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Friday, September 25, 2020

Heatwaves, floods, droughts: projections for India in coming decades

Heatwaves, floods, droughts: Every decade between 1951-2015 had 7.4 warmer days and 3.1 warmer nights than the annual averages for daily maximum and nightly minimum respectively.

Written by Anjali Marar | Pune | Updated: July 23, 2020 9:20:53 am
India climate, India Heatwaves, India floods, India droughts, India Heatwaves projections, India floods projections, climate change, Indian express A man walks through Kolkata Maidan on July 20, 2020. (Express Photo: Partha Paul)

The first ‘Assessment of Climate Change over Indian Region’, released by the Ministry of Earth Sciences recently, warns of tropical cyclones, thunderstorms, heat waves, floods and droughts in India unless mitigation measures are adopted soon. The projections are for the decades leading to the end of the 21st century.

Temperature

* Surface air temperature over India has risen by 0.6°C per year during 1901-2018.

* Regions of North India have undergone warming more than the South, where warming has been mainly during winters.

* Every decade between 1951-2015 had 7.4 warmer days and 3.1 warmer nights than the annual averages for daily maximum and nightly minimum respectively.

* The frequency of warm days is projected to increase by 55% and that of warm nights by 70%, both relative to 1976- 2005.

* In coming decades, the average duration of heatwaves during April-June is projected to double, and their frequency to rise by 3 to 4 times compared to 1976-2005.

* By the end of the 21st century, average temperature over India is projected to rise by 4.4°C, relative to the average temperature during 1976-2005.

* Sea surface temperatures on the tropical Indian Ocean have been rising by an average 1°C annually over 1951-2015.

Monsoon

* During 1951-2015, annual rainfall over India showed a declining trend. The reduction ranged between 1-5 mm over central India, Kerala and the far Northeast regions.

* Contrarily, precipitation increased over J&K and Northwest India.

* The coming decades are projected to witness a considerable rise in the mean, extreme and inter-annual variability of rainfall associated with monsoon.

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Droughts and floods

* Since the 1950s, the frequency and intensity of both heavy rainfall events and dry days have gone up. These trends are prominent over Central India and South Peninsular regions during the southwest monsoon (June-September) and northeast monsoon (October-December) respectively.

* Since 1901, India has experienced 22 droughts during monsoon. In addition to an increase in the area under drought, frequency and severity too have increased during 1951-2016.

* Flood risks are higher over the east coast, West Bengal, eastern Uttar Pradesh, Gujarat, Konkan and cities like Mumbai, Chennai and Kolkata.

* The Himalayan flood basins are projected to greater floods, due to the faster glacial and snow melting. Major flooding events are projected over the Brahmaputra, Ganga and Indus.

* Central India, Kerala, and some areas in South Peninsular and Eastern India experienced at least two droughts during 1901-2016.

* Projections suggest an increase by one or two events per decade over Central and Northern India. Eastern India could face two more droughts per decade compared to what was experienced during 1976-2005, while the Southern Peninsula is projected to experience one or two droughts fewer.

Sea level

* During 1993-2015, the sea level over the North Indian Ocean (Arabian Sea and Bay of Bengal) rose by 3.3 mm per year, which is in tune with the Global Mean Sea Level (GMSL) rise.

* In an extreme climate scenario projected by the report, a risk of inundation looms over Andhra Pradesh and Ganga-Brahmaputra-Meghna delta basins. By 2030, some 340 million coastal residents of the North Indian Ocean and its islands would be exposed to coastal hazards.

Tropical cyclones

* Before the 1950s, 94 severe cyclonic storms formed in the Bay of Bengal, a number that jumped to 140 post the 1950s. For those formed in the Arabian Sea, the number has risen from 29 to 44 in the same period.

* Storms in the Arabian Sea are gaining more strength and the trend is projected to continue. The number of extremely severe cyclonic storms formed in the Arabian Sea has increased in the last 20 years.

Himalaya snow cover

* During the last seven decades, the Hindukush Himalayas have warmed at an average 0.2°C per decade, leading to a decline in snow cover and glaciers in the last four to five decades. The Karakoram Himalayas have reported an increase in snowfall during winter.

* By the end of the century, the Hindukush Himalayas are projected to be warmer by 2.6-4.6°C.

Cause & effect

* The main contributor to climate change is anthropogenic activities pushing up concentrations of greenhouse gases. This has led to rise in temperature and atmospheric moisture content.

* A higher concentration of water vapour, in turn, leads to intense rainfall during monsoon.

* Heating leads to vaporisation, which is directly linked to decreasing soil moisture, resulting in droughts. This can lead to reduction in food production and in availability of potable water, the report says.

* Rising sea levels would make India’s big cities vulnerable to erosion and damage to coastal projects, the report says.

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