this century. As tundra is recognized to be among the most vulnerable biomes, we exposed patches of arctic tundra vegetation to an experimental heatwave (by infrared irradiation), followed by a recovery period. The heating increased the surface temperature with an average of 7·6 °C during 13 days, which slightly exceeded the longest climatic episode with such a temperature deviation since 1961. 2The heatwave decreased stomatal conductance (gs) and PSII maximum efficiency (Fv/Fm), although there were differences in response among the four target species. Salix arctica Pall. (shrub) was affected during the heatwave and could not recover. In Carex bigelowii Tor. ex Schwein (sedge) and Pyrola grandiflora Radius (forb), on the other hand, the effects on gs and Fv/Fm became clear, particularly in the aftermath of the heatwave, whereas Polygonum viviparum L. (forb) was never stressed. 3Effects of the heat on gs were mainly indirect, through increased desiccation, whereas effects on Fv/Fm were more related to leaf temperature (although not in all species). The observed changes can therefore probably be ascribed to a combination of heat and drought causing dysfunctions that ultimately led to senescence. 4Two conclusions of this study, species-specific responses and increased leaf mortality, indicate that more frequent extreme temperature events accompanied by desiccation might alter/endanger tundra communities in a future climate. Predictions of global change effects on arctic ecosystems should therefore take into account the impact of extremes. [source]

Performance of High Arctic tundra plants improved during but deteriorated after exposure to a simulated extreme temperature event

GLOBAL CHANGE BIOLOGY, Issue 12 2005
Fleur L. Marchand
Abstract Arctic ecosystems are known to be extremely vulnerable to climate change. As the Intergovernmental Panel on Climate Change scenarios project extreme climate events to increase in frequency and severity, we exposed High Arctic tundra plots during 8 days in summer to a temperature rise of approximately 9°C, induced by infrared irradiation, followed by a recovery period. Increased plant growth rates during the heat wave, increased green cover at the end of the heat wave and higher chlorophyll concentrations of all four predominating species (Salix arctica Pall., Arctagrostis latifolia Griseb., Carex bigelowii Torr. ex Schwein and Polygonum viviparum L.) after the recovery period, indicated stimulation of vegetative growth. Improved plant performance during the heat wave was confirmed at plant level by higher leaf photochemical efficiency (Fv/Fm) and at ecosystem level by increased gross canopy photosynthesis. However, in the aftermath of the temperature extreme, the heated plants were more stressed than the unheated plants, probably because they acclimated to warmer conditions and experienced the return to (low) ambient as stressful. We also calculated the impact of the heat wave on the carbon balance of this tundra ecosystem. Below- and aboveground respiration were stimulated by the instantaneous warmer soil and canopy, respectively, outweighing the increased gross photosynthesis. As a result, during the heat wave, the heated plots were a smaller sink compared with their unheated counterparts, whereas afterwards the balance was not affected. If other High Arctic tundra ecosystems react similarly, more frequent extreme temperature events in a future climate may shift this biome towards a source. It is uncertain, however, whether these short-term effects will hold when C exchange rates acclimate to higher average temperatures. [source]

Variability of extreme temperature events in south,central Europe during the 20th century and its relationship with large-scale circulation

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2003
Peter Domonkos
Abstract The variability of winter extreme low-temperature events and summer extreme high-temperature events was investigated using daily temperature series (1901,98) from 11 sites in central and southern Europe. An extreme temperature event (EXTE) is defined by various threshold values of daily temperature or daily temperature anomaly. Systematic changes in the frequencies of EXTEs are investigated by the Mann,Kendall test and a method based on the Wilcoxon test. The catalogue of macrocirculation types over central Europe (the Hess,Brezowsky classification) is applied to investigate the connections between EXTEs and large-scale circulation. Circulation classes (HBC) are defined, and mostly spatial averages of EXTEs are examined. There were large long-term fluctuations in the frequencies of both winter extreme cold events (EXCEs) and summer extreme warm events (EXWEs) during the 20th century. The systematic changes referring to the entire period indicate a slight warming tendency, but only a few of the changes, mostly in the northernmost sites, are statistically significant. Strong connections are present between the frequencies of EXTEs and the large-scale circulation on various time scales, particularly for EXCEs. The spatial differences of EXTE fluctuations and EXTE,HBC connections are small within the study area. Northerlies and easterlies, as well as meridional and anticyclonic situations, are favourable for EXCEs, whereas southerlies and persistent anticyclonic situations are favourable for EXWE occurrences. In the latest decades, a decline in the frequency of EXCEs and a sharp increase in the frequency of EXWEs happened, and the residence times of the circulation patterns over central Europe became longer both in winter and summer. Copyright © 2003 Royal Meteorological Society [source]