How is the rainfall performance during the ongoing monsoon season?

The monsoon got a good start in June. It covered the southern peninsula ahead of time, bringing widespread rainfall until it covered central India. However, the June rainfall over the country ended at being 11% below normal.

The rainfall picked up intensity after the monsoon covered the entire country on July 2. A majority of regions continued to experience good rainfall throughout July.

The overall seasonal performance improved due to the rainfall recorded between July 18 and July 24. During this period, a low pressure system developed in the Bay of Bengal and subsequently intensified to keep the monsoon either active or vigorous. The system weakened around July 23.

Between July 19 and July 25, India received 41% surplus rainfall, which was 80.5 mm against a normal of 57.2 mm. The rainfall was largely concentrated over southern peninsular (except Tamil Nadu) and central India regions.

Region-wise rainfall performance

IMD data show that between June 1 and July 19, Maharashtra, Gujarat, and Madhya Pradesh received close to normal rainfall. In the same period, Odisha and Chhattisgarh reported rainfall deficits of 25% and 34%, respectively. Until the third week of July, 12 states were in the “deficit” category.

The situation turned around as the west coast and central regions began to receive unabated heavy rainfall between July 18 and July 24. During this period, Central India recorded 107% excess rainfall — 137.8 mm against the normal of 66.6 mm — and southern peninsular India received 82.6 mm against the normal of 42 mm — 97% surplus for this time of the season.

Gujarat, Dadra and Nagar Haveli, Goa, Maharashtra, Andhra Pradesh, and Tamil Nadu received excess rainfall. Odisha, Madhya Pradesh, Chhattisgarh, Andaman and Nicobar Islands, Kerala, and Lakshadweep saw normal rainfall.

However, regions along the northwest, extreme north, east, and northeast India remained largely dry in recent weeks — rainfall deficits here are between 8% and 16%. Despite early monsoon onset in these parts, significant rainfall is yet to be realised.

High rainfall receiving areas such as Nagaland, Manipur, Mizoram, Tripura, Jharkhand, Bihar, Haryana, Chandigarh, Punjab, Himachal Pradesh, and Jammu and Kashmir have remained in the rainfall “deficient” category.

Reasons behind skewed rainfall distribution

The central and southern peninsular regions have received a surplus rainfall primarily due to the position of the monsoon trough — a semi-permanent, low-pressure area extending between Pakistan and the Bay of Bengal during the monsoon season — which usually oscillates between north and south within the season. Whenever it moves towards the south, as it has done in the present case, more rainfall can take place in central, eastern, and peninsular India. When it shifts towards the north, the Himalayan foothills are likely to receive more rainfall but the rest of India sees a drop in rainfall.

Other rain-bearing weather systems such as an off-shore trough (a shallow trough of low pressure, which develops along India’s coast during the monsoon) have also contributed to the surplus rainfall in the central and southern peninsular regions.

Region-wise rainfall departures in % (June 1 – July 25)

Given that the monsoon trough is yet to move northwards, rainfall has remained deficient over northwest, extreme north, east, and northeast regions, so far this season. Moreover, there have been fewer rain-bearing weather systems, and those that formed did not reach and bring rainfall over these regions.

What could make matters worse is that IMD’s forecast does not indicate much rainfall for northwest or north India during early August.

The skewed rainfall distribution can severely impact Kharif crops — sown between June 15 and July 15 — and their yield. For instance, excessive rainfall in Maharashtra’s Sindhudurg district forced many paddy farmers to resow their crops this season.