Amplified risk of compound heat stress-dry spells in Urban India

Journal of Geophysical Research: Atmospheres

Recent heat waves have been a matter of serious concern for India because of potential impacts on agriculture, food security, and socioeconomic progress. This study examines the trends and variability in frequency, duration, and intensity of hot episodes during three time periods (1951-2013, 1981-2013 and 1998-2013) by defining heat waves based on the percentile of maximum, minimum, and mean temperatures. The study also explores heat waves and their relationships with hydroclimatic variables, such as rainfall, terrestrial water storage, Palmer drought severity index, and sea surface temperature. Results reveal that the number, frequency, and duration of daytime heat waves increased considerably during the post-1980 dry and hot phase over a large area. The densely populated and agriculturally dominated northern half of India stands out as a key region where the nighttime heat wave metrics reflected the most pronounced amplifications. Despite the recent warming hiatus in India and other parts of the world, we find that both daytime and nighttime extreme measures have undergone substantial changes during or in the year following a dry year since 2002, with the probability distribution functions manifesting a hotter-than-normal climate during 1998-2013. This study shows that a few months preceding the 2010 record-breaking heat wave in Russia, India experienced the largest hot episode in the country's history. Interestingly, both these mega events are comparable in terms of their evolution and amplification. These findings emphasize the importance of planning for strategies in the context of the rising cooccurrence of dry and hot events. Plain Language Summary Consistent with model projection and physical understanding, the multiaspect framework of heat wave and warm spells exhibits clear spatial and temporal patterns. Most perceptible change in heat waves is observed during the post-1998 warming hiatus period, mainly exacerabated by droughts. The 2009-2010 drought and heat wave in India can be compared with that of the 2010 record-breaking Russian hot episode in terms of evolution and amplification.

Current Science, 2020

This study analysed gridded temperature dataset for last six decades over India and its different agroclimatic zones to determine the changes in land area affected by extreme warm day temperatures. The results indicated an unequivocal increase in the area influenced by different levels of extreme warm days over the country; the rate was significantly higher during the last three decades. The increase in land area affected by extreme-of-extreme temperature events occurred at a higher rate compared to the lowfrequency extremes. Statistical tests indicated clear change in the probability distribution of the land area affected by extremes, signifying that comparatively high-frequency extremes are occurring over larger areas. The results showed regional dissimilarity, with five agro-climatic zones (ACZ-02, 09, 10, 11, 12) showing increase in land area under most levels of extremes, and three agro-climate zones (ACZ-08, 13, 14) showing increase in land area for a few extreme levels.

Theoretical and Applied Climatology, 2018

Intergovernmental Panel on Climate Change (IPCC) promulgated a clear message that there have been many extreme weather and climate events observed globally since 1950, and these changes occurred mainly due to anthropogenic causes and emission of greenhouse gases. A computation study was carried out to assess the extreme temperature and rainfall events for the period 1984-2015 at the Indian Agricultural Research Institute, New Delhi by using ETCCDI indices through RClimDex software. The statistical significance of time series data and various calculated indices was done by linear regression as well as by Mann-Kendall test. Results indicated that annual mean maximum temperature decreased significantly at 0.019°C/year and annual mean minimum temperature showed an increasing trend but without statistical significance. Alteration has happened in atmospheric properties, both physical and chemical over Delhi region during the period because of rapid urbanization and, increased concentration of aerosol. Fossil fuel/biomass waste burning, transportation of sand dust from Thar Desert, and reduction in incoming solar radiation have contributed both for fall in daytime temperature and rise in nighttime temperature. The changes in temperature would affect agricultural production through reduction in the rate of photosynthesis and excessive nocturnal respiration. Frequency and magnitude of coolest day (maximum temperature < 15°C) and night (minimum temperature < 5°C) have been rising at IARI, New Delhi. In the case of rainfall-based indices, annual rainfall (PRCPTOT), consecutive wet days (CWD), and number of days with rainfall ≥ 20 mm (R20) showed significant increasing tendency. Increasing trend in simple daily intensity index (SDII), rainy days (R2.5), and declining trend of consecutive dry days (CDD) indicates better distribution of rainfall. Nevertheless, increasing tendency in RX1day, RX5day, and R99p indicates possibilities of heavy rainfall events although the trend has been found insignificant.

Scientific Reports, 2021

Compared to any single hydroclimatic variable, joint extremes of multiple variables impact more heavily on the society and ecosystem. In this study, we developed new joint extreme indices (JEIs) using temperature and precipitation, and investigated its spatio-temporal variation with observed records across Indian mainland. Analysis shows an alarming rate of change in the spatial extent of some of the joint extreme phenomena, tending to remain above normal. For example, above normalhot nights and wet daysevents expands at a rate of 0.61% per year considering entire Indian mainland. If the historical trend continues at the same rate, consecutivecold and wet dayevents will drop below the threshold of mean value observed in the base line period (1981–2010) everywhere in the country by the end of the twenty-first century. In contrast, the entire country will be covered byhot nights and wet daysevents only (frequency of occurrence will cross the threshold of mean value observed in the bas...

Science advances, 2017

Rising global temperatures are causing increases in the frequency and severity of extreme climatic events, such as floods, droughts, and heat waves. We analyze changes in summer temperatures, the frequency, severity, and duration of heat waves, and heat-related mortality in India between 1960 and 2009 using data from the India Meteorological Department. Mean temperatures across India have risen by more than 0.5°C over this period, with statistically significant increases in heat waves. Using a novel probabilistic model, we further show that the increase in summer mean temperatures in India over this period corresponds to a 146% increase in the probability of heat-related mortality events of more than 100 people. In turn, our results suggest that future climate warming will lead to substantial increases in heat-related mortality, particularly in developing low-latitude countries, such as India, where heat waves will become more frequent and populations are especially vulnerable to th...

International Journal of Climatology, 2014

This study provides the comprehensive analysis of changes in mean and extreme temperature indices of India to assist the climate change mitigation and adaptation strategies and to add information for the global comparisons, using a high-resolution daily gridded temperature data set (1 • × 1 • ) during 1971-2005. In addition to the indices recommended by the World Meteorological Organization/CLIVAR Expert Team on Climate Change Detection and Indices, few more indices having social and agricultural implication are investigated at the seasonal and annual scales, utilizing widely adopted statistical methodologies in climate research. The results show, in general, a robust signal of warming, broadly consistent with what has been observed and predicted in other parts of the world in the context of global warming. The frequency and intensity of warm extremes, especially representing the daily minimum temperature, have increased with simultaneous decreases in cold extremes in large parts of the country, but the spatial distribution of the trend magnitude reflects the complex natural climatic settings of India and its possible interaction with the anthropogenic forcing. Seasonal analysis reveals a faster warming in day and night temperatures in winter affecting the major wheat crop. In summer, however, both human and ecosystems appear to be more vulnerable to the increasing tendency of the heatwave occurrences, particularly during night-time, since the 1990s. The relationship with the large-scale natural climatic modes indicates that the warming indices tend to increase in the year following the El Niño events as evident from the correlation with the NINO3.4 index, with a relatively higher association in the monsoon season. Moreover, the concurrent correspondence of the summer heatwaves with the north Indian Ocean sea surface temperature suggests a degree of predictability of the heat stress episode.

2022

Extreme temperatures are directly related to the occurrence of atmospheric extreme events, such as draughts, wildfires, and pollution level increases in urban areas. Policy makers, as well as society, can address such phenomenon by developing and applying methods which estimate and anticipate maximum temperature occurrences. In this research we aim to develop a spatiotemporal model which analyzes maximum temperature trends values in the Indian 543 microregions between 1951 and 2020. In 27% of those, a maximum temperature above 45 • C was observed, at least in a year, with the results of the analysis testifying that 80% of the microregions have an median yearly maximum temperature above 40 • C. Additionally, the results unveiled that East, Southwest and Northwest microregions were the ones where the maximum temperatures had a higher increase with 2 • C being the average. The model developed is based on a Generalized Extreme Value (GEV) methodology, to estimate the maximum temperature values from 20 to 50 years. The projection for 20 years showed that in 16% of those microregions at least one occurrence of a maximum temperature above 45 • C would occur; while in the 50 years one it would happen in 22% of the microregions analyzed.

2017

Heat wave is an important class of climate hazard due to its impact on human health. Changes in characteristics of heat waves such as intensity, duration, frequency and geographical exposure have the potential to have serious societal impacts. Observations suggest that in some parts of the world such changes are already happening, leading to impact on human health in terms of heat-stress and mortality. Heat waves are expected to intensify around the globe in the future, with potential increase in heat stress and heat-induced mortality in the absence of adaptation measures. India has a high current exposure to heat waves, and with limited adaptive capacity, impacts of increased heat waves might be quite severe. An understanding of heat wave characteristics is a pre-requisite to assess vulnerabilities due to heat waves. &lt;br&gt; &lt;br&gt; The primary objective of this thesis was to understand and analyze the climatic mechanisms that are driving changes in heat waves in India. Daily...

2021

Climatic warming in the global mean has significantly increased the probability of occurrence of heat extremes on time scales ranging from months to seasons. As extreme heat events are most likely to become intense and frequent over the next decades, thus it's important to examine these events to mitigate its negative impacts on public health and society. This study focuses on Karachi heat extremes over the last 23 years. The power spectral analyses of Karachi heat extremes records have been carried out by considering two indices: Heat Index (HI) and Effective Temperature Index (TEE), which are also found to be significantly correlated. The result indicates a regular cyclic pattern of 4.5 years which is estimated to face a heat index of more than 73.63℃, associated with the El Niño-Southern Oscillation (ENSO). Other peaks are observed at 2.8 and 2.2 years with the expected value of the Karachi heat index of 70.53℃ and 68.71℃, respectively. The probabilistic approach is also used to predict the future heatwave events of Karachi. Generalized Extreme Value (GEV) distribution is found to be the best-fitted probability distribution for the extreme heatwave events on the basis of goodness of fit test. Furthermore, the estimation of the return period of the heatwave event reveals that Karachi will be facing a maximum heat index of 84.37℃ or more in the coming 33 years, which suggests an urgent need for mitigation strategies in Karachi to overcome the effects of extreme heatwave events.

On 19 May 2016 the afternoon temperature reached 51.0 • C in Phalodi in the northwest of India-a new record for the highest observed maximum temperature in In-dia. The previous year, a widely reported very lethal heat wave occurred in the southeast, in Andhra Pradesh and Telan-gana, killing thousands of people. In both cases it was widely assumed that the probability and severity of heat waves in India are increasing due to global warming, as they do in other parts of the world. However, we do not find positive trends in the highest maximum temperature of the year in most of India since the 1970s (except spurious trends due to missing data). Decadal variability cannot explain this, but both increased air pollution with aerosols blocking sunlight and increased irrigation leading to evaporative cooling have counteracted the effect of greenhouse gases up to now. Current climate models do not represent these processes well and hence cannot be used to attribute heat waves in this area. The health effects of heat are often described better by a combination of temperature and humidity, such as a heat index or wet bulb temperature. Due to the increase in humidity from irrigation and higher sea surface temperatures (SSTs), these indices have increased over the last decades even when extreme temperatures have not. The extreme air pollution also exacerbates the health impacts of heat. From these factors it follows that, from a health impact point of view, the severity of heat waves has increased in India. For the next decades we expect the trend due to global warming to continue but the surface cooling effect of aerosols to diminish as air quality controls are implemented. The expansion of irrigation will likely continue, though at a slower pace, mitigating this trend somewhat. Humidity will probably continue to rise. The combination will result in a strong rise in the temperature of heat waves. The high humidity will make health effects worse, whereas decreased air pollution would decrease the impacts.