Weather and Epidemics: A strange early summer in India

Will warmer weather stop the spread of the coronavirus? | Science ...
Will warmer weather stop the spread of the coronavirus? |

Biswanath Dash, Ph.D. and Md. Shahid Akhter 16 April 2020


The relation between weather and disease is known since ancient times. Greek physician Hippocrates’s concept of ‘Epidemics’ described spread of disease through a population in a season. In his work around 380 BCE, he linked spread of the disease to human constitution and its interaction with physical environment (Polgreen and Polgreen, 2018). The same conception was carried forward by Roman physician, Galen (179-216 CE) who viewed disease to be an internalization of weather (Fisman, 2007). Hippocratic tradition of correlating propagation of disease with weather and season continued for a long period in western medicine, until seventeenth century germ or pathogen theories gained ground in the backdrop of advances in microscopy, physiology, anatomy and chemistry (Porter, 1997). During much of nineteenth and twentieth centuries, the focus of understanding related to disease and infection moved away from its association with weather and climate to host and pathogen, germ theories (Polgreen and Polgreen, 2018). This evolution resulted in the rejection of an erstwhile popular ‘miasmatic’ theory which related disease to bad odor or ‘miasma’. Emergence of climate change debate in recent times has resurrected the connection between weather and climate with new disease and infection, across geo-climatic regions. The ongoing global pandemic due to Corona is further likely to revive this debate in times to come.

 Role of weather condition in Corona spread

In the midst of an extended national lockdown in India to contain the spread of ‘Corona’ or ‘2019-nCoV’ virus, there is one aspect that deserves more attention than it has received so far. To what extent, tropical weather in general or Indian summer in particular will play out during this battle against an invisible virus. SARS outbreak in 2014 which happened to be from the same Corona family of pathogens was found to be environmentally sensitive, with its outer layer found to be breaking down at high temperature. Limited information about the novel corona virus such as its ability to survive and mutate in diverse environmental conditions has constrained a more systematic analysis. However a number of early studies have pointed out the need to look further in this direction. Wang et al. (2020) examined limited sample from China to argue that like earlier SARS CoV and Influenza; 2019-nCoV is also sensitive to increase in temperature and humidity. Sajadi et al. (2020) and Bu et al. (2020) contend that temperature, humidity and latitude are key analytical points to understand its propagation Chen at al. (2020) demonstrate that instead of single meteorological variable, a combination of them; air temperature, relative humidity, wind speed and visibility together can be used to model the spread of infection between January 20 to March 11 over 430 cities in China, 21 cities/provinces each in Italy and Japan and fifty one other countries. Bukhari & Jameel (2020) analyzed the spread of the virus until 22nd March, and observe that the growth is much rapid in areas such as Italy, South Korea, New York and Washington which have similar weather pattern as Hubei region of China with a mean temperature between 3-10 ° centigrade during months of February and March. In contrast, warmer and humid climatic countries such as Singapore, Malaysia, Thailand and Indonesia show a much slower growth rate possibly due to their warmer and humid conditions. An important factor that may be obfuscating this analysis is the testing strategy adopted in countries like India. Bukhari & Jameel (2020) acknowledge this dimension and observe, if there were significant population being affected but untested, it would eventually reflect in a steep surge in the number of respiratory patients at the hospital that will overwhelm existing capacities, as it turned out to be in Italy.

Notwithstanding findings of these aforementioned studies, there are a number of other studies which have contested the claims over the role of weather in virus transmission. For example, Luo et al. (2020) have argued that meteorological conditions may have some impact but will not determine the overall spread. Hence appropriate public health interventions are absolutely necessary. On the request of US government, an expert group under ‘The National Academies of Science, Engineering and Medicine’ has carried out a rapid analysis on extent of sensitivity of 2019-nCoV to temperature and humidity and seasonal change. In this review dated 7th April 2020, the panel argues that though there are experimental reports of environmental sensitivity, data support is rather limited and hence should be taken with much caution. Besides, there is contradictory evidence such as Australia and Iran where rising temperature fails to show a declining trend (TNASEM, 2020).

Indian summer so far: A strange weather

The annual mean land surface temperature for India is seen to be warmer particularly in the last four years or during 2016-2019. It was an all-time high in 2016 (since 1901) exhibiting an increase of 0.91°C over the average for the period 1961-1990. For the months of January-February in 2916, it was warmer by 1.43° C and during March-May of the same year, it was +1.36 °C (India Meteorological Department [IMD], 2017). The following year or 2017, the annual mean surface temperature was again 0.71°C higher than the mean temperature recorded over 1971-2000 and it was the fourth warmest since 1901. The months of January-February in 2017 showed an anomaly of +0.77°C and March-May period was also relatively warmer (IMD, 2018). During the last two years 2018 and 2019, the average land surface temperature was higher by +0.41° and + 0.36°C respectively over the average for the period 1981-2000, making them  the sixth and seventh warmest year respectively (IMD, 2019; 2020).

In this backdrop, India Meteorological Department (henceforth IMD) forecasts for the period December 2019-February 2020 was a warmer winter over most parts of the country except northern-most regions (IMD, 2019); and a similar forecast for the period of March to May 2020 predicting it to be warmer over most part of north-west, west and central India and some parts of south India (IMD, 2020b). Confirming to the forecast, January 2020 was observed to be relatively warmer, with South Peninsula showing an average of 26.32 degree C, an all-time high over the last eighty years (Madan, 2020). However ever since then, weather condition across the country is found to be generally less warm, which appears to have continued during most part of March and well into first week of April. Though the notion of a much cooler early summer remains to be supported by detailed observational records, there is another related aspect which merits further attention. Rainfall data for March 2020 culled out from IMD weekly bulletin (Table 1) shows a significant surplus in ‘received rainfall’ during the month of March, supporting the general perception of a lower than average surface temperature. 

Table 1: Average Weekly Rainfall for India during 27th Feb-1st April 2020

Time period (27th Feb-1st April 2020)Actual Rainfall (mm)Normal Rainfall (mm)% Departure from Long Period Average (LPA)
27th Feb-4th March4.75.1– 08%
05th-11th March14.16.1+ 131%
12-18th March14.16.1+131%
19-25th March5.48.3– 34%
26th March-1st April10.37.2+44%

Source: Compiled from IMD Fortnight Weather Status and Outlook, New Delhi

Detailed mean surface temperature for March 2020 is yet to be released by IMD. However Table 2 shows that during 2000-2017, the average mean temperature during the month of March was highest in 2016 at 26.61°C and lowest in 2000 at 23.22°C with an average of 24.46° C. From this perspective, if the mean surface temperature for March 2020 shows a further dip than the lower range, it raises a pointer and the need for a closer examination of prevalent meteorological conditions and corresponding spread of the epidemic. The exact temperature drop is unknown at this point, however, USA based National Oceanic and Atmospheric Administration (NOAA) in its report on Climate Assessment; dated 13th April 2020 shows that most part of India had cooler temperature in March 2020 except the southern most states of Tamilnadu and Kerala which recorded an average temperature as compared to the reference year range 1981-2010. This trend for India runs against a global pattern; during March 2020, the global average temperature blended for surface and ocean together is the second highest since 1880, and is next only to that of 2016; a year characterized with a strong El-Nino in tropical Pacific Ocean (NOAA, 2020). What explains such anomalies or a cooler March in India and how does that correspond to the epidemic rate of propagation and mortality?

Table 2: Average Mean Temperature (°C) in India during 2000-17

  Average in °C19.11521.1727824.46

                       (Source: IMD Mean Temperature Data)

Given the significance of collecting all relevant inputs for a better understanding of this deadly epidemic, It is important to analyze the temperature and humidity data in India, region wise for the month of February to May 2020 and find if there is any correlation between temperature variance and infection spread and rate of mortality besides establishing, the role of higher temperature and humidity in its virality. Take for example, state of Kerala and Tamilnadu both as of now, have good number of corona confirmed cases and are also impressive as far as number of people who have recovered. The hypothesis; weather condition an important attribute in the spread can be easily verified as a scorching April-June should stabilize the overall situation in these states as well as other similarly impacted ones such as Rajasthan, Telengana, Madhya Pradesh etc. Laboratory experiments can at best mimic the actual environment conditions, which is why there is a need to look beyond such studies to include observed weather parameters and disease impact. Notwithstanding results of studies conducted in the context of China, USA and elsewhere, Indian climate is varied and on account of its unique features, requires to be brought into relation with 2019-nCoV virus’ sustenance and its durability in these conditions. Such analysis will be useful for the policy makers as well in their endeavor to decide on an effective medium term containment strategy.

1. Biswanath Dash, Ph.D., Assistant Professor, Department of Humanities and Social Science, BITS Pilani, Hyderabad Campus, Hyderabad-500076, Telengana Email:

2. Md. Shahid Akhther, Research scholar, Department of Humanities and Social Science , BITS Pilani, Hyderabad Campus, Hyderabad-500076, Telengana.


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