Heatwaves in South Asia: Characterization, Consequences on Human Health, and Adaptation Strategies

Abstract

South Asia, with more than one-fifth of the world’s population, is highly vulnerable to heatwaves and associated health consequences. The population experiences considerably higher residential vulnerability due to limited infrastructural capacities, economic resources, and health and environmental quality deficiencies. However, a limited number of studies are available from the region to account for the health effects of heatwaves. Therefore, this study has conducted a comprehensive review to characterize heatwaves across South Asian countries. The review explicitly identifies the population’s vulnerability to heatwaves during recent years and heatwave management policies in the region. The literature review suggests increased heat-related deaths in most South Asian countries, with few exceptions. In addition, the analysis of historical temperature records identified an upward trend in annual average temperature across the South Asian countries. The study highlights various heatwave definitions that have been used in the region to facilitate comparative evidence. The review of policies identified that only a few South Asian countries have functional heatwave management plans and majorly lack community and residential preparedness for heatwaves. Therefore, this study identifies potential community- and residential-based adaptation strategies to mitigate heat discomfort. As prospective solutions, the study recommends adaptation strategies such as blue–green spaces, indoor passive cooling, infrastructural adjustments, heat action plans, etc. However, such adaptation measures require a holistic amalgamation of different stakeholders to fabricate heatwave-resilient cities.

1. Introduction

It is unequivocal to say that anthropogenic activities have influenced the atmosphere leading to weather and climate extremes. According to the Intergovernmental Panel on Climate Change (IPCC) 2021 report, the global surface temperature has been 1.09 °C higher in recent decades, i.e., 2011–2020, than 1850–1900 [1]. The human-mediated global surface temperature increase is around 1.07 °C from 1850 to 2019 [1]. Furthermore, the IPCC has elucidated that the frequency and intensity of hot extremes (including heatwaves) have become severe across most regions. Heatwaves are high-surface--temperature episodes, persisting for several days during summers [2]. Especially over the last century, heatwaves have become more frequent in developing regions [1]. The warming trend over Asia reported 2020 as the warmest year on record, with mean temperature being 1.39 °C higher than the average from 1981 to 2010 [3]. Compared to the global mean surface, land, and air temperature, the surface temperature over Asian countries has risen considerably [4]. Moreover, future projections suggest that annual average temperatures will increase by 1.6 °C (2.9 °F) by 2050 in South Asia under the climate-sensitive scenario [5]. Additionally, heatwaves and heat stress will be more intense and frequent in South Asia [6].

Even though the frequencies and intensities of heatwaves are increasing considerably, there is no universal definition of a heatwave [7,8]. This is mainly due to a lack of consensus and varied population responses to heatwaves across different regions [9]. Different studies use diverse definitions, and it is widely understood as the exceedance of fixed absolute values and deviation from normal. According to IPCC, warm spells or heatwaves are abnormally warm weather [1]. The World Meteorological Organization (WMO) defined a heatwave as “A period of marked unusual hot weather over a region persisting for at least three consecutive days during the warm period of the year based on local climatological conditions, with thermal conditions recorded above-given thresholds” [10]. Without an adequate, universally accepted definition, it is difficult to quantify the severity and intensities of heatwaves for future assessment and projections. Moreover, it is difficult to assess the cost–benefits of adaptations responding to heatwaves, such as a heatwave warning system.

Heatwaves have been recognized as a public health concern due to the adverse thermoregulatory response of the population [11,12]. The risk of morbidity and mortality varies across the population depending upon tolerance limits and days of exposure [13,14,15]. The body of literature reveals that heatwaves negatively affect air quality, infrastructure, energy supply, and the health and well-being of people [16,17,18]. Overheating effects lead to higher mortality; for instance, the summer heatwaves of 2003 in Europe registered around 40,000 deaths [19].

The South Asian region, encompassing more than one-fifth of the world’s population [20] with dry, temperate, and tropical climates, as per Köppen–Geiger classification, is considerably more vulnerable [21]. The hot and humid climatic conditions in summers, dense populations, and rapid urban agglomeration lead to urban heat island effects and further increase the region’s vulnerability to long-lasting heatwaves [18,22,23]. Due to poor air-conditioning access and reliance on agricultural and labor work, staying indoors and escaping heatwaves is difficult for the population [22]. In terms of vulnerability, 30.4% of the South Asian urban population lives in informal settlements, the share being considerably higher for countries such as Afghanistan (62.7%), Bangladesh (55.1%), Nepal (54.3%), and Pakistan (45.5%) [23]. Furthermore, it has been projected that tropical and subtropical countries might experience more prominent seasonal and annual mean temperatures than mid-latitudes [24]. Hence, it is necessary to radically alter the current trajectories of heat extremes by suitable adaptation strategies, including residential, behavioral, and policy modifications.

Thus, to articulate the heatwave-related loss to health and economy, it is necessary to understand heatwave classification explicitly. Some studies have suggested that even a minor change in definition leads to an apparent effect on the estimated health impacts [11,25]. Hence, this study aims to identify various heatwave definitions and thresholds to facilitate comparative evidence. Due to the higher heat-based vulnerability of South Asia, it requires a thorough review of the temperature trends, heatwave-associated health risks, current practices, and policies in the region. Although temperature trends have been analyzed in the literature, the literature detailing temperature trends and extreme temperature events in the South Asian region is relatively scant. Therefore, this paper has comprehensively and critically reviewed existing literature to characterize heatwaves in South Asian countries. Furthermore, the study has worked towards compiling various heatwave adaptation strategies, which can help policymakers, administrators, and the scientific community worldwide.

2. Method

Heatwaves have not been defined explicitly, and there are many definitions of heatwaves in use. This paper reviews various definitions of heatwaves that have been used in literature in the South Asian region to facilitate comparative evidence. The review has specifically identified the population’s vulnerability to heatwaves during recent years and heatwave management policies in the region. The literature was searched using Google Scholar, PubMed, and SCOPUS. The keywords used for the literature search included “heatwaves”, “temperature thresholds”, “health risk”, “South Asia”, “heatwave-adaptations”, “thermal-adaptations”, and “respective South Asian countries like India, Pakistan etc.”. The study included all the relevant literature related to the review and study area.

Furthermore, to understand the time series trend of average annual temperature in South Asian countries, we retrieved open-source temperature data from World Bank (available at: https://climateknowledgeportal.worldbank.org/download-data, accessed on 3 February 2022) from 1900 to 2020. R studio’s Kendall package was used to perform the Mann–Kendall test for trends. Map was created using QGIS Geographic Information System, Open Source Geospatial Foundation Project (http://qgis.osgeo.org, accessed on 3 February 2022).

Finally, the study investigated various adaptation strategies for South Asian countries to mitigate the associated risk of heatwaves.

3. Heatwave Scenario in Global South Asian Countries

3.1. Historical Temperature Trends

Around 26% of the total world’s population lives in Southern Asia [26], and the region constitutes eight countries, including Afghanistan, India, Pakistan, Bangladesh, Sri Lanka, Nepal, Bhutan, and the Maldives (Figure 1). The average annual temperature is heterogeneous in the region (

Table 1. Average temperature trends in South Asian countries.

Countries	Annual Average Temperature Range (1990–2010)	Historic Trend (per Decade) (1990–2010)	Increased Trend (1950–2010)
Afghanistan	5 to 15 °C	0.27 °C	2.5 °C to 3.0 °C
Pakistan	15 to 20 °C	0.17 °C	2.5 °C to 3.0 °C
Nepal	−5 to 15 °C	0.14 °C	1.0 °C to 1.5 °C
Bhutan	−5 to 15 °C	0.15 °C	N/A
India	20 to 30 °C	0.11 °C	1.0 °C to 1.5 °C
Bangladesh	25 to 30 °C	0.09 °C	1.0 °C to 3.0 °C
Sri Lanka	25 to 30 °C	0.17 °C	1.0 °C to 3.0 °C
Maldives	25 to 30 °C	0.07 °C	0.8 °C

Reference: [5].

). Similar to Sri Lanka and Maldives, island countries surrounded by the Indian Ocean experience higher annual average temperatures of 26.70 °C and 27.66 °C. However, Afghanistan, Nepal, and Bhutan have comparatively colder climates, with annual average temperatures of 12.99 °C, 12.77 °C, and 11.61 °C, respectively.

The data of historical temperature trends from 1990 to 2010 revealed higher temperature changes per decade for Afghanistan (0.27 °C), Pakistan (0.17 °C), and Sri Lanka (0.17 °C), while comparatively lower changes were observed per decade for Bangladesh (0.09 °C), India (0.11 °C), Nepal (0.14 °C), Bhutan (0.15 °C), and Maldives (0.07 °C) [5]. In comparison, Afghanistan and Pakistan experienced the highest temperature change with 2.5 °C to 3.0 °C annual average temperature rise from 1950 to 2010, while other South Asian countries, except for Maldives and Bhutan, experienced a rise in annual average temperatures of 1.0 °C to 3.0 °C for the same time frame. The Maldives experienced the smallest temperature change, with a rise of 0.80 °C. Likewise, a study from Bhutan reports an increasing trend in the country’s mean temperature; however, the exact temperature change is not available; the change ranged between 0.74 °C to 0.85 °C [27].

Varying mechanisms can explain the differential changes in annual average temperature trends. The small rise in annual average temperatures in Maldives and Bhutan, with a population of 533,900 [28] and 763,092 [29] as of 2019, respectively, can be linked to the least anthropological intrusions. On the other hand, based on the geographical placement, countries surrounded by oceans experience reduced surface temperature and heat stress on the human body due to the cooling effects of sea breeze [30]. In contrast, inland areas with arid and semiarid regions (such as Pakistan, parts of India, and Afghanistan) where dry soil heats very fast in direct sunlight experience greater vulnerability and sensitivity to increasing temperatures. In addition, the literature suggests that urban heat island effect shows an increasing trend from low to high latitudes, thereby varying annual average temperature change [31].

The test results of all the countries revealed a statistically significant (at 0.05 level of significance) upward trend in the annual average temperature series, as shown in Figure 2. Nepal, India, Pakistan, Afghanistan, and Sri Lanka have experienced a steep rise in annual average temperature starting from the 1980s, while countries such as Bhutan, Bangladesh, and the Maldives have not encountered rapid change. The prior studies estimated that temperature change varies across South Asian countries, but the direction of the changes was unambiguous [5]. Especially for countries such as Afghanistan, Bhutan, and Maldives, limited literature detailing the temperature trend is available.

3.2. Heatwave Definitions

South Asian countries are experiencing prevailing heatwaves [33], and the definition varies across the countries with differential temperature intensity, threshold, and durations. It is necessary to understand the regional characteristics of heatwaves based on topographies to facilitate comparative evidence and future projections. Out of the reviewed literature in the South Asian region, most of the studies utilized relative thresholds, while few studies considered absolute temperature thresholds [23,25,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63]. However, heatwaves are declared in respective countries based on the exceedance of absolute temperature thresholds. It is questionable whether temperature thresholds, relative or absolute robustly, explain the heat-associated health risk? Different temperature indicators such as mean temperature, maximum temperature, and minimum temperature were used to quantify heatwaves with varied duration ranging between two to eight days. The common percentile thresholds used in different studies include 85th, 90th, 95th, 97th, and 99th percentiles. The detailed information of various heatwave definitions used in the region is shown in

Table 2. Different definitions of heatwaves across South Asian countries.

Country	Threshold	Duration	Heatwave Definition	Reference
Afghanistan	90th percentile	3 consecutive days	Heatwaves are defined as in a year with at least three consecutive days above the threshold for the reference period 1981–2010. The threshold is calculated as the 90th percentile of daily maxima, centered on a 31-day window.	[25]
Pakistan	>40 °C and 45 °C	5 or 7 consecutive days	Temperature >40 °C and 45 °C for five and seven consecutive days.	[34]
Pakistan	45 °C or above	5 consecutive days	45 °C or above temperature for five consecutive days is considered a heatwave.	[42]
Pakistan	90th, 95th, and 99th percentile	-	The maximum temperature above different percentiles, namely, 90th, 95th, and 99th, is a heatwave.	[45]
Pakistan	>45 °C and >40 °C	-	Heatwave will be considered when the maximum temperature for the understudy meteorological station is >45 °C for plains and >40 °C for hilly areas.	[36]
Pakistan	42 °C, then a noted rise of 5 °C to 6 °C	8 consecutive days	When the average maximum temperature of the understudy station is equal to 42 °C, then a noted rise of 5 °C to 6 °C for 8 days or more is considered as a heatwave.	[36]
Pakistan	>45 °C	8 consecutive days	When the maximum temperature for a station is >45 °C for >8 days, it is considered a heatwave irrespective of the normal temperature trend.	[38]
Nepal	-	-	“Heatwave” is defined as a period of abnormally and uncomfortably hot and humid weather.	[39]
Bhutan, Maldives	95th percentile	≥3 days	A heatwave is defined as a period of three or more days where the daily temperature is above the long-term 95th percentile of the daily mean temperature.	[28,29]
India	44.5–46.8 °C	-	Qualified as a “heatwave” with daily maximum temperatures varying between 44.5–46.8 °C.	[36]
India	85th and 90th percentile	3 or 5 consecutive days	The number of three or five consecutive days with maximum temperature above the 90th percentile.	[43]
India	90th percentile	-	90th percentile of daily maximum (daytime) temperatures.	[41]
India	≥97th percentile	≥2 days	Heatwaves were defined as ≥2 days with local temperature ≥97th percentile.	[40]
Bangladesh	95th percentile	3 consecutive days	Daily minimum and maximum temperatures over the 95th percentile for three consecutive days are qualified as heatwaves.	[39]
Sri Lanka	95th percentile	≥3 days	A heatwave is defined as a period of three or more days where the daily temperature is above the long-term 95th percentile of the daily mean temperature.	[35]

. Studies from India and Pakistan qualified heatwaves based on a direct temperature threshold, i.e., the daily maximum temperature ranged between 40 to 45 °C without considering duration or periods [34,36]. However, this qualification narrows down the quantification of heatwaves and allows the declaration of a single day as a heatwave, in contrast to a common understanding of consecutive days. A notable exception to heatwave definitions is from one of Nepal’s studies. They considered qualitative explanation of abnormally hot and humid days as heatwaves (maximum temperature above 45 °C during summer) [37]. However, the Nepal Health Research Council (NHRC) 2018 report has proposed using a heat index to quantify the health risk associated with heatwaves [44]. Regrettably, for Bhutan and Maldives, there is no direct study or document available to define heatwaves. The definition of heatwaves considered here for Bhutan and Maldives reports World Bank classification and projections [28,29].

Other than absolute and relative temperature thresholds, some studies quantify heatwaves based on the Heat Wave Magnitude Index (HWMI), which considers both magnitude and duration. The HWMI is defined as the maximum magnitude of the heatwave in a year with more than three consecutive days of maximum temperature above the daily threshold for 1981–2010. The threshold is the 90th percentile of daily maxima, centered on a 31-day window [46]. The HWMI classifies heatwaves as severe (3.00–3.99), extreme (4.00–7.99), very extreme (8.00–15.99), super extreme (16.00–31.99), and ultra-extreme (>32.00) [48,49]. However, this index has been utilized by a limited number of studies [25] to quantify the number of heatwaves. Another index utilized by one of the Indian studies is the excess heat factor (EHF), which captures the human health outcomes based on thermal intensity [42]. The EHF index considers both minimum and maximum temperature and explicitly accounts for long- and short-term anomalies [42,48].

Across South Asia, different countries are still relying on different metrics of heatwaves. These different metrics of heatwaves (absolute versus relative) provide different interpretations across the countries for different intensities and frequencies, creating difficulties and biasedness in epidemiological comparisons. Additionally, an absolute definition of heatwave implies more frequent heatwave episodes in warmer regions than colder regions [8]. In contrast, the relative threshold assumes an equal load of heatwaves across the regions [8]. However, the comparative evidence of which classification is robust is relatively scant. Moreover, a correct choice of definition to classify heatwaves in epidemiological studies and from a public health perspective is critically important. Thus, there is a need for a standardized definition of heatwave, at least on the regional scale; it stands to benefit public health policies [8,49].

4. Health Risk Associated with Heatwaves in South Asian Countries

South Asian countries are experiencing a higher risk of mortality associated with high temperatures [50].

Table 3. Health impact of heatwaves across South Asian countries.

Location	Study Period	Impacts of Heatwaves	Reference
Pakistan	2015 heatwaves	The 2015 heatwaves in Pakistan resulted in the death toll of 1233 due to hyperthermia. Around 65,000 people were treated for heatstroke.	[56]
Pakistan	2000–2019	All-cause mortality increased by 27% with a temperature range between 35–40 °C, while by 11% with a temperature range between 30–35 °C.	[60]
Karachi, Pakistan	2015 heatwaves	Heat-related causes of death during June 2015 heatwaves were 18% higher than the reference period of June 2014 [95% CI: 13.87–22.53].	[55]
Nepal	2009–2014	Hospitalization/death increased by 2.1% to 7.3% per 1 °C rise in temperature. All-cause deaths rose by 0.9% to 8.2% per 1 °C change in temperature below or above 20 °C.	[57]
Bhutan	1961–1990	Heat-related deaths in people above 65 years could increase to 49 deaths per 100,000 by the 2080s.	[29]
Ahmedabad, India	May 2010 heatwave	Around 4462 all-cause deaths occurred, comprising 1344 excess all-cause deaths, an estimated 43.1% increase compared to 2009 and 2011 (3118 deaths).	[36]
India	2000–2012	Across communities, total mortality increased by 18.1% during heatwave days compared to non-heatwave days [95% CI: −5.3, 47.3].	[49]
India	1992–2016	Across India, in the 24 years between 1992 and 2016, 25,716 heat-related deaths were reported, with 1111 and 2040 deaths reported in 2015 and 2016, respectively.	[51]
India	1972, 1988, 1998, and 2003	During the 1972, 1988, 1998, and 2003 heatwaves, with over ten heatwave days on average across India, heat-related mass mortality ranged between 650 and 1500 people.	[52]
Bangladesh	1989–2011	Mortality increased by 22% during heatwave days [95% CI: 8–38].	[39]
Bangladesh	2003–2007	Heat effects increased the all-cause mortality by 1–3%.	[61]
Sri Lanka	2019	The outbreak of diseases caused by heatwaves was identified as a serious concern.	[62]
Maldives	2015–2016	Severe heat stress resulted in high coral mortality on Maldivian Reefs following the 2015–2016 El Niño event.	[63]

presents the sensitivity and vulnerability of the population to recent heatwaves in South Asian countries. However, a limited number of studies have estimated the health risk attributed to heatwaves in these countries. From the Indian continent, a few studies reported increased all-cause deaths during heatwave days compared to non-heatwave days [36,49,50,51,52]. Between 1992 and 2016, India had experienced 25,716 heat-related deaths [51]. Bangladesh reported an increase in mortality by 22% during heatwave days [39].

In contrast, a few studies from Bangladesh suggested that heatwaves do not affect health due to better adaptation responses of populations, while cold spells cause an increase in all-cause mortality [53,54]. On the other hand, Pakistan also has accounted for a higher death toll during the 2015 heatwave event, with a 17% increase in the mortality rate compared to 2014 [55]. Heatwaves in Pakistan in 2015 resulted in around 1233 deaths among the population due to hyperthermia [56]. A study from Nepal also reported a higher death toll of 7.3%, with a 1 °C rise in temperature [57]. Based on the United Nations Office for Disaster Risk Reduction (UNISDR) data source, in Nepal, 49 cases of heatwaves were reported from 1970 to 2013 [58]. Even though mortality rates associated with heatwaves in South Asian countries are considerable, only a few studies are available for quantification. During the past three decades, mostly India and Pakistan have reported a higher death toll due to heatwaves [59]. In Pakistan and parts of India, climatic conditions are arid and semiarid, where dry soil heats fast in the direct sunlight and can be linked to high surface temperatures and thermal discomfort. However, it would be naïve to say that other countries did not experience severe health consequences of heatwaves, considering only a few studies from other countries reported heat-associated health risks.

There is no study available for Afghanistan, Bhutan, Sri Lanka, and the Maldives to quantify the associated morbidity or mortality directly. Sri Lanka has reported an increased incidence of disease outbreaks during heatwave days; however, death tolls have not been accounted [62]. According to the World Bank Report of 2021, Bhutan is expected to experience 49 deaths per 100,000 population by 2080 due to heatwaves [29]. In Maldives, due to the limitation of no heat-related health-risk estimation, this review has considered heat stress linked to high coral reef mortality, however, raising concern for population health [63]. Even though the Maldives has experienced the smallest temperature change over the decades, it is necessary to quantify the impact of heatwaves on the population, which is currently limited.

Additionally, most studies have only quantified heat-associated mortality; however, the region rarely considers heat-associated morbidity. Some studies from South Asian countries have identified increased rates of infectious diseases such as diarrhea [64,65,66,67] and cholera [68,69] with an increase in temperature. However, the effect of extreme temperature or heatwaves on the health risk of various infectious and non-infectious diseases is evaluated rarely. It would be interesting and rather necessary to understand the health risks in extreme temperature (heat spells) scenarios.

5. Existing Policies for Climate Change Mitigation and Heatwave Management

The review of existing policies revealed that most of the actions consider the overall climate change picture [28,29,35,70,71,72,73,74,75,76,77,78]. There are limited policies available to address heatwave management plans in South Asian countries, as shown in

Table 4. Present national action plans and strategies for heatwave and climate change mitigation in South Asian countries. The grey colored shaded areas denote heatwave-specific policies or actions in each country.

Countries	Nation/Local Action Plans	Interventions	Reference
Afghanistan	» National Adaptation Program of Action for Climate Change (NAPA) » Disaster Management Strategy (2014–2017) » Nationally Determined Contribution (NDC), 2016	» Climate-smart water and agriculture management; resilient natural capital » Shock-responsive social protection, multi-hazard risk information, and early warning » Resilient infrastructure and clean energy	[72]
Pakistan	» Technology Needs Assessment for Climate Change Adaptation, 2016 » National Disaster Risk Reduction Policy	» Energy decarbonization » Agriculture–water nexus » Climate-resilient infrastructure and communities	[70]
	» National Disaster Management Authority: Heat Action Plan	» Community outreach to build public awareness » Early warning systems and inter-agency coordination: three-tier alerting system	[75]
Nepal	» National Disaster Response Framework (NDRF) » National Adaptation Programme of Action (NAPA) to Climate Change	» Water and resilient natural capital » Climate-resilient cities, towns, viable state, and local governments » Clean energy » Climate-smart transport networks » Human development for economic and environmental resilience	[78]
	» Red Cross Red Crescent Climate Centre: Heat actions plans for Nepalgunj in Nepal	» Guidance note on early warning, early actions (EWEA)	[76]
Bhutan	» Bhutan National Adaptation Program of Action (NAPA) » Disaster Management Act of Bhutan, 2013	» Sustainable renewable natural resources » Resilient infrastructure » Human capital for resilience » Macro-fiscal resilience and risk-informed decision-making	[29]
India	» National Action Plan on Climate Change (2008)	» Decarbonization (energy and transport) » Agriculture–water–energy–air nexus » Sustainable urbanization » Public awareness campaigns » Department coordination and water supply	[71]
	» National Resource Defense Council (NRDC): Heat Action Plan (HAP)	» Cool roofs and adaptive measures » Community outreach to build public awareness » Early warning systems and inter-agency coordination: three-tier alerting system » Addressing vulnerable groups	[74]
Bangladesh	» National Adaptation Program of Action (NAPA), 2005 » Climate Change Strategy and Action Plan (BCCSAP), 2008	» Adaptive delta management and coastal resilience » Human capital for resilience » Community-supported agriculture » Low-carbon and resilient infrastructure » Green growth and macro-fiscal resilience	[73]
	» Red Cross Red Crescent Climate Centre: Heat actions plans for Rajshahi in Bangladesh	» Guidance note on early warning, early actions (EWEA) » Development of information, education, and communication (IEC) material	[76]
Sri Lanka	» National Adaptation Plan (NAP) for Climate Change Impacts in Sri Lanka » National Policy on Disaster Management	» Resilient infrastructure and livelihoods » Integrated landscape management, agriculture, watershed management, and forests » Clean energy	[35]
Maldives	» Strategic Action Plan 2019–2023 » Maldives Climate Change Policy Framework » National Adaptation Program of Action (NAPA)	» Coastal and infrastructure resilience » Government, island, and atoll council capacity, development » Livelihoods resilience » Clean energy	[28]

. Countries such as Nepal, India, Pakistan, and Bangladesh have established heatwave management plans with different spatial presences. However, Afghanistan, Maldives, Sri Lanka, and Bhutan do not have specific policies to address heatwaves. Among South Asian countries, the Ahmedabad, India, Heat Action Plan (HAP) of 2013 was the pioneer to ramp cities, states, and national levels for heat preparedness [74]. Later, Pakistan also developed an HAP for Karachi city with the support of the Climate and Development Knowledge Network (CDKN) to develop a heatwave management plan [75]. The HAPs of Nepal and Bangladesh, supported by the Red Cross Red Crescent Climate Centre, are concentrated locally [76]. Both countries’ programs focus on developing guidance notes on early warning, early actions (EWEA) and dissemination of information, education, and communication (IEC) materials such as videos, leaflets, etc. [76]. Similarly, early warning systems for heatwaves in Afghanistan have not yet been established, but policy documents are under discussion [77].

On the other hand, less impacted countries such as Bhutan and Maldives rely on broader climate change policies under the National Adaptation Program of Action (NAPA) [28,29]. However, integrating climate change policies into heatwave management plans is an area of concern in LMICs due to the lack of resources and institutional capacities [79]. In addition, the review of present policy documents revealed a lack of integration of community-based adaptations, and only India and Pakistan could develop a heat alert system. Therefore, the next section of this paper focuses on refining adaptation strategies for South Asian countries to reduce the health risk associated with heatwaves and thermal discomfort.

6. Community-Based Adaptation Strategies for Heatwave Moderation

Sustainable transformation and heatwave preparedness can only be achieved in communities if different mainstreaming adaptation strategies are integrated into the system. The review of different adaptation strategies and prevailing approaches is presented in

Table 5. Potential adaptation and mitigation strategies for heatwaves in South Asian Countries.

Approach	Adaptation Strategies	Stakeholders	Significance	Reference
Outdoor cooling strategies	- Pavements: Use of higher albedo materials	- Government administrators and urban planners	- High albedo can reduce the urban heat island effects	[18,79,80]
	- Urban parks: Different vegetation species utilization	- Government administrators and urban planners	- Reduce temperature and increase evapotranspiration	[18]
	- Urban shading	- Community and government administrators	- Improved outdoor thermal comfort	[81,82]
	- Urban blue–green space	- Urban planners	- Cooling effects	[83,84]
Infrastructural	- Blue–green infrastructure in buildings	- Government administrators, urban planners and community	- Reduce temperature and increase evapotranspiration	[85,86,87]
	- Structural parameters of buildings: height of a building, percentage of built area, rooftop spectral attributes, aspect, slope	- Urban planners, community and architects	- Building density and height dictate the value of the surface temperature	[88,89,90,91,92,93,94]
Passive cooling strategies(indoor)	- Green roofing, louvre shading devices	- Government administrators, urban planners, and community	- Effective roof insulation	[91,95]
	- Double glazing, light color coatings with high reflection		- Reduce the heat gain	[95]
	- Natural ventilation: wind catcher and cross ventilation		- Introduce cool air in the building	[95,96]
Heat action plans (HAPs)	- Heatwave early warning systems	- National agencies, government administrators, and researchers	- Heatwave preparedness	[81,97]
	- Assessment of vulnerability: safeguard outdoor workers- Develop a heat vulnerability index for high-risk subgroups		- Reduce health risk and vulnerability	[17,98,99,100]
	- Assessment of disease burdens associated with the heatwave		- Risk assessment and mitigations	[101,102,103]
Administrative and policy	- Spatial mapping approach for urban planners	- Government administrators, researchers, and urban planners	- Guided planning of urban cities	[104,105]
	- Developing collaborative partnerships to bridge technical deficits	- Government administrators	- Better policy dialogues	[106,107]
	- Building political consensus for climate action	- Government administrators, national, and international agencies	- Better policy dialogues	[106]
	- Local planning initiatives while building broader support for substantial climate action	- National/local agencies, government administrators, and NGOs	- Better policy dialogues and community awareness	[106]
	- Better flexibility in the number of ambulances, increased response times - Establish medical support via telephones as an effective pre-hospital measure for people and hospitals.	- Healthcare agencies, government administrators	- Health sector preparedness for health hazards	[17,40,49,102,103,106]
	- Developing workplace policies to avoid occupational hazards	- Policymakers, national/international agencies	- Occupational health	[17]
	- Distribution of oral rehydration solutions (ORS) as a preventive measure	- Healthcare agencies, government administrators, and NGOs	- Health sector preparedness	[107]
Behavioral	- Raise awareness: regular showers, drinking plenty of water, spending summer nights outside on lawns or the rooftops, and tree shelters during peak summer hot hours	- National agencies, government administrators, NGOs, and community	- Reduced vulnerability, awareness, and behavioral changes	[36,94]

. Adaptation measures are categorized under the following categories: outdoor cooling strategies, infrastructural, passive cooling strategies (indoor), heat action plans (HAPs), administrative and policy mitigations, and behavioral measures. Further, key stakeholders required to draw actions and future development are also identified. Most adaptation strategies are not yet translated into practice in South Asian countries and require cooperation among stakeholders.

6.1. Outdoor Cooling Strategies

The health risk and thermal discomfort of South Asian communities are majorly experienced in the outer environment due to higher involvement in labor works, industries, and agricultural activities. A solution to warming urban spaces in the cities is to modify pavement structures via adjustment of surface albedo. Albedo measures how well a surface reflects solar energy; the values range between zero to one, and a value of zero indicates a surface with perfect absorbing capacity. The present pavement constructions constitute granite with an albedo of 0.4. Increasing the albedo can improve pedestrian thermal comfort [18,79,80]. A study conducted by Falasca et al. mentioned that heatwaves increase the temperature up to 4 °C at 2 m height, while higher albedo materials covering all urban built surfaces (rooftops, pavements) could stabilize this increase [80].

In addition, urban blue–green spaces, a new architectural tool for urban spaces in cities, provide synergistic cooling effects and moderate the urban heat island effect, thus providing thermal comfort for users. The model of green spaces is an effective strategy in open spaces to reduce temperature and increase evapotranspiration [18]. Trees with wide crowns and high trunks are recommended for their effect on the airflow and to counteract the impact of increased thermal stress [108]. Tree species with higher leaf area index (LAI) showed better below-canopy surface cooling, and simultaneously, incorporation of cluster tree planting provides better thermal comfort [109]. Strategic selection and placement of trees with dense canopies can reduce the urban heat island effect and reduce air temperatures by 2 °C and 8 °C [110,111]. Large tree canopies and canopy-covered pedestrian areas result in the thermal comfort of the community during outdoor activities [85]. A study in Beijing, China, identified the potential of a long belt-shaped park (around 9 km) and its landscape parameters’ effects on increased thermal comfort [108]. Another study reported that increasing ecological land coverage and urban water bodies in metropolitan cities could significantly reduce urban heat island effects [84]. The green cover ratio, i.e., the total area of all green spaces (above the canopy) to the land area, effectively improves urban thermal comfort [88]. Urban parks and pedestrian spaces are the best areas to incorporate green patches and water bodies to reduce heating effects in cities.

Outdoor urban shadings from buildings, trees, and umbrellas/shade covers can also instigate cooling effects [83,85]. A study in Canada reported that urban shading from buildings, followed by trees and umbrellas, is an effective cooling strategy on sunny days. At the same time, it can vary during non-sunny days [112]. The potential effects of building density (% of built area) and canyon effect (building height) are also considerable parameters. A study from Rome, Italy, reported that taller buildings result in lower surrounding temperatures; this can be due to the shading effect of taller buildings at street level. However, higher building density can increase the outdoor temperature around the buildings [113]. Therefore, high ratios of building heights and less density are two crucial aspects for urban planners to reduce heating effects.

6.2. Infrastructural Adaptations

Growing unplanned urbanization without the resilient infrastructure to cope with rising temperatures in South Asian countries results in hazardous heat exposure to the population [114]. The government administrators and urban planners across South Asian nations require physical interventions for environmentally conscious urban development, such as blue–green infrastructures, while developing new settlements in cooperation with the community. Blue–green infrastructures explicitly focus on integrating vegetation and water spaces in buildings to reduce the temperature [87,88,89]. A study in Colombo, Sri Lanka, identified a reduction in temperature by 1.6 to 1.7 °C around the buildings integrated with “green walls”. Further, a reduced outer temperature can significantly improve the indoor temperature of buildings [87]. Similar articulations were also made in North America and Europe, where studies mentioned that temperature decreases by around 10 °C or more with increased vegetation than on an impervious surface [88,89]. Urban greenery systems provide the potential for energy savings in buildings [115]. Further, green spaces also improve air quality via air purification, better circulation efficiency [115,116,117,118], and help in reducing the concentration of particulate matter [111,112,113], which could co-benefit health outcomes [119].

Furthermore, slight modifications in structural parameters while constructing new settlements can also help reduce indoor temperatures. Architects and urban planners need to consider structural parameters such as the height of the buildings, built area, rooftop spectral attributes, slopes, etc. [91,92,93,94,114,115,116]. Studies claim that sprawling urban areas with complex structures of buildings affect the heat storage capability of the buildings [90]. Urban geometry (spacing between buildings), building height, the ratio of a building’s height to its width (H/W), and shape manipulate the surface albedo and lead to higher indoor temperature [94]. With the integration of smart design to sense and regulate temperature change, buildings can become a futuristic norm for resilient cities, although retrofitting old infrastructures is also a choice.

6.3. Passive Cooling Strategies (Indoor)

Passive cooling strategies to reduce indoor temperature are sustainable solutions that can eventually reduce greenhouse gas emissions through reduced energy load [120,121,122]. Passive cooling strategies prevent heat from entering or allow heat dissipation with low or no energy consumption. A study conducted in the United Arab Emirates (U.A.E.) studied the effects of eight passive cooling strategies, including wind catcher/cross ventilation, green roofs, louvre shading devices, double glazing, insulation, higher solar reflection (light color coatings), evaporative (fountains), and indirect radiant cooling [95]. Another study reported that out of glazing, shading, and ventilation, ventilation has better cooling effects in a dry and humid environment [123]. The passive cooling strategies can also reduce the cooling load by 9% and even reduce energy consumption by around 24% [95].

Further, cool coatings over buildings are also a potential intervention; coating materials should be intrinsically characterized by high albedo [122]. A study reported that cool coatings over roofs could reduce 18–93% of cooling load and 11–27% of air-conditioning demands in buildings [123]. However, passive cooling strategies depend upon the climatic conditions and should be utilized accordingly. Therefore, further studies are necessary to test whether these strategies are applicable in South Asian countries.

6.4. Heat Action Plans (HAPs)

Heat action plans (HAPs) are an administrative tool that defines heat emergencies at the city/local level and increases the population’s preparedness against scorching heat extremes [100]. It was observed that the heatwave response system exists in India, Bangladesh, Pakistan, Sri Lanka, Bangladesh, Nepal, and Afghanistan; however, it has not been scaled up to a large scale [23]. Further, HAPs are majorly adopted in Pakistan and India to build public awareness, heatwave early warning systems, capacity building of health professionals, and reduce heat exposure via adaptive measures. The Ahmedabad HAP focused on building community outreach to build public awareness and developed a three-tier alerting system with different color codes. HAPs also focus on the community’s vulnerability assessment and safeguarding outdoor workers [81]. In 2016, the National Disaster Management Authority (NDMA) of India issued “Guidelines for Preparation of Action Plan-Prevention and Management of Heat-Wave” for other cities and updated it in 2017 and 2019; however, it has not yet been scaled up [23].

Developing early warning systems for extreme heat and heatwaves induces a dynamical statistical temperature forecast system [100]. Although most South Asian countries do not have active heat alerting systems, this is majorly due to a lack of data availability and research capacity. Therefore, a common heatwave early warning system can be developed; however, it requires a uniform enactment and understanding of heatwaves in the region. The estimated cost of running heat warning systems is USD 210,000 [124], and therefore creates a financial barrier for developing countries. However, one of the studies from Australia suggested that a heatwave warning system can save attributable health costs between AUD 1,498,000–2,513,000 (USD 1 = AUD 1.35) [125]. An integrated investment in early warning systems in a region can reduce cost and developmental burden for South Asian countries. The body of literature supports the notion that a heatwave warning system can be an effective tool in reducing heat-related mortality and morbidity [36,124]. For instance, a study from France estimated that nearly 4400 excess deaths were avoided with the development of a heatwave warning system in 2006 [126].

6.5. Administrative and Policy Measures

South Asian countries require fewer resource-intensive adaptation strategies and less planning at a local level to overcome inherent local resource constraints and institutional limitations. The potential strategies identified in this study aim at implementing adaptation related to local planning initiatives. Spatial planning is an appropriate tool against future vulnerabilities, and the government/researcher/urban planners can develop spatial planning models to combat heatwave exposures. The spatial mapping approach for urban planners integrated with climate change is a key tool for resilient cities and regions [104,127].

Another crucial aspect of success in mitigation strategies is the holistic involvement of various stakeholders to initiate better policy dialogues [59]. Developing collaborative partnerships to bridge technical deficits, reforming local organizational structures to generate internal resources, and building political consensus for climate action is essential for successful climate adaptation [106]. Stakeholder engagement will ensure that the needs of the end-users are understood and incorporated carefully. A successful case study from Ahmedabad HAP advocated the integration of meteorological and healthcare departments for substantial heatwave preparedness [36].

Further, awareness, education, and public outreach activities via government training workshops, billboards, pamphlets, and print advertisements are also necessary to disseminate the severity of heat stress [36,77]. Better healthcare system flexibilities such as increased ambulance response time [17,100,102,103] and healthcare support systems via telephones are some pre-hospitalization measures [40,100]. To enhance the healthcare delivery and preventive measures at local scales, NGOs can be involved; for instance, the distribution of O.R.S. via NGOs can improve the resiliency of the health sector. Further, policymakers and authorities must develop workplace policies to avoid prolonged heat exposure and occupational hazards [17].

6.6. Behavioral Measures

Adaptation to heatwaves also requires behavior adjustment to reduce the adverse health effects of any calamity. Behavioral changes (e.g., staying indoors, clothing choices, water consumption) offer a high degree of acclimatization against changing thermal discomfort [49], reducing the relative health impacts. Behavioral changes have been successfully brought about via awareness programs and community outreach [128]. The behavioral mitigation measures by Ehsaan et al. for heatwaves suggested regular showers, plenty of water consumption, spending summer nights on lawns or rooftops, taking shades outside during peak hours, and plantation of trees with greenery and thick canopy [94]. In addition, the series of outreach programs via NGOs and government agencies through televisions, radios, newspapers, and pamphlets can result in the development of local campaigns and increased awareness among communities against heat illness [81]. The public’s outreach and communication can increase the public’s heat preparedness to address health threats.

Further, the communication activities can be scaled up through formal information-exchange opportunities such as workshops, training, and conferences [100]. Another solution for LMICs is increasing access to water (via keeping water pots/tanks) at different city locations to reduce heat-related health hazards [36,77]. This practice can increase the frequency of water consumption among the population and help avoid heat strokes.

7. Remarks

All South Asian countries have undergone a rise in average annual temperature, which statistical testing has justified. This study adds value to the scientific community as the literature detailing temperature trends in South Asian countries is relatively scant. Unfortunately, only a few studies have quantified the impact of heatwaves in the South Asian region, and countries such as Afghanistan, Sri Lanka, Bhutan, and Maldives still lack heat-based health-risk assessment. It is essential to mention that the lack of literature in the region reporting heat-associated health risks needs attention.

As per the study of relevant policy documents, only a few countries in the region have developed a heat response system, but they have not been scaled up in the large parts of the countries. Therefore, a heatwave warning system under the unified classification of heatwaves is recommended to improve the heatwave preparedness of communities and cities. The South Asian population is highly vulnerable and sensitive to increasing heatwave events due to higher dependency on natural systems, unplanned urbanization, and city planning without resilient infrastructures. Therefore, this necessitates a set of capacities to generate and disseminate meaningful warning information to communities, health sectors, and individuals. The appropriate and quick population response with an enhanced warning system can help to reduce possible health hazards. Currently, if developed, heatwave operating systems will rely upon different thresholds, intensities, and frequencies of temperature for forecasting; however, to some extent, it can degrade the predictive performance. Therefore, early warning systems should evaluate different epidemiological data based on a common foundation of heatwave warnings. Additionally, quantifying health risks based on different heatwave scenarios creates difficulties in comparing heat-associated health burdens and associated cost–benefit analysis.

Additionally, the scarcity of resources, capacities, and data sources to push forward scientific evidence of heatwave-associated health risks is acknowledged in this review. Even though a heatwave warning system is a potential solution to improve public health resiliency, it requires ample support and coordination from public health authorities and other sectors. Moreover, more scientific studies in the region to support the development of heatwave warning systems and preparedness are required.

Finally, the study suggests local landscape-based adaptation strategies; nevertheless, the interventions proposed in this study can be used to complement the decision-making of authorities and policymakers. Additionally, a holistic amalgamation of different stakeholders to support heatwave preparedness of cities would be beneficial.

8. Conclusions

The current review unravels the higher heat-related deaths and severe changes in temperature trends in a decade in the South Asian region. Indeed, the understanding of heat-associated mortality and morbidity is essential in tropical and sub-tropical countries of South Asia. It should be noted that the accuracy of these various considered heatwave definitions has not been confirmed and checked. Therefore, this study recommends enacting a common heatwave characterization measure worldwide or within the same geographical terrain. A unified definition of heatwave can enable smooth heat-based health-risk estimation and robust warning systems. In addition, it is essential to mention that adaptation strategies recommended in this study can improve cities’ resiliency against heatwaves. Including these adaptation strategies in the public health programs via the involvement of different sectors can increase public awareness and preparedness. Since evidence has recommended that a heatwave warning system can substantially reduce heat-associated health risks, at the initial stage, HAPs, along with behavioral measures across the South Asian region, can be useful. Moreover, the fabrication of resilient and sustainable cities through adaptation approaches and holistic amalgamation of different sectors stands to enormously benefit heatwave preparedness.