Longer monsoon spell, warm winter lengthen mosquito-borne disease outbreaks across India
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By mid-September this year, the hill state of Himachal Pradesh erringly stared at a dengue outbreak like never before. It reported a sevenfold increase in dengue cases: from 453 in 2017 to 2,800 till mid-September. The Indian Council of Medical Research rushed teams to study the situation as an outbreak of that extent is rare in the hills.
This year it came early, in May, unlike last year when dengue cases were first reported in October. As government officials reported that people are storing water in open to tide over scarce spells, government resorted to “dry day” systems— water supply was stopped every Thursday to force people spend all stored water.
By November, vector-borne diseases tend to decline as winter sets in. But this year, like in the recent past, outbreaks of malaria, dengue and Chikungunya continue beyond this period. And its spread has been pan-India, from Arunachal Pradesh to Kerala.
According to the data of the National Vector Borne Disease Control Programme, by September the country has reported 0.32 million cases of malaria, dengue and Chikungunya. Currently, 30 states/Union Territories are reporting all of them or at least one of them. At 40,868 cases, dengue continues to spread. At the onset of monsoon in July, the country reported just 14,000 confirmed cases of dengue. There have been 0.27 million malaria cases and some 5,789 cases of Chikungunya have been reported.
There is an intimate linkage between weather condition and spells of vector-borne diseases. A longer rainy season creates the right situation for mosquitoes to breed while a warmer winter usually sustains the infection period.
This raises an alarm this year. The India Meteorological Department (IMD) has already warned of a warmer winter. The November till now has reported above normal temperature. And add to this the threat of the El Nino.
Media reports from across the states, including Delhi, has carried reports of doctors attributing to the warmer winter to the current spell of disease outbreak preceded by longer rain spells.
“Currently, moderate El Nino Southern Oscillation (ENSO) conditions are prevailing over equatorial Pacific Ocean. The current SST of Nino 3.4 is 0.7°C. El Nino is likely to develop in the next couple of months. Minimum temperatures are likely to be slight above normal over parts northwest, adjoining central and west India and some pocket of northeastern states and south Interior Karnataka till December 6,” according to IMD’s latest weather bulletin.
Though many states such as Maharashtra, Tamil Nadu, Jharkhand and Andhra Pradesh have reported slight declines in reported cases of vector-borne disease in comparison to last month, many other states continue to report fresh cases. But a warmer weather condition would just sustain this outbreak. IMD is expected to release a winter temperature forecast bulletin soon for December, January and February. But it has already forecast that during October-December the temperature would be above normal.
The 2017-2018 winters were the third consecutive warmer winter in India. February 2018 was the warmest in the last 118 years. Mean temperatures for January-February 2018 were 0.53°C higher than the normal of 22.17°C for this period.
DS Pai, head of IMD’s Climate Prediction Group, recently told the media that global warming could also be playing a role. “El Nino has not set in yet, so there may not be a big impact on the current temperatures. However, the phenomenon may reach threshold values during the October-November-December period, which might subsequently impact winter temperatures.
“Apart from El Nino, global warming could also be playing a role here as the temperatures in northwest India have been generally above the normal over the past few years. Last year’s winter too saw normal to slightly above-normal temperatures,” he added.
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