My Science School

Last month’s flooding is attributed to a combination of factors including strong winds, heavy rains, high tides, which were pushed into Venice by southerly winds. Besides, rising sea levels make the city built amid a system of canals even more vulnerable to inundation.

The sea level around Venice has been rising steadily for decades and it has been attributed to climate change. Globally, the mean sea level is now estimated to be more than 20 cm higher than it was a century ago. Studies show that sea level is still rising 2.4mm a year along Venice. Some estimates suggest the Mediterranean Sea levels will rise by five feet by the end of the century, which could cause the city to flood twice daily. Currently, Venice experiences flooding about four times annually.

Further, the soft and the shifting geological terrain of the city has made the ground level sink gradually by an estimated one millimetre a year. Local industries around Venice make things worse by pumping groundwater from the aquifer under the lagoon.

Because of the combined effect of the city’s terrain and the rising of the sea, the water is now 30 cm higher against the buildings than it was when record-keeping began in 1873.

 

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Acqua Alta or ‘high waters’ is a seasonal phenomenon in Venice. The term is used to refer the exceptionally high tides that occur in the northern Adriatic Sea. The peaks reach their maximum in the Venetian Lagoon and causes flooding in coastal cities Venice and Chioggia.

The phenomenon occurs annually in November and December, when seasonal winds drive strong high tides up canals, through drains, and into the streets of the city.

Venice, built on a cluster of small islands, has always lived with tides that usually create variations of around 50 cm in sea levels but which can sometimes be more extreme, such as the ones experienced last month.

Climate scientists note that exceptional tides – those over 4 feet – have become much more frequent in the past two decades.

Of the 20 exceptional tides recorded since 1936, more than half have occurred after the year 2000.

 

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Last month, Venice was hit by three back-to-back floods in less than a week. They sent waist-high water flowing through the Italian city, threatening its iconic Saint Mark’s Basilica and other historic structures. More than 85% of Venice was inundated. The flooding was second only to the waters that inundated the city in 1956, when levels crossed 6 feet.

Venice’s huge Saint Mark’s Square was submerged by more than a metre of water, while the adjacent Basilica was flooded for the sixth time in 1,200 years – but the fourth in the last 20 years.

The floods were primarily driven by the aqua alta, or high tides, which is an annual phenomenon here. But other factors such as climate change and sea level rise made it worse. Experts say that floods of such intensities could become frequent in the coming years.

What is a flood?

A flood is a natural event when an area gets submerge under water for a while. Some floods can occur suddenly and recede in no time. Others take days or even months to build and recede.

Floods can develop in many ways. Heavy rain is one of the major reasons. If it rains hard enough or long enough, low-lying areas get inundated. The flow exceeds the capacity of waterbodies such as rivers, lakes and oceans. When water overflows beyond their boundaries, it leads to flooding. Breach in dams can also cause flooding.

Storm surge – abnormal rise in seawater level during a storm caused primarily by winds – causes the sea to rush inland.

Floods are destructive in nature as huge amounts of water get discharged, leaving no time for evacuation. Sometimes, floods are triggered by other natural disasters such as earthquakes and tsunamis.

What makes an area susceptible to floods?

Any plain low-lying area adjacent to a river or lake is more likely to experience floods whenever the water level rises – for example, a coastal city or a city with a river running through it.

A place’s susceptibility to floods also depends on the capacity of the catchment areas the volume of water hat a river or canal can hold without overflowing. When the amount of rainwater exceeds this capacity, floods may occur.

What is Venice like?

Venice is situated on a group of 118 small islands that are separated by canals and linked by over 400 bridges. The islands are located in the shallow Venetian Lagoon at the head of the Adriatic Sea in Northern Italy. The whole city is an extraordinary architectural masterpiece. The lagoon and a part of the city are listed as a UNESCO World Heritage Site.

 

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Farmers are not the only reason for air pollution.  Stubble burning does contribute to Delhi’s pollution in a major way, but it is episodic and depends a lot on wind direction and other meteorological factors. According to the Centre for Science and Environment (CSE), about 65% of pollution in Delhi is due to local sources.

Dust is a major contributor to air pollution. Unpaved roads, and digging for various infrastructural construction expose the loose soil, contributing as much as 17% of the particulate matter (PM) in the air. A TERI-ARAI study published in 2018 on PM 2.5 emissions showed that transport contributed 39%, road dust 18%, construction activities 8%, followed by power plants 11% to the air pollution in Delhi. Pollution mitigation efforts should take these factors into account.

 

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On November 6, the Supreme Court of India ordered an incentive of Rs 100 per quintal for small and marginal farmers who engage in the management of the residue of their non-Basmati variety rice crop in Punjab, Haryana and Uttar Pradesh.

The SC Bench also ordered the States to distribute crop residue management tools and machines to small and marginal farmers free of cost. The States need to use their own funds to finance the scheme, it said.

Meanwhile, it asked the Delhi government to submit an action plan to deal with issues of garbage dumping and burning, pock-marked roads and the state of traffic congestion in the capital city. The court gave the government three weeks to repair the potholes.

 

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• Even with capital subsidy, machines like Happy Seeder are not considered economical, as their demand is seasonal. The high cost of the machines and the rising price of diesel put pressure on farmers. For them, stubble burning is a cheaper option. A Happy Seeder machine is priced at Rs 1.5 lakhs. Though the government offers a 50% subsidy on the purchase of Happy Seeders to individual farmers, the machine still remains unaffordable. Also not all tractors are capable of pulling a happy seeder along, only those with a capacity of 65 horsepower would be able to drag an additional device mounted on it.


• Farmers remain sceptical about the efficiency of these machines. They fear the machines will affect productivity and damage the soil. Besides, they feel using machinery is time-consuming.


• The farmers have expressed that the number of machines provided is extremely inadequate.

How can stubble burning problem be solved?

• The equipment has to be supplied quickly and in good numbers. There are reports that subsidized agromachines being provided by the government have not reached many villages and whenever given, the number is too low.


• It is important to find other uses for stubble such as biomass, which may encourage farmers to look for alternative sources of income.

 

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Farmers can use devices such as mulchers (that cut up grass, leaves, etc., for use as mulch), rotavators (a machine with rotating blades for breaking up or tilling the soil), Happy Seeders and straw management system to manage and utilise stubble.

Happy Seeder is nothing but a tractor-mounted device which can cut and lift the previous crop (in this case the rice straw) and sow a new (wheat) crop in its place simultaneously. It also deposits the straw over the sown area as mulch. Mulch enriches and insulates the soil.

The straw management system involves the use of a machine attached to a harvester chopper, which spreads loose straw uniformly. Here, the straw serves as mulch.

Straw could also be used as feeder.

(However, farmers in these regions report a lower preference for paddy straw because of the comparatively high silica content in it. There are also reports of wheat straw rejection due to fuel spillover during harvesting by machines.)

 

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