Warm Spells Research Articles

Is it possible to fit extreme climate change indices together seamlessly in the era of accelerated warming?

AbstractThis study examines the problematic impact of selecting a different base period (colder 1961–1990 vs. warmer 1988–2017), on the trend magnitude of widely used percentile‐based extreme temperature indices (e.g., warm/cold spells, warm/cold days and nights). The percentile‐based indices are part of a core set of indices (27 in total) that have become a common standard for monitoring climate change, as recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI). The indices were designed to be comparable across regions provided that similar analyses are employed. Unfortunately, the use of different base periods and periods of interest to explore local and global climate change undermines the comparability of findings across regions. When utilizing “day‐count” indices with fixed thresholds, the use of different base/reference periods changes the intercept without influencing the slope (for a given period length). However, this assertion does not hold with percentile‐based indices. Our analyses show that percentile‐based temperature indices (e.g., days with temperature below the 10th or above the 90th percentiles) are particularly susceptible to the problematic use of different base periods. Hence, using percentile‐based indices may have adverse effects on researchers' conclusions. The current paper reports the results of a comparative study that used different base periods for the most commonly used percentile‐based extreme temperature indices. It was found that the (negative) trend magnitude of the cold percentile‐based indices (frequency of cold days and nights and cold spells) is strongly amplified while the (positive) trend magnitude of the warm indices (frequency of warm days and nights and warm spells) is dramatically diminished when percentiles were derived from a base period that included records from the last two decades (e.g., 1981–2010, 1988–2017). These features are even more pronounced when the study period covers only the last 30–40 years.

Trends in Winter Warm Spells in the Central England Temperature Record

AbstractAn important impact of climate change on agriculture and the sustainability of ecosystems is the increase of extended warm spells during winter. We apply crossing theory to the central England temperature time series of winter daily maximum temperatures to quantify how increased occurrence of higher temperatures translates into more frequent, longer-lasting, and more intense winter warm spells. We find since the late 1800s an overall two- to threefold increase in the frequency and duration of winter warm spells. A winter warm spell of 5 days in duration with daytime maxima above 13°C has a return period that was often over 5 years but now is consistently below 4 years. Weeklong warm intervals that return on average every 5 years now consistently exceed ~13°C. The observed changes in the temporal pattern of environmental variability will affect the phenology of ecological processes and the structure and functioning of ecosystems.

Future heat waves over the Mediterranean from an Euro-CORDEX regional climate model ensemble

Heat waves are among the most relevant extreme climatic events due to their effects on society, agriculture and environment. The aim of this work is to improve our understanding of heat waves over the Mediterranean basin during the 21st century from an ensemble of Regional Climate Models (RCMs). Focus has been placed on sensitivities to forcing global models, emissions scenarios and the RCM resolution, being the first work based on Euro-CORDEX simulations to fully analyze future heat waves in the Mediterranean. Heat wave features are studied with Warm Spell Duration Index (WSDI, duration) and Heat Wave Magnitude Index daily (HWMId, intensity). Results indicate a large increase by the end of the century in both intensity and length of heat waves from all emissions scenarios, global models, and regional models at any resolution. Exceptional heat waves observed early on the century could then become normal by the end of this period. Forcing global models and emissions scenarios play a major role. Clear added value on spatial distribution and heat wave indices are obtained from global to regional models dynamical downscaling, related to the important coastal or orographic aspects widely present over the Mediterranean.

Assessment of changes in climate extremes of temperature and precipitation over Iran

Intense industrial activity has led to an increase in greenhouse gas concentration in the Earth’s atmosphere over the past few decades, whereby the climate change phenomenon has been recognized. Increasing greenhouse gases have been changing patterns and trends of extreme climate variables that are of great importance in agriculture, water resources, and environmental hazards. In the present study, the changes and trends in climate extremes of temperature and precipitation were evaluated based on various extreme-related indices over Iran. For this purpose, both daily temperature and precipitation data of 76 synoptic stations were selected for trend analysis throughout Iran during the period 1981–2010. The nonparametric Mann-Kendall trend test and Sen’s slope estimator are used to investigate the trends in the selected data sets. The results of 11 extreme temperature-related indices showed, in general, warm indices such as the number of warm days (TX90p), warm nights (TN90p), and warm spell duration (WSDI) had an increasing trend whereas trends in cold indices such as the number of cool days (TX10p), cool nights (TN10p), and cold spell duration (CSDI) decreased. The monthly maximum value of daily maximum (TXx) and minimum (TNx) temperatures increased by 0.3 and 0.4 °C/decade on average, respectively; and the monthly minimum value of daily maximum (TXn) and minimum (TNn) temperatures increased by 0.1 and 0.3 °C/decade, respectively, on average during the study period. In the case of the extreme precipitation-related indices, the results indicated both a decreasing trend in precipitation amount and intensity, and an increasing trend in the number of consecutive dry days (CDD) at most of the selected stations. Surveys demonstrated that the western, northern, and northwestern regions of Iran were most affected by the risk of climate extremes. Thus, these extreme changes will make people more vulnerable to natural hazards and make proper management in the face of climate crises more necessary.

Climatic risk in the Mexico city metropolitan area due to urbanization

The Mexico City Metropolitan Area (MCMA) had a rapid demographic and urban growth during the second half of the twentieth century that led to development of an intense Urban Heat Island (UHI). In the urbanized zone, the mean maximum and minimum temperatures have had significant increases of the order of 3 and 4°C during the last one hundred years. Even more, the areas of larger mean annual temperature approximately match the urbanization patters, showing the MCMA UHI has expanded to the eastern – northeastern and northwestern zones, along with the urbanization. There has also been a change in the precipitation regime over most of the city, since annual mean precipitation, for instance over the western part of the MCMA, has increased in almost 40% during the last century. In summary, the natural hazards related to warm spells (maximum temperature > 30 °C) or intense storms (precipitation > 20 mm/day) have increased along with the UHI. When some factors of the MCMA vulnerability are considered (i.e., loss of natural vegetation), it is concluded that the urban growth of the region has led to higher climatic risk and to more negative impacts, such as urban floods.

Extreme climate indices in Brazil: evaluation of downscaled earth system models at high horizontal resolution

This study evaluated the performance of 25 earth system models (ESMs), statistically and dynamically downscaled to a high horizontal resolution (0.25° of latitude/longitude), in simulating extreme climate indices of temperature and precipitation for 1980–2005. Datasets analyzed include 21 statistically downscaled ESMs from the National Aeronautics and Space Administration (NASA) Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) and dynamically downscaled Eta Regional Climate Model simulations driven by 4 ESMs generated by the Brazilian National Institute for Space Research (INPE). Downscaled outputs were evaluated against observational gridded datasets at 0.25° resolution over Brazil, quantifying the skill in simulating the observed spatial patterns and trends of climate extremes. Results show that the downscaled products are generally able to reproduce the observed climate indices, although most of them have poorest performance over the Amazon basin for annual and seasonal indices. We find larger discrepancies in the warm spell duration index for almost all downscaled ESMs. The overall ranking shows that three downscaled models (CNRM-CM5, CCSM4, and MRI-CGCM3) perform distinctively better than others. In general, the ensemble mean of the statistically downscaled models achieves better results than any individual models at the annual and seasonal scales. This work provides the largest and most comprehensive intercomparison of statistically and dynamically downscaled extreme climate indices over Brazil and provides a useful guide for researchers and developers to select the models or downscaling techniques that may be most suitable to their applications of interest over a given region.

Warm Spells and Climate Risk to Human Health in the Mexico City Metropolitan Area

AbstractDuring the second half of the twentieth century, rapid demographic growth and urban expansion led to the development of the Mexico City metropolitan area (MCMA) urban heat island (UHI). The thermal gradient between rural and urban regions is used to define the UHI in the transition zone along the 26°C isotherm of mean maximum temperature. As the MCMA expands, more natural vegetation is replaced with urbanization, and the spatial extent of the 26°C isotherm grows. The loss of natural vegetation, in a densely populated region of Mexico, leads to the formation of a canopy-layer UHI. The intensification of the MCMA UHI results in an increase in the frequency of daily maximum temperatures above 30°C (above 26°C on a weekly average), a threshold value that constitutes a natural hazard. Warm-spell occurrences are related to an increase in the number of acute diarrhea diseases (ADD), mainly in zones of the MCMA where the socioeconomic and environmental conditions are low (e.g., insufficient access to potable water). Vulnerable people are mostly located in new settlements along the periphery of the MCMA, where large numbers of hospital discharges due to ADD are reported. The combined effect of more frequent warm spells and increasing vulnerability results in higher levels of risk of suffering this type of health problem, mainly during the warmest part of the year. This analysis may serve to develop UHI mitigation strategies and early warning systems to manage high levels of ADD risk during warm spells.

A comprehensive statistical assessment of drought indices to monitor drought status in Bangladesh

In Bangladesh, drought has negative consequences on agriculture, environments, livelihood, and food security. However, a comprehensive statistical assessment of drought indices has rarely been found in the existing literature. To address this issue, firstly, this paper used daily temperature and precipitation data from the Bangladesh Meteorological Department (BMD) to calculate Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI). After that, we performed a statistical assessment, for instance, Pearson correlation coefficient, cross-correlation, cross-wavelet transform, and root mean square error, to identify the strengths of SPI and SPEI. Our findings showed that though both indices had a strong correlation with each other, SPEI performed better than SPI because evaporative demand has a positive impact on defining drought conditions in Bangladesh. Temperature and rainfall indices, for example, warm spell duration indicator (WSDI) and maximum amount of rain (Rx5day) that falls in five consecutive days, have been applied to find out the relationship between climate extremes and drought indices using cross-wavelet transform. Our results suggested that climate extremes such as WSDI and Rx5day have an influence on droughts in Bangladesh. Our results recommended that multi indices of drought assessment should be required in order to draw a robust conclusion.

Analysis of Climate Extreme Indices in the MATOPIBA Region, Brazil

The identification of the spatial and temporal variability of meteorological variables, as well as of climate extreme events, such as the duration of dry spells, duration of warm spells and rainfall intensity, is crucial for agrometeorological studies, since they can negatively impact yields through the exposure of the crop to critical conditions. Thus, this study analyzed trends in 23 rainfall and temperature climate extreme indices in the MATOPIBA region, currently a strategic area for investments in soybean cultivation, playing a major role in ensuring global food security. Daily time series of rainfall and temperature (maximum and minimum) data in the 1980–2013 period were used, arranged in a 0.25° × 0.25° grid, covering 963 points over the studied region. The data set was submitted to cluster analysis, the Mann–Kendall non-parametric test and extremes indices and their trends were estimated through the RClimdex software. Trends in rainfall rates and in mean, maximum and minimum temperatures were evaluated for each cluster and shifts from the climatological patterns of these variables were detected. Only some of the rainfall climate extreme indices presented significant increase and/or decrease in the CI and CII subregions. On the other hand, there was a significant increase in almost all temperature climate extreme indices in all clusters. The persistency of these trends may lead to impacts on soybean cultivation in the MATOPIBA region, and therefore these results are crucial for the elaboration of strategies for agricultural planning.

Cold Acclimation and Deacclimation of Two Garden Rose Cultivars Under Controlled Daylength and Temperature.

Low temperature stress is an important abiotic stress for garden roses in northern regions. Two garden rose cultivars (‘Dagmar Hastrup’ and ‘Chandos Beauty’) were selected to study the role of dehydrin and of carbohydrate metabolism during cold acclimation and deacclimation under the controlled daylength and temperature. The presence of bud dormancy was also observed as this could prevent budburst during warm spells. Both cultivars showed a similar changing pattern of cold acclimation and deacclimation and did not differ in their lowest LT50 values. Dehydrin (RhDHN5) was up-regulated by low temperatures and not by dehydration stress as the stem water content remained stable during the treatments. Total soluble sugars accumulated with a transient up-regulation of RhBAM3 (a key gene in starch hydrolysis) for ‘Dagmar Hastrup’ at 2°C and a strong expression under both 2 and −3°C for ‘Chandos Beauty’. At 2 and −3°C, raffinose and stachyose strongly accumulated though the up-regulation of RhRS6 and RhGK differed in the cultivars. Although similar cold hardiness levels were reached, carbohydrate metabolism in response to cold stress is different in the two cultivars. Increasing the temperature after a cold period resulted in fast deacclimation as found by the downregulation of RhDHN5 and RhBAM3, the decrease of raffinose and stachyose. Bud endodormancy was hardly present in both cultivars.

Analysis of Temperature and Precipitation Trends Observed at Some Selected Districts of Punjab, Pakistan

Present study examines the trends of extreme daily temperature and rainfall indices in some selectedmeteorological stations/districts of the Punjab. Due to paucity of data only six weather stations were selected from thewhole Punjab, having data of 33 years for temperature and precipitation on daily basis. A set of 14 indices(recommended by climate ET) were used to calculate the trends over a period of 32 years (1985–2017) by usingRClimDex (1.0) software package. These results showed that the number of tropical nights (TR20) and warm nights(TN90p) has been increasing in selected weather stations/districts and number for cool nights (TN10p) has been falling.Other temperature related indices trends such as, summer days, warms days, warm spell duration indicator (WSDI) andcool spell duration (CSDI) shows a mix pattern. The precipitation indices like SDII, RX1day, R10mm and PRCPTOTshowed an increasing trend in some selected stations. Most of the trends were not significant at level of 0.05 % whilemaximum day temperature increase has been observed at five out of six selected stations. Similarly, an average increasein precipitation in the vicinity of 3 mm per decade has been noted. The annual total rainfall and number of heavyrainfall days has also increased by 18 mm and 8.4 mm respectively during each decade. The analysis identified andhighlighted a slight change which was not temporally and spatially rational. However, there is need to more andadequate yearly data of different weather stations across the Punjab to identify the ongoing apparent and impeccablechanges in climate of the Punjab province.

Analysis of Temperature and Precipitation Trends Observed at Some Selected Districts of Punjab, Pakistan

Present study examines the trends of extreme daily temperature and rainfall indices in some selectedmeteorological stations/districts of the Punjab. Due to paucity of data only six weather stations were selected from thewhole Punjab, having data of 33 years for temperature and precipitation on daily basis. A set of 14 indices(recommended by climate ET) were used to calculate the trends over a period of 32 years (1985–2017) by usingRClimDex (1.0) software package. These results showed that the number of tropical nights (TR20) and warm nights(TN90p) has been increasing in selected weather stations/districts and number for cool nights (TN10p) has been falling.Other temperature related indices trends such as, summer days, warms days, warm spell duration indicator (WSDI) andcool spell duration (CSDI) shows a mix pattern. The precipitation indices like SDII, RX1day, R10mm and PRCPTOTshowed an increasing trend in some selected stations. Most of the trends were not significant at level of 0.05 % whilemaximum day temperature increase has been observed at five out of six selected stations. Similarly, an average increasein precipitation in the vicinity of 3 mm per decade has been noted. The annual total rainfall and number of heavyrainfall days has also increased by 18 mm and 8.4 mm respectively during each decade. The analysis identified andhighlighted a slight change which was not temporally and spatially rational. However, there is need to more andadequate yearly data of different weather stations across the Punjab to identify the ongoing apparent and impeccablechanges in climate of the Punjab province.

Extreme Temperature Events during 1960–2017 in the Arid Region of Northwest China: Spatiotemporal Dynamics and Associated Large-Scale Atmospheric Circulation

Studying the dynamic changes of extreme temperatures and associated large-scale atmospheric circulation is important for predicting the occurrence of extreme temperatures and reducing their adverse impact and damage. Based on the surface temperature data sets collected from 87 weather stations over the arid region of Northwest China (ARNC) during 1960–2017, the Sen’s slope estimator, Mann–Kendall test, Cumulative anomaly, Moving t-test, and Synthetic analysis methods were used to analyze the spatiotemporal dynamics and breaking-point change characteristics of extreme temperatures, and to discuss its associated large-scale atmospheric circulation. The results revealed that at the temporal scale, summer days (SU25), warm days (TX90p), warm nights (TN90p), and warm spell duration indicator (WSDI) showed a remarkable increasing trend at the rates of 2.27, 1.49, 3, and 2.28 days/decade, respectively. The frost days (FD), cold days (TX10p), cold nights (TN10p), and cold spell duration indicator (CSDI) significantly decreased at the rates of −3.71, −0.86, −1.77, and −0.76 days/decade, respectively, during the study period. Spatially, the warming trend in the study area is very obvious as a whole, despite pronounced spatial differences in warming rate. After the breakpoint years, the frequency and probability distribution for extreme warm and cold indices were all inclined to the hotter part of the density distribution. This indicates that the climate over the study region shifted sharply and tended to be warmer. The analysis of large-scale atmospheric circulation indicates that the warming trend in the arid region of Northwest China (ARNC) is positively correlated with geopotential height at 500 hPa and negatively correlated with total cloudiness. The findings from this study have important implications for forecasting extreme temperature events and mitigating the impacts of climatological disasters in this region.

The record‐breaking warm spell of February 2019 in Britain, the Channel Islands, France and the Netherlands

The record‐breaking warm spell of February 2019 in Britain, the Channel Islands, France and the Netherlands

Conspicuous temperature extremes over Southeast Asia: seasonal variations under 1.5 °C and 2 °C global warming

Guided by the Paris Agreement, the IPCC Special Report on Global Warming of 1.5 °C reported potential risks of climate change at different global warming levels (GWLs). To provide fundamental information on future temperature extremes over Southeast Asia (SEA), projected changes in temperature extreme indices are evaluated for different seasons at 1.5 °C and 2 °C GWLs against the historical reference period of 1976–2005 based on the ensemble of CORDEX simulations. Results show that the temperature indices increase significantly across the Indochina Peninsula and Maritime Continent at both GWLs except for decreasing daily temperature range (DTR) in the dry season, with more pronounced magnitudes at 2 °C GWL. Moreover, the regionally averaged ensemble medians of the indices show various changes over different subregions. At 1.5 °C and 2 °C GWLs, most pronounced increases of threshold indices. i.e. summer days (SU) and tropical nights (TR), are projected in Sumatra and Sulawesi for both wet and dry seasons. The warm spell duration (WSDI) increases generally, with strongest magnitudes for Sumatra and Sulawesi (Philippines and Sulawesi) in the wet (dry) season. On the other hand, significant increases of warm days and nights can also be observed at 2 °C GWL compared to 1.5 °C, particularly in the dry season, suggesting the high sensitivity of temperature extremes over the SEA. The projected potentially conspicuous temperature extremes under global warming of 1.5 °C and 2 °C primarily concentrate on the densely populated coastal regions of the main islands, showing the necessity of restricting global warming to 1.5 °C aiming at the eradication and reduction of regional climate stress for the human system in the developing countries over the SEA.

Effect of Elevated Temperatures on Lateral Earth Pressures in Unsaturated Soils

Near-surface unsaturated soils can be exposed to elevated temperatures due to soil-atmospheric interactions under drought events, wildfires, heatwaves, and warm spells, or the heat induced by emerging geotechnical and geo-environmental technologies such as geothermal boreholes and thermally active earthen systems. Elevated temperatures can affect the hydro-mechanical characteristics of unsaturated soils, which in turn can alter lateral earth pressures developed in the backfill soil. The main objective of this study is to quantify the effect of elevated temperatures on active and passive earth pressures of unsaturated soils. For this purpose, the paper presents the derivation of an analytical framework to extend Rankine’s earth pressure theory to account for the effect of temperature under hydrostatic conditions. The equations are derived by incorporating the effect of temperature into the soil water retention curve and a suction stress-based effective stress representation. The proposed effective stress equation considers the temperature-induced changes in the contact angle, surface tension, and enthalpy of immersion. To investigate the impact of temperature on active and passive earth pressures, the proposed method is then used in a set of parametric studies to determine active and passive earth pressure profiles for three hypothetical soils of clay, silt, and sand at different temperatures. Results suggest that elevated temperatures can cause variation in active and passive earth pressures for all the soils considered. The findings of this study can contribute toward analyzing earth retaining structures subjected to elevated temperatures.

Toward understanding 1.5°C global warming influences on temperature and precipitation extremes at different timings: before and after overshooting

To better understand the long-term influences of the 1.5°C target, we provide an assessment of the changes in climate extremes under same warming level but at different timings, based on the magnitude of change, the internal variability, and the model agreement derived from CMIP5. Our findings imply that the changes in climate extremes and their impacts under 1.5°C warming level are projected to be more modest at the stage after overshoot. Specifically, less shares of land area will experience robust increase in extreme hot event and warm spell duration. Potential less cold events after overshooting are also projected. The land areas and population directly experiencing increase in heavy precipitation intensity are projected to slightly increase, whereas more land areas will benefit from the robust decrease in dry spell length. Nevertheless, most of climate extremes analysed in our study will change beyond the upper limit of present-day natural variability.

Winter on the Outs

Winter on the Outs William Logan (bio) WINTER ON THE OUTS Rain swiped the mossy shallows,obscuring whatever lay outside.The dead garden's roses pruned almost to the root, peoniesawaited the warm spell, the budsminiature red thumbs. The St. John's wort stoodupended like an old besom,bristled twigs bound to a stave. On the scurf of ivy, green heartspressed their suits this way and that,a few still hoping for marriage. Something shoved at the groundfrom below, a mole on the hunt,old age taking a fresh turn, or a dead thing on the wrong side of history. [End Page 96] William Logan WILLIAM LOGAN's most recent books are Rift of Light (poems, 2017) and Dickinson's Nerves, Frost's Woods: Poetry in the Shadow of the Past (essays, 2018). He teaches at the University of Florida. Copyright © 2020 Johns Hopkins University Press

Twenty-First Century Projected Changes in Extreme Temperature over Côte d’Ivoire (West Africa)

The projection of the future climate changes is of paramount importance inasmuch as it contributes to provide useful information for adaptation planning worldwide to local scales. This study investigated the future changes using four temperature related indices based on an ensemble of 14 CORDEX-Africa simulations at 0.44° × 0.44° of resolution under the RCP4.5 and RCP8.5 scenarios. These indices indicate moderate extremes over Côte d’Ivoire. The results show an increase in the warm extreme indices such as the warm spell days index (HWFI), very warm days frequency index (TX90P), and the warm nights frequency index (TN90P) over the entire country under both emission scenarios. The increase in these indices was higher under RCP8.5 and reached 85, 72, and 90% for HWFI, TX90P, and TN90P respectively. In addition, the magnitude of the changes is relevant along the coastal areas in the 2031–2060 and 2071–2100 periods. Moreover, the intra period extreme temperature range (ETR) shows future decrease following a south-north gradient with values in the range [−0.5; 1.5°C] over the country during January–March (JFM) and October–December (OND) seasons whereas an increase (~0.5°C) is projected for April–June (AMJ) and July–September (JAS) seasons, particularly in the central and northern parts. The minimum temperature increases faster than the maximum, except in AMJ and JAS in the central and northern regions. On the other hand, the changes in the indices based on the mean values of the reference period (1976–2005) are in concordance to the expected warming at the end of the twenty-first century with important trends. The projected changes are, however, subject to uncertainties, which are higher under RCP8.5 than under RCP4.5 scenarios. Overall, these changes are meaningful as all the 14 CORDEX-Africa simulations agree to an increase of warm extreme temperature.

Impact of Shrubs on Winter Surface Albedo and Snow Specific Surface Area at a Low Arctic Site: In Situ Measurements and Simulations

AbstractErect shrubs in the Arctic reduce surface albedo when branches protrude above the snow and modify snow properties, in particular specific surface area (SSA). Important consequences are changes in the land surface–atmosphere energy exchange and the increase of snow melting in autumn, possibly inducing reduced soil thermal insulation and in turn permafrost cooling. Near Umiujaq (56.5°N, 76.5°W) in the Canadian low Arctic where dwarf birches (Betula glandulosa) are expanding, spectral albedo (400–1080 nm) under diffuse light and vertical profiles of SSA were measured in November and December 2015 at four sites: three with protruding branches and one with only snow. At the beginning of the snow season (8 November), shrub-induced albedo reductions were found to be wavelength dependent and as high as 55% at 500 nm and 18% at 1000 nm, which, integrated over the measurement range (400–1080 nm), corresponds to 70 W m−2 of additional absorbed energy. The impact of shrubs is not just snow darkening. They also affect snow SSA in multiple ways, by accumulating snow with high SSA during cold windy precipitation and favoring SSA decrease by inducing melting during warm spells. However, the impact on the radiation budget of direct darkening from shrubs likely dominates over the indirect change in SSA. Spectral albedo was simulated with a linear mixing equation (LME), which fitted well with observed spectra. The average root-mean-square error was 0.009. We conclude that LMEs are a suitable tool to parameterize mixed surface albedo in snow and climate models.