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River network raises crop fears

New Delhi, March 30: The proposed network of canals to link the country’s rivers might worsen fog during winters and devastate important crops across northern India, says a study.

The report, in the latest issue of Himal — a Nepal-based journal that focuses on South Asian issues — draws a link between existing irrigation canals and embankments across the Indo-Gangetic plain and the persistence of fog that can damage winter crops.

The proliferation of canals has led to unprecedented surface moisture in the Indus-Ganga belt during winter months when, normally, the land should be dry, except for brief spells of winter rain, says the report.

The resultant surface moisture, along with groundwater exploitation, contributes to winter humidity, triggering dense fog.

Meteorologists, however, say the link between irrigation canals and fog needs to be verified through long-term studies.

“An increase in surface moisture could, in principle, cause dense and persistent fog,” said Govind Pant, director, Indian Institute of Tropical Meteorology, Pune. “But we need to corroborate this through long-term studies of ground-level moisture in winter and fog over specific regions.”

The network of canals in the Indo-Gangetic plain has grown from a few hundred kilometres in the 1950s to several thousands of kilometres transporting water through the year to “command areas” across Punjab, Haryana, Uttar Pradesh and Bihar.

In Uttar Pradesh, the stretch of canals grew by 3,000 km between 1972 and 1986.

The canals and groundwater exploitation increase the moisture content of the soil. As a result, river embankments block floodwaters during monsoons and prevent water drainage into rivers.

According to the report, the likely effects of the proposed canals link to the country’s rivers need to be scientifically studied.

The Centre is examining a Rs 5,60,000-crore plan to connect tributaries of the Brahmaputra to the Mahanadi via the Ganga through a 10,000-km long maze of 30 canals. These canals would irrigate water-starved regions and boost food production. But agricultural scientists fear foggier winters could harm the country’s yield of winter crops such as potatoes, tomatoes, and brinjals.

Short-duration winter vegetables are particularly vulnerable to fog, incapable of tolerating even five hours of high humidity in combination with low temperatures of 7-12 degrees Celsius.

The Himal report says in the 2002-03 winter, potato farmers along the northern plains all the way to north Bengal “suffered crushing losses possibly because of the very irrigation network that enables this unnatural cultivation to take place in the first place”.

An Indian Meteorological Department study has shown the number of winter days with low visibility in several north Indian cities shot up from less than seven during the 1970s to more than 60 in the 1990s.

The study cites the example of Amritsar, which had just two low-visibility days in the 1970s, and an average of 72 such days during winters in the 1990s. Patna now has 75 low-visibility days compared with just 12 in the 1950s.

While low visibility during winters has been traditionally attributed to pollution by dust and tiny soot particles, weather scientists say an increase in surface moisture triggered by the canals could also be a reason for excess of fog.

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