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Extreme rain events: How unusual, what is causing them

GS Paper 1

 Syllabus: Physical Geography of India (Drainage, Climate)


Source: TH

 Context: Northern India is currently in the midst of an extremely wet phase of the monsoon.


What is an extremely heavy rainfall event?

  • It occurs when more than 205 mm of rainfall happens at any place within a 24-hour period. (IMD)
  • Such events of extremely heavy rainfall are not unexpected during the monsoon season.
  • After the 2013 Uttarakhand tragedy, there has not been a single year without at least one major disaster-like situation produced by an extreme rainfall event.


Trends in recent years:


  • Overall rainfall during the monsoon has remained more or less constant over the last two decades.
  • But the intra-seasonal variation has increased – fewer days are producing a bulk of the seasonal rainfall, while the rest of the days remain dry.


How is this year’s monsoon rainfall unusual?

  • The monsoon season this year was not expected to be very wet.
  • July rainfall in Himachal Pradesh, Haryana, Punjab, Rajasthan, Uttarakhand and Uttar Pradesh is substantially higher (by 26%) than normal.
  • Heavy rain has resulted in large-scale destruction and loss of lives, particularly in the hilly areas.

Reasons for this extreme rainfall:

  • Rains induced by the Biparjoy cyclone: By the first two weeks of the monsoon, India had accumulated a rainfall deficit of more than 50%. However, this deficit had come down to 8% by the end of June.
  • Western disturbances: IMD has attributed this spell to an interaction between the monsoon winds and western disturbances that converged over northern India.
  • Climate change: It is known to increase the possibility, frequency and intensity of extreme weather events, including heavy rainfall and heat waves.
  • Warming of the Arabian Sea: Excess rainfall over northwest India is consistent with the Arabian Sea having warmed by about 1.5 degrees Celsius since January.


How can Indian cities bring themself out of these troubled waters?

  • The authorities need to plan the usage of shallow aquifers to prevent waterlogging.
  • At the same time, the city needs to recharge the deeper aquifers with rainwater.
  • Forming a water plan to recharge aquifers
  • Rainwater harvesting structures along the stormwater drains can help mitigate floods while utilizing rainwater resources.


Conclusion: Only improved forecasts with sufficient granularity in space and time can reduce the element of surprise resulting from these extreme weather events.


Insta Links:

Cyclone Biparjoy


Prelims Links: UPSC 2020

With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct?

  1. OMT is measured up to a depth of 26°C isotherm which is 129 meters in the southwestern Indian Ocean during January — March.
  2. OMT collected during January — March can be used in assessing whether the amount of rainfall in the monsoon will be less or more than a certain long-term mean.

Select the correct answer using the code given below:

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2


Ans: 2