Climatological Understanding of Heat and Cold Wave Variability in Eastern Uttar Pradesh

Anthropogenic greenhouse gas emissions are expected to lead to more frequent and intense summer temperature extremes, not only due to the mean warming itself, but also due to changes in temperature variability. To test this hypothesis, we analyse daily output of ten PRUDENCE regional climate model scenarios over Europe for the 2071–2100 period. The models project more frequent temperature extremes particularly over the Mediterranean and the transitional climate zone (TCZ, between the Mediterranean to the south and the Baltic Sea to the north). The projected warming of the uppermost percentiles of daily summer temperatures is found to be largest over France (in the region of maximum variability increase) rather than the Mediterranean (where the mean warming is largest). The underlying changes in temperature variability may arise from changes in (1) interannual temperature variability, (2) intraseasonal variability, and (3) the seasonal cycle. We present a methodology to decompose the total daily variability into these three components. Over France and depending upon the model, the total daily summer temperature variability is projected to significantly increase by 20–40% as a result of increases in all three components: interannual variability (30–95%), seasonal variability (35–105%), and intraseasonal variability (10–30%). Variability changes in northern and southern Europe are substantially smaller. Over France and parts of the TCZ, the models simulate a progressive warming within the summer season (corresponding to an increase in seasonal variability), with the projected temperature change in August exceeding that in June by 2–3 K. Thus, the most distinct warming is superimposed upon the maximum of the current seasonal cycle, leading to a higher intensity of extremes and an extension of the summer period (enabling extreme temperatures and heat waves even in September). The processes driving the variability changes are different for the three components but generally relate to enhanced land–atmosphere coupling and/or increased variability of surface net radiation, accompanied by a strong reduction of cloudiness, atmospheric circulation changes and a progressive depletion of soil moisture within the summer season. The relative contribution of these processes differs substantially between models.

ABSTRACTIn this paper, we investigated changes in heat and cold waves in Romania over the period 1961–2015 by employing a new and superior approach. It consists in using excess heat factor to identify heat waves and excess cold factor to identify cold waves. Five indices were calculated and then analysed for both heat waves and cold waves resulting in a set of ten indices. Indices for heat waves were analysed for the extended summer season (May–September), whereas those for cold waves were assessed for the extended winter (November–March). The intensity threshold was set to be equal or above the 90th percentile for heat waves, and equal or below the 10th percentile for cold waves, while the duration threshold for both heat and cold waves was of at least three consecutive days. For a better comparison with other studies conducted worldwide, and to get more information from the data sets, the percentile thresholds for heat and cold waves identification were calculated based on three reference periods: 1961–1990, 1971–2000, and 1981–2010. Trends were calculated using ordinary least square method, whereas statistical significance was assessed by the t‐test. The main results indicated that changes are more substantial in the case of indices calculated based on excess heat factor compared to those based on excess cold factor, suggesting that the warming process is more reflected in heat waves rather than in cold waves. Thus, heat waves became more frequent, longer, and more intense, while cold waves became less frequent, but more intense. When the reference period for percentile threshold calculation was changed from the earliest to the most recent ones, the frequency of increasing and significant increasing trends decreased for some of the heat wave indices, while for the cold wave indices the significant downward trends increased.

In the current context of global warming, heat waves are extreme climate events that have captured the focused attention of the scientific community due to their increasing impact on public health, energy consumption, fire risk, and agriculture livestock. Although less studied, cold waves remain an extreme climate event to be reckoned with, with implications for transport systems, energy consumption, crops, and human health. This paper presents an analysis of the representative concentration pathway (RCP) 4.5 and RCP 8.5 scenarios under European Coordinated Regional Downscaling Experiment simulations using the excess heat factor (EHF) and excess cold factor indices for the Iberian Peninsula and the Balearic Islands (IPB). The study period is the second half of the 21st Century (2050–2095) with respect to the historical reference period (1971–2000), and the dimensions analysed are intensity and spatial extent. The projected EHF results show a very significant increase on these dimensions. The average change in maximum heat wave intensity for the IPB is projected to be 144%, which is 40% more than in the 2021–2050 period. The largest changes are expected in the east and southeast and will reach 300%. The average spatial extent of heat waves is projected to increase by 1–2.7% per decade, significantly amplifying fire risk, energy demand, and human exposure. For cold waves, both dimensions will decrease. The average change in maximum cold wave intensity will be − 16%, and the maximum extent will decrease much more than the average, with decreases between − 0.7%/decade and − 3.2%/decade, which will imply lower exposure. Despite this, the RCP 8.5 scenario will record a higher maximum intensity of cold waves in the IPB than the RCP 4.5 scenario, demonstrating that such events will continue to exist in the second half of the century, even with high radiative forcing.

Heat wave intensity and daily mortality in four of the largest cities of Spain

Periods of successive extreme heat and cold temperature have major effects on human health and increase rates of health service utilisation. The severity of these events varies between geographic locations and populations. This study aimed to estimate the effects of heat waves and cold waves on health service utilisation across urban, regional and remote areas in New South Wales (NSW), Australia, during the 10-year study period 2005-2015. We divided the state into three regions and used 24 over-dispersed or zero-inflated Poisson time-series regression models to estimate the effect of heat waves and cold waves, of three levels of severity, on the rates of ambulance call-outs, emergency department (ED) presentations and mortality. We defined heat waves and cold waves using excess heat factor (EHF) and excess cold factor (ECF) metrics, respectively. Heat waves generally resulted in increased rates of ambulance call-outs, ED presentations and mortality across the three regions and the entire state. For all of NSW, very intense heat waves resulted in an increase of 10.8% (95% confidence interval (CI) 4.5, 17.4%) in mortality, 3.4% (95% CI 0.8, 7.8%) in ED presentations and 10.9% (95% CI 7.7, 14.2%) in ambulance call-outs. Cold waves were shown to have significant effects on ED presentations (9.3% increase for intense events, 95% CI 8.0-10.6%) and mortality (8.8% increase for intense events, 95% CI 2.1-15.9%) in outer regional and remote areas. There was little evidence for an effect from cold waves on health service utilisation in major cities and inner regional areas. Heat waves have a large impact on health service utilisation in NSW in both urban and rural settings. Cold waves also have significant effects in outer regional and remote areas. EHF is a good predictor of health service utilisation for heat waves, although service needs may differ between urban and rural areas.

Progressive intensification and proliferation of heat waves impose extensively impacts on entire environment and ecology. The far‐reaching implications of heat waves and the severe future projections emphasize the imperative need to explore the driving factors and their quantitative contribution to heat wave variations. In this study, a multiaspect characteristic of heat waves across China during 1961–2017 is evaluated using excess heat factor. Results showed that the number of events, frequency, duration, and intensity has heterogeneous spatial patterns, with a consistent abrupt transition in 1996–1997. The robust positive correlations between heat wave characteristics and warming sea surface temperature (SST) indicate the association of heat wave with SST anomalies. Except the number of events, the other factors (including the frequency, duration, and intensity) of heat waves are strongly influenced by El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). However, the influences have significant variations from region to region, with the central regions experiencing significant decreases in the frequency, duration, and intensity of heat waves during the simultaneous ENSO phases (El Niño‐La Niña), in comparison with northern and western regions dominated by IOD (positive‐negative) experiencing longer and more frequent heat waves. Particularly, the mild heat waves are more vulnerable to the warming SST modes than severe heat waves. The decrease of heat waves is affected by the convergent winds bringing cold air from the high latitude, while the extensively significant increase of heat waves is controlled by the anomalously sinking motions.

Recent temperature extremes have highlighted the importance of assessing projected changes in the variability of temperature as well as the mean. A large fraction of present-day temperature variance is associated with thermal advection, as anomalous winds blow across the land–sea temperature contrast, for instance. Models project robust heterogeneity in the twenty-first-century warming pattern under greenhouse gas forcing, resulting in land–sea temperature contrasts increasing in summer and decreasing in winter and the pole-to-equator temperature gradient weakening in winter. In this study, future changes in monthly variability of near-surface temperature in the 17-member ensemble ESSENCE (Ensemble Simulations of Extreme Weather Events under Nonlinear Climate Change) are assessed. In winter, variability in midlatitudes decreases whereas in very high latitudes and the tropics it increases. In summer, variability increases over most land areas and in the tropics, with decreasing variability in high latitude oceans. Multiple regression analysis is used to determine the contributions to variability changes from changing temperature gradients and circulation patterns. Thermal advection is found to be of particular importance in the Northern Hemisphere winter midlatitudes, where the change in mean state temperature gradients alone could account for over half the projected changes. Changes in thermal advection are also found to be important in summer in Europe and coastal areas, although less so than in winter. Comparison with CMIP5 data shows that the midlatitude changes in variability are robust across large regions, particularly high northern latitudes in winter and middle northern latitudes in summer.

Increased temperature will result in longer, more frequent, and more intense heat waves. Changes in temperature variability have been deemed necessary to account for future heat wave characteristics. However, this has been quantified only in Europe and North America, while the rest of the globe remains unexplored. Using late century global climate projections, we show that annual mean temperature increases is the key factor defining heat wave changes in most regions. We find that commonly studied areas are an exception rather than the standard and the mean climate change signal generally outweighs any influence from variability changes. More importantly, differences in warming across seasons are responsible for most of the heat wave changes and their consideration relegates the contribution of variability to a marginal role. This reveals that accurately capturing mean seasonal changes is crucial to estimate future heat waves and reframes our interpretation of future temperature extremes.

ABSTRACTThe past two decades of the 20th century and the first of the 21st century have been characterized by global temperature rise and increased frequency of weather‐induced extreme events such as floods, droughts, heavy rainfall, and heat waves. We investigated the heat and the cold waves in the Carpathian Region, an area whose rich biosphere is endangered by extreme events. We used the daily minimum (TN) and maximum (TX) temperature data collected in the framework of the CARPATCLIM project. Such high‐resolution (0.1° × 0.1°) gridded data range from January 1961 to December 2010. In this study, a heat wave occurs when temperature is above the 90th percentile for at least five consecutive days and a cold wave occurs when temperature is below the 10th percentile for at least five consecutive days. The percentiles have been computed over the baseline period 1971–2000. We distinguish between night‐time and daytime events and we discuss heat (and cold) waves considering at least five consecutive night and days with temperature above (below) the selected percentile. For each heat or cold wave event, we assigned duration, severity, and intensity. For these parameters and for frequency, we performed linear trend analysis for the period 1961–2010. The trends have been computed on an annual and seasonal basis and tested for statistical significance. Different spatial patterns of heat and cold waves characterize the Carpathian Region: heat wave events show general increase in all the parameters considered, while cold wave events show a decrease in all the variables West to the Carpathians and an increase North–East to the Carpathians. We also compiled a list of the most relevant heat waves that hit the Carpathian Region from 1961 to 2010: out of seven events, four occurred from 2000 to 2010. Instead, the 1960s and the 1980s have been the decades most hit by severe cold waves.

Heat waves (HWs) and cold waves (CWs) are well-known forms of extreme weather events. The observed frequency, magnitude, and duration of heat waves (HWs) and cold waves (CWs) over the Indian main land have been studied. For this daily maximum temperature of 103 stations during the hot weather (AMJ (April–June)) season for the period 1961–2020 and daily minimum temperature data of 86 stations during the cold weather (DJF (December of previous year to current year February) season for the period 1971–2020 were used. The trends in the seasonal frequency of these extreme temperature events as well as their association with the ENSO events have also been examined. During the AMJ season, HWs are generally experienced over the north, northwest, central, east India, and northeast Peninsula [together called core HW zone (CHZ)] with the highest frequency during May. Noticeable increase (decrease) in the frequency and spatial coverage of HW/SHW days compared to their climatological values were observed during the El-Nino (La-Nina) years. There are significant increasing trends in the HW/SHW days at most of the stations from CHZ. The total number of HW/SHW days over CHZ showed noticeable increase during the recent decades 1991–2000, 2001–2010, and 2011–2020 compared to the previous three decades. During DJF, the CWs are generally experienced in the core CW zone (CCZ) that is nearly the same as CHZ with the highest frequency during January. Noticeable decrease (increase) in the frequency and spatial coverage of CW/SCW days were observed during the El-Nino (La-Nina) years compared to their climatological values. The total number of CW/SCW days over CCZ decreased during the recent decades, namely, 1991–2000, 2001–2010, and 2011–2020 as compared to the previous two decades. However, the areas of CW days of ≥8 days on an average increased over north along the plains of Himalayas and central India in the latest decade (2011–2020) as compared to the previous decade (2001–2010). This study coincided with the fact that the latest three decades were the warmest decades for the country as well as for the globe. Associated with intense and persistent extreme temperature events, large human mortality was reported during some years of the study period. India Meteorological Department has recently established a seamless forecasting strategy from short-range forecasts to seasonal forecasts for HWs and CWs. With this new development, IMD is able to forewarn the agencies and people and save thousands of lives.KeywordsHeat wavesCold wavesTrendsClimatologyEl Nino/La Nina

Cardiovascular disease is the most common cause of death globally. Examining the relationship between the extreme temperature events (e.g. heat and cold waves) and cardiovascular mortality has profound public significance. However, this evidence is scarce, particularly those from China. We collected daily data on cardiovascular mortality and meteorological conditions from 31 major Chinese cities during the maximum period of 2007–2013. A two-stage analysis was used to estimate the effects of heat and cold waves, and the potential effect modification of their characteristics (intensity, duration, and timing in season) on cardiovascular mortality. Firstly, a generalized quasi-Poisson regression combined with distributed lag nonlinear model was used to evaluate city-specific effects. Then, the meta-analysis was performed to pool effect estimates at the national scale. Overall, cardiovascular mortality risk increased by 19.03% (95%CI: 11.92%, 26.59%) during heat waves and 54.72% (95%CI: 21.20%, 97.51%) during cold waves. The effect estimates varied by the wave’s characteristics. In heat wave days, the cardiovascular mortality risks increased by 3.28% (95%CI: −0.06%, 6.73%) for every 1 °C increase in intensity, 2.84% (95%CI: 0.92%, 4.80%) for every 1-d more in duration and −0.07% (95%CI: −0.38%, 0.24%) for every 1-d late in the staring of heat wave; the corresponding estimates for cold wave were 1.82% (95%CI: −0.04%, 3.72%), 1.52% (95%CI: 0.60%, 2.44%) and −0.26% (95%CI: −0.67%, 0.16%). Increased susceptibility to heat and cold waves was observed among patients with ischemic heart disease, females, the elderly, and those with lower education level. And consistent vulnerable populations were found for the effects of changes in cold and heat wave’s characteristics. The findings have important implications for the development of early warning systems and plans in response to heat and cold waves, which may contribute to mitigating health threat to vulnerable populations.

Extreme temperatures have caused various damages to society around the world. In Brazil, an example of that is the impact of cold and heat waves on public health. In order to analyse the temporal and spatial variability of such events, this study applied a single criterion to identify cold and heat waves. The study collected data on the events from daily temperature records from 264 weather stations over 56 years (1961–2016). The following parameters were used to describe each event: frequency, duration, severity, and intensity. The results showed that in all the Brazilian regions the frequency of heat waves increased and that of cold waves decreased between the years 1961 and 2016. The number of heat waves per year, notably, was greater than that of cold waves, and the mean duration of heat waves was about 1 day longer than that of cold waves. Additionally, it was found that cold waves were more severe and intense in areas often reached by cold air masses with temperatures below zero in most of Southern Brazil. In terms of severity and intensity of heat waves, two different configurations were observed: They were more severe in the Southern region and more intense in the Midwestern region of the country, and not so expressive in the Northern and Northeastern regions. Those findings justify the need for continuous updating of public policies focused on sectors often affected by cold and heat.

High relative humidity (RH) and temperature extremes can occur simultaneously and persist for periods of time, resulting in serious harm to human health, especially in humid regions. Here, in the case of the Gan River Basin, we used air temperature and RH from the observed and ERA5 reanalysis datasets to construct the apparent temperature and investigate the characteristics of heat and cold waves. Heat waves showed the increasing trends from 1961 to 2018 (particularly from 1997 to 2018), whereas during the same period, cold waves showed the significant decreasing trends. In general, ERA5 reasonably reflected the spatiotemporal characteristics of heat and cold waves, and the ability to simulate cold waves was slightly greater than that of heat waves. The amplifying effect of high RH on heat waves was significantly greater than on cold waves. The increasing rates of heat waves in ERA5 at the mild, moderate, and severe grades were slightly greater than the observations. Cold waves at various grades showed significant downward trends, and the decreasing rates of cold waves in the observations were slightly greater than those in ERA5. Using an analysis of the return period (occurrence probability), traditional univariate risk assessment methods based on maximum or minimum temperature may substantially underestimate the risk of extreme events, such as the 2014 heat wave and the 1969 cold wave, because the effects of RH were ignored.

Heat and cold waves are extreme temperature events with a high potential of causing negative impacts on human health, and natural and socioeconomic systems, depending on their duration and intensity. There is, however, no consensual approach to address their definition, which is critical to set priority action areas to prevent such risks. Mainland Spain experiences heat and cold waves every year with important impacts especially in the most populated areas with mild or transition climates. Here we used a high-resolution (5 × 5 km) gridded daily temperature dataset and employed a combination of threshold exceedances of maximum and minimum temperature in the same day to identify heat and cold wave events over 75 years (1940–2014). We further examined the duration and the seasonal/annual intensities to detect potential spatial and temporal patterns. Additionally, we used the days within the most widespread events to perform a synoptic classification to categorise the atmospheric conditions leading to high-risk situations. Our results show a similar historical duration of heat and cold waves (4–5 days) and a much higher seasonal intensity of cold ones (double than heat waves). We find a tipping point in the early 1980s from which heat waves became more frequent, longer, and more intense than cold waves. Finally, we discern between 9 historical weather types with a dominance of southern advections driving heat waves and cold continental north-northeast air masses causing cold waves. Understanding the patterns and trends of heat and cold waves, as well as the mechanisms of their genesis is key to assist in risk management in mainland Spain, especially in the context of a warming climate scenario.

Changes in heat waves in Chile