A strange stop-start-pour pattern

The overall numbers: As of today, the country has received 850.3 mm of rain—which is 2% short of normal. But the total disguises a far-from-normal pattern of rainfall—which suggests climate change predictions are already coming true. 

Neither slow nor steady: The entire country has witnessed a topsy-turvy pattern over the monsoon months. Long Period Average (LPA) is the average rainfall received during a particular month between 1961 and 2010—and is the benchmark against which we decide if the amount of rainfall is “normal” or not. And here’s how we fared:

• June brought in lots of rain—especially in the South, thanks to Cyclone Yaas. And average rainfall across the country was up 9.6%. 
• Then we had a dry spell of 23 days. And the cumulative rainfall for July was 6.8% below normal. 
• In fact, the average rainfall was below normal from July and all through September 21. It was minus-4% in the Northwest, and minus-13% in East and Northeast India.
• But during August, there were extreme rain events in parts of Uttarakhand, Madhya Pradesh, Odisha, and Jharkhand—even while the rest of the country was mostly dry.
• Then the monsoon came back with a vengeance in September. So far, we have recorded 205.4 mm rain just this month—which marks a surplus of 29.3%.

The quote to note: President of Skymet—a private weather monitoring company—sums up why even forecasters were confused:

“Monsoon rains have been a bumpy ride this year and aren’t on expected lines. June was a surplus and even the deviation in July was as expected, with rainfall on the lower side. The shock came in August—which was expected to do better with 99% of average rainfall, but for most of the month, ‘break’ conditions remained. The rainfall for August has been short by around 25-26 per cent, which will be a record.”

Monsoon whiplash: is painfully evident in the regional numbers:

• The Northwest—i.e. states like Uttar Pradesh, Punjab, Himachal Pradesh, Jammu and Kashmir—witnessed severe monsoon whiplash. They went from receiving 226% of the LPA in June to 85% in mid-July.
• The wettest parts of the country—Nagaland, Manipur, Mizoram, Tripura—recorded below average rainfall for 17 consecutive weeks.
• Kerala experienced an 11-week dry spell from June 23 to September 1.

The Delhi example: is the most extreme and telling. The city went from minus-47% in June to plus-140%, back to minus-13% in August, and way up to plus-193% as of September 11. And it recorded seven days of “heavy rain”—i.e. above 64.4 mm—which set a new record. Earlier this month, parts of the city recorded between 81.3 mm and 98 mm of rain over just three hours.

An unmistakable shift in geography 

In his newsletter, Anil Padmanabhan offers this comparison between two meteorological maps. First is the pattern of rainfall distribution this year—as of September 26:

He compares this with a map of the average rainfall distribution of the Monsoon over 50 years ended 2000.

Padmanabhan says the big shift is hard to miss—even if the big picture implications are still unclear:

“Even a cursory glance reveals how traditionally surplus regions, Kerala and the North-East, are now progressively receiving less rainfall. In fact, the North East is now in deficit, while Kerala just about reports normal rainfall. To be sure this is a comparison of the average against the actual of one year’s rainfall. While we can infer trends it is not wise to make specific conclusions. The big takeaway is that there is a new regional variation in rainfall.”

The causes: short term and long term

The bizarre pattern has partly to do with specific weather anomalies that occurred this year:

One: Fewer low pressure systems developed over the seas. These are mainly responsible for the monsoons. There were only two in August. And many of these did not intensify into depressions or make landfall.

Two: During the monsoon season, an elongated low-pressure zone is formed—running parallel to the Himalayan mountains from the west toward the east. This ‘monsoon trough’ remained to the north of its normal position for most of August. This in turn brought a long dry spell to most parts of Northwest India.

Three: Remnants of typhoons that cross over from Myanmar usually bring rainfall, as well. But there was very little typhoon activity this year—as a result of which Central India didn’t get much rain.

Four: OTOH, we had crazy amounts of rain in Delhi due to an abnormally high number of convective or cumulonimbus clouds. Thanks to the long, dry stretches, the air was hotter. The atmosphere therefore carried more moisture and the hot air rose—which in turn form cumulonimbus clouds that bring thunderstorms, lightning, and extremely heavy rain. These kinds of clouds are more common before the monsoon kicks off. The actual rainy season typically sees altostratus clouds which bring continuous slow rain—not massive downpours. 

The real culprit: is, of course, climate change. In August, the Intergovernmental Panel on Climate Change—set up by the UN—issued a report that included projections for the Indian monsoon. Cut through the jargon, and what it predicts is fairly straightforward: As the planet continues to warm up—and as do the seas—the length of the monsoon will increase, stretching over more months. And it will bring a mix of extreme weather events—both droughts and floods. Also this: “The number of rainy days may decrease, but then when heavy rains occur they will happen in short spells. So the frequency of heavy rainfall events are expected to increase.”

Sound familiar? Delhi aside, this year, the overall number of rainy days have actually declined. As Skymet officials note:

“The number of rainy days has reduced over the last four to five years, and there has been an increase in extreme weather events. We have been recording short and intense bouts of rain, sometimes around 100 mm rainfall in just 24 hours. In the past, this much precipitation would occur over a period of 10 to 15 days.”

As for the length of this season, monsoons are typically expected to recede by mid-September. But this year, it will likely hang around until October 6.

Big point to note: The overall totals for the year are misleading precisely because of severe and unusual downpours. And this on-off pattern poses a real threat to farmers and water supplies. The sudden downpours do not replenish groundwater reservoirs—but instead the water is lost in runoffs. And they wreak havoc on crops.

The bottomline: Our climate is already changing.

Reading list

Indian Express and The Print have all the stats you need on the 2021 monsoon. Hindustan Times looks at what’s happening in Delhi. India Today and The Weather Channel have more on the IPCC report. Be sure to read Anil Padmanabhan’s newsletter on the shifting Indian monsoon—which includes an interesting discussion about sea temperatures.