Mumbai likely to see heavy rains from this Friday

In the last few weeks, Pakistan has witnessed the most catastrophic floods in a generation. According to the UN, 20 million people have been affected, a fifth of the country is under water, 1,600 are dead, two million rendered homeless.

This has occurred due to a heavy rainfall in the catchment of the Indus river. But our study has shown that the rains were caused by a persistent moisture-laden south-easterly wind flow striking the western Himalayas at an angle that favoured an upward motion of the air mass. A low pressure area over Rajasthan adjoining Gujarat brought moist-laden south-westerly flow over the region.

As a result, two air masses were converging over north and west Pakistan. The descent of cold air from Siberia and north-west Tibet combined with the ascent of moist monsoon air from beneath formed powerful thunderstorms that gave very heavy rainfall.

Heavy rainfall forecast over north Pakistan and adjoining Jammu and Kashmir on Tuesday and Wednesday might exacerbate the flood situation. Simultaneously, Russia is in the grip of a severe heat wave. The two phenomena seem to be related. There was an upper atmospheric pattern that locked the Rosby wave pattern (they are alternating low-pressure and high-pressure patterns that move from west to east in the upper atmosphere).

This quasi-persistent wave pattern existed from western Europe to West Asia such that there was low-pressure trough (inducing rain) over western Europe and high-pressure ridge (inducing heat wave) over Russia and a low-pressure trough (inducing floods) over west Pakistan. The Russian heat wave is a once-in-a-400-year phenomenon. Similar heat wave was seen in France a decade ago.

Good rainfall over the past week in north and south India has enhanced the water storage position in India’s reservoirs to 49%, according to the Central Water Commission (CWC). This is 10 percentage points more than the same period last year. According to a report by the Ministry of Agriculture, the sowing coverage of all Kharif crops is up except soya bean.

Current enhanced precipitation over India is expected to continue well into the next week. Karnataka, Andhra Pradesh and Maharashtra could be the main beneficiaries. Rain may get enhanced in the north east/ east. After two days, rainfall in north India will start reducing but the Mumbai region might start witnessing heavy spells from August 27.

(The author is Skymet CEO)