Why does Mumbai sink in monsoon?

In fact, several parts of Konkan recorded heavy to very heavy rain. Between Monday and Tuesday morning, Alibaug recording 161 mm of rainfall, while rainfall in the regions such as Dahanu (190 mm), Harnai (180 mm) and Mahabaleshwar (170 mm) far surpassed the volume of rain that Mumbai witnessed. According to the IMD, the incessant rain since Monday is a result of westward movement of a low-pressure area that had developed over Odisha and southwest Madhya Pradesh. The India Meteorological Department (IMD) has sent out the warning of heavy rainfall in Mumbai and its suburbs at least for the next 24 hours. In the past 12 hours, rain has already flooded some low-lying areas and water logging on tracks has started delaying trains. The heavy spell caused water logging in Sion, Lower Parel, Dadar, Mumbai Central, Andheri, Kurla, and Sakinaka, which ultimately resulted in slowing down the traffic. The Met department has advised people not to leave their homes unless absolutely necessary. Mumbai airport has suspended operations.

The 2017 monsoon has been all about the floods. Parts of Gujarat, Rajasthan, Assam, Bihar, and Bengaluru have all been inundated by reportedly historic levels of floodwater following incessant rainfall during this season. At least 11 states have experienced floods since the onset of monsoon in June. Nearly 150 districts have already received more than 100 mm of rains in a single day. But as we roll into the fourth quarter of the monsoon, around 40 per cent of the districts have had deficient rains. Parts of states across north, central and south India are bracing for a drought over the next year. According to the met department's current weather status and two-week outlook, rainfall over the country as a whole has been normal—four per cent below the long-term average. Rainfall in all four geographical regions is within the margins of "normal". A closer look at the distribution and the patterns of rainfall show that the monsoon has actually been anything but normal. Temporal distribution across the country has been all over the place. The IMD issues week-by-week observations of rainfall activity categorised according to the quantum of rain received during the week. So far, about 400 weekly observations from 36 meteorological sub-divisions have been listed. Less than a fourth of these fall under the normal category, and yet rainfall over the country as a whole is normal.

Extreme rain has compensated (and in some cases over compensated) striking deficiencies in other weeks, indicating a contraction in the distribution of rains this year. Rajasthan is a glaring example. The state has currently registered an excess rainfall of about 23 per cent. West Rajasthan received more than three times its normal rainfall between June 20 and August 2. Most of this was received by incessant rains over Rajasthan, Saurashtra, and Gujarat between June 24 and 28. Apart from these few rainy days, there have been fewer than usual rainy days. The Gujarat subdivision has seen four weeks when rainfall exceeded the normal levels by more than 50 per cent, two weeks when it exceeded the normal by more than 20 per cent and five weeks when rainfall was deficient by more than 60 per cent, according to the weekly normal. During these eleven weeks, not a single week has registered normal rainfall. A similar story can be told of Saurashtra and Kutch, too. Heavier rains over fewer days have propped up overall figures in several states, including Bihar, Jharkhand, Odisha, and West Bengal.

In stark contrast, rain-rich regions of Kerala and coastal Karnataka have received deficient rainfall while the rain shadow regions in southern Tamil Nadu have received rains far above normal, thanks to the heavy rains in August.

The situation in Maharashtra is yet another failure where drought-prone Marathwada and Vidarbha witnessed 32 and 28 per cent deficits respectively. Farmers have been particularly affected due to significant levels of moisture stress following a near complete failure of monsoon this year. After two weeks of strong pre-monsoon showers in June, farmers faced heavy deficits in seven out of nine weeks (five weeks saw more than 60 per cent deficit). Despite the third wave of floods ongoing in Assam and excesses in Tripura and Mizoram, Manipur has received less than half of its normal rainfall.

Back in April, the IMD's first long-range forecast showed a "normal" 2017 monsoon. They reiterated their belief in the update to the forecast, issued at the beginning of June. If the monsoon ends with similar numbers, the prediction will be counted as a success when IMD comes out with forecasts for the future. While this might boost the met department's credibility, it also raises serious questions about how we understand and classify our monsoons. As much as IMD's claim stands vindicated, its errors are also revealed.

Both long-range forecasts were criticised for large margins of errors and inconclusive probabilities on which the forecasts rested. The current monsoon is challenging India's conventional simplistic nomenclature when describing complex global circulations like the monsoon. Depending only on the quantity of rainfall to describe monsoon performance without accounting for distribution and influential atmospheric conditions would again lead to a misreading of monsoon.

(The views expressed are those of Down to Earth.)