Local weather plays a vital role in the spread of infectious and vector-borne diseases. A study by a team of experts in Pune has tracked and linked temperature and rainfall variations to the emergence of malaria and diarrhoea cases in Pune and Nagpur cities.

Led by A K Sahai from Indian Institute of Tropical Meteorology (IITM), the team tried to understand the role of these key weather parameters in the prevalence of malaria and diarrhoea and their spread, especially among children.

From over 3 lakh cases in 1996, India’s malaria cases had dropped to 34,000 in 2018. Similarly, deaths caused due to malaria in the country during the 1990s were above 1,000. However, in recent years, the mortality has been controlled and brought close to 100, as of 2018, stated data issued by the National Vector Borne Disease Control Programme (NVBDCP).

This year, the progressive cases of malaria (till July 28) have been the highest in Odisha (19,001), Chhattisgarh (18,933), Uttar Pradesh (4,667), Jharkhand (3,991) and Maharashtra (3,090), read NVBDCP statistics.

Monsoon is the transmission season for the majority of vector-borne diseases. But the Diurnal Temperature Range (DTR), which is the difference between the day’s maximum and minimum temperatures, is more crucial in the spread of diseases, co-author Dr Pradip Awate, state surveillance officer, Integrated Disease Surveillance Programme, Maharashtra, told The Indian Express.

Normally, the onset of the Southwest monsoon occurs first over Pune, around the middle of June and the season lasts till mid-October. Monsoon onset over Nagpur is realised towards the end of June and continues till September.

Apart from the onset and duration of monsoon in Pune and Nagpur, Dr Awate said the other major difference during this season was that “the weather is cooler in Pune during monsoon as opposed to dry weather conditions prevailing over Nagpur during this period. These variations also factor in the disease caseload from city to city.”

According to the study findings, Nagpur reports more malaria cases than Pune. Cases of malaria start to peak by July and continue to remain high till November in Nagpur. On the other hand, malaria cases in Pune start to emerge during the pre-monsoon season, that is, from May onwards. A sustained number of cases through the four-month rainy season are reported in the city, the researchers found.

Experts traced a higher number of diarrhoea cases being reported in Pune than Nagpur. The case trended during all the four monsoon months in Pune, whereas, caseload grew post July in Nagpur.

“What we understand is that even minor variations in temperature or rainfall over a short period of time combined with the city’s geography contributes to the spread of diseases,” said Sahai, who presently leads the country’s Monsoon Mission team at IITM.

Experts from the India Meteorological Department (IMD) and Savitribai Phule Pune University (SPPU), who were also part of the study published on Tuesday in the Scientific Reports of Nature, used health and climatological data between 2009 and 2016 for the two cities in Maharashtra.

On the applications of the study findings, the senior IITM scientist said, “Every city has a different geography and climatic conditions. If we are able to combine the climate and health data, it is possible to issue probabilistic health indicator forecasts for Indian cities at least two weeks in advance.”

On the biggest advantage of having an early disease outbreak warning, the Awate said it would allow the government time to arrange adequate medical supplies in addition to the required planning needed to tackle the diseases well in advance.