Whole monsoon rainfall in 2020, as of 8.30am on Sunday, is the eleventh highest for this era since 1901. Nonetheless, 2020 appears to be an outlier when learn with long-term rainfall statistics. Monsoon rainfall in India has been steadily declining for the reason that Nineteen Fifties. This development has been accompanied by rains changing into extra skewed; a lot of the rains fall over a smaller time frame. Rains are additionally getting extra intense, that means there are fewer episodes of rain, however when it rains, it pours. In 2019, heavy and excessive depth rainfall was the best since 1901.
Whole monsoon rainfall within the nation this 12 months, as of 8.30am on Sunday, has been 771.1 mmWhole monsoon rainfall within the nation this 12 months, as of 8.30am on Sunday, has been 771.1 mm, in keeping with the India Meteorological Division (IMD)’s gridded rainfall knowledge set. That is the eleventh highest monsoon rainfall for the June 1-August 30 interval since 1901. That makes 2020 an outlier already. Decadal averages of monsoon rainfall as much as August 30 recommend that complete monsoon rainfall in India has been declining. The interval from June 1 to September 30 is taken into account the monsoon season
Not solely are rains declining, they’re additionally getting skewed
This lower in complete rainfall has accompanied one other development: the lower within the variety of days on which no less than half the rain falls. Within the final decade (2020 has been excluded to see the sample over the whole monsoon season), 50% of the rainfall over the 122-day monsoon was seen on a median of 40.4 days. This was the quickest within the 12 a long time since 1901. To make certain, the corresponding time for 75% of rainfall and 90% was solely the fourth highest (70.6 days and 94.3 days respectively), though the long-term development for these greater shares of rainfall can also be the identical: it takes fewer days now.
Regional variations within the variety of days it takes for rainfall to happen
The all-India numbers cover a major regional variation on this sample. For instance, Delhi acquired 50% of its complete monsoon rainfall in 2011-19 in simply 83 days. This quantity was 30 for Karnataka.
When it rains, it pours
Skewed rainfall may imply a rise in heavy and excessive rainfall. And this has certainly occurred for India as an entire for the reason that second half of the final century. Mixed heavy and excessive depth rainfall was the third highest on this decade. In 2019, heavy and excessive depth rainfall was the best since 1901. A 24-hour rainfall between 35.5 mm and 244.5 mm in a grid – this evaluation makes use of IMD’s gridded rainfall knowledge set – is taken into account heavy depth rainfall and that above 244.5 mm, excessive rainfall. A grid is a field sure by two latitudes and longitudes 0.25 levels aside.
Skewed rainfall doesn’t assure heavy rainfall
The 2 tendencies – days taken for a sure proportion of monsoon rain to fall, and its depth – can diverge when the full monsoon rainfall is lowering. That is precisely what has occurred over north-central India, the lndo-Gangetic plains and the northeastern states. With declining complete rainfall, the quantity of heavy depth rainfall has decreased though the variety of days it takes for 50% of monsoon rainfall to fall has decreased.