From 19% seasonal deficit to 106% excess rain in 24 hours: Warning signals from Gujarat

Flooding in the Bopal area of Ahmedabad. Photo: Abhishek Chatterjee

The flooding in Chhota Udepur, Ahmedabad, Panchmahal and Tapi districts of Gujarat July 10, 2022 is the perfect example of floods in the time of drought, a phenomenon symptomatic of global warming.

All four districts had deficit rainfall before the incessant rains July 10. Ahmedabad had the maximum deficit of 37 per cent between June 1 and the morning of July 10.

Panchmahal, Chhota Udepur and Tapi received 30 per cent, 19 per cent and seven per cent less rains than normal in the period, according to data from the India Meteorological Department (IMD).

The situation changed drastically by the morning of July 11 with Ahmedabad’s deficit reducing by 26 percentage points to 11 per cent.

The district received 52.4 millimetres (mm) of rainfall as against the normal of 7.9 mm, an excess of 563 per cent, between the mornings of July 10 and July 11. Many parts of Ahmedabad city, especially the Bopal area got inundated due to the rains.

The most dramatic situation was in Chhota Udepur district where the 19 per cent deficit changed to 106 per cent excess, which was a swing of 125 percentage points, in a matter of 24 hours.

The district received 322.4 mm of rainfall between the morning of July 10 and July 11 as against the normal of 10.5 mm, an astronomical excess of 2,970 percent. This was one-third of the season’s rainfall for the district.

A few talukas within the district such as Bodeli, Kavant and Chhota Udepur bore the brunt of the rains. According to data from the State Emergency Operations Centre (SEOC) in Gandhinagar, Bodeli received 549 mm of rainfall between 6 am of July 10 and 6 am of July 11.

Kavant received 432 mm and Chhota Udepur received 330 mm of rainfall. Such rainfall is expected in the Western Ghats region or a few places in North East India and even there, these numbers for a day’s rainfall would be considered as extremely severe.

Another district that witnessed a turn of fortune for the worse was Panchmahal as its rainfall situation changed to 33 per cent excess from a 30 per cent deficit in the same period, a jump of 63 percentage points.

The district received almost 150 mm rainfall in the 24 hours, which was an excess of 919 per cent. Jambughoda taluka of the district was the worst-hit, with 426 mm of rains in the 24 hours, according to data from SEOC.

Drastic changes

What has been observed July 10 in Chhota Udepur district is also consistent with the long-term trends in monsoon rainfall.

There has been a significant decrease in rainy days in stations in Chhota Udepur district between 1989 and 2018. This is according to the Observed Rainfall Variability and Changes Over Gujarat State published by IMD in January 2020.

This would mean that whatever rainfall falls in the district would come in a smaller number of days like July 10. In addition, there is also a significant increasing trend in the number of heavy rainfall days and significant decrease in the number of dry days in the district for the monsoon season.

A flood-like situation is also prevalent in the Valsad and Narmada districts which already had excess and normal rainfall respectively for the period of June 1 to July 10. The situation in Valsad is not under control, according to the latest media reports.

Gujarat’s rainfall condition changed within the past couple of weeks. It was suffering from a rainfall deficit of 47 per cent at the beginning of July.

This brought it to the edge of drought-like conditions. Only three of its 34 districts had received normal monsoon rains by that time and no districts had excess or large excess rainfall.

The rest of the districts had deficient (20 to 59 per cent less rains than normal) or large deficient (>60 less rains than normal) rains.

By July 5 the situation changed quite a bit with the state’s deficit coming down to 22 per cent and seven districts with normal rainfall for the period (June 1 to July 5) and two districts with excess rainfall.

In the next couple of days (by July 7) the number of districts with normal rainfall (for the period between June 1 and July 7) increased to 12 and six districts had excess or large excess rains.

The state’s deficit further reduced to 10 per cent. On July 10, after three days of consistent rains, the number of districts with normal rainfall increased to 15 and number for excess or large excess increased to 12.

The state’s deficit turned to an excess of 29 per cent. By July 11, the state’s excess had increased to 44 per cent and only three districts had deficit rainfall for the monsoon period, showing a complete reversal of circumstances in a matter of 10 days.

The main reason for the excess rainfall in the past few days in Gujarat is the monsoon trough which is extremely active right now and south of its normal position, according to IMD.

Another reason is an off-shore trough from the Gujarat coast down to the Karnataka coast that also forms during the monsoon and is responsible for most of the rainfall along the western coast during the season.

The same systems are going to bring more rains to the region, especially for the Dangs, Navsari and Valsad districts, in the next few days till at least July 14, according to the latest forecast by IMD. This could bring floods and flood like situation to many more areas of the state.

The Intergovernmental Panel on Climate Change (IPCC), as part of its AR6 Working Group 1 report released in August 2021, added that “changes to monsoon precipitation are expected, which will vary by region.”

The reason for such extreme excess rainfall along the northern part of India’s west coast is the northern swing of the low level jet. It is a band of winds in the lower layer of the atmosphere, that usually brings moisture from the surrounding oceans to India during the monsoon.

Raghu Murtugudde, a climate scientist at the University of Maryland in the United States told Down To Earth:

As the winds have moved northward in recent decades, intra-seasonal variability of rain over the central-western region of India and the northeast corner of the Arabian Sea has increased.

“Hence, the active / break periods of monsoon have changed with more intense heavy rain events during the active period,” he added. The southwest monsoon season is currently in an active period.

Murtugudde further added that the trend in the Arabian heat low still favours the strong southwesterly winds which are bringing more moisture from the warm Arabian Sea into the northern Western Ghats situated in Maharashtra and Gujarat.

The Arabian heat low is a hot, low pressure region over the Arabian Peninsula usually responsible for summer heat waves in northwest India.

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