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Wednesday, October 20, 2021

Explained: The declining monsoon rainfall in Punjab over last two decades

Punjab has seen a declining trend in rainfall during monsoon in the past two decades. The only silver lining was that the rainfall pattern was good this year, which was witnessed after a long gap.

Written by Anju Agnihotri Chaba | Chandigarh |
Updated: October 19, 2021 8:29:03 am
Weather scientists say Punjab has not only been recording below normal rainfall but also deficient rainfall in the past two decades.(Express Photo /File)

Punjab has received below normal rainfall this monsoon, which has withdrawn in the past couple of days from the state. Not just this year, the state has seen a declining trend in rainfall during monsoon in the past two decades. The only silver lining was that the rainfall pattern was good this year, which was witnessed after a long gap.

How much rainfall did the state receive this monsoon period?

Though the formal period of monsoon in Punjab from June 1 to September 30 is over, monsoons are yet to withdraw from northern India. According to Indian Meteorological Department (IMD) records, 436.8 mm rainfall has been recorded in Punjab this year against the normal required 467.3 mm from June 1 to September 30 — which is 7 per cent below the normal monsoon rain.

Less rain in the monsoon period leads to less annual rainfall in the state because around 79 per cent of the annual rain of the state takes place in monsoon period. Punjab’s annual rainfall is around 650 mm, which has decreased from around 800 mm in the 1980s.

What has been the trend of rainfall in the past two decades in the state?

Weather scientists say Punjab has not only been recording below normal rainfall but also deficient rainfall in the past two decades. Anything less than the normal, which can be even 1 per cent less, is called below average rain, but rainfall is categorised as ‘deficient’ when it is less than 20 per cent of the normal average.

In the past two decades, the number of years with below average (467 mm) monsoon rainfall has increased to 8 per decade. According to records, between 2000 to 2009 and 2010 to 2019, there were eight years each decade with below normal rainfall, while the number of deficient rainfall years has also increased in this period as compared to the previous decades, which is a huge shift. Between 2010 to 2019, there were six years with deficient rainfall including 2014 (50% deficient rain), 2012 (46%), 2015 (31%), 2011 (28%) 2016 (25%), 2017 (22%), while 2010 and 2019 recorded below normal rainfall with (7% less rain) in each. Even in 2020, there was 17 per cent less rain from the average. Between 2000 to 2009, there were four years which had recorded deficient rainfall including 2002 (27.2% less), 2004 (44.1%), 2007 (32.2%) and 2009 (34.9%) and the other four recorded below normal rain out of total eight below average rainfall years in this decade.

This is a very bad trend for a state like Punjab where less rain means extracting more water from the ground for irrigation purposes, when the water table in 84 per cent of the state is already over-exploited.

How much deficient rainfall did the state record in previous decades?

From 1990 to 1999, there were only three years of below normal rainfall while there was no deficient rainfall year recorded in this decade. Between 1980 and 1989, there were two years 1982 (24.9%) and 1987 (67.6%) with deficient rainfall. Between 1970 and 1979, there were three years including 1972 (27.6%), 1974 (36.1%) and 1979 (38.3%) with deficient rainfall. From 1960 to 1969 and 1950 to 1959, there were three and one years with deficient rainfall, respectively.

According to Indian Meteorological Department (IMD), there were 35 years of deficient rain in Punjab between 1901 and 2017 (117 years) out of which 10 years of deficient rain were recorded between 2000 and 2019 itself, which means 29 per cent deficient rainfall years in just 17 per cent of over a century.

Why despite below normal rain, is this monsoon being considered good by weather experts?

Dr Prabhjyot Kaur Sidhu, head of the Department for Climate Change and Agricultural Meteorology, Punjab Agriculture University (PAU), Ludhiana, said: “During this monsoon we witnessed a good pattern of rainfall. For instance, if 100 mm rainfall was witnessed in an area then it rained in 8-10 hours, while in the recent years, we had witnessed that 100 to 110 mm rain in just one or two hours which was just a waste of precious rainwater and that pattern was creating flash floods, which was bad for ground water recharging too.”

“If good amount of rain is falling continuously for longer period — 10 to 12 hours — then it is a boon for groundwater recharging because this rain water then seeps into the ground completely and does not accumulate on the surface and thus helps in water recharging,” she said, adding that such monsoons used to occur long ago when light to moderate rains used to take place continuously for days together.

“In Ludhiana we witnessed around 100 mm rainfall thrice this monsoon and every time, this amount of rainfall was recorded during an 8 to 10 hours duration instead one to two hours,” she added.

She also said that this monsoon was quite peculiar because it was advanced by two weeks and then there was a rain break for two weeks in July and August, while in September it rained again and surplus rain was recorded, after which the monsoon finally withdrew in October, while usually, monsoon withdraws by September-end in the state.

What are the factors driving the below normal rain trend?

Dr Prabhjyot said there are several factors and they are not Punjab-specific but a global phenomenon due to which erratic weather changes are occurring, for which a collective approach is required to minimise the effect of global warming to control extreme weather variables.

Experts said deforestation in the state is also one of the causes of the decreasing rainfall trend.

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