The evolved technology of Irrigation system have witnessed the Indo-Gangetic plains (IGP) become India’s food basket. But it is leading lives miserable for both farming and non farming community in this richly-irrigated area. It is reported by a study published in Nature Geoscience on Monday evening.
The study, carried out by Mr. Vimal Mishra and team of the Indian Institute of Technology, Gandhinagar has revealed that irrigation is amplifying humidity, which is in turn increasing ‘moist heat stress’ encountered by 46 million people living in IGP belt. The human body experiences Heat stress when the body cannot cool itself. Moist heat stress is seen to be potentially more life threatening as compared to dry heat stress, which happens when the atmosphere temperature is high.
While humans naturally have an ability to withstand relatively high dry temperatures but this comes down significantly when exposed to humidity. Studies have shown that a wet-bulb temperature of 35°C shows humans’ upper physiological limit, and there are alerting health and fertility issues even at much lower temperatures.
“Moist heat stress is strongly associated to the mortality than dry heat stress. It also related with higher discomfort for people working outside,” Mishra said.
India’s net irrigated area rose from 31 million hectares in 1970, to 60 million hectares by 2007. And it has increased upward since then. IGP is one of the most intensively irrigated regions in the world with more than 60-70 % of the area irrigated with surface or groundwater (open or bore wells).
Ongoing human-induced climate change has already intensified extreme temperature and is expected to get peak in India. This could further worsen heat stress, mainly among those working outdoors.
Cooling due to water evaporating from irrigation systems might partially counteract dry heat stress, although associated changes in humidity that could affect moist heat stress are poorly understood.
Mishra and his team analyzed the effects of irrigation on both dry and moist heat stress using a variety of in situ and satellite observations, together with numerical simulations.
The research team found that although irrigation causes land surface cooling, it also leads to substantially higher surface humidity. This is reducing the height of the lowest part of the atmosphere, known as the planetary boundary layer. As a result, irrigation mitigated dry heat stress, but increased moist heat stress.
The study has concluded that recent intensification of irrigation practices in India has increased the moist heat stress, and the associated risks to human health in the region. It also influencing neighbouring countries of Pakistan and Afghanistan. They also said that similar impacts from irrigation could be anticipated in other regions with similar semi-arid and monsoon climates.