Unusual dry spell may continue till end of monsoon in Mumbai

Aug 14, 2015, 06:40 IST | Tanvi Deshpande

Blaming weak atmospheric pressure and wind movements, weather experts say the dry spell is likely to continue in the city, which has so far recorded less than 60% of the expected rainfall

The unusual dry spell may continue till the end of monsoon in Mumbai, suggest weather experts. Since the heavy showers on June 18 and 19, rainfall has dwindled which is why the city has only managed to record a paltry 59.71% of the season’s average rainfall, compared to 72.4% last year.

Related Story: Monsoon gives Mumbai a break

This falling trend is especially worrying since there has also been less rainfall in the catchment areas that supply water to Mumbai. The ‘season’s rainfall’ is the average expected rainfall through monsoon, which the India Meteorological Department (IMD) has pegged at 2,558 mm.

Bhatsa lake’s water level is currently 128.08 m, the lowest in three years. The catchment areas in the surburbs in particular have seen less rainfall than the rest of the city. File pic
Bhatsa lake’s water level is currently 128.08 m, the lowest in three years. The catchment areas in the surburbs in particular have seen less rainfall than the rest of the city. File pic

The June 19 shower this year was reminiscent of the deluge on July 26, 2005, as the city came to a standstill with just 280 mm rainfall. As a result, by the end of the day, the city had already recorded almost 50% of the entire season’s rainfall. However, since then the city has experienced an unusually dry July and August.

The same trend continued on Wednesday, which saw a mere 1.9 mm rainfall (recorded by BMC from 8 am Wednesday to 8 am Thursday), taking the total rain received so far to 1,527.5 mm, or 59.71% of the city’s average. In comparison, the city had registered 1,852 mm around the same time last year.

According to both IMD and Skymet, a New-Delhi-based private weather forecasting agency, this is due to a change in weather patterns this year. The city normally experiences gusty winds with heavy rainfall during monsoon, however, this year it has seen fewer bouts of sustained showers due to weak pressure gradients and offshore troughs.

Explaining this phenomenon, IMD director Shubhangi Bhute said, “Wind movements create a weather condition called a trough which is conducive and highly essential for rainfall. There has been a persistent trough sitting at the base of the Himalayas, which has resulted in very good rainfall in North India.

But what we lack is an offshore trough in the Arabian Sea to allow for good rains on the West coast.” She added, “Low-pressure area and depression are the factors required to pull moisture towards Western India. June 19 rains were an exception when there was a low pressure area formed over the Arabian Sea but since then, the troughs have been very weak.”

Even Skymet has predicted a sporadic monsoon. “Past records have shown that July and August do not fail together in the same year. But this year, even half of August has failed. But we are predicting that monsoon will pick up in Mumbai this weekend and then again towards the end of the month,” said G P Sharma, vice-president of Skymet.

Also Read: Dry spell in Mumbai could end soon, predicts IMD

The private forecaster has also predicted only short bursts of rain for the next 10 days, attributing this to monsoon systems being erratic. “Mumbai is not an exception in this matter; even Goa and Konkan coast have experienced 30% less than average, coastal Karnataka is 25% less and Kerala 30% less. But what is worrying is that even in Mumbai’s catchment areas, the rainfall doesn’t look promising,” Sharma said.

Water supply
The BMC concurs with this assessment, and has recorded less rainfall (47.41%) in the suburbs than in the island city (53.73%). This is important because the catchment area, with lakes such as Vihar, is located in the suburbs.

While lake levels have been stable this year and are mostly at par with last year’s figures, the water level is an unsatisfactory 128.08 m at Bhatsa one of the biggest suppliers of water to the city. This is the lowest level witnessed by Bhatsa in three years. The level was higher last year (136.97 m) and in 2013 (140.82 m).

However, the BMC is yet to take a decision on whether or not to implement water cuts. The city currently has a total of 9,01,182 million litres of water available, which is enough to last 240 days. “That is why we are not considering a water cut yet. The decision will be taken at the end of the season in October,” said an official from the BMC’s hydraulic department.


Changing patterns
Asked whether Mumbai’s weather patterns have changed over the past decade, IMD director Shubhangi Bhute confirmed there was definite change. “Earlier, there used to be moderate rainfall throughout the season interspersed with heavy rainfall.

July and August would make up 70% of the season’s rainfall. But now monsoon has been stretched to October, which creates a lot of health problems and agricultural crises.”

2,558 mm
The average rainfall expected through monsoon

1,527.5 mm
The total rainfall received this year so far

Rainfall received so far this year

Rainfall received till this time last year

* Figures according to India Meteorological Department

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