Rain falling on fewer days now

There were five years in the 2011-2020 decade that saw an unusually high number of days with a lot of rainfall. If years are ranked on the basis of the number of days in the year which figure in the top 10% of highest rainfall days of the monsoon since 1901, 2019 ranks first with 30 days. Another four years (2011, 2013, 2016, and 2020) rank within the top 50 years.

2014 and 2017 are ranked 51st. Until August 31, 2021 has seen five days among the top decile of highest rainfall. Such high rainfall days are also complemented by long dry spells. It now takes fewer days for 50% of monsoon rains to fall. At the all-india level, this has decreased from 41.34 days (average in 1961-2010) to 40.9 days (average in 2011-2020). In several northern and north-eastern states, this change is more: from 21.74 days to 19.4 days in Bihar, for example, or 20.54 days to 16.7 days in Manipur. In all, 19 of 29 states (including Delhi) have seen a reduction in number of days it takes for 50% of monsoon rains to take place. And 24 states have seen a reduction in number of days it takes for 99% of monsoon to take place.

Number of days

2021 (till Aug 31

2012

2018

2015

2014

2017

2011

2016

2020

2013

2019

While this shows that most places are now seeing fewer rainfall days, it is also possible that places that have seen an increase in days have seen a reduction in number of hours of rainfall. IMD’S gridded rainfall dataset, however, gives only data by day, so instances such as Wednesday’s morning rain in Delhi, when 75.6mm of rain fell in three hours between 8.30am and 11.30am at the Safdarjung station can potentially get missed as a spell of very intense rainfall. 1961-2010 2011-2020 (Change)

+3% -5.7%

-8.9%

+4%

-18.7%

-15.3%

-4.1%

-15%

+12%

+1% -10.8%

-6.4%

-13.4%

-3.1% -11.5%

-4.1%

+2%

-8.4% -15.7% -6% -1.4%

0% +3%

+12% -0.9%

+9% -4.1%

-8.8%

+4%